Author name code: demoulin
ADS astronomy entries on 2022-09-14
author:"Demoulin, Pascal" 
------------------------------------------------------------------------  

Title: Over-expansion of coronal mass ejections modelled using 3D
    MHD EUHFORIA simulations
Authors: Verbeke, Christine; Schmieder, Brigitte; Démoulin, Pascal;
   Dasso, Sergio; Grison, Benjamin; Samara, Evangelia; Scolini, Camilla;
   Poedts, Stefaan
Bibcode: 2022AdSpR..70.1663V
Altcode: 2022arXiv220703168V
  Coronal mass ejections (CMEs) are large scale eruptions observed close
  to the Sun. They are travelling through the heliosphere and possibly
  interacting with the Earth environment creating interruptions or even
  damaging new technology instruments. Most of the time their physical
  conditions (velocity, density, pressure) are only measured in situ
  at one point in space, with no possibility to have information on
  the variation of these parameters during their journey from Sun to
  Earth. Our aim is to understand the evolution of internal physical
  parameters of a set of three particular fast halo CMEs. These
  CMEs were launched between 15 and 18 July 2002. Surprisingly, the
  related interplanetary CMEs (ICMEs), observed near Earth, have a low,
  and in one case even very low, plasma density. We use the EUropean
  Heliosphere FORecasting Information Asset (EUHFORIA) model to simulate
  the propagation of the CMEs in the background solar wind by placing
  virtual spacecraft along the Sun--Earth line. We set up the initial
  conditions at 0.1 au, first with a cone model and then with a linear
  force free spheromak model. A relatively good agreement between
  simulation results and observations concerning the speed, density and
  arrival times of the ICMEs is obtained by adapting the initial CME
  parameters. In particular, this is achieved by increasing the initial
  magnetic pressure so that a fast expansion is induced in the inner
  heliosphere. This implied the develop First, we show that a magnetic
  configuration with an out of force balance close to the Sun mitigates
  the EUHFORIA assumptions related to an initial uniform velocity. Second,
  the over-expansion of the ejected magnetic configuration in the inner
  heliosphere is one plausible origin for the low density observed
  in some ICMEs at 1 au. The in situ observed very low density has a
  possible coronal origin of fast expansion for two of the three ICMEs.

Title: Interpreting the Two-step Forbush Decrease with a closer
    look at the two substructures modulating Galactic Cosmic Rays within
    Coronal Mass Ejections
Authors: Janvier, Miho; Dasso, Sergio; Demoulin, Pascal; Guo, Jingnan;
   Regnault, Florian; Perri, Barbara; Guttierez, Christian
Bibcode: 2022cosp...44.1272J
Altcode:
  Interplanetary Coronal Mass Ejections (CMEs) are magnetic structures
  emanating from the Sun. A consequence of their passage at planetary
  bodies can be seen as the reduction of galactic cosmic rays (GCRs),
  a phenomenon called a Forbush decrease. These decreases are routinely
  monitored with neutron detectors around the world, while ICMEs are
  measured directly in situ by spacecraft dedicated to the monitoring of
  the solar wind. In particular, these detections show that ICMEs may or
  not build a sheath of compressed solar wind at their front, preceded in
  some cases by a shock. Then, the question remains which substructure
  may, and how, drive the Forbush decrease. Here, we will discuss how
  statistical analyses such as superposed epoch studies can be applied
  to ICME-induced Forbush decreases. In particular, by selecting ICMEs
  with or without a sheath, we will show that magnetic ejecta alone can
  drive Forbush decreases as strong as those with a sheath. Different
  from previous studies, we find with such a study that it is the magnetic
  field intensity, rather than its fluctuations, that is the main driver
  of Forbush decreases. Finally, we will show how the passage of isolated
  magnetic ejecta reveal an anisotropy in the level of GCRs in the solar
  wind at 1 au, a finding that we explain as related to the gradient of
  the GCR flux found at different distances in the heliosphere, i.e.,
  the GCR flux is slightly higher at a larger heliospheric distance.

Title: Bayesian approach for modeling global magnetic parameters of
    solar active regions
Authors: Mandrini, Cristina H.; Lopez Fuentes, Marcelo; Poisson,
   Mariano; Demoulin, Pascal; Grings, Francisco
Bibcode: 2022cosp...44.2413M
Altcode:
  Active regions (ARs) appear in the solar atmosphere as a consequence
  of the emergence of magnetic flux tubes. The magnetic field of
  these flux tubes acquires twist as it crosses the convection zone,
  building magnetic flux ropes (FRs). Due to the presence of twist,
  during the emergence of these FRs the photospheric line-of-sight (LOS)
  magnetograms show elongations of the AR polarities, also known as
  magnetic tongues. Since magnetic tongues can affect the measurement
  of AR characteristics during their emergence phase (e.g. their tilt
  angle, magnetic flux, and size, among others), direct estimations of
  the FR global quantities which do not consider this effect have to be
  revised. In this work we aim to model the emergence of ARs using a FR
  model based on a half-torus magnetic structure. We generate synthetic
  magnetograms introducing non-linear perturbations in order to reproduce
  the small scale features, asymmetries, and noise observed in real
  magnetograms. We characterize the half-torus model by generating
  1000 synthetic AR magnetograms using a Bayesian scheme to infer the
  posterior probability distribution of the model parameters. We propose
  models introducing different temporal correlations of the parameters;
  this allows us to estimate expectation values for the tilt angle,
  magnetic helicity, and magnetic flux, which are consistent with the
  input parameters of the generated ARs.

Title: Magnetic field lines configuration inside magnetic clouds:
    observations at 1 au
Authors: Dasso, Sergio; Demoulin, Pascal; Janvier, Miho; Lanabere,
   Vanina
Bibcode: 2022cosp...44.2435D
Altcode:
  Flux ropes, which are twisted magnetic flux tubes, are of major
  interest in different space and astrophysical domains, such as the Sun,
  planetary environments, and stellar physics. In particular, these
  structures are observed in the solar photosphere, the corona, the
  interplanetary medium, and also in planetary magnetospheres. Magnetic
  flux ropes in the solar wind can reach huge sizes in the heliosphere,
  storing significant amounts of magnetic energy and helicity. Thus,
  interplanetary flux ropes (IFRs) transport these quantities from the
  Sun to the outer heliosphere. A few analytical models provide the IFR
  internal magnetic configuration, which can then be compared with in
  situ observations at 1 au. This provides hints (or information) on the
  associated coronal magnetic configuration at the origin of the event.The
  derived magnetic structure of IFRs has also implications to improve
  models for propagation of energetic particles inside IFRs. Finally,
  magnetic clouds are the clearest observed sub-set of IFRs, so that a
  detailed analysis and modelisation of the observed data can be performed
  to derive their magnetic twist profile. In this review talk we will
  present a summary of the state of the art about the quantification of
  the magnetic twist  distribution in magnetic clouds from 'in-situ'
  observations at 1 au.

Title: Evolution of Plasma Composition in an Eruptive Flux Rope
Authors: Baker, Deborah; Demoulin, Pascal; Long, David; Janvier, Miho;
   Green, Lucie; Brooks, David; van Driel-Gesztelyi, Lidia; Mihailescu,
   Teodora; To, Andy S. H.; Yardley, Stephanie; Valori, Gherardo
Bibcode: 2022cosp...44.1361B
Altcode:
  Magnetic flux ropes are bundles of twisted magnetic field enveloping a
  central axis. They harbor free magnetic energy and can be progenitors
  of coronal mass ejections (CMEs). However, identifying flux ropes on
  the Sun can be challenging. One of the key coronal observables that
  has been shown to indicate the presence of a flux rope is a peculiar
  bright coronal structure called a sigmoid. In this work, we show Hinode
  EUV Imaging Spectrometer observations of sigmoidal active region (AR)
  10977. We analyze the coronal plasma composition in the AR and its
  evolution as a sigmoid (flux rope) forms and erupts as a CME. Plasma
  with photospheric composition was observed in coronal loops close to
  the main polarity inversion line during episodes of significant flux
  cancellation, suggestive of the injection of photospheric plasma into
  these loops driven by photospheric flux cancellation. Concurrently,
  the increasingly sheared core field contained plasma with coronal
  composition. As flux cancellation decreased and a sigmoid/flux
  rope formed, the plasma evolved to an intermediate composition in
  between photospheric and typical AR coronal compositions. Finally,
  the flux rope contained predominantly photospheric plasma during and
  after a failed eruption preceding the CME. Hence, plasma composition
  observations of AR 10977 strongly support models of flux rope formation
  by photospheric flux cancellation forcing magnetic reconnection first
  at the photospheric level then at the coronal level.

Title: Bayesian approach for modeling solar active region global
    magnetic parameters
Authors: Poisson, M.; Grings, F.; Mandrini, C. H.; López-Fuentes,
   M.; Démoulin, P.
Bibcode: 2022arXiv220705900P
Altcode:
  Context. Active regions (ARs) appear in the solar atmosphere as a
  consequence of the emergence of magnetic flux tubes. The presence
  of elongated magnetic polarities in line-of-sight (LOS) magnetograms
  indicates the existence of twist in the flux tubes forming them. These
  polarity elongations, called magnetic tongues, bias the measurement of
  AR characteristics obtained during their emergence phase (e.g. their
  tilt angle and magnetic flux, among others). In particular, obtaining
  a good estimation of the tilt angle evolution plays a key role in
  constraining flux-transport dynamo models. Aims. In this work we aim
  to estimate the intrinsic properties of the twisted flux tubes, or
  flux ropes, that form ARs by quantitatively comparing observed LOS
  magnetograms with synthetic ones derived from a toroidal magnetic
  flux tube model. Methods. For this reason, we develop a Bayesian
  inference method to obtain the statistical distributions of the
  inferred model parameters. As an example, we apply the method to NOAA
  AR 10268. Next, we test the results using a synthetic-AR generator to
  quantify the effect of small scale perturbations over the inferred
  parameter distributions. Results. We conclude that this method can
  significantly remove the effects of magnetic tongues on the derived AR
  global characteristics, providing a better knowledge of the intrinsic
  properties of the emerging flux rope. Conclusions. These results provide
  a framework for future analysis of the physical properties of emerging
  ARs using Bayesian statistics.

Title: Analysis of the Evolution of a Multi-Ribbon Flare and Failed
    Filament Eruption
Authors: Joshi, Reetika; Mandrini, Cristina H.; Chandra, Ramesh;
   Schmieder, Brigitte; Cristiani, Germán D.; Mac Cormack, Cecilia;
   Démoulin, Pascal; Cremades, Hebe
Bibcode: 2022SoPh..297...81J
Altcode: 2022arXiv220600531J
  How filaments form and erupt are topics about which solar researchers
  have wondered for more than a century and they are still open
  to debate. We present observations of a filament formation, its
  failed eruption, and the associated flare (SOL2019-05-09T05:51)
  that occurred in active region (AR) 12740 using data from the
  Solar Dynamics Observatory (SDO), the Solar-Terrestrial Relations
  Observatory A (STEREO-A), the Interface Region Imaging Spectrograph
  (IRIS) and the Learmonth Solar Observatory (LSO) of the National Solar
  Observatory/Global Oscillation Network Group (NSO/GONG). AR 12740
  was a decaying region formed by a very disperse following polarity
  and a strong leading spot, surrounded by a highly dynamic zone where
  moving magnetic features (MMFs) were seen constantly diverging from
  the spot. Our analysis indicates that the filament was formed by the
  convergence of fibrils at a location where magnetic flux cancellation
  was observed. Furthermore, we conclude that its destabilisation was also
  related to flux cancellation associated with the constant shuffling
  of the MMFs. A two-ribbon flare occurred associated with the filament
  eruption; however, because the large-scale magnetic configuration of
  the AR was quadrupolar, two additional flare ribbons developed far from
  the two main ones. We model the magnetic configuration of the AR using
  a force-free field approach at the AR scale size. This local model is
  complemented by a global potential-field source-surface one. Based on
  the local model, we propose a scenario in which the filament failed
  eruption and the flare are due to two reconnection processes, one
  occurring below the erupting filament, leading to the two-ribbon flare,
  and another one above it between the filament flux-rope configuration
  and the large-scale closed loops. Our computation of the reconnected
  magnetic flux added to the erupting flux rope, compared to that of
  the large-scale field overlying it, allows us to conclude that the
  latter was large enough to prevent the filament eruption. A similar
  conjecture can be drawn from the computation of the magnetic tension
  derived from the global field model.

Title: Statistical Analysis of the Radial Evolution of the Solar Winds
    between 0.1 and 1 au, and their Semi-empirical Iso-poly Fluid Modeling
Authors: Dakeyo; Maksimovic; Démoulin; Halekas; Stevens
Bibcode: 2022arXiv220703898D
Altcode:
  Statistical classification of the Helios solar wind observations into
  several populations sorted by bulk speed has revealed an outward
  acceleration of the wind. The faster the wind is, the smaller is
  this acceleration in the 0.3 - 1 au radial range (Maksimovic et
  al. 2020). In this article we show that recent measurements from the
  Parker Solar Probe (PSP) are compatible with an extension closer to
  the Sun of the latter Helios classification. For instance the well
  established bulk speed/proton temperature (u,Tp) correlation and bulk
  speed/electron temperature (u,Te) anti-correlation, together with the
  acceleration of the slowest winds, are verified in PSP data. We also
  model the combined PSP and Helios data, using empirical Parker-like
  models for which the solar wind undergoes an "iso-poly" expansion:
  isothermal in the corona, then polytropic at distances larger than
  the sonic point radius. The polytropic indices are derived from the
  observed temperature and density gradients. Our modelling reveals
  that the electron thermal pressure has a major contribution in the
  acceleration process of slow and intermediate winds (in the range of
  300-500 km/s at 1 au), over a broad range of distances and that the
  global (electron and protons) thermal energy, alone, is able to explain
  the acceleration profiles. Moreover, we show that the very slow solar
  wind requires in addition to the observed pressure gradients, another
  source of acceleration.

Title: Pressure balance of coronal mass ejections during their
    Sun-Earth journey modelled by 3D MHD EUHFORIA simulations
Authors: Schmieder, Brigitte; Dasso, Sergio; Grison, Benjamin;
   Demoulin, Pascal; Verbeke, Christine; Scolini, Camilla; Samara,
   Evangelia; Poedts, Stefaan
Bibcode: 2022cosp...44.2474S
Altcode:
  The aim of this work is to understand the signatures of three coronal
  mass ejections (CMEs) at the Lagrange point L1 launched from the Sun
  between 15 and 18 July 2002. We use the EUropean Heliosphere FORecasting
  Information Asset (EUHFORIA) model to simulate their propagation and
  interaction in the background solar wind. The approach is to place
  virtual spacecraft along the Sun-Earth line. We set up the initial
  conditions at 0.1 au, modelling each CME using the linear force free
  spheromak model. We perform an analysis on the pressures acting
  within the first and the last CMEs of the series (CME1 and CME3)
  and investigate the role of pressure (un)balance in their expansion,
  while the second CME (CME2) was too compressed to be able to expand
  its ejecta during propagation. We find that the magnetic pressure
  within CME1 and CME3 was prominent at 0.1 au and rapidly decreased
  between 0.1 au and Earth, so that the gas pressure was progressively
  dominating in their extended ejecta.

Title: Eruption of the EUV Hot Channel from the Solar Limb and
    Associated Moving Type IV Radio Burst
Authors: Vemareddy, P.; Démoulin, P.; Sasikumar Raja, K.; Zhang,
   J.; Gopalswamy, N.; Vasantharaju, N.
Bibcode: 2022ApJ...927..108V
Altcode: 2022arXiv220106899V
  Using the observations from the Solar Dynamics Observatory, we study
  an eruption of a hot-channel flux rope (FR) near the solar limb on 2015
  February 9. The pre-eruptive structure is visible mainly in EUV 131 Å
  images, with two highly sheared loop structures. They undergo a slow
  rising motion and then reconnect to form an eruptive hot channel,
  as in the tether-cutting reconnection model. The J-shaped flare
  ribbons trace the footpoint of the FR that is identified as the hot
  channel. Initially, the hot channel is observed to rise slowly at 40
  km s<SUP>-1</SUP>, followed by an exponential rise from 22:55 UT at a
  coronal height of 87 ± 2 Mm. Following the onset of the eruption at
  23:00 UT, the flare reconnection then adds to the acceleration process
  of the coronal mass ejection (CME) within 3 R <SUB>⊙</SUB>. Later
  on, the CME continues to accelerate at 8 m s<SUP>-2</SUP> during its
  propagation period. Further, the eruption also launched type II radio
  bursts, which were followed by type III and type IVm radio bursts. The
  start and end times of the type IVm burst correspond to the CME's
  core height of 1.5 and 6.1 R <SUB>⊙</SUB>, respectively. Also, the
  spectral index is negative, suggesting that nonthermal electrons are
  trapped in the closed loop structure. Accompanied by this type IVm
  burst, this event is unique in the sense that the flare ribbons are
  very clearly observed together with the erupting hot channel, which
  strongly suggests that the hooked parts of the J-shaped flare ribbons
  outline the boundary of the erupting FR.

Title: A solar flare driven by thermal conduction observed in
    mid-infrared
Authors: López, Fernando M.; Giménez de Castro, Carlos Guillermo;
   Mandrini, Cristina H.; Simões, Paulo J. A.; Cristiani, Germán D.;
   Gary, Dale E.; Francile, Carlos; Démoulin, Pascal
Bibcode: 2022A&A...657A..51L
Altcode: 2021arXiv211015751L
  Context. The mid-infrared (mid-IR) range has been mostly unexplored
  for the investigation of solar flares. It is only recently that new
  mid-IR flare observations have begun opening a new window into the
  response and evolution of the solar chromosphere. These new observations
  have been mostly performed by the AR30T and BR30T telescopes that are
  operating in Argentina and Brazil, respectively. <BR /> Aims: We present
  the analysis of SOL2019-05-15T19:24, a GOES class C2.0 solar flare
  observed at 30 THz (10 μm) by the ground-based telescope AR30T. Our
  aim is to characterize the evolution of the flaring atmosphere and
  the energy transport mechanism in the context of mid-IR emission. <BR
  /> Methods: We performed a multi-wavelength analysis of the event by
  complementing the mid-IR data with diverse ground- and space-based data
  from the Solar Dynamics Observatory (SDO), the H-α Solar Telescope
  for Argentina, and the Expanded Owens Valley Solar Array (EOVSA). Our
  study includes the analysis of the magnetic field evolution of the
  flaring region and of the development of the flare. <BR /> Results:
  The mid-IR images from AR30T show two bright and compact flare sources
  that are spatially associated with the flare kernels observed in
  ultraviolet (UV) by SDO. We confirm that the temporal association
  between mid-IR and UV fluxes previously reported for strong flares
  is also observed for this small flare. The EOVSA microwave data
  revealed flare spectra consistent with thermal free-free emission,
  which lead us to dismiss the existence of a significant number of
  non-thermal electrons. We thus consider thermal conduction as the
  primary mechanism responsible for energy transport. Our estimates
  for the thermal conduction energy and total radiated energy fall
  within the same order of magnitude, reinforcing our conclusions. <P
  />Movies associated to Figs. 1, 2 and 4 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202141967/olm">https://www.aanda.org</A>

Title: Evolution of Plasma Composition in an Eruptive Flux Rope
Authors: Baker, D.; Green, L. M.; Brooks, D. H.; Démoulin, P.;
   van Driel-Gesztelyi, L.; Mihailescu, T.; To, A. S. H.; Long, D. M.;
   Yardley, S. L.; Janvier, M.; Valori, G.
Bibcode: 2022ApJ...924...17B
Altcode: 2021arXiv211011714B
  Magnetic flux ropes are bundles of twisted magnetic field enveloping a
  central axis. They harbor free magnetic energy and can be progenitors
  of coronal mass ejections (CMEs). However, identifying flux ropes on
  the Sun can be challenging. One of the key coronal observables that
  has been shown to indicate the presence of a flux rope is a peculiar
  bright coronal structure called a sigmoid. In this work, we show Hinode
  EUV Imaging Spectrometer observations of sigmoidal active region (AR)
  10977. We analyze the coronal plasma composition in the AR and its
  evolution as a sigmoid (flux rope) forms and erupts as a CME. Plasma
  with photospheric composition was observed in coronal loops close to
  the main polarity inversion line during episodes of significant flux
  cancellation, suggestive of the injection of photospheric plasma into
  these loops driven by photospheric flux cancellation. Concurrently,
  the increasingly sheared core field contained plasma with coronal
  composition. As flux cancellation decreased and a sigmoid/flux
  rope formed, the plasma evolved to an intermediate composition in
  between photospheric and typical AR coronal compositions. Finally,
  the flux rope contained predominantly photospheric plasma during and
  after a failed eruption preceding the CME. Hence, plasma composition
  observations of AR 10977 strongly support models of flux rope formation
  by photospheric flux cancellation forcing magnetic reconnection first
  at the photospheric level then at the coronal level.

Title: The Two-step Forbush Decrease: A Tale of Two Substructures
    Modulating Galactic Cosmic Rays within Coronal Mass Ejections
Authors: Janvier, Miho; Démoulin, Pascal; Guo, Jingnan; Dasso, Sergio;
   Regnault, Florian; Topsi-Moutesidou, Sofia; Gutierrez, Christian;
   Perri, Barbara
Bibcode: 2021ApJ...922..216J
Altcode: 2021arXiv210914469J
  Interplanetary coronal mass ejections (ICMEs) are known to modify
  the structure of the solar wind as well as interact with the space
  environment of planetary systems. Their large magnetic structures have
  been shown to interact with galactic cosmic rays (GCRs), leading to the
  Forbush decrease (FD) phenomenon. We revisit in the present article
  the 17 yr of Advanced Composition Explorer spacecraft ICME detection
  along with two neutron monitors (McMurdo and Oulu) with a superposed
  epoch analysis to further analyze the role of the magnetic ejecta in
  driving FDs. We investigate in the following the role of the sheath and
  the magnetic ejecta in driving FDs, and we further show that for ICMEs
  without a sheath, a magnetic ejecta only is able to drive significant
  FDs of comparable intensities. Furthermore, a comparison of samples with
  and without a sheath with similar speed profiles enable us to show that
  the magnetic field intensity, rather than its fluctuations, is the main
  driver for the FD. Finally, the recovery phase of the FD for isolated
  magnetic ejecta shows an anisotropy in the level of the GCRs. We relate
  this finding at 1 au to the gradient of the GCR flux found at different
  heliospheric distances from several interplanetary missions.

Title: Filament Eruption Driving EUV Loop Contraction and Then
    Expansion above a Stable Filament
Authors: Chandra, Ramesh; Démoulin, Pascal; Devi, Pooja; Joshi,
   Reetika; Schmieder, Brigitte
Bibcode: 2021ApJ...922..227C
Altcode: 2021arXiv210907821C
  We analyze the observations of EUV loop evolution associated with the
  filament eruption located at the border of an active region (AR). The
  event SOL2013-03-16T14:00 was observed with a large difference in
  view point by the Solar Dynamics Observatory and Solar Terrestrial
  Relations Observatory. The filament height is fitted with the sum of
  a linear and exponential function. These two phases point to different
  physical mechanisms such as tether-cutting reconnection and a magnetic
  instability. While no X-ray emission is reported, this event presents
  classical eruption features like separation of double ribbons and the
  growth of flare loops. We report the migration of the southern foot of
  the erupting filament flux rope due to the interchange reconnection
  with encountered magnetic loops of a neighboring AR. Parallel to the
  erupting filament, a stable filament remains in the core of the AR. The
  specificity of this eruption is that coronal loops, located above the
  nearly joining ends of the two filaments, first contract in phase, then
  expand and reach a new stable configuration close to the one present at
  the eruption onset. Both contraction and expansion phases last around
  20 minutes. The main difference with previous cases is that the PIL bent
  about 180° around the end of the erupting filament because the magnetic
  configuration is at least tripolar. These observations are challenging
  for models that interpreted previous cases of loop contraction within
  a bipolar configuration. New simulations are required to broaden the
  complexity of the configurations studied.

Title: Plasma Upflows Induced by Magnetic Reconnection Above an
    Eruptive Flux Rope
Authors: Baker, Deborah; Mihailescu, Teodora; Démoulin, Pascal;
   Green, Lucie M.; van Driel-Gesztelyi, Lidia; Valori, Gherardo; Brooks,
   David H.; Long, David M.; Janvier, Miho
Bibcode: 2021SoPh..296..103B
Altcode: 2021arXiv210616137B
  One of the major discoveries of Hinode's Extreme-ultraviolet
  Imaging Spectrometer (EIS) is the presence of upflows at the edges
  of active regions. As active regions are magnetically connected
  to the large-scale field of the corona, these upflows are a likely
  contributor to the global mass cycle in the corona. Here we examine
  the driving mechanism(s) of the very strong upflows with velocities
  in excess of 70 km s<SUP>−1</SUP>, known as blue-wing asymmetries,
  observed during the eruption of a flux rope in AR 10977 (eruptive flare
  SOL2007-12-07T04:50). We use Hinode/EIS spectroscopic observations
  combined with magnetic-field modeling to investigate the possible
  link between the magnetic topology of the active region and the strong
  upflows. A Potential Field Source Surface (PFSS) extrapolation of the
  large-scale field shows a quadrupolar configuration with a separator
  lying above the flux rope. Field lines formed by induced reconnection
  along the separator before and during the flux-rope eruption are
  spatially linked to the strongest blue-wing asymmetries in the upflow
  regions. The flows are driven by the pressure gradient created when
  the dense and hot arcade loops of the active region reconnect with
  the extended and tenuous loops overlying it. In view of the fact
  that separator reconnection is a specific form of the more general
  quasi-separatrix (QSL) reconnection, we conclude that the mechanism
  driving the strongest upflows is, in fact, the same as the one driving
  the persistent upflows of ≈10 - 20 km s<SUP>−1</SUP> observed in
  all active regions.

Title: ICMEs and low plasma density in the solar wind observed at L1
Authors: Schmieder, Brigitte; Verbeke, Christine; Chané, Emmanuel;
   Démoulin, Pascal; Poedts, Stefaan; Grison, Benjamin
Bibcode: 2021EGUGA..23.1799S
Altcode:
  Different regimes of the solar wind have been observed at L1 during and
  after the passage of ICMEs, particularly anomalies with very low plasma
  density. From the observations at L1 (ACE) we identified different
  possible cases. A first case was explained by the evacuation of the
  plasma due over expansion of the ICME (May 2002). The second case on
  July 2002 is intriguing.In July 2002, three halo fast speed ICMEs,
  with their origin in the central part of the Sun, have surprisingly
  a poor impact on the magnetosphere (Dst &gt; -28 nT). Analyzing the
  characteristics of the first ICME at L1, we conclude that the spacecraft
  crosses the ICME with a large impact (Bx component in GSE coordinates is
  dominant). The plasma density is low, just behind this first ICME. Next,
  we explore the generic conditions of low density formation in the
  EUHFORIA simulations.The very low density plasma after the sheath
  could be explained by the spacecraft crossing, on the side of the
  flux rope, while behind the front shock. We investigate two possible
  interpretations. The shock was able to compress and accelerate so much
  the plasma that a lower density is left behind. This can also be due
  to an effect of the sheath magnetic field which extends the flux rope
  effect on the sides of it, so a decrease of plasma density could occur
  like behind a moving object (here the sheath field). The following ICME,
  with also a low density, could be an intrinsic case with the formation
  in the corona of a cavity. Finally, we present some runs of EUHFORIA
  which fit approximately these data and argue in favor of the possible
  interpretations detailed above.

Title: Over-expansion of a coronal mass ejection generates
    sub-Alfvénic plasma conditions in the solar wind at Earth
Authors: Chané, E.; Schmieder, B.; Dasso, S.; Verbeke, C.; Grison,
   B.; Démoulin, P.; Poedts, S.
Bibcode: 2021A&A...647A.149C
Altcode:
  Context. From May 24-25, 2002, four spacecraft located in the solar
  wind at about 1 astronomical unit (au) measured plasma densities
  one to two orders of magnitude lower than usual. The density was
  so low that the flow became sub-Alfvénic for four hours, and the
  Alfvén Mach number was as low as 0.4. Consequently, the Earth lost
  its bow shock, and two long Alfvén wings were generated. <BR />
  Aims: This is one of the lowest density events ever recorded in the
  solar wind at 1 au, and the least documented one. Our goal is to
  understand what caused the very low density. <BR /> Methods: Large
  Angle and Spectrometric Coronagraph (LASCO) and in situ data were
  used to identify whether something unusual occurred that could have
  generated such low densities <BR /> Results: The very low density was
  recorded inside a large interplanetary coronal mass ejection (ICME),
  which displayed a long, linearly declining velocity profile, typical
  of expanding ICMEs. We deduce a normalised radial expansion rate of
  1.6. Such a strong expansion, occurring over a long period of time,
  implies a radial size expansion growing with the distance from the Sun
  to the power 1.6. This can explain a two-orders-of-magnitude drop in
  plasma density. Data from LASCO and the Advanced Composition Explorer
  show that this over-expanding ICME was travelling in the wake of a
  previous ICME. <BR /> Conclusions: The very low densities measured
  in the solar wind in May 2002 were caused by the over-expansion of
  a large ICME. This over-expansion was made possible because the ICME
  was travelling in a low-density and high-velocity environment present
  in the wake of another ICME coming from a nearby region on the Sun and
  ejected only three hours previously. Such conditions are very unusual,
  which explains why such very low densities are almost never observed.

Title: Observations of a prominence eruption and loop contraction
Authors: Devi, Pooja; Démoulin, Pascal; Chandra, Ramesh; Joshi,
   Reetika; Schmieder, Brigitte; Joshi, Bhuwan
Bibcode: 2021A&A...647A..85D
Altcode: 2021arXiv210107682D
  Context. Prominence eruptions provide key observations to understand
  the launch of coronal mass ejections as their cold plasma traces a
  part of the unstable magnetic configuration. <BR /> Aims: We select a
  well observed case to derive observational constraints for eruption
  models. <BR /> Methods: We analyze the prominence eruption and loop
  expansion and contraction observed on 02 March 2015 associated with
  a GOES M3.7 class flare (SOL2015-03-02T15:27) using the data from
  Atmospheric Imaging Assembly (AIA) and the Reuven Ramaty High Energy
  Solar Spectroscopic Imager (RHESSI). We study the prominence eruption
  and the evolution of loops using the time-distance techniques. <BR />
  Results: The source region is a decaying bipolar active region where
  magnetic flux cancellation is present for several days before the
  eruption. AIA observations locate the erupting prominence within a flux
  rope viewed along its local axis direction. We identify and quantify
  the motion of loops in contraction and expansion located on the side
  of the erupting flux rope. Finally, RHESSI hard X-ray observations
  identify the loop top and two foot-point sources. <BR /> Conclusions:
  Both AIA and RHESSI observations support the standard model of eruptive
  flares. The contraction occurs 19 min after the start of the prominence
  eruption indicating that this contraction is not associated with
  the eruption driver. Rather, this prominence eruption is compatible
  with an unstable flux rope where the contraction and expansion of
  the lateral loop is the consequence of a side vortex developing
  after the flux rope is launched. <P />Movies are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202040042/olm">https://www.aanda.org</A>

Title: The Magnetic Environment of a Stealth Coronal Mass Ejection
Authors: O'Kane, Jennifer; Mac Cormack, Cecilia; Mandrini, Cristina H.;
   Démoulin, Pascal; Green, Lucie M.; Long, David M.; Valori, Gherardo
Bibcode: 2021ApJ...908...89O
Altcode: 2020arXiv201203757O
  Interest in stealth coronal mass ejections (CMEs) is increasing due to
  their relatively high occurrence rate and space weather impact. However,
  typical CME signatures such as extreme-ultraviolet dimmings and
  post-eruptive arcades are hard to identify and require extensive image
  processing techniques. These weak observational signatures mean that
  little is currently understood about the physics of these events. We
  present an extensive study of the magnetic field configuration in which
  the stealth CME of 2011 March 3 occurred. Three distinct episodes
  of flare ribbon formation are observed in the stealth CME source
  active region (AR). Two occurred prior to the eruption and suggest the
  occurrence of magnetic reconnection that builds the structure that will
  become eruptive. The third occurs in a time close to the eruption of
  a cavity that is observed in STEREO-B 171 Å data; this subsequently
  becomes part of the propagating CME observed in coronagraph data. We
  use both local (Cartesian) and global (spherical) models of the coronal
  magnetic field, which are complemented and verified by the observational
  analysis. We find evidence of a coronal null point, with field lines
  computed from its neighborhood connecting the stealth CME source region
  to two ARs in the northern hemisphere. We conclude that reconnection
  at the null point aids the eruption of the stealth CME by removing the
  field that acted to stabilize the preeruptive structure. This stealth
  CME, despite its weak signatures, has the main characteristics of
  other CMEs, and its eruption is driven by similar mechanisms.

Title: Magnetic twist distribution inside interplanetary flux ropes
Authors: Dasso, Sergio; Rodriguez, Luciano; Demoulin, Pascal;
   Masias-Meza, Jimmy J.; Janvier, Miho; Lanabere, Vanina
Bibcode: 2021cosp...43E1756D
Altcode:
  Twisted magnetic flux tubes, also known as flux ropes, are ubiquitous
  in solar, stellar, and planetary environments. They are present in the
  photosphere of the Sun, the solar corona, the solar wind, and also in
  different locations of planetary magnetospheres and ionospheres. In
  particular, interplanetary flux ropes (IFRs) can store magnetic energy
  and, because their magnetic field lines are twisted around the tube
  axis, also can store important amounts of magnetic helicity. Thus, IFRs
  can transport these quantities from the Sun to the outer space of the
  heliosphere. The internal distribution of the magnetic twist forming
  the flux rope (i.e., the number of turns per unit length), is a key
  property to link IFRs with their solar origin and ejection processes,
  to improve the knowledge of coronal structures in equilibrium, and
  also to better understand the energetic particle propagation inside
  these interplanetary structures. Quantifying the magnetic twist
  distribution in IFRs from 'in-situ' observations of single events has
  a major difficulty produced by the significant field fluctuations
  in the interplanetary magnetic field. Magnetic clouds (MCs) are a
  sub-set of Interplanetary Coronal Ejections (ICMEs), which present
  clear signatures of flux ropes when 'in-situ' observed. In this work,
  we apply a superposed epoch analysis to a significant sample of MCs
  observed at 1 au, to extract their common features, and to remove the
  peculiarity and eventual high level of noise present in individual
  cases. From this analysis, we quantify the typical twist distribution
  inside the flux ropes forming MCs. As one of the main results, we find
  that the twist is nearly uniform in the core (central half part around
  the flux rope axis), and it increases moderately, up to a factor two,
  towards the MC boundaries. These results will allow to better understand
  these magnetic structures and to link them with their solar origin.

Title: 20 years of ACE data: how superposed epoch analyses reveal
    generic features in interplanetary CME profiles
Authors: Regnault, Florian; Dasso, Sergio; Auchere, Frederic; Demoulin,
   Pascal; Janvier, Miho; Strugarek, Antoine
Bibcode: 2021cosp...43E1017R
Altcode:
  Interplanetary Coronal Mass Ejections (ICMEs) result from solar flares
  occurring in our star's atmosphere. These large-scale magnetized
  structures propagate in the interplanetary medium where they can be
  probed by spacecraft. Depending on their speed, ICMEs may accumulate
  enough solar wind plasma to form a turbulent sheath ahead of them. They
  therefore consist of two main substructures : a sheath and a magnetic
  ejecta (ME). The magnetic ejecta is the main body of an ICME where
  the magnetic field is more intense and with less variance than that
  of the ambient solar wind. We present a statistical study using the
  superposed epoch analysis technique on a catalog of around 400 ICMEs
  where we consider the profiles of the physical parameters of the ICMEs
  (the magnetic field intensity, the speed, temperature, ...) seen at
  1 AU by the ACE spacecraft. In particular, we investigate different
  possible classifications of ICMEs, for example based on their speeds,
  the phase of the solar cycle when they are detected, and the detection
  of an associated magnetic cloud (MCs, a subset of MEs with a clear
  rotation of the magnetic field as well as a low plasma temperature
  compared with the solar wind). We confirm that slow ICMEs have a
  more symmetric profile than fast ICMEs, therefore generalizing the
  work made on a sample of 44 ICMEs with clearly identified magnetic
  clouds by Masias-Meza et al. (2016). We also find that fast ICMEs
  show signs of compression in both their magnetic ejecta and in their
  sheath. Furthermore, we do not find any impact of the solar cycle on the
  generic features of ICMEs. However, more extreme events are observed
  during the active parts of the cycle, widening the distributions of
  all parameters. Finally, we find that ICMEs with or without a detected
  magnetic cloud show similar profiles, which confirms the hypothesis
  that both types of events correspond to similar ICMEs, and that the
  ones with no detected magnetic clouds may be observed when crossed
  sufficiently away from the flux rope core.

Title: Initiation of CMEs and their geo-effectiveness
Authors: Schmieder, Brigitte; Poedts, Stefaan; Grison, Benjamin;
   Demoulin, Pascal; Kim, Rok-Soon; Verbeke, Christine
Bibcode: 2021cosp...43E1013S
Altcode:
  Physical conditions of solar eruptions triggering coronal mass ejections
  (CMEs) have been determined by recent multi-wavelength observations
  as well by numerical simulations (e.g. OHM). CMEs and flares are the
  seeds of the Space Weather. Our analyze consists on a few case studies
  of CMEs which have all the good proxies for inducing geo-effectivity
  e.g. fast halo CME, central solar disk source. We follow the CMEs
  surfing in the solar wind as interplanetary coronal mass ejections
  (ICME) or magnetic clouds. We use numerical simulations (EUHFORIA) to
  investigate the geo-effectiveness of these ICMEs We study the degree
  of deviation of these halo CMEs from the Sun-Earth axis as well as
  their deformation and erosion due to their interaction with the ambient
  solar wind resulting in magnetic reconnections according to the input
  of parameters and their chance to hit other planets. The inhomogeneous
  nature of the solar wind and encounters are also important parameters
  influencing the impact of CMEs on planetary magnetospheres

Title: A method to correct the effect of magnetic tongues and its
    application to measure active-region tilt angles
Authors: Mandrini, Cristina H.; Lopez Fuentes, Marcelo; Poisson,
   Mariano; Demoulin, Pascal
Bibcode: 2021cosp...43E1760M
Altcode:
  The presence of elongated magnetic polarities in active-region (AR)
  line-of-sight (LOS) magnetograms indicates the existence of twist
  in the flux tube forming them. These elongations, called magnetic
  tongues, which are mostly visible during the emergence phase of ARs,
  affect the measurement of several AR characteristics; in particular,
  their tilt angles. Tilt angles have been measured thoroughly using LOS
  magnetograms and, historically speaking, long-term white-light (WL)
  databases, sometimes combined with magnetic field information. Since
  the influence of magnetic tongues on tilt measurements has not yet been
  taken into account in these measurements, we aim to investigate their
  impact on the different methods used to compute tilt values. We apply
  standard methods to WL data and LOS magnetograms, some developed by us
  and others used in long-term databases, and show that the computed tilt
  values are affected by the presence of magnetic tongues. Therefore,
  we apply the newly developed Core Field Fit Estimator (CoFFE) method
  to separate the magnetic flux in the tongues from that in the AR core
  when using LOS magnetograms. We compare all the determined tilt-angle
  values and find that, for ARs with low magnetic flux tongues, all of
  them report consistent values. But for ARs with high flux tongues,
  there are noticeable discrepancies between all methods, indicating
  that these features affect differently WL and magnetic data. However,
  in general, CoFFE achieves a better estimation of the main bipole tilt
  because it removes the effect of tongues, as well as the influence of
  the emergence of secondary bipoles.

Title: Alfvénic Perturbations in a Sunspot Chromosphere Linked to
    Fractionated Plasma in the Corona
Authors: Baker, Deborah; Stangalini, Marco; Valori, Gherardo; Brooks,
   David H.; To, Andy S. H.; van Driel-Gesztelyi, Lidia; Démoulin,
   Pascal; Stansby, David; Jess, David B.; Jafarzadeh, Shahin
Bibcode: 2021ApJ...907...16B
Altcode: 2020arXiv201204308B
  In this study, we investigate the spatial distribution of highly
  varying plasma composition around one of the largest sunspots of solar
  cycle 24. Observations of the photosphere, chromosphere, and corona
  are brought together with magnetic field modeling of the sunspot
  in order to probe the conditions that regulate the degree of plasma
  fractionation within loop populations of differing connectivities. We
  find that, in the coronal magnetic field above the sunspot umbra,
  the plasma has photospheric composition. Coronal loops rooted in the
  penumbra contain fractionated plasma, with the highest levels observed
  in the loops that connect within the active region. Tracing field
  lines from regions of fractionated plasma in the corona to locations
  of Alfvénic fluctuations detected in the chromosphere shows that they
  are magnetically linked. These results indicate a connection between
  sunspot chromospheric activity and observable changes in coronal
  plasma composition.

Title: 20 Years of ACE Data: How Superposed Epoch Analyses Reveal
    Generic Features in Interplanetary CME Profiles
Authors: Regnault, F.; Janvier, M.; Démoulin, P.; Auchère, F.;
   Strugarek, A.; Dasso, S.; Noûs, C.
Bibcode: 2020JGRA..12528150R
Altcode: 2020arXiv201105050R
  Interplanetary coronal mass ejections (ICMEs) are magnetic structures
  propagating from the Sun's corona to the interplanetary medium. With
  over 20 years of observations at the L1 libration point, ACE offers
  hundreds of ICMEs detected at different times during several solar
  cycles and with different features such as the propagation speed. We
  investigate a revisited catalog of more than 400 ICMEs using the
  superposed epoch method on the mean, median, and the most probable
  values of the distribution of magnetic and plasma parameters. We also
  investigate the effects of the speed of ICMEs relative to the solar
  wind, the solar cycle, and the existence of a magnetic cloud on the
  generic ICME profile. We find that fast-propagating ICMEs (relatively
  to the solar wind in front) still show signs of compression at 1 au, as
  seen by the compressed sheath and the asymmetric profile of the magnetic
  field. While the solar cycle evolution does not impact the generic
  features of ICMEs, there are more extreme events during the active part
  of the cycle, widening the distributions of all parameters. Finally, we
  find that ICMEs with or without a detected magnetic cloud show similar
  profiles, which confirms the hypothesis that ICMEs with no detected
  magnetic clouds are crossed further away from the flux rope core. Such
  a study provides a generic understanding of processes that shape the
  overall features of ICMEs in the solar wind and can be extended with
  future missions at different locations in the solar system.

Title: Additivity of relative magnetic helicity in finite volumes
Authors: Valori, Gherardo; Démoulin, Pascal; Pariat, Etienne; Yeates,
   Anthony; Moraitis, Kostas; Linan, Luis
Bibcode: 2020A&A...643A..26V
Altcode: 2020arXiv200800968V
  Context. Relative magnetic helicity is conserved by magneto-hydrodynamic
  evolution even in the presence of moderate resistivity. For that reason,
  it is often invoked as the most relevant constraint on the dynamical
  evolution of plasmas in complex systems, such as solar and stellar
  dynamos, photospheric flux emergence, solar eruptions, and relaxation
  processes in laboratory plasmas. However, such studies often indirectly
  imply that relative magnetic helicity in a given spatial domain can be
  algebraically split into the helicity contributions of the composing
  subvolumes, in other words that it is an additive quantity. A limited
  number of very specific applications have shown that this is not the
  case. <BR /> Aims: Progress in understanding the nonadditivity of
  relative magnetic helicity requires removal of restrictive assumptions
  in favor of a general formalism that can be used in both theoretical
  investigations and numerical applications. <BR /> Methods: We derive the
  analytical gauge-invariant expression for the partition of relative
  magnetic helicity between contiguous finite volumes, without any
  assumptions on either the shape of the volumes and interface, or the
  employed gauge. <BR /> Results: We prove the nonadditivity of relative
  magnetic helicity in finite volumes in the most general, gauge-invariant
  formalism, and verify this numerically. We adopt more restrictive
  assumptions to derive known specific approximations, which yields a
  unified view of the additivity issue. As an example, the case of a
  flux rope embedded in a potential field shows that the nonadditivity
  term in the partition equation is, in general, non-negligible. <BR
  /> Conclusions: The nonadditivity of relative magnetic helicity can
  potentially be a serious impediment to the application of relative
  helicity conservation as a constraint on the complex dynamics of
  magnetized plasmas. The relative helicity partition formula can be
  applied to numerical simulations to precisely quantify the effect of
  nonadditivity on global helicity budgets of complex physical processes.

Title: The Magnetic Environment of a Stealth CME
Authors: O'Kane, J.; Mandrini, C.; Demoulin, P.; Green, L.; Valori,
   G.; Long, D.
Bibcode: 2020SPD....5121005O
Altcode:
  Interest in Stealth Coronal Mass Ejections (CMEs) is increasing due to
  their relatively high occurrence rate and space weather impact. However,
  typical CME signatures such as EUV dimmings and post-eruptive arcades
  are hard to identify for stealth CMEs and require extensive image
  processing techniques. These weak observational signatures mean little
  is currently understood about the physics of these events. We present
  an extensive study of the magnetic field configuration in which the
  stealth CME of 3 March 2011 occurred. The magnetic field prior to the
  eruption is evaluated using a Linear Force Free Field (LFFF) model
  and a Potential Field Source Surface (PFSS) model, and complemented
  by in-depth observational analysis. The models are verified using
  observations of plasma emission structures in the stealth CME source
  region and trans-equatorial loops. We find evidence of a high-altitude
  null point in both the LFFF model and the PFSS model, with surrounding
  field lines connecting two active regions on the solar disk. One of
  these active regions in the Southern Hemisphere is shown to be the
  source region of the stealth CME. Three distinct episodes of flare
  ribbon formation are observed in AIA 304Å. Two occurred prior to
  the eruption and suggest the occurrence of magnetic reconnection that
  builds the eruptive structure. The third occurs at the same time as an
  erupting cavity is observed in STEREO-B 171Å data; this subsequently
  becomes part of the propagating CME observed in COR1. We conclude that
  reconnection at the null point, driven by eruptive activity in the
  complex northern active region, aids the eruption of the stealth CME
  by removing field that acted to stabilise the pre-eruptive structure.

Title: Contribution of the ageing effect to the observed asymmetry
    of interplanetary magnetic clouds
Authors: Démoulin, P.; Dasso, S.; Lanabere, V.; Janvier, M.
Bibcode: 2020A&A...639A...6D
Altcode: 2020arXiv200505049D
  Context. Large magnetic structures are launched away from the
  Sun during solar eruptions. They are observed as (interplanetary)
  coronal mass ejections (ICMEs or CMEs) with coronal and heliospheric
  imagers. A fraction of them are observed in situ as magnetic clouds
  (MCs). Fitting these structures properly with a model requires a better
  understanding of their evolution. <BR /> Aims: In situ measurements
  are made locally when the spacecraft trajectory crosses the magnetic
  configuration. These observations are taken for different elements
  of plasma and at different times, and are therefore biased by the
  expansion of the magnetic configuration. This ageing effect means that
  stronger magnetic fields are measured at the front than at the rear of
  MCs. This asymmetry is often present in MC data. However, the question
  is whether the observed asymmetry can be explained quantitatively from
  the expansion alone. <BR /> Methods: Based on self-similar expansion,
  we derived a method for estimating the expansion rate from the observed
  plasma velocity. We next corrected the observed magnetic field and
  the spatial coordinate along the spacecraft trajectory for the ageing
  effect. This provided corrected data as in the case when the MC internal
  structure were observed at the same time. <BR /> Results: We apply the
  method to 90 best-observed MCs near Earth (1995-2012). The ageing effect
  is the main source of the observed magnetic asymmetry for only 28%
  of the MCs. After correcting for the ageing effect, the asymmetry is
  almost symmetrically distributed between MCs with a stronger magnetic
  field at the front and those at the rear of MCs. <BR /> Conclusions:
  The proposed method can efficiently remove the ageing bias within
  in situ data of MCs, and more generally, of ICMEs. This allows us
  to analyse the data with a spatial coordinate, such as in models or
  remote-sensing observations.

Title: Active-region Tilt Angles from White-light Images and
Magnetograms: The Role of Magnetic Tongues
Authors: Poisson, Mariano; Démoulin, Pascal; Mandrini, Cristina H.;
   López Fuentes, Marcelo C.
Bibcode: 2020ApJ...894..131P
Altcode: 2020arXiv200407345P
  The presence of elongations in active-region (AR) polarities, called
  magnetic tongues, is mostly visible during their emergence phase. AR
  tilts have been measured thoroughly using long-term white-light (WL)
  databases, sometimes combined with magnetic-field information. Since
  the influence of magnetic tongues on WL tilt measurements has not
  been taken into account before, we aim to investigate their role in
  tilt-angle values and to compare them with those derived from LOS
  magnetograms. We apply four methods to compute the tilt angle of
  generally bipolar ARs: one applies the k-means algorithm to WL data,
  a second one includes the magnetic-field sign of the polarities to WL
  data, and a third one uses the magnetic flux-weighted center of each
  polarity. The tilt values computed in any of these ways are affected
  by the presence of magnetic tongues. Therefore, we apply the newly
  developed Core Field Fit Estimator (CoFFE) method to separate the
  magnetic flux in the tongues from that in the AR core. We compare the
  four computed tilt-angle values, as well as these with the ones reported
  in long-term WL databases. For ARs with low-magnetic-flux tongues,
  the different methods report consistent tilt-angle values. But for ARs
  with high-flux tongues, there are noticeable discrepancies between all
  methods, indicating that magnetic tongues differently affect WL and
  magnetic data. However, in general, CoFFE achieves a better estimation
  of the main bipole tilt because it removes both the effect of tongues
  as well as the emergence of secondary bipoles when it occurs in between
  the main bipole magnetic polarities.

Title: Can Subphotospheric Magnetic Reconnection Change the Elemental
    Composition in the Solar Corona?
Authors: Baker, Deborah; van Driel-Gesztelyi, Lidia; Brooks, David H.;
   Démoulin, Pascal; Valori, Gherardo; Long, David M.; Laming, J. Martin;
   To, Andy S. H.; James, Alexander W.
Bibcode: 2020ApJ...894...35B
Altcode: 2020arXiv200303325B
  Within the coronae of stars, abundances of those elements with low
  first ionization potential (FIP) often differ from their photospheric
  values. The coronae of the Sun and solar-type stars mostly show
  enhancements of low-FIP elements (the FIP effect) while more active
  stars such as M dwarfs have coronae generally characterized by the
  inverse-FIP effect (I-FIP). Here we observe patches of I-FIP effect
  solar plasma in AR 12673, a highly complex βγδ active region. We
  argue that the umbrae of coalescing sunspots, and more specifically
  strong light bridges within the umbrae, are preferential locations for
  observing I-FIP effect plasma. Furthermore, the magnetic complexity
  of the active region and major episodes of fast flux emergence also
  lead to repetitive and intense flares. The induced evaporation of
  the chromospheric plasma in flare ribbons crossing umbrae enables
  the observation of four localized patches of I-FIP effect plasma in
  the corona of AR 12673. These observations can be interpreted in the
  context of the ponderomotive force fractionation model which predicts
  that plasma with I-FIP effect composition is created by the refraction
  of waves coming from below the chromosphere. We propose that the waves
  generating the I-FIP effect plasma in solar active regions are generated
  by subphotospheric reconnection of coalescing flux systems. Although
  we only glimpse signatures of I-FIP effect fractionation produced by
  this interaction in patches on the Sun, on highly active M stars it
  may be the dominant process.

Title: Using Forbush decreases at Earth and Mars to measure the
    radial evolution of ICMEs
Authors: von Forstner, Johan; Guo, Jingnan; Wimmer-Schweingruber,
   Robert F.; Dumbović, Mateja; Janvier, Miho; Démoulin, Pascal;
   Veronig, Astrid; Temmer, Manuela; Papaioannou, Athanasios; Dasso,
   Sergio; Hassler, Donald M.; Zeitlin, Cary J.
Bibcode: 2020EGUGA..22.7838V
Altcode:
  Interplanetary coronal mass ejections (ICMEs), large clouds of plasma
  and magnetic field regularly expelled from the Sun, are one of the
  main drivers of space weather effects in the solar system. While
  the prediction of their arrival time at Earth and other locations
  in the heliosphere is still a complex task, it is also necessary to
  further understand the time evolution of their geometric and magnetic
  structure, which is even more challenging considering the limited number
  of available observation points.Forbush decreases (FDs), short-term
  drops in the flux of galactic cosmic rays (GCR), can be caused by the
  shielding from strong and/or turbulent magnetic structures in the solar
  wind, such as ICMEs and their associated shock/sheath regions. In the
  past, FD observations have often been used to determine the arrival
  times of ICMEs at different locations in the solar system, especially
  where sufficient solar wind plasma and magnetic field measurements are
  not (or not always) available. One of these locations is Mars, where the
  Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory
  (MSL) mission's Curiosity rover has been continuously measuring GCRs and
  FDs on the surface for more than 7 years.In this work, we investigate
  whether FD data can be used to derive additional information about the
  ICME properties than just the arrival time by performing a statistical
  study based on catalogs of FDs observed at Earth or Mars. In particular,
  we find that the linear correlation between the FD amplitude and the
  maximum steepness, which was already seen at Earth by previous authors
  (Belov et al., 2008, Abunin et al., 2012), is likewise present at Mars,
  but with a different proprtionality factor.By consulting physics-based
  analytical models of FDs, we find that this quantity is not expected to
  be influenced by the different energy ranges of GCR particles observed
  by the instruments at Earth and Mars. Instead, we suggest that the
  difference in FD characteristics at the two planets is caused by the
  radial enlargement of the ICMEs, and particularly their sheath regions,
  as they propagate from Earth (1 AU) to Mars (~ 1.5 AU). This broadening
  factor derived from our analysis extends observations for the evolution
  closer to the Sun by Janvier et al. (2019, JGR Space Physics) to larger
  heliocentric distances and is consistent with these results.

Title: Low Geo-Effectiveness of Fast Halo CMEs Related to the 12
    X-Class Flares in 2002
Authors: Schmieder, B.; Kim, R. -S.; Grison, B.; Bocchialini, K.;
   Kwon, R. -Y.; Poedts, S.; Démoulin, P.
Bibcode: 2020JGRA..12527529S
Altcode: 2020arXiv200310777S
  It is generally accepted that extreme space weather events tend to be
  related to strong flares and fast halo coronal mass ejections (CMEs). In
  the present paper, we carefully identify the chain of events from
  the Sun to the Earth induced by all 12 X-class flares that occurred
  in 2002. In this small sample, we find an unusual high rate (58%) of
  solar sources with a longitude larger than 74°. Yet all 12 X-class
  flares are associated with at least one CME. The fast halo CMEs (50%)
  are related to interplanetary CMEs (ICMEs) at L1 and weak Dst minimum
  values (more than -51 nT), while five (41%) of the 12 X-class flares
  are related to solar proton events (SPEs). We conclude that (i) all
  12 analyzed solar events, even those associated with fast halo CMEs
  originating from the central disk region, and those ICMEs and SPEs
  were not very geo-effective. This unexpected result demonstrates that
  the suggested events in the chain (fast halo CME, X-class flares,
  central disk region, ICME, and SPE) are not infallible proxies for
  geo-effectiveness. (ii) The low value of integrated and normalized
  southward component of the interplanetary magnetic field (Bz*) may
  explain the low geo-effectiveness for this small sample. In fact,
  Bz* is well correlated to the weak Dst and low auroral electrojet
  activity. Hence, the only space weather impact at Earth in 2002 we
  can explain is based on Bz* at L1.

Title: Magnetic twist profile inside magnetic clouds derived with
    a superposed epoch analysis
Authors: Lanabere, V.; Dasso, S.; Démoulin, P.; Janvier, M.;
   Rodriguez, L.; Masías-Meza, J. J.
Bibcode: 2020A&A...635A..85L
Altcode: 2020arXiv200210606L
  Context. Magnetic clouds (MCs) are large-scale interplanetary
  transient structures in the heliosphere that travel from the Sun
  into the interplanetary medium. The internal magnetic field lines
  inside the MCs are twisted, forming a flux rope (FR). This magnetic
  field structuring is determined by its initial solar configuration,
  by the processes involved during its eruption from the Sun, and
  by the dynamical evolution during its interaction with the ambient
  solar wind. <BR /> Aims: One of the most important properties of the
  magnetic structure inside MCs is the twist of the field lines forming
  the FR (the number of turns per unit length). The detailed internal
  distribution of twist is under debate mainly because the magnetic
  field (B) in MCs is observed only along the spacecraft trajectory,
  and thus it is necessary to complete observations with theoretical
  assumptions. Estimating the twist from the study of a single event
  is difficult because the field fluctuations significantly increase
  the noise of the observed B time series and thus the bias of the
  deduced twist. <BR /> Methods: The superposed epoch applied to MCs
  has proven to be a powerful technique, permitting the extraction of
  their common features, and removing the peculiarity of individual
  cases. We apply a superposed epoch technique to analyse the magnetic
  components in the local FR frame of a significant sample of moderately
  asymmetric MCs observed at 1 au. <BR /> Results: From the superposed
  profile of B components in the FR frame, we determine the typical
  twist distribution in MCs. The twist is nearly uniform in the FR core
  (central half part), and it increases moderately, up to a factor two,
  towards the MC boundaries. This profile is close to the Lundquist field
  model limited to the FR core where the axial field component is above
  about one-third of its central value.

Title: Comparing the Properties of ICME-Induced Forbush Decreases
    at Earth and Mars
Authors: Freiherr von Forstner, Johan L.; Guo, Jingnan;
   Wimmer-Schweingruber, Robert F.; Dumbović, Mateja; Janvier, Miho;
   Démoulin, Pascal; Veronig, Astrid; Temmer, Manuela; Papaioannou,
   Athanasios; Dasso, Sergio; Hassler, Donald M.; Zeitlin, Cary J.
Bibcode: 2020JGRA..12527662F
Altcode: 2020arXiv200303157V
  Forbush decreases (FDs), which are short-term drops in the flux
  of galactic cosmic rays, are caused by the shielding from strong
  and/or turbulent magnetic structures in the solar wind, especially
  interplanetary coronal mass ejections (ICMEs) and their associated
  shocks, as well as corotating interaction regions. Such events can be
  observed at Earth, for example, using neutron monitors, and also at
  many other locations in the solar system, such as on the surface of
  Mars with the Radiation Assessment Detector instrument onboard Mars
  Science Laboratory. They are often used as a proxy for detecting the
  arrival of ICMEs or corotating interaction regions, especially when
  sufficient in situ solar wind measurements are not available. We
  compare the properties of FDs observed at Earth and Mars, focusing
  on events produced by ICMEs. We find that FDs at both locations show
  a correlation between their total amplitude and the maximum hourly
  decrease, but with different proportionality factors. We explain this
  difference using theoretical modeling approaches and suggest that it is
  related to the size increase of ICMEs, and in particular their sheath
  regions, en route from Earth to Mars. From the FD data, we can derive
  the sheath broadening factor to be between about 1.5 and 1.9, agreeing
  with our theoretical considerations. This factor is also in line with
  previous measurements of the sheath evolution closer to the Sun.

Title: Correcting the effect of magnetic tongues on the tilt angle
    of bipolar active regions
Authors: Poisson, M.; López Fuentes, M. C.; Mandrini, C. H.;
   Démoulin, P.; MacCormack, C.
Bibcode: 2020A&A...633A.151P
Altcode: 2019arXiv191212990P
  Context. The magnetic polarities of bipolar active regions (ARs)
  exhibit elongations in line-of-sight magnetograms during their
  emergence. These elongations are referred to as magnetic tongues and
  attributed to the presence of twist in the emerging magnetic flux-ropes
  (FRs) that form ARs. <BR /> Aims: The presence of magnetic tongues
  affects the measurement of any AR characteristic that depends on its
  magnetic flux distribution. The AR tilt-angle is one of them. We aim
  to develop a method to isolate and remove the flux associated with
  the tongues to determine the AR tilt-angle with as much precision
  as possible. <BR /> Methods: As a first approach, we used a simple
  emergence model of a FR. This allowed us to develop and test our aim
  based on a method to remove the effects of magnetic tongues. Then,
  using the experience gained from the analysis of the model, we applied
  our method to photospheric observations of bipolar ARs that show clear
  magnetic tongues. <BR /> Results: Using the developed procedure on the
  FR model, we can reduce the deviation in the tilt estimation by more
  than 60%. Next we illustrate the performance of the method with four
  examples of bipolar ARs selected for their large magnetic tongues. The
  new method efficiently removes the spurious rotation of the bipole. This
  correction is mostly independent of the method input parameters and
  significant since it is larger than all the estimated tilt errors. <BR
  /> Conclusions: We have developed a method to isolate the magnetic
  flux associated with the FR core during the emergence of bipolar
  ARs. This allows us to compute the AR tilt-angle and its evolution as
  precisely as possible. We suggest that the high dispersion observed in
  the determination of AR tilt-angles in studies that massively compute
  them from line-of sight magnetograms can be partly due to the existence
  of magnetic tongues whose presence is not sufficiently acknowledged. <P
  />Movies associated to Figs. 1, 2, 3, 5-10, and A.1 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201936924/olm">https://www.aanda.org</A>

Title: Comparing the Properties of ICME-Induced Forbush Decreases
    at Earth and Mars
Authors: Freiherr von Forstner, J. L.; Guo, J.; Wimmer-Schweingruber,
   R. F.; Dumbovic, M.; Janvier, M.; Demoulin, P.; Veronig, A.; Temmer,
   M.; Hassler, D.; Zeitlin, C.
Bibcode: 2019AGUFMSH41D3339F
Altcode:
  Forbush decreases (FDs), short-term drops in the flux of galactic
  cosmic rays (GCR), can be caused by the shielding from strong and/or
  turbulent magnetic structures in the solar wind, i.e. interplanetary
  coronal mass ejections (ICMEs) and their associated shocks as well
  as corotating interaction regions (CIRs). FDs are often used as a
  proxy for detecting the arrival of ICMEs or CIRs at locations where
  sufficient in situ solar wind measurements are not or not always
  available, such as at Mars. The Radiation Assessment Detector (RAD)
  onboard the Mars Science Laboratory (MSL) mission's Curiosity rover
  has been continuously measuring the GCR environment on the surface
  of Mars for more than 7 years since its landing in August 2012 and is
  thus an excellent source for measurements of FDs at Mars (see e.g. <A
  href="https://doi.org/10.1051/0004-6361/201732087">Guo et al. 2018,
  A&amp;A</A>). <P />Based on the large catalog of FDs at Mars compiled
  by <A href="https://doi.org/10.1007/s11207-019-1454-2">Papaioannou et
  al. (2019, Solar Physics)</A> as well as results from our previous
  work (<A href="https://doi.org/10.1029/2018SW002138">Freiherr von
  Forstner et al., 2019, Space Weather</A>), we study the parameters
  of FDs at Mars and their relations, focusing on events produced by
  ICMEs. We then compare these data with catalogs of terrestrial FDs,
  investigating whether and to what extent the differences of certain FD
  characteristics between the two planets, at two different heliospheric
  distances, are related to the evolution of ICMEs between Earth and
  Mars. <P />Our results show that there is a linear correlation between
  the FD amplitude (drop percentage) and the maximum hourly GCR decrease
  during the FD, which was already found at Earth by previous authors (<A
  href="https://doi.org/10.1017/S1743921309029676">Belov et al., 2008</A>,
  <A href="https://doi.org/10.1134/S0016793212030024">Abunin et al.,
  2012</A>). However, this correlation has a different proprtionality
  factor at Mars than at Earth, especially for ICME-induced events. As
  we do not find a clear dependence of this relationship on the observed
  GCR energy range, we suggest that this difference is probably caused by
  the expansion of the ICME sheath region as it propagates outward from
  1 AU to ∼1.5 AU. The expansion factor derived from our analysis is in
  line with expansion factors of ICME sheaths within the inner heliosphere
  observed by &lt;a href="https://doi.org/10.1029/2018JA025949&gt;Janvier
  et al. (2019, JGR Space Physics).

Title: Re-analysis of Lepping's Fitting Method for Magnetic Clouds:
    Lundquist Fit Reloaded
Authors: Démoulin, Pascal; Dasso, Sergio; Janvier, Miho; Lanabere,
   Vanina
Bibcode: 2019SoPh..294..172D
Altcode: 2019arXiv191209829D
  Magnetic clouds (MCs) are a subset of ejecta, launched from the Sun as
  coronal mass ejections. The coherent rotation of the magnetic field
  vector observed in MCs leads to envision MCs as formed by flux ropes
  (FRs). Among all the methods used to analyze MCs, Lepping's method
  (Lepping, Burlaga, and Jones in J. Geophys. Res.95, 11957, 1990) is the
  broadest used. While this fitting method does not require the axial
  field component to vanish at the MC boundaries, this idea is largely
  spread in publications. We revisit Lepping's method to emphasize its
  hypothesis and the meaning of its output parameters. As originally
  defined, these parameters imply a fitted FR which could be smaller
  or larger than the studied MC. We rather provide a re-interpretation
  of Lepping's results with a fitted model limited to the observed
  MC interval. We find that typically the crossed FRs are asymmetric
  with a larger side both in size and magnetic flux before or after
  the FR axis. At the boundary of the largest side we find an axial
  magnetic field component distributed around zero which we justify by
  the physics of solar eruptions. In contrast, at the boundary of the
  smaller side the axial field distribution is shifted to positive values,
  as expected with erosion acting during the interplanetary travel. This
  new analysis of Lepping's results has several implications. First,
  global quantities, such as magnetic fluxes and helicity, need to be
  revised depending on the aim (estimating global properties of FRs just
  after the solar launch or at 1 au). Second, the deduced twist profiles
  in MCs range quasi-continuously from nearly uniform, to increasing
  away from the FR axis, up to a reversal near the MC boundaries. There
  is no trace of outsider cases, but a continuum of cases. Finally, the
  impact parameter of the remaining FR crossed at 1 au is revised. Its
  distribution is compatible with weakly flattened FR cross-sections.

Title: Do Current and Magnetic Helicities Have the Same Sign?
Authors: Russell, A. J. B.; Demoulin, P.; Hornig, G.; Pontin, D. I.;
   Candelaresi, S.
Bibcode: 2019ApJ...884...55R
Altcode:
  Current helicity, H <SUB> c </SUB>, and magnetic helicity, H <SUB>
  m </SUB>, are two main quantities used to characterize magnetic
  fields. For example, such quantities have been widely used
  to characterize solar active regions and their ejecta (magnetic
  clouds). It is commonly assumed that H <SUB> c </SUB> and H <SUB> m
  </SUB> have the same sign, but this has not been rigorously addressed
  beyond the simple case of linear force-free fields. We aim to answer
  whether H <SUB> m </SUB> H <SUB> c </SUB> ≥ 0 in general, and whether
  it is true over some useful set of magnetic fields. This question is
  addressed analytically and with numerical examples. The main focus is on
  cylindrically symmetric straight flux tubes, referred to as flux ropes
  (FRs), using the relative magnetic helicity with respect to a straight
  (untwisted) reference field. Counterexamples with H <SUB> m </SUB> H
  <SUB> c </SUB> &lt; 0 have been found for cylindrically symmetric FRs
  with finite plasma pressure, and for force-free cylindrically symmetric
  FRs in which the poloidal field component changes direction. Our main
  result is a proof that H <SUB> m </SUB> H <SUB> c </SUB> ≥ 0 is true
  for force-free cylindrically symmetric FRs where the toroidal field and
  poloidal field components are each of a single sign, and the poloidal
  component does not exceed the toroidal component. We conclude that the
  conjecture that current and magnetic helicities have the same sign is
  not true in general, but it is true for a set of FRs of importance to
  coronal and heliospheric physics.

Title: Definition of the Spatial Propagator and Implications for
    Magnetic Field Properties
Authors: Edmondson, Justin K.; Démoulin, Pascal
Bibcode: 2019SoPh..294...76E
Altcode:
  We present a theoretical framework to analyze the 3D coronal vector
  magnetic-field structure. We assume that the vector magnetic field
  exists and is a priori smooth. We introduce a generalized connectivity
  phase space associated with the vector magnetic field in which the basic
  elements are the field line and its linearized variation: the Spatial
  Propagator. We provide a direct formulation of these elements in terms
  of the vector magnetic field and its spatial derivatives, constructed
  with respect to general curvilinear coordinates and the equivalence
  class of general affine parameterizations. The Spatial Propagator
  describes the geometric organization of the local bundle of field
  lines, equivalent to the kinematic deformation of a propagated volume
  tied to the bundle. The Spatial Propagator's geometric properties are
  characterized by dilation, anisotropic stretch, and rotation. Extreme
  singular values of the Spatial Propagator describe quasi-separatrix
  layers (QSLs), while true separatrix surfaces and separator lines
  are identified by the vanishing of one and two singular values,
  respectively. Finally, we show that, among other possible applications,
  the squashing factor [Q ] is easily constructed from an analysis of
  particular sub-matrices of the Spatial Propagator.

Title: Transient Inverse-FIP Plasma Composition Evolution within a
    Solar Flare
Authors: Baker, Deborah; van Driel-Gesztelyi, Lidia; Brooks, David
   H.; Valori, Gherardo; James, Alexander W.; Laming, J. Martin; Long,
   David M.; Démoulin, Pascal; Green, Lucie M.; Matthews, Sarah A.;
   Oláh, Katalin; Kővári, Zsolt
Bibcode: 2019ApJ...875...35B
Altcode: 2019arXiv190206948B
  Understanding elemental abundance variations in the solar corona
  provides an insight into how matter and energy flow from the
  chromosphere into the heliosphere. Observed variations depend on the
  first ionization potential (FIP) of the main elements of the Sun’s
  atmosphere. High-FIP elements (&gt;10 eV) maintain photospheric
  abundances in the corona, whereas low-FIP elements have enhanced
  abundances. Conversely, inverse FIP (IFIP) refers to the enhancement of
  high-FIP or depletion of low-FIP elements. We use spatially resolved
  spectroscopic observations, specifically the Ar XIV/Ca XIV intensity
  ratio, from Hinode’s Extreme-ultraviolet Imaging Spectrometer to
  investigate the distribution and evolution of plasma composition
  within two confined flares in a newly emerging, highly sheared
  active region. During the decay phase of the first flare, patches
  above the flare ribbons evolve from the FIP to the IFIP effect, while
  the flaring loop tops show a stronger FIP effect. The patch and loop
  compositions then evolve toward the preflare basal state. We propose
  an explanation of how flaring in strands of highly sheared emerging
  magnetic fields can lead to flare-modulated IFIP plasma composition
  over coalescing umbrae which are crossed by flare ribbons. Subsurface
  reconnection between the coalescing umbrae leads to the depletion of
  low-FIP elements as a result of an increased wave flux from below. This
  material is evaporated when the flare ribbons cross the umbrae. Our
  results are consistent with the ponderomotive fractionation model for
  the creation of IFIP-biased plasma.

Title: Modeling the Effect of Mass-draining on Prominence Eruptions
Authors: Jenkins, Jack M.; Hopwood, Matthew; Démoulin, Pascal; Valori,
   Gherardo; Aulanier, Guillaume; Long, David M.; van Driel-Gesztelyi,
   Lidia
Bibcode: 2019ApJ...873...49J
Altcode: 2019arXiv190110970J
  Quiescent solar prominences are observed within the solar atmosphere
  for up to several solar rotations. Their eruption is commonly preceded
  by a slow increase in height that can last from hours to days. This
  increase in the prominence height is believed to be due to their host
  magnetic flux rope transitioning through a series of neighboring
  quasi-equilibria before the main loss of equilibrium that drives
  the eruption. Recent work suggests that the removal of prominence
  mass from a stable, quiescent flux rope is one possible cause for
  this change in height. However, these conclusions are drawn from
  observations and are subject to interpretation. Here, we present a
  simple model to quantify the effect of “mass-draining” during the
  pre-eruptive height evolution of a solar flux rope. The flux rope is
  modeled as a line current suspended within a background potential
  magnetic field. We first show that the inclusion of mass, up to
  10<SUP>12</SUP> kg, can modify the height at which the line current
  experiences loss of equilibrium by up to 14%. Next, we show that
  the rapid removal of mass prior to the loss of equilibrium can allow
  the height of the flux rope to increase sharply and without an upper
  bound as it approaches its loss-of-equilibrium point. This indicates
  that the critical height for the loss of equilibrium can occur at a
  range of heights depending explicitly on the amount and evolution of
  mass within the flux rope. Finally, we demonstrate that for the same
  amount of drained mass, the effect on the height of the flux rope is
  up to two orders of magnitude larger for quiescent prominences than
  for active region prominences.

Title: Generic Magnetic Field Intensity Profiles of Interplanetary
    Coronal Mass Ejections at Mercury, Venus, and Earth From Superposed
    Epoch Analyses
Authors: Janvier, Miho; Winslow, Reka M.; Good, Simon; Bonhomme,
   Elise; Démoulin, Pascal; Dasso, Sergio; Möstl, Christian; Lugaz,
   Noé; Amerstorfer, Tanja; Soubrié, Elie; Boakes, Peter D.
Bibcode: 2019JGRA..124..812J
Altcode: 2019arXiv190109921J
  We study interplanetary coronal mass ejections (ICMEs) measured by
  probes at different heliocentric distances (0.3-1 AU) to investigate
  the propagation of ICMEs in the inner heliosphere and determine how
  the generic features of ICMEs change with heliospheric distance. Using
  data from the MErcury Surface, Space ENvironment, GEochemistry, and
  Ranging (MESSENGER), Venus Express and ACE spacecraft, we analyze with
  the superposed epoch technique the profiles of ICME substructures,
  namely, the sheath and the magnetic ejecta. We determine that the
  median magnetic field magnitude in the sheath correlates well with
  ICME speeds at 1 AU, and we use this proxy to order the ICMEs at all
  spacecraft. We then investigate the typical ICME profiles for three
  categories equivalent to slow, intermediate, and fast ICMEs. Contrary
  to fast ICMEs, slow ICMEs have a weaker solar wind field at the front
  and a more symmetric magnetic field profile. We find the asymmetry to
  be less pronounced at Earth than at Mercury, indicating a relaxation
  taking place as ICMEs propagate. We also find that the magnetic
  field intensities in the wake region of the ICMEs do not go back
  to the pre-ICME solar wind intensities, suggesting that the effects
  of ICMEs on the ambient solar wind last longer than the duration of
  the transient event. Such results provide an indication of physical
  processes that need to be reproduced by numerical simulations of ICME
  propagation. The samples studied here will be greatly improved by
  future missions dedicated to the exploration of the inner heliosphere,
  such as Parker Solar Probe and Solar Orbiter.

Title: Physical Processes Involved in the EUV "Surge" Event of 9
    May 2012
Authors: López Fuentes, Marcelo; Mandrini, Cristina H.; Poisson,
   Mariano; Démoulin, Pascal; Cristiani, Germán; López, Fernando M.;
   Luoni, Maria Luisa
Bibcode: 2018SoPh..293..166L
Altcode: 2018arXiv181012403L
  We study an extreme ultraviolet (EUV) confined ejection observed
  on 9 May 2012 in Active Region (AR) NOAA 11476. For the analysis
  we use observations in multiple wavelengths (EUV, X-rays, Hα , and
  magnetograms) from a variety of ground- and space-based instruments. The
  magnetic configuration showed two rotating bipoles within the following
  polarity of the AR. This evolution was present some tens of hours before
  the studied event and continued thereafter. During this period, the
  magnetic flux of both bipoles continuously decreased. A mini-filament
  with a length of ≈30<SUP>″</SUP> lay along the photospheric
  inversion line of the largest bipole. The mini-filament was observed
  to erupt, accompanied by an M4.7 flare (SOL20120509T12:23:00). This
  injected dense material as well as twist along closed loops in the
  form of a very broad ejection whose morphology resembled that of
  typical Hα surges. We conclude that the flare and eruption can be
  explained as due to two reconnection processes, one occurring below
  the erupting mini-filament, and another above it. This second process
  injects the mini-filament plasma within the reconnected closed loops
  linking the main AR polarities. By analyzing the magnetic topology
  using a force-free model of the coronal field, we identify the location
  of quasi-separatix layers, where reconnection is prone to occur, and
  present a detailed interpretation of the chromospheric and coronal
  eruption observations. In particular, this event, in contrast to what
  has been proposed in several models explaining surges and/or jets,
  is not produced by magnetic flux emergence, but by magnetic flux
  cancellation accompanied by the rotation of the bipoles. In fact,
  the conjunction of these two processes, flux cancellation and bipole
  rotations, is at the origin of a series of events, homologous to the
  event we analyze in this article, which occurred in AR 11476 from 8
  to 10 May 2012.

Title: Recurrent eruptions by converging and shearing polarities in
    a solar AR 12371
Authors: Vemareddy, P.; Demoulin, P.
Bibcode: 2018csc..confE..67V
Altcode:
  Solar eruptions, which include flares and CMEs, influence the
  heliosphere and planetary atmosphere in a wide range of physical
  phenomena. Powerful, spectacular eruptions occur in active regions (ARs)
  with distinct evolving conditions. In the space weather perspective,
  they are of great scientific interest compared to non-eruptive ARs. To
  this end, we consider the AR 12371 producing faster CMEs recurrently in
  a week time of observation. Coronal observations from AIA/SDO reveal
  inverse S-sigmoid morphology to the magnetic structure. The HMI/SDO
  magnetic field observations show converging and shearing motion of
  opposite polarity regions co-spatial with the twisted core flux system
  of the sigmoid. From these observations, we propose continuous shearing
  and submerging motion of opposite polarity regions lead to formation
  of sheared arcade, which upon slow reconnection forms flux rope being
  erupted by tether-cutting reconnection. Various magnetic non-potential
  parameters support this scenario of energy build up and release by
  eruptions. We further analyzed modeling aspect of AR magnetic structure
  and feasibility conditions for eruption. We further study the magnetic
  structure of successively erupting sigmoid in active region (AR) 12371
  by modeling the quasi-static coronal field evolution with non-linear
  force-free field (NLFFF) equilibria. The modelled structure captured
  major features of sigmoid-to-arcade-to-sigmoid transformation, that is
  being recurrent under continuous photospheric flux motions. Calculations
  of the field line twist reveal a fractional increase followed by a
  decrease of the number of pixels having a range of twist. This traces
  the buildup process of twisted core field by slow photospheric motions
  and the relaxation after eruption, respectively. Our study infers that
  the large eruptivity of this AR is due to a steep decrease of the
  overlying coronal field meeting the torus instability criteria from
  a significantly lower height (≈50 Mm) in contrast to non-eruptive ARs.

Title: The nature of imploding loops during solar eruptions as
    revealed by MHD simulations and AIA observations
Authors: Aulanier, Guillaume; Dudik, Jaroslav; Zucarello, F. P.;
   Demoulin, Pascal; Schmieder, Brigitte
Bibcode: 2018csc..confE..19A
Altcode:
  Over the last years AIA revealed the frequent occurence of contracting
  loops at the flanks of erupting active regions. Those have often
  been interpreted as an evidence of the implosion conjecture that
  relates magnetic energy decreases with volume contractions in the Sun's
  corona. So as to unveil the physical nature of these features we carried
  out observational analyses of two solar eruptions observed with AIA with
  different projection angles, which we coupled with new analyses of a
  generic zero-beta MHD simulation of an asymmetric eruption driven by the
  torus instability, that was not designed for this particular study. The
  simulation does display contracting loops in general. And the synthetic
  time-slices of the simulation, when rotated to the right projections,
  do match the observed ones. But in the simulation these inward motions
  are not due to any volume contraction. Instead they are associated
  with two large-scale quasi-incompressible coronal-vortices. Those
  develop at the flanks of the erupting flux ropes, as most of the
  compressive component of the flow is evacuated away by an Alfven wave
  in the early stages of the eruption. We argue that this behavior is
  merely a magnetic version of the usual pressure-driven formation of
  vortex rings in hydrodyanmics. This result implies that during a solar
  eruption, the free magnetic-energy from the pre-erupting active-region
  is converted not only in the flare and the CME, but is also "lost"
  in the generation of these two large-scale coronal vortices.

Title: Exploring the biases of a new method based on minimum variance
    for interplanetary magnetic clouds
Authors: Démoulin, P.; Dasso, S.; Janvier, M.
Bibcode: 2018A&A...619A.139D
Altcode: 2018arXiv180900522D
  Context. Magnetic clouds (MCs) are twisted magnetic structures ejected
  from the Sun and probed by in situ instruments. They are typically
  modeled as flux ropes (FRs). <BR /> Aims: Magnetic field measurements
  are only available along the 1D spacecraft trajectory. The determination
  of the FR global characteristics requires the estimation of the FR axis
  orientation. Among the developed methods, the minimum variance (MV)
  is the most flexible, and features only a few assumptions. However,
  as other methods, MV has biases. We aim to investigate the limits
  of the method and extend it to a less biased method. <BR />
  Methods: We first identified the origin of the biases by testing
  the MV method on cylindrical and elliptical models with a temporal
  expansion comparable to the one observed in MCs. Then, we developed
  an improved MV method to reduce these biases. <BR /> Results: In
  contrast with many previous publications we find that the ratio of
  the MV eigenvalues is not a reliable indicator of the precision of
  the derived FR axis direction. Next, we emphasize the importance of
  the FR boundaries selected since they strongly affect the deduced
  axis orientation. We have improved the MV method by imposing that the
  same amount of azimuthal flux should be present before and after the
  time of closest approach to the FR axis. We emphasize the importance
  of finding simultaneously the FR axis direction and the location of
  the boundaries corresponding to a balanced magnetic flux, so as to
  minimize the bias on the deduced FR axis orientation. This method
  can also define an inner flux-balanced sub-FR. We show that the MV
  results are much less biased when a compromize in size of this sub-FR
  is achieved. <BR /> Conclusions: For weakly asymmetric field temporal
  profiles, the improved MV provides a very good determination of the FR
  axis orientation. The main remaining bias is moderate (lower than 6°)
  and is present mostly on the angle between the flux rope axis and the
  plane perpendicular to the Sun-Earth direction.

Title: Sequential Eruptions Triggered by Flux Emergence: Observations
    and Modeling
Authors: Dacie, S.; Török, T.; Démoulin, P.; Linton, M. G.; Downs,
   C.; van Driel-Gesztelyi, L.; Long, D. M.; Leake, J. E.
Bibcode: 2018ApJ...862..117D
Altcode: 2018arXiv180700020D
  We describe and analyze observations by the Solar Dynamics Observatory
  of the emergence of a small, bipolar active region within an area of
  unipolar magnetic flux that was surrounded by a circular, quiescent
  filament. Within only 8 hours from the start of the emergence, a
  partial splitting of the filament and two consecutive coronal mass
  ejections took place. We argue that all three dynamic events occurred
  as a result of particular magnetic-reconnection episodes between
  the emerging bipole and the pre-existing coronal magnetic field. To
  substantiate our interpretation, we consider 3D magnetohydrodynamic
  simulations that model the emergence of magnetic flux in the vicinity of
  a large-scale coronal flux rope. The simulations qualitatively reproduce
  most of the reconnection episodes suggested by the observations, as
  well as the filament splitting, the first eruption, and the formation
  of sheared/twisted fields that may have played a role in the second
  eruption. Our results suggest that the position of emerging flux with
  respect to the background magnetic configuration is a crucial factor for
  the resulting evolution, while previous results suggest that parameters
  such as the orientation or the amount of emerging flux are important
  as well. This poses a challenge for predicting the onset of eruptions
  that are triggered by flux emergence, and calls for a detailed survey
  of the relevant parameter space by means of numerical simulations.

Title: Manifestation of Coronal Mass Ejections near Earth: A review
Authors: Dasso, Sergio; Rodriguez, . Luciano, , dr.; Demoulin, Pascal;
   Masias-Meza, Jimmy J.; Janvier, Miho; Lanabere, Vanina
Bibcode: 2018cosp...42E.768D
Altcode:
  Coronal Mass Ejections (CMEs) are launched from the Sun, as a result of
  magnetic instabilities, carrying away a huge amount of magnetic flux
  and helicity. Interplanetary CMEs (ICMEs) are their manifestations
  observed further away in the heliosphere. ICMEs contain different
  plasma and magnetic field properties, compared with those of the
  ambient solar wind. From the large number of observed ICMEs in the
  past years, we significantly increased our knowledge on several of
  their properties such as: their global 3D shape, the identification
  of the composing sub-structures, the amount of magnetohydrodynamical
  quantities transported, as well as how the plasma and magnetic field
  are typically distributed inside them.In the present talk we will
  present a general review of these aspects of ICMEs. In particular we
  will focus on the total amount of magnetic flux and helicity ejected
  by CMEs from the Sun along a solar cycle, and on plasma and magnetic
  properties of their shock/sheath/flux-rope/wake. These results can
  help to understand their interaction with the ambient solar wind and
  with planetary magnetic environments. They are particularly crucial
  for a better understanding of the Sun-Earth coupling.

Title: The effect of magnetic tongues in the determination of
    Joy's law
Authors: Poisson, Mariano; Mandrini, Cristina H.; Lopez Fuentes,
   Marcelo; Demoulin, Pascal
Bibcode: 2018cosp...42E2706P
Altcode:
  We study the emergence of 186 bipolar active regions (ARs) to determine
  the relation between the tilt angle formed with respect to the E-W
  direction and the latitude of emergence. This relation, known as Joy's
  law, plays a fundamental role to test the ability of dynamo models to
  explain, among other things, the equatorial flux cancelation and the
  inversion of the poloidal magnetic field between solar cycles. The
  methods used in recent works to determine this law are based on
  the automatic computation of the tilt angle from line-of-sight (LOS)
  magnetograms (Stenflo &amp; Kosovichev 2012; Wang et al. 2015). However,
  since those results show a large dispersion, the precise latitudinal
  depedence on the tilt is still a topic of discussion. We consider that
  an important part of this dispersion can be due to the effect of the
  so called magnetic tongues. These are produced by the line of sight
  projection of the azimuthal magnetic field of the twisted emerging
  flux-tubes that form ARs. The tongues are observed in LOS magnetograms
  as an elongation of the magnetic polarities. In Poisson et al. (2016,
  Solar Phys., 291, 1625-1646) we showed that the magnetic tongues affect
  the photospheric field distribution observed in LOS magnetograms and,
  consequently, impact on the determination of the tilt angle. In this
  work we test a novel method to remove the effect of the tongues on the
  tilt angle determination and we quantify the effect of this correction
  on Joy's law. Furthermore, we study the relation of the latitudinal
  dependence of the corrected tilt with other AR properties such as the
  magnetic helicity sign, the hemisphere of emergence, and the sense of
  rotation of the bipoles.

Title: Constructing a Generic Icme from the Sun to Earth from
    Statistical Studies of in Situ Data
Authors: Janvier, Miho; Dasso, Sergio; Demoulin, Pascal
Bibcode: 2018cosp...42E1600J
Altcode:
  Interplanetary Coronal Mass Ejections (ICMEs) are detected in situ by
  instruments measuring the magnetic field and plasma properties of the
  ambient solar wind. In particular, a subset of ICMEs, referred to as
  Magnetic Clouds (MCs), is well defined by the presence of a rotating
  magnetic field, indicative of a twisted magnetic structure. Shocks,
  on the other hand, are also well defined in the interplanetary medium
  as sharp discontinuities in the plasma and magnetic properties. Both
  structures then allow defining the presence of a sheath region between
  the shock and the MC. Over the past years, we have proposed and refined
  new statistical methods aiming at analyzing ICME properties, so as
  to assess the existence of a generic shape and a generic internal
  profile of ICMEs at different distances from the Sun. These methods
  rely on the computation from the data of the distribution of the
  shock normal and the flux-rope axis directions. From these analysis,
  we were able to constrain an analytical shape that describes best these
  observed distributions. Another method is a superposed epoch analysis
  so as to obtain typical profiles of ICME substructures at different
  distances from the Sun. Next, we compare such generic features of
  ICMEs to numerical simulations and heliospheric images of CMEs. We
  will discuss the commonalities, then the discrepancies that need to
  be further understood between the models and the constraints given
  by the in situ data. This is important in completing the scenario of
  the evolution of solar eruptive flares, from their start in the Sun's
  atmosphere to their evolution in the solar wind.

Title: Coronal Elemental Abundances in Solar Emerging Flux Regions
Authors: Baker, Deborah; Brooks, David H.; van Driel-Gesztelyi,
   Lidia; James, Alexander W.; Démoulin, Pascal; Long, David M.; Warren,
   Harry P.; Williams, David R.
Bibcode: 2018ApJ...856...71B
Altcode: 2018arXiv180108424B
  The chemical composition of solar and stellar atmospheres differs from
  the composition of their photospheres. Abundances of elements with low
  first ionization potential (FIP) are enhanced in the corona relative
  to high-FIP elements with respect to the photosphere. This is known as
  the FIP effect and it is important for understanding the flow of mass
  and energy through solar and stellar atmospheres. We used spectroscopic
  observations from the Extreme-ultraviolet Imaging Spectrometer on board
  the Hinode observatory to investigate the spatial distribution and
  temporal evolution of coronal plasma composition within solar emerging
  flux regions inside a coronal hole. Plasma evolved to values exceeding
  those of the quiet-Sun corona during the emergence/early-decay phase
  at a similar rate for two orders of magnitude in magnetic flux, a rate
  comparable to that observed in large active regions (ARs) containing
  an order of magnitude more flux. During the late-decay phase, the rate
  of change was significantly faster than what is observed in large,
  decaying ARs. Our results suggest that the rate of increase during the
  emergence/early-decay phase is linked to the fractionation mechanism
  that leads to the FIP effect, whereas the rate of decrease during
  the later decay phase depends on the rate of reconnection with the
  surrounding magnetic field and its plasma composition.

Title: Studying the Transfer of Magnetic Helicity in Solar Active
    Regions with the Connectivity-based Helicity Flux Density Method
Authors: Dalmasse, K.; Pariat, É.; Valori, G.; Jing, J.; Démoulin, P.
Bibcode: 2018ApJ...852..141D
Altcode: 2017arXiv171204691D
  In the solar corona, magnetic helicity slowly and continuously
  accumulates in response to plasma flows tangential to the photosphere
  and magnetic flux emergence through it. Analyzing this transfer of
  magnetic helicity is key for identifying its role in the dynamics of
  active regions (ARs). The connectivity-based helicity flux density
  method was recently developed for studying the 2D and 3D transfer
  of magnetic helicity in ARs. The method takes into account the 3D
  nature of magnetic helicity by explicitly using knowledge of the
  magnetic field connectivity, which allows it to faithfully track the
  photospheric flux of magnetic helicity. Because the magnetic field is
  not measured in the solar corona, modeled 3D solutions obtained from
  force-free magnetic field extrapolations must be used to derive the
  magnetic connectivity. Different extrapolation methods can lead to
  markedly different 3D magnetic field connectivities, thus questioning
  the reliability of the connectivity-based approach in observational
  applications. We address these concerns by applying this method to the
  isolated and internally complex AR 11158 with different magnetic field
  extrapolation models. We show that the connectivity-based calculations
  are robust to different extrapolation methods, in particular with
  regard to identifying regions of opposite magnetic helicity flux. We
  conclude that the connectivity-based approach can be reliably used in
  observational analyses and is a promising tool for studying the transfer
  of magnetic helicity in ARs and relating it to their flaring activity.

Title: Field distribution of magnetograms from simulations of active
    region formation
Authors: Dacie, S.; van Driel-Gesztelyi, L.; Démoulin, P.; Linton,
   M. G.; Leake, J. E.; MacTaggart, D.; Cheung, M. C. M.
Bibcode: 2017A&A...606A..34D
Altcode:
  Context. The evolution of the photospheric magnetic field distributions
  (probability densities) has previously been derived for a set of active
  regions. Photospheric field distributions are a consequence of physical
  processes that are difficult to determine from observations alone. <BR
  /> Aims: We analyse simulated magnetograms from numerical simulations,
  which model the emergence and decay of active regions. These simulations
  have different experimental set-ups and include different physical
  processes, allowing us to investigate the relative importance of
  convection, magnetic buoyancy, magnetic twist, and braiding for flux
  emergence. <BR /> Methods: We specifically studied the photospheric
  field distributions (probability densities found with a kernel density
  estimation analysis) and compared the results with those found from
  observations. <BR /> Results: Simulations including convection most
  accurately reproduce the observed evolution of the photospheric field
  distributions during active region evolution. <BR /> Conclusions: This
  indicates that convection may play an important role during the decay
  phase and also during the formation of active regions, particularly
  for low flux density values.

Title: Studying the transfer of magnetic helicity in solar active
    regions
Authors: Dalmasse, Kevin; Valori, Gherardo; Jing, Ju; Pariat, Etienne;
   Demoulin, Pascal
Bibcode: 2017SPD....4811206D
Altcode:
  Analyzing the transfer of magnetic helicity in active regions is a
  key component for understanding the nature of its coronal storage
  and release and for identifying its role in the coronal dynamics
  of active regions. We recently developed a method for studying the
  photospheric flux of magnetic helicity in both 2D and 3D. The method
  takes into account the 3D nature of magnetic helicity by explicitly
  using knowledge of the magnetic field connectivity. Since the coronal
  magnetic field in active regions is not measured, we rely on the
  non-unique 3D solution obtained from force-free coronal magnetic
  field extrapolations to derive the magnetic field connectivity. In
  this poster, we apply the method to the complex and highly-flaring
  active region NOAA 11158 using the magnetic field connectivity derived
  from different force-free extrapolation models and implementations. We
  show that the calculations of photospheric flux of magnetic helicity
  are robust to different extrapolation methods and assumptions, in
  particular with regards to identifying regions of opposite magnetic
  helicity flux. Finally, we discuss the implications of our results
  for tracking the transfer of magnetic helicity in active regions and
  relate it to their flaring activity.

Title: Expanding and Contracting Coronal Loops as Evidence of Vortex
    Flows Induced by Solar Eruptions
Authors: Dudík, J.; Zuccarello, F. P.; Aulanier, G.; Schmieder, B.;
   Démoulin, P.
Bibcode: 2017ApJ...844...54D
Altcode: 2017arXiv170604783D
  Eruptive solar flares were predicted to generate large-scale vortex
  flows at both sides of the erupting magnetic flux rope. This process
  is analogous to a well-known hydrodynamic process creating vortex
  rings. The vortices lead to advection of closed coronal loops located
  at the peripheries of the flaring active region. Outward flows are
  expected in the upper part and returning flows in the lower part of the
  vortex. Here, we examine two eruptive solar flares, the X1.1-class flare
  SOL2012-03-05T03:20 and the C3.5-class SOL2013-06-19T07:29. In both
  flares, we find that the coronal loops observed by the Atmospheric
  Imaging Assembly in its 171 Å, 193 Å, or 211 Å passbands show
  coexistence of expanding and contracting motions, in accordance with
  the model prediction. In the X-class flare, multiple expanding and
  contracting loops coexist for more than 35 minutes, while in the C-class
  flare, an expanding loop in 193 Å appears to be close by and cotemporal
  with an apparently imploding loop arcade seen in 171 Å. Later, the 193
  Å loop also switches to contraction. These observations are naturally
  explained by vortex flows present in a model of eruptive solar flares.

Title: Studying the transfer of magnetic helicity in solar active
    regions
Authors: Dalmasse, Kévin; Jing, J.; Pariat, E.; Valori, G.;
   Démoulin, P.
Bibcode: 2017shin.confE.160D
Altcode:
  Analyzing the transfer of magnetic helicity in active regions is a
  key component for understanding the nature of its coronal storage
  and release and for identifying its role in the coronal dynamics
  of active regions. We recently developed a method for studying the
  photospheric flux of magnetic helicity in both 2D and 3D. The method
  takes into account the 3D nature of magnetic helicity by explicitly
  using knowledge of the magnetic field connectivity. Since the coronal
  magnetic field in active regions is not measured, we rely on the
  approximate 3D solution obtained from force-free coronal magnetic
  field extrapolations to derive the magnetic field connectivity. In
  this poster, we apply the method to the complex and highly-flaring
  active region NOAA 11158 using the magnetic field connectivity derived
  from different force-free extrapolation models and implementations. We
  show that the calculations of photospheric flux of magnetic helicity
  are robust to different extrapolation methods and assumptions, in
  particular with regards to identifying regions of opposite magnetic
  helicity flux. Finally, we discuss the implications of our results
  for tracking the transfer of magnetic helicity in active regions and
  relate it to their flaring activity.

Title: A study of the long term evolution in active region upflows
Authors: Harra, Louise K.; Ugarte-Urra, Ignacio; De Rosa, Marc;
   Mandrini, Cristina; van Driel-Gesztelyi, Lidia; Baker, Deborah;
   Culhane, J. Leonard; Démoulin, Pascal
Bibcode: 2017PASJ...69...47H
Altcode:
  Since their discovery, upflows at the edges of active regions have
  attracted a lot of interest, primarily as they could potentially
  contribute to the slow solar wind. One aspect that has not been studied
  yet is how the long term evolution of active regions impacts the
  upflows. In this work, we analyze one active region that survives three
  solar rotations. We track how the flows change with time. We use local
  and global modeling of the decaying active region to determine how the
  age of the active region will impact the extent of the open magnetic
  fields, and then how some of the upflows could become outflows. We
  finish with a discussion of how these results, set in a broader context,
  can be further developed with the Solar Orbiter mission.

Title: Apparent and Intrinsic Evolution of Active Region Upflows
Authors: Baker, Deborah; Janvier, Miho; Démoulin, Pascal; Mandrini,
   Cristina H.
Bibcode: 2017SoPh..292...46B
Altcode: 2017arXiv170206022B
  We analyze the evolution of Fe XII coronal plasma upflows from
  the edges of ten active regions (ARs) as they cross the solar disk
  using the Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) to do
  this. Confirming the results of Démoulin et al. (Sol. Phys.283, 341,
  2013), we find that for each AR there is an observed long-term evolution
  of the upflows. This evolution is largely due to the solar rotation
  that progressively changes the viewpoint of dominantly stationary
  upflows. From this projection effect, we estimate the unprojected
  upflow velocity and its inclination to the local vertical. AR upflows
  typically fan away from the AR core by 40° to nearly vertical
  for the following polarity. The span of inclination angles is more
  spread out for the leading polarity, with flows angled from −29°
  (inclined toward the AR center) to 28° (directed away from the
  AR). In addition to the limb-to-limb apparent evolution, we identify
  an intrinsic evolution of the upflows that is due to coronal activity,
  which is AR dependent. Furthermore, line widths are correlated with
  Doppler velocities only for the few ARs with the highest velocities. We
  conclude that for the line widths to be affected by the solar rotation,
  the spatial gradient of the upflow velocities must be large enough
  such that the line broadening exceeds the thermal line width of Fe
  XII. Finally, we find that upflows occurring in pairs or multiple
  pairs are a common feature of ARs observed by Hinode/EIS, with up to
  four pairs present in AR 11575. This is important for constraining the
  upflow-driving mechanism as it implies that the mechanism is not local
  and does not occur over a single polarity. AR upflows originating from
  reconnection along quasi-separatrix layers between overpressure AR
  loops and neighboring underpressure loops is consistent with upflows
  occurring in pairs, unlike other proposed mechanisms that act locally
  in one polarity.

Title: Vortex and Sink Flows in Eruptive Flares as a Model for
    Coronal Implosions
Authors: Zuccarello, F. P.; Aulanier, G.; Dudík, J.; Démoulin, P.;
   Schmieder, B.; Gilchrist, S. A.
Bibcode: 2017ApJ...837..115Z
Altcode: 2017arXiv170200199Z
  Eruptive flares are sudden releases of magnetic energy that
  involve many phenomena, several of which can be explained by the
  standard 2D flare model and its realizations in 3D. We analyze a 3D
  magnetohydrodynamics simulation, in the framework of this model, that
  naturally explains the contraction of coronal loops in the proximity
  of the flare sites, as well as the inflow toward the region above the
  cusp-shaped loops. We find that two vorticity arcs located along the
  flanks of the erupting magnetic flux rope are generated as soon as the
  eruption begins. The magnetic arcades above the flux rope legs are then
  subjected to expansion, rotation, or contraction depending on which
  part of the vortex flow advects them. In addition to the vortices,
  an inward-directed magnetic pressure gradient exists in the current
  sheet below the magnetic flux rope. It results in the formation of a
  sink that is maintained by reconnection. We conclude that coronal loop
  apparent implosions observed during eruptive flares are the result
  of hydromagnetic effects related to the generation of vortex and sink
  flows when a flux rope moves in a magnetized environment.

Title: Successive injection of opposite magnetic helicity in solar
    active region NOAA 11928
Authors: Vemareddy, P.; Démoulin, P.
Bibcode: 2017A&A...597A.104V
Altcode: 2016arXiv161100699V
  <BR /> Aims: Understanding the nature and evolution of the photospheric
  helicity flux transfer is crucial to revealing the role of magnetic
  helicity in coronal dynamics of solar active regions. <BR /> Methods:
  We computed the boundary-driven helicity flux with a 12-min cadence
  during the emergence of the AR 11928 using SDO/HMI photospheric vector
  magnetograms and the derived flow velocity field. Accounting for
  the footpoint connectivity defined by nonlinear, force-free magnetic
  extrapolations, we derived and analyzed the corrected distribution
  of helicity flux maps. <BR /> Results: The photospheric helicity flux
  injection is found to change sign during the steady emergence of the
  AR. This reversal is confirmed with the evolution of the photospheric
  electric currents and with the coronal connectivity as observed in EUV
  wavelengths with SDO/AIA. During approximately the three first days
  of emergence, the AR coronal helicity is positive while later on the
  field configuration is close to a potential field. As theoretically
  expected, the magnetic helicity cancellation is associated with
  enhanced coronal activity. <BR /> Conclusions: The study suggests
  a boundary driven transformation of the chirality in the global AR
  magnetic structure. This may be the result of the emergence of a flux
  rope with positive twist around its apex while it has negative twist in
  its legs. The origin of such mixed helicity flux rope in the convective
  zone is challenging for models.

Title: Evolution of the magnetic field distribution of active regions
Authors: Dacie, S.; Démoulin, P.; van Driel-Gesztelyi, L.; Long,
   D. M.; Baker, D.; Janvier, M.; Yardley, S. L.; Pérez-Suárez, D.
Bibcode: 2016A&A...596A..69D
Altcode: 2016arXiv160903723D
  <BR /> Aims: Although the temporal evolution of active regions (ARs)
  is relatively well understood, the processes involved continue to be
  the subject of investigation. We study how the magnetic field of a
  series of ARs evolves with time to better characterise how ARs emerge
  and disperse. <BR /> Methods: We examined the temporal variation in
  the magnetic field distribution of 37 emerging ARs. A kernel density
  estimation plot of the field distribution was created on a log-log
  scale for each AR at each time step. We found that the central portion
  of the distribution is typically linear, and its slope was used to
  characterise the evolution of the magnetic field. <BR /> Results:
  The slopes were seen to evolve with time, becoming less steep as the
  fragmented emerging flux coalesces. The slopes reached a maximum value
  of -1.5 just before the time of maximum flux before becoming steeper
  during the decay phase towards the quiet-Sun value of -3. This behaviour
  differs significantly from a classical diffusion model, which produces
  a slope of -1. These results suggest that simple classical diffusion
  is not responsible for the observed changes in field distribution, but
  that other processes play a significant role in flux dispersion. <BR />
  Conclusions: We propose that the steep negative slope seen during the
  late-decay phase is due to magnetic flux reprocessing by (super)granular
  convective cells.

Title: Tracing the Evolution of ICMEs from Sun to Earth
Authors: Janvier, M.; Demoulin, P.; Dasso, S.; Masias, J.
Bibcode: 2016AGUFMSH53A..03J
Altcode:
  Coronal Mass Ejections (CMEs) are the result of magnetic instabilities
  in the Sun's atmosphere, which are consequently launched into the
  heliosphere. As their interplanetary counterparts (ICMEs) propagate
  in the interplanetary medium, they can interact with the magnetized
  environment of planets and other objects in the solar system. They
  are believed to be the main drivers of space weather. Over the past
  decades, the multiplication of space missions has led to a gold mine in
  ICME data, allowing us to deepen our knowledge on their properties and
  evolution from the Sun to the Earth. In particular, the identification
  of substructures such as shocks and magnetic clouds and their typical
  profiles, as well as their properties, can be traced at different
  locations away from the Sun. Here, we will review different aspects
  of ICMEs, such as their 3D generic shape, the transported physical
  quantities as well as their evolution (such as the expansion) in the
  inner heliosphere. These aspects can be quantified by in situ data, and
  consequently they can provide useful information to constrain analytical
  and numerical models as well as remote-sensing data interpretation. They
  also provide key questions to be addressed by the future Solar Orbiter
  and Solar Probe Plus missions.

Title: Quantitative model for the generic 3D shape of ICMEs at 1 AU
Authors: Démoulin, P.; Janvier, M.; Masías-Meza, J. J.; Dasso, S.
Bibcode: 2016A&A...595A..19D
Altcode: 2016arXiv160808550D
  Context. Interplanetary imagers provide 2D projected views of the
  densest plasma parts of interplanetary coronal mass ejections (ICMEs),
  while in situ measurements provide magnetic field and plasma parameter
  measurements along the spacecraft trajectory, that is, along a 1D
  cut. The data therefore only give a partial view of the 3D structures
  of ICMEs. <BR /> Aims: By studying a large number of ICMEs, crossed at
  different distances from their apex, we develop statistical methods
  to obtain a quantitative generic 3D shape of ICMEs. <BR /> Methods:
  In a first approach we theoretically obtained the expected statistical
  distribution of the shock-normal orientation from assuming simple
  models of 3D shock shapes, including distorted profiles, and compared
  their compatibility with observed distributions. In a second approach
  we used the shock normal and the flux rope axis orientations together
  with the impact parameter to provide statistical information across the
  spacecraft trajectory. <BR /> Results: The study of different 3D shock
  models shows that the observations are compatible with a shock that is
  symmetric around the Sun-apex line as well as with an asymmetry up to
  an aspect ratio of around 3. Moreover, flat or dipped shock surfaces
  near their apex can only be rare cases. Next, the sheath thickness and
  the ICME velocity have no global trend along the ICME front. Finally,
  regrouping all these new results and those of our previous articles,
  we provide a quantitative ICME generic 3D shape, including the global
  shape of the shock, the sheath, and the flux rope. <BR /> Conclusions:
  The obtained quantitative generic ICME shape will have implications for
  several aims. For example, it constrains the output of typical ICME
  numerical simulations. It is also a base for studying the transport
  of high-energy solar and cosmic particles during an ICME propagation
  as well as for modeling and forecasting space weather conditions
  near Earth.

Title: Why Are Flare Ribbons Associated with the Spines of Magnetic
    Null Points Generically Elongated?
Authors: Pontin, David; Galsgaard, Klaus; Démoulin, Pascal
Bibcode: 2016SoPh..291.1739P
Altcode: 2016arXiv160505704P; 2016SoPh..tmp..101P
  Coronal magnetic null points exist in abundance, as demonstrated by
  extrapolations of the coronal field, and have been inferred to be
  important for a broad range of energetic events. These null points
  and their associated separatrix and spine field lines represent
  discontinuities of the field line mapping, making them preferential
  locations for reconnection. This field line mapping also exhibits strong
  gradients adjacent to the separatrix (fan) and spine field lines, which
  can be analysed using the "squashing factor", Q . In this article we
  analyse in detail the distribution of Q in the presence of magnetic
  nulls. While Q is formally infinite on both the spine and fan of the
  null, the decay of Q away from these structures is shown in general to
  depend strongly on the null-point structure. For the generic case of a
  non-radially-symmetric null, Q decays most slowly away from the spine or
  fan in the direction in which |B | increases most slowly. In particular,
  this demonstrates that the extended elliptical high-Q halo around the
  spine footpoints observed by Masson et al. (Astrophys. J.700, 559,
  2009) is a generic feature. This extension of the Q halos around the
  spine or fan footpoints is important for diagnosing the regions of the
  photosphere that are magnetically connected to any current layer that
  forms at the null. In light of this, we discuss how our results can be
  used to interpret the geometry of observed flare ribbons in circular
  ribbon flares, in which typically a coronal null is implicated. We
  conclude that both the physics in the vicinity of the null and how
  this is related to the extension of Q away from the spine or fan can be
  used in tandem to understand observational signatures of reconnection
  at coronal null points.

Title: Properties of Magnetic Tongues over a Solar Cycle
Authors: Poisson, Mariano; Démoulin, Pascal; López Fuentes, Marcelo;
   Mandrini, Cristina H.
Bibcode: 2016SoPh..291.1625P
Altcode: 2016arXiv160900329P; 2016SoPh..tmp..109P
  The photospheric spatial distribution of the main magnetic polarities of
  bipolar active regions (ARs) present during their emergence deformations
  are known as magnetic tongues. They are attributed to the presence of
  twist in the toroidal magnetic-flux tubes that form the ARs. The aim
  of this article is to study the twist of newly emerged ARs from the
  evolution of magnetic tongues observed in photospheric line-of-sight
  magnetograms. We apply the procedure described by Poisson et al. (Solar
  Phys.290, 727, 2015a) to ARs observed over the full Solar Cycle 23 and
  the beginning of Cycle 24. Our results show that the hemispherical
  rule obtained using the tongues as a proxy of the twist has a weak
  sign dominance (53 % in the southern hemisphere and 58 % in the
  northern hemisphere). By defining the variation of the tongue angle,
  we characterize the strength of the magnetic tongues during different
  phases of the AR emergence. We find that there is a tendency of the
  tongues to be stronger during the beginning of the emergence and to
  become weaker as the AR reaches its maximum magnetic flux. We compare
  this evolution with the emergence of a toroidal flux-rope model with
  non-uniform twist. The variety of evolution of the tongues in the
  analyzed ARs can only be reproduced when using a broad range of twist
  profiles, in particular having a large variety of twist gradients in
  the direction vertical to the photosphere. Although the analytical
  model used is a special case, selected to minimize the complexity of
  the problem, the results obtained set new observational constraints
  to theoretical models of flux-rope emergence that form bipolar ARs.

Title: Superposed epoch study of ICME sub-structures near Earth and
    their effects on Galactic cosmic rays
Authors: Masías-Meza, J. J.; Dasso, S.; Démoulin, P.; Rodriguez,
   L.; Janvier, M.
Bibcode: 2016A&A...592A.118M
Altcode: 2016arXiv160508130M
  Context. Interplanetary coronal mass ejections (ICMEs) are the
  interplanetary manifestations of solar eruptions. The overtaken
  solar wind forms a sheath of compressed plasma at the front of
  ICMEs. Magnetic clouds (MCs) are a subset of ICMEs with specific
  properties (e.g. the presence of a flux rope). When ICMEs pass near
  Earth, ground observations indicate that the flux of Galactic cosmic
  rays (GCRs) decreases. <BR /> Aims: The main aims of this paper
  are to find common plasma and magnetic properties of different ICME
  sub-structures and which ICME properties affect the flux of GCRs near
  Earth. <BR /> Methods: We used a superposed epoch method applied to
  a large set of ICMEs observed in situ by the spacecraft ACE, between
  1998 and 2006. We also applied a superposed epoch analysis on GCRs time
  series observed with the McMurdo neutron monitors. <BR /> Results: We
  find that slow MCs at 1 AU have on average more massive sheaths. We
  conclude that this is because they are more effectively slowed down
  by drag during their travel from the Sun. Slow MCs also have a more
  symmetric magnetic field and sheaths expanding similarly as their
  following MC, while in contrast, fast MCs have an asymmetric magnetic
  profile and a sheath in compression. In all types of MCs, we find that
  the proton density and the temperature and the magnetic fluctuations
  can diffuse within the front of the MC due to 3D reconnection. Finally,
  we derive a quantitative model that describes the decrease in cosmic
  rays as a function of the amount of magnetic fluctuations and field
  strength. <BR /> Conclusions: The obtained typical profiles of sheath,
  MC and GCR properties corresponding to slow, middle, and fast ICMEs,
  can be used for forecasting or modelling these events, and to better
  understand the transport of energetic particles in ICMEs. They are
  also useful for improving future operative space weather activities.

Title: Typical Profiles and Distributions of Plasma and Magnetic
    Field Parameters in Magnetic Clouds at 1 AU
Authors: Rodriguez, L.; Masías-Meza, J. J.; Dasso, S.; Démoulin,
   P.; Zhukov, A. N.; Gulisano, A. M.; Mierla, M.; Kilpua, E.; West,
   M.; Lacatus, D.; Paraschiv, A.; Janvier, M.
Bibcode: 2016SoPh..291.2145R
Altcode: 2016SoPh..tmp..113R
  Magnetic clouds (MCs) are a subset of interplanetary coronal mass
  ejections (ICMEs). They are important because of their simple internal
  magnetic field configuration, which resembles a magnetic flux rope,
  and because they represent one of the most geoeffective types of solar
  transients. In this study, we analyze their internal structure using
  a superposed epoch method on 63 events observed at L1 by the Advance
  Composition Explorer (ACE), between 1998 and 2006. In this way, we
  obtain an average profile for each plasma and magnetic field parameter
  at each point of the cloud. Furthermore, we take a fixed time-window
  upstream and downstream from the MC to also sample the regions preceding
  the cloud and the wake trailing it. We then perform a detailed analysis
  of the internal characteristics of the clouds and their surrounding
  solar wind environments. We find that the parameters studied are
  compatible with log-normal distribution functions. The plasma β and
  the level of fluctuations in the magnetic field vector are the best
  parameters to define the boundaries of MCs. We find that one third
  of the events shows a peak in plasma density close to the trailing
  edge of the flux ropes. We provide several possible explanations for
  this result and investigate if the density peak is of a solar origin
  (e.g. erupting prominence material) or formed during the magnetic cloud
  travel from the Sun to 1 AU. The most plausible explanation is the
  compression due to a fast overtaking flow, coming from a coronal hole
  located to the east of the solar source region of the magnetic cloud.

Title: Manifestation of Coronal Mass Ejections near Earth: A review
Authors: Dasso, Sergio; Rodriguez, Luciano; Demoulin, Pascal;
   Masías-Meza, Jimmy J.; Janvier, Miho
Bibcode: 2016cosp...41E.405D
Altcode:
  Coronal Mass Ejections (CMEs) are launched from the Sun, as a result of
  magnetic instabilities, carrying away a huge amount of magnetic flux and
  helicity. Interplanetary CMEs (ICMEs) are their manifestation observed
  further away in the heliosphere. ICMEs produce important changes of
  plasma and magnetic field properties in the interplanetary medium, with
  respect to the ones of the ambient solar wind. From the large number
  of observed ICMEs, in the past years we significantly increased our
  kwnoledge on several of their properties, such as: the identification
  of the composing sub-structures and their local properties, their global
  3D shape, the amount of magnetohydrodynamical quantities transported in
  the heliosphere by the associated flux ropes, as well as how the plasma
  and magnetic field are distributed inside them. In the present talk we
  will present a general review of these aspects of ICMEs. In particular
  we will focuss on the total amount of magnetic flux and helicity ejected
  by CMEs from the Sun along a solar cycle, and on plasma and magnetic
  properties of their shock-sheath-flux_rope-wake. These results can
  help to understand their interaction with the ambient solar wind and
  with planetary magnetic environments. They are particularly crucial
  for a better understanding of the Sun-Earth coupling.

Title: Why are flare ribbons generically elongated in configurations
    with magnetic null points?
Authors: Pontin, David Iain; Galsgaard, Klaus; Demoulin, Pascal
Bibcode: 2016SPD....47.0625P
Altcode:
  Coronal magnetic null points exist in abundance as demonstrated by
  extrapolations of the coronal field, and have been inferred to be
  important for a broad range of energetic events. These null points
  and their associated separatrix and spine field lines represent
  discontinuities of the field line mapping, making them preferential
  locations for reconnection in the corona. In addition, the field line
  mapping in the vicinity of these null points exhibits strong gradients
  as measured by the “squashing factor”, Q. We demonstrate that
  the extension of the Q halos around the spine/fan footpoints is in
  general important for diagnosing the regions of the photosphere that are
  magnetically connected to any current layer that forms at the null. In
  light of this, we discuss the extent to which our results can be used
  to interpret the geometry of observed flare ribbons in events in which
  a coronal null is implicated. We conclude that together the physics
  in the vicinity of the null and how this is related to the extension
  of Q away from the spine/fan can be used in tandem to understand
  observational signatures of reconnection at coronal null points.

Title: Homologous Solar Events on 2011 January 27: Build-up and
    Propagation in a Complex Coronal Environment
Authors: Pick, M.; Stenborg, G.; Démoulin, P.; Zucca, P.; Lecacheux,
   A.
Bibcode: 2016ApJ...823....5P
Altcode:
  In spite of the wealth of imaging observations at the
  extreme-ultraviolet (EUV), X-ray, and radio wavelengths, there are
  still relatively few cases where all of the imagery is available to
  study the full development of a coronal mass ejection (CME) event and
  its associated shock. The aim of this study is to contribute to the
  understanding of the role of the coronal environment in the development
  of CMEs and the formation of shocks, and their propagation. We have
  analyzed the interactions of a couple of homologous CME events with
  ambient coronal structures. Both events were launched in a direction
  far from the local vertical, and exhibited a radical change in their
  direction of propagation during their progression from the low corona
  into higher altitudes. Observations at EUV wavelengths from the
  Atmospheric Imaging Assembly instrument on board the Solar Dynamic
  Observatory were used to track the events in the low corona. The
  development of the events at higher altitudes was followed by
  the white-light coronagraphs on board the Solar and Heliospheric
  Observatory. Radio emissions produced during the development of the
  events were well recorded by the Nançay solar instruments. Thanks
  to their detection of accelerated electrons, the radio observations
  are an important complement to the EUV imaging. They allowed us to
  characterize the development of the associated shocks, and helped to
  unveil the physical processes behind the complex interactions between
  the CMEs and ambient medium (e.g., compression, reconnection).

Title: Magnetic Flux and Helicity of Magnetic Clouds
Authors: Démoulin, P.; Janvier, M.; Dasso, S.
Bibcode: 2016SoPh..291..531D
Altcode: 2015SoPh..tmp..183D; 2015arXiv150901068D
  Magnetic clouds (MCs) are formed by flux ropes (FRs) launched from
  the Sun as part of coronal mass ejections (CMEs). They carry away
  a large amount of magnetic flux and helicity. The main aim of this
  study is to quantify these amounts from in situ measurements of MCs
  at 1 AU. The fit of these data by a local FR model provides the axial
  magnetic field strength, the radius, the magnetic flux, and the helicity
  per unit length along the FR axis. We show that these quantities are
  statistically independent of the position along the FR axis. We then
  derive the generic shape and length of the FR axis from two sets of
  MCs. These results improve the estimation of magnetic helicity. Next,
  we evaluate the total magnetic flux and helicity that cross the
  sphere of radius of 1 AU, centred at the Sun, per year and during a
  solar cycle. We also include in the study two sets of small FRs that
  do not have all the typical characteristics of MCs. While small FRs
  are at least ten times more numerous than MCs, the magnetic flux and
  helicity are dominated by the contribution from the larger MCs. In
  one year they carry away the magnetic flux of about 25 large active
  regions and the magnetic helicity of 200 of them. MCs carry away an
  amount of unsigned magnetic helicity similar to the amount estimated
  for the solar dynamo and that measured in emerging active regions.

Title: Erratum to: The Magnetic Helicity Budget of a CME-Prolific
    Active Region
Authors: Green, L. M.; López Fuentes, M.; Mandrini, C. H.; Démoulin,
   P.; van Driel-Gesztelyi, L.; Culhane, J. L.
Bibcode: 2016SoPh..291..335G
Altcode: 2015SoPh..tmp..179G
  No abstract at ADS

Title: From Coronal Observations to MHD Simulations, the Building
    Blocks for 3D Models of Solar Flares (Invited Review)
Authors: Janvier, M.; Aulanier, G.; Démoulin, P.
Bibcode: 2015SoPh..290.3425J
Altcode: 2015SoPh..tmp...63J; 2015arXiv150505299J
  Solar flares are energetic events taking place in the Sun's atmosphere,
  and their effects can greatly impact the environment of the surrounding
  planets. In particular, eruptive flares, as opposed to confined flares,
  launch coronal mass ejections into the interplanetary medium, and
  as such, are one of the main drivers of space weather. After briefly
  reviewing the main characteristics of solar flares, we summarise the
  processes that can account for the build-up and release of energy
  during their evolution. In particular, we focus on the development
  of recent 3D numerical simulations that explain many of the observed
  flare features. These simulations can also provide predictions of the
  dynamical evolution of coronal and photospheric magnetic field. Here
  we present a few observational examples that, together with numerical
  modelling, point to the underlying physical mechanisms of the eruptions.

Title: Active-Region Twist Derived from Magnetic Tongues and Linear
    Force-Free Extrapolations
Authors: Poisson, Mariano; López Fuentes, Marcelo; Mandrini, Cristina
   H.; Démoulin, Pascal
Bibcode: 2015SoPh..290.3279P
Altcode: 2015SoPh..tmp..183P
  The main aim of this study is to compare the amount of twist present in
  emerging active regions (ARs) from photospheric and coronal data. We
  use linear force-free field models of the observed coronal structure
  of ARs to determine the global twist. The coronal twist is derived,
  on one hand, from the force-free parameter [α ] of the model and, on
  the other, from the computed coronal magnetic helicity normalized by
  the magnetic flux squared. We compare our results, for the same set of
  ARs, with those of Poisson et al. (Solar Phys.290, 727, 2015), in which
  the twist was estimated using the so-called magnetic tongues observed
  in line-of-sight magnetograms during AR emergence. We corroborate
  the agreement between the photospheric and coronal twist-sign
  and the presence of magnetic tongues as an early proxy of the AR
  non-potentiality. We find a globally linear relationship between the
  coronal twist and the one previously deduced for the emerging AR flux
  rope at the photospheric level. The coronal-twist value is typically
  lower by a factor of six than the one deduced for the emerging flux
  rope. We interpret this result as due to the partial emergence of the
  flux rope that forms the region.

Title: The Origin of Net Electric Currents in Solar Active Regions
Authors: Dalmasse, K.; Aulanier, G.; Démoulin, P.; Kliem, B.; Török,
   T.; Pariat, E.
Bibcode: 2015ApJ...810...17D
Altcode: 2015arXiv150705060D
  There is a recurring question in solar physics regarding whether or not
  electric currents are neutralized in active regions (ARs). This question
  was recently revisited using three-dimensional (3D) magnetohydrodynamic
  (MHD) numerical simulations of magnetic flux emergence into the solar
  atmosphere. Such simulations showed that flux emergence can generate
  a substantial net current in ARs. Other sources of AR currents are
  photospheric horizontal flows. Our aim is to determine the conditions
  for the occurrence of net versus neutralized currents with this second
  mechanism. Using 3D MHD simulations, we systematically impose line-tied,
  quasi-static, photospheric twisting and shearing motions to a bipolar
  potential magnetic field. We find that such flows: (1) produce
  both direct and return currents, (2) induce very weak compression
  currents—not observed in 2.5D—in the ambient field present in the
  close vicinity of the current-carrying field, and (3) can generate
  force-free magnetic fields with a net current. We demonstrate that
  neutralized currents are in general produced only in the absence of
  magnetic shear at the photospheric polarity inversion line—a special
  condition that is rarely observed. We conclude that photospheric flows,
  as magnetic flux emergence, can build up net currents in the solar
  atmosphere, in agreement with recent observations. These results thus
  provide support for eruption models based on pre-eruption magnetic
  fields that possess a net coronal current.

Title: Parallel Evolution of Quasi-separatrix Layers and Active
    Region Upflows
Authors: Mandrini, C. H.; Baker, D.; Démoulin, P.; Cristiani, G. D.;
   van Driel-Gesztelyi, L.; Vargas Domínguez, S.; Nuevo, F. A.; Vásquez,
   A. M.; Pick, M.
Bibcode: 2015ApJ...809...73M
Altcode: 2015arXiv150701264M
  Persistent plasma upflows were observed with Hinode’s EUV
  Imaging Spectrometer (EIS) at the edges of active region (AR)
  10978 as it crossed the solar disk. We analyze the evolution of
  the photospheric magnetic and velocity fields of the AR, model
  its coronal magnetic field, and compute the location of magnetic
  null-points and quasi-sepratrix layers (QSLs) searching for the origin
  of EIS upflows. Magnetic reconnection at the computed null points
  cannot explain all of the observed EIS upflow regions. However, EIS
  upflows and QSLs are found to evolve in parallel, both temporarily
  and spatially. Sections of two sets of QSLs, called outer and
  inner, are found associated to EIS upflow streams having different
  characteristics. The reconnection process in the outer QSLs is forced
  by a large-scale photospheric flow pattern, which is present in the AR
  for several days. We propose a scenario in which upflows are observed,
  provided that a large enough asymmetry in plasma pressure exists
  between the pre-reconnection loops and lasts as long as a photospheric
  forcing is at work. A similar mechanism operates in the inner QSLs; in
  this case, it is forced by the emergence and evolution of the bipoles
  between the two main AR polarities. Our findings provide strong support
  for the results from previous individual case studies investigating the
  role of magnetic reconnection at QSLs as the origin of the upflowing
  plasma. Furthermore, we propose that persistent reconnection along
  QSLs does not only drive the EIS upflows, but is also responsible for
  the continuous metric radio noise-storm observed in AR 10978 along
  its disk transit by the Nançay Radio Heliograph.

Title: Testing magnetic helicity conservation in a solar-like
    active event
Authors: Pariat, E.; Valori, G.; Démoulin, P.; Dalmasse, K.
Bibcode: 2015A&A...580A.128P
Altcode: 2015arXiv150609013P
  Context. Magnetic helicity has the remarkable property of being a
  conserved quantity of ideal magnetohydrodynamics (MHD). Therefore, it
  could be used as an effective tracer of the magnetic field evolution
  of magnetized plasmas. <BR /> Aims: Theoretical estimations indicate
  that magnetic helicity is also essentially conserved with non-ideal MHD
  processes, for example, magnetic reconnection. This conjecture has been
  barely tested, however, either experimentally or numerically. Thanks
  to recent advances in magnetic helicity estimation methods, it is
  now possible to numerically test its dissipation level in general
  three-dimensional datasets. <BR /> Methods: We first revisit the
  general formulation of the temporal variation of relative magnetic
  helicity on a fully bounded volume when no hypothesis on the gauge is
  made. We introduce a method for precisely estimating its dissipation
  independently of which type of non-ideal MHD processes occurs. For
  a solar-like eruptive-event simulation, using different gauges, we
  compare an estimate of the relative magnetic helicity computed in a
  finite volume with its time-integrated flux through the boundaries. We
  thus test the conservation and dissipation of helicity. <BR /> Results:
  We provide an upper bound of the real dissipation of magnetic helicity:
  It is quasi-null during the quasi-ideal MHD phase. Even with magnetic
  reconnection, the relative dissipation of magnetic helicity is also very
  low (&lt;2.2%), in particular compared to the relative dissipation
  of magnetic energy (&gt;30 times higher). We finally illustrate
  how the helicity-flux terms involving velocity components are gauge
  dependent, which limits their physical meaning. <BR /> Conclusions:
  Our study paves the way for more extended and diverse tests of the
  magnetic helicity conservation properties. Our study confirms the
  central role of helicity in the study of MHD plasmas. For instance,
  the conservation of helicity can be used to track the evolution of
  solar magnetic fields from when they form in the solar interior
  until their detection as magnetic clouds in the interplanetary
  space. <P />Appendix A is available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201525811/olm">http://www.aanda.org</A>

Title: Strong coronal channelling and interplanetary evolution of
    a solar storm up to Earth and Mars
Authors: Möstl, Christian; Rollett, Tanja; Frahm, Rudy A.; Liu,
   Ying D.; Long, David M.; Colaninno, Robin C.; Reiss, Martin A.;
   Temmer, Manuela; Farrugia, Charles J.; Posner, Arik; Dumbović,
   Mateja; Janvier, Miho; Démoulin, Pascal; Boakes, Peter; Devos, Andy;
   Kraaikamp, Emil; Mays, Mona L.; Vršnak, Bojan
Bibcode: 2015NatCo...6.7135M
Altcode: 2015arXiv150602842M; 2015NatCo...6E7135M
  The severe geomagnetic effects of solar storms or coronal mass
  ejections (CMEs) are to a large degree determined by their propagation
  direction with respect to Earth. There is a lack of understanding of
  the processes that determine their non-radial propagation. Here we
  present a synthesis of data from seven different space missions of a
  fast CME, which originated in an active region near the disk centre
  and, hence, a significant geomagnetic impact was forecasted. However,
  the CME is demonstrated to be channelled during eruption into a
  direction +37+/-10° (longitude) away from its source region, leading
  only to minimal geomagnetic effects. In situ observations near Earth
  and Mars confirm the channelled CME motion, and are consistent with
  an ellipse shape of the CME-driven shock provided by the new Ellipse
  Evolution model, presented here. The results enhance our understanding
  of CME propagation and shape, which can help to improve space weather
  forecasts.

Title: Comparing generic models for interplanetary shocks and magnetic
    clouds axis configurations at 1 AU
Authors: Janvier, M.; Dasso, S.; Démoulin, P.; Masías-Meza, J. J.;
   Lugaz, N.
Bibcode: 2015JGRA..120.3328J
Altcode: 2015arXiv150306128J
  Interplanetary coronal mass ejections (ICMEs) are the manifestation
  of solar transient eruptions, which can significantly modify the
  plasma and magnetic conditions in the heliosphere. They are often
  preceded by a shock, and a magnetic flux rope is detected in situ
  in a third to half of them. The main aim of this study is to obtain
  the best quantitative shape for the flux rope axis and for the shock
  surface from in situ data obtained during spacecraft crossings of
  these structures. We first compare the orientation of the flux rope
  axes and shock normals obtained from independent data analyses of
  the same events, observed in situ at 1 AU from the Sun. Then we
  carry out an original statistical analysis of axes/shock normals
  by deriving the statistical distributions of their orientations. We
  fit the observed distributions using the distributions derived from
  several synthetic models describing these shapes. We show that the
  distributions of axis/shock orientations are very sensitive to their
  respective shape. One classical model, used to analyze interplanetary
  imager data, is incompatible with the in situ data. Two other models
  are introduced, for which the results for axis and shock normals lead
  to very similar shapes; the fact that the data for MCs and shocks
  are independent strengthens this result. The model which best fits
  all the data sets has an ellipsoidal shape with similar aspect ratio
  values for all the data sets. These derived shapes for the flux rope
  axis and shock surface have several potential applications. First,
  these shapes can be used to construct a consistent ICME model. Second,
  these generic shapes can be used to develop a quantitative model to
  analyze imager data, as well as constraining the output of numerical
  simulations of ICMEs. Finally, they will have implications for space
  weather forecasting, in particular, for forecasting the time arrival
  of ICMEs at the Earth.

Title: Electric current neutralization in solar active regions
Authors: Dalmasse, Kévin; Aulanier, Guillaume; Török, Tibor;
   Démoulin, Pascal; Pariat, Etienne; Kliem, Bernhard
Bibcode: 2015TESS....111303D
Altcode:
  There is a recurring question in solar physics of whether or not
  photospheric vertical electric currents are neutralized in solar active
  regions, i.e., whether or not the total electric current integrated
  over a single magnetic polarity of an active region vanishes. While
  different arguments have been proposed in favor of, or against, the
  neutralization of electric currents, both theory and observations are
  still not fully conclusive. Providing the answer to this question is
  crucial for theoretical models of solar eruptions. Indeed, if currents
  are neutralized in active regions, then any eruption model based on net
  - i.e., non-zero - electric currents, such as the torus instability,
  requires further consideration. We address the question of electric
  current neutralization in active regions using 3D zero-beta MHD
  simulations of line-tied, slow photospheric driving motions imposed
  on an initially potential magnetic field. We compare our results to a
  recent study of the build-up of coronal electric currents in an MHD
  simulation of the emergence of a current-neutralized twisted flux
  tube into the solar atmosphere. Our parametric study shows that, in
  accordance with the flux emergence simulation, photospheric motions are
  associated with the formation of both direct and return currents. It
  further shows that both processes (flux emergence and photospheric
  flows) can lead to the formation of strong net currents in the solar
  corona, and that the non-neutralization of electric currents is related
  to the presence of magnetic shear at the polarity inversion line. We
  discuss the implications of our results for the observations and for
  theoretical models of solar eruptions.

Title: FIP Bias Evolution in a Decaying Active Region
Authors: Baker, D.; Brooks, D. H.; Démoulin, P.; Yardley, S. L.;
   van Driel-Gesztelyi, L.; Long, D. M.; Green, L. M.
Bibcode: 2015ApJ...802..104B
Altcode: 2015arXiv150107397B
  Solar coronal plasma composition is typically characterized by
  first ionization potential (FIP) bias. Using spectra obtained by
  Hinode’s EUV Imaging Spectrometer instrument, we present a series
  of large-scale, spatially resolved composition maps of active region
  (AR)11389. The composition maps show how FIP bias evolves within the
  decaying AR during the period 2012 January 4-6. Globally, FIP bias
  decreases throughout the AR. We analyzed areas of significant plasma
  composition changes within the decaying AR and found that small-scale
  evolution in the photospheric magnetic field is closely linked to the
  FIP bias evolution observed in the corona. During the AR’s decay
  phase, small bipoles emerging within supergranular cells reconnect
  with the pre-existing AR field, creating a pathway along which
  photospheric and coronal plasmas can mix. The mixing timescales are
  shorter than those of plasma enrichment processes. Eruptive activity
  also results in shifting the FIP bias closer to photospheric in the
  affected areas. Finally, the FIP bias still remains dominantly coronal
  only in a part of the AR’s high-flux density core. We conclude that
  in the decay phase of an AR’s lifetime, the FIP bias is becoming
  increasingly modulated by episodes of small-scale flux emergence,
  i.e., decreasing the AR’s overall FIP bias. Our results show that
  magnetic field evolution plays an important role in compositional
  changes during AR development, revealing a more complex relationship
  than expected from previous well-known Skylab results showing that
  FIP bias increases almost linearly with age in young ARs.

Title: Strong coronal deflection of a CME and its interplanetary
    evolution to Earth and Mars
Authors: Möstl, Christian; Rollett, Tanja; Frahm, Rudy A.; Liu, Ying
   D.; Long, David M.; Colaninno, Robin C.; Reiss, Martin A.; Temmer,
   Manuela; Farrugia, Charles J.; Posner, Arik; Dumbovic, Mateja; Janvier,
   Miho; Demoulin, Pascal; Boakes, Peter; Devos, Andy; Kraaikamp, Emil;
   Mays, Mona L.; Vrsnak, Bojan
Bibcode: 2015EGUGA..17.1366M
Altcode:
  We discuss multipoint imaging and in situ observations of the coronal
  mass ejection (CME) on January 7 2014 which resulted in a major false
  alarm. While the source region was almost at disk center facing Earth,
  the eruption was strongly deflected in the corona, and in conjunction
  with its particular orientation this CME missed Earth almost entirely,
  leading to no significant geomagnetic effects. We demonstrate this
  by a synthesis of data from 7 different heliospheric and planetary
  space missions (STEREO-A/B, SOHO, SDO, Wind, Mars Express, Mars
  Science Laboratory). The CMEs ecliptic part was deflected by 37
  ± 10° in heliospheric longitude, a value larger than previously
  thought. Multipoint in situ observations at Earth and Mars confirm
  the deflection, and are consistent with an elliptical interplanetary
  shock shape of aspect ratio 1.4 ± 0.4. We also discuss our new method,
  the Ellipse Evolution (ElEvo) model, which allows us to optimize the
  global shape of the CME shock with multipoint in situ observations of
  the interplanetary CME arrival. ElEvo, which is an extension to the
  Drag-Based-Model by Vrsnak et al., may also be used for real time space
  weather forecasting. The presented results enhance our understanding
  of CME deflection and shape, which are fundamental ingredients for
  improving space weather forecasts.

Title: Evidence of Twisted Flux-Tube Emergence in Active Regions
Authors: Poisson, M.; Mandrini, C. H.; Démoulin, P.; López Fuentes,
   M.
Bibcode: 2015SoPh..290..727P
Altcode: 2015arXiv150501805P; 2014SoPh..tmp..196P
  Elongated magnetic polarities are observed during the emergence phase of
  bipolar active regions (ARs). These extended features, called magnetic
  tongues, are interpreted as a consequence of the azimuthal component
  of the magnetic flux in the toroidal flux-tubes that form ARs. We
  develop a new systematic and user-independent method to identify AR
  tongues. Our method is based on determining and analyzing the evolution
  of the AR main polarity inversion line (PIL). The effect of the tongues
  is quantified by measuring the acute angle [τ] between the orientation
  of the PIL and the direction orthogonal to the AR main bipolar axis. We
  apply a simple model to simulate the emergence of a bipolar AR. This
  model lets us interpret the effect of magnetic tongues on parameters
  that characterize ARs (e.g. the PIL inclination and the tilt angles,
  and their evolution). In this idealized kinematic emergence model,
  τ is a monotonically increasing function of the twist and has
  the same sign as the magnetic helicity. We systematically apply
  our procedure to a set of bipolar ARs (41 ARs) that were observed
  emerging in line-of-sight magnetograms over eight years. For most
  of the cases studied, the tongues only have a small influence on the
  AR tilt angle since tongues have a much lower magnetic flux than the
  more concentrated main polarities. From the observed evolution of τ,
  corrected for the temporal evolution of the tilt angle and its final
  value when the AR is fully emerged, we estimate the average number of
  turns in the subphotospherically emerging flux-rope. These values for
  the 41 observed ARs are below unity, except for one. This indicates
  that subphotospheric flux-ropes typically have a low amount of twist,
  i.e. highly twisted flux-tubes are rare. Our results demonstrate that
  the evolution of the PIL is a robust indicator of the presence of
  tongues and constrains the amount of twist in emerging flux-tubes.

Title: Statistical study of magnetic cloud erosion by magnetic
    reconnection
Authors: Ruffenach, A.; Lavraud, B.; Farrugia, C. J.; Démoulin, P.;
   Dasso, S.; Owens, M. J.; Sauvaud, J. -A.; Rouillard, A. P.; Lynnyk,
   A.; Foullon, C.; Savani, N. P.; Luhmann, J. G.; Galvin, A. B.
Bibcode: 2015JGRA..120...43R
Altcode:
  recent studies suggest that magnetic reconnection is able to erode
  substantial amounts of the outer magnetic flux of interplanetary
  magnetic clouds (MCs) as they propagate in the heliosphere. We
  quantify and provide a broader context to this process, starting from
  263 tabulated interplanetary coronal mass ejections, including MCs,
  observed over a time period covering 17 years and at a distance of 1
  AU from the Sun with Wind (1995-2008) and the two STEREO (2009-2012)
  spacecraft. Based on several quality factors, including careful
  determination of the MC boundaries and main magnetic flux rope axes,
  an analysis of the azimuthal flux imbalance expected from erosion
  by magnetic reconnection was performed on a subset of 50 MCs. The
  results suggest that MCs may be eroded at the front or at rear and in
  similar proportions, with a significant average erosion of about 40%
  of the total azimuthal magnetic flux. We also searched for in situ
  signatures of magnetic reconnection causing erosion at the front
  and rear boundaries of these MCs. Nearly ~30% of the selected MC
  boundaries show reconnection signatures. Given that observations
  were acquired only at 1 AU and that MCs are large-scale structures,
  this finding is also consistent with the idea that erosion is a
  common process. Finally, we studied potential correlations between
  the amount of eroded azimuthal magnetic flux and various parameters
  such as local magnetic shear, Alfvén speed, and leading and trailing
  ambient solar wind speeds. However, no significant correlations were
  found, suggesting that the locally observed parameters at 1 AU are not
  likely to be representative of the conditions that prevailed during the
  erosion which occurred during propagation from the Sun to 1 AU. Future
  heliospheric missions, and in particular Solar Orbiter or Solar Probe
  Plus, will be fully geared to answer such questions.

Title: Magnetic Flux Erosion and Redistribution during CME Propagation
Authors: Lavraud, B.; Ruffenach, A.; Manchester, W.; Farrugia, C. J.;
   Demoulin, P.; Dasso, S.; Sauvaud, J. A.; Rouillard, A. P.; Foullon,
   C.; Owens, M. J.; Savani, N.; Kajdic, P.; Luhmann, J. G.; Galvin, A. B.
Bibcode: 2014AGUFMSH22A..01L
Altcode:
  We will review recent works which highlight the occurrence of magnetic
  flux erosion and redistribution at the front of coronal mass ejections
  (when they have the structure of a well-defined magnetic cloud). Two
  main processes have been found and will be presented. The first comes
  from the occurrence of magnetic reconnection between the magnetic
  cloud and its sheath ahead, leading to magnetic flux erosion and
  redistribution, with associated large scale topological changes. The
  second may occur when dense filament material in the coronal mass
  ejection pushes its way through the structure and comes in direct
  contact with the shocked plasma in the sheath ahead. This leads to
  diverging non-radial flows in front of the CME which transport poloidal
  flux of the flux rope to the sides of the magnetic cloud.

Title: How Can Active Region Plasma Escape into the Solar Wind from
    Below a Closed Helmet Streamer?
Authors: Mandrini, C. H.; Nuevo, F. A.; Vásquez, A. M.; Démoulin,
   P.; van Driel-Gesztelyi, L.; Baker, D.; Culhane, J. L.; Cristiani,
   G. D.; Pick, M.
Bibcode: 2014SoPh..289.4151M
Altcode: 2014arXiv1409.7369M; 2014SoPh..tmp..115M
  Recent studies show that active-region (AR) upflowing plasma,
  observed by the EUV-Imaging Spectrometer (EIS) onboard Hinode, can
  gain access to open-field lines and be released into the solar wind
  (SW) via magnetic-interchange reconnection at magnetic null-points in
  pseudo-streamer configurations. When only one bipolar AR is present
  on the Sun and is fully covered by the separatrix of a streamer, such
  as AR 10978 in December 2007, it seems unlikely that the upflowing AR
  plasma can find its way into the slow SW. However, signatures of plasma
  with AR composition have been found at 1 AU by Culhane et al. (Solar
  Phys.289, 3799, 2014) that apparently originated west of AR 10978. We
  present a detailed topology analysis of AR 10978 and the surrounding
  large-scale corona based on a potential-field source-surface (PFSS)
  model. Our study shows that it is possible for the AR plasma to move
  around the streamer separatrix and be released into the SW via magnetic
  reconnection, which occurs in at least two main steps. We analyse data
  from the Nançay Radioheliograph (NRH) in a search for evidence of the
  chain of magnetic reconnections that we propose. We find a noise storm
  above the AR and several varying sources at 150.9 MHz. Their locations
  suggest that they might be associated with particles accelerated during
  the first-step reconnection process at a null point well outside of
  the AR. We find no evidence of the second reconnection step in the
  radio data, however. Our results demonstrate that even when it appears
  highly improbable for the AR plasma to reach the SW, indirect channels
  involving a sequence of reconnections can make it possible.

Title: Understanding Coronal Mass Ejections and Associated Shocks
    in the Solar Corona by Merging Multiwavelength Observations
Authors: Zucca, P.; Pick, M.; Démoulin, P.; Kerdraon, A.; Lecacheux,
   A.; Gallagher, P. T.
Bibcode: 2014ApJ...795...68Z
Altcode: 2014arXiv1409.3691Z
  Using multiwavelength imaging observations, in EUV, white light
  and radio, and radio spectral data over a large frequency range,
  we analyzed the triggering and development of a complex eruptive
  event. This one includes two components, an eruptive jet and a coronal
  mass ejection (CME), which interact during more than 30 minutes, and
  can be considered as physically linked. This was an unusual event. The
  jet is generated above a typical complex magnetic configuration that
  has been investigated in many former studies related to the build-up of
  eruptive jets; this configuration includes fan-field lines originating
  from a corona null point above a parasitic polarity, which is embedded
  in one polarity region of a large active region. The initiation and
  development of the CME, observed first in EUV, does not show usual
  signatures. In this case, the eruptive jet is the main actor of this
  event. The CME appears first as a simple loop system that becomes
  destabilized by magnetic reconnection between the outer part of the jet
  and the ambient medium. The progression of the CME is closely associated
  with the occurrence of two successive type II bursts from a distinct
  origin. An important part of this study is the first radio type II burst
  for which the joint spectral and imaging observations were allowed:
  (1) to follow, step by step, the evolution of the spectrum and of the
  trajectory of the radio burst, in relationship with the CME evolution
  and (2) to obtain, without introducing an electronic density model,
  the B field and the Alfvén speed.

Title: Tracking Solar Active Region Outflow Plasma from Its Source
    to the Near-Earth Environment
Authors: Culhane, J. L.; Brooks, D. H.; van Driel-Gesztelyi, L.;
   Démoulin, P.; Baker, D.; DeRosa, M. L.; Mandrini, C. H.; Zhao, L.;
   Zurbuchen, T. H.
Bibcode: 2014SoPh..289.3799C
Altcode: 2014SoPh..tmp...90C; 2014arXiv1405.2949C
  Seeking to establish whether active-region upflow material contributes
  to the slow solar wind, we examine in detail the plasma upflows from
  Active Region (AR) 10978, which crossed the Sun's disc in the interval 8
  to 16 December 2007 during Carrington rotation (CR) 2064. In previous
  work, using data from the Hinode/EUV Imaging Spectrometer, upflow
  velocity evolution was extensively studied as the region crossed the
  disc, while a linear force-free-field magnetic extrapolation was used
  to confirm aspects of the velocity evolution and to establish the
  presence of quasi-separatrix layers at the upflow source areas. The
  plasma properties, temperature, density, and first ionisation potential
  bias [FIP-bias] were measured with the spectrometer during the disc
  passage of the active region. Global potential-field source-surface
  (PFSS) models showed that AR 10978 was completely covered by the
  closed field of a helmet streamer that is part of the streamer
  belt. Therefore it is not clear how any of the upflowing AR-associated
  plasma could reach the source surface at 2.5 R<SUB>⊙</SUB> and
  contribute to the slow solar wind. However, a detailed examination of
  solar-wind in-situ data obtained by the Advanced Composition Explorer
  (ACE) spacecraft at the L<SUB>1</SUB> point shows that increases in
  O<SUP>7+</SUP>/O<SUP>6+</SUP>, C<SUP>6+</SUP>/C<SUP>5+</SUP>, and Fe/O -
  a FIP-bias proxy - are present before the heliospheric current-sheet
  crossing. These increases, along with an accompanying reduction in
  proton velocity and an increase in density are characteristic of
  both AR and slow-solar-wind plasma. Finally, we describe a two-step
  reconnection process by which some of the upflowing plasma from the
  AR might reach the heliosphere.

Title: Recurrent Coronal Jets Induced by Magnetic Emergence in the
    Solar Atmosphere
Authors: Guo, Y.; Démoulin, P.; Schmieder, B.; Ding, M. D.; Vargas
   Domínguez, S.; Liu, Y.
Bibcode: 2014RMxAC..44...45G
Altcode:
  Jets are part of the observed phenomenology in the solar corona. They
  are thought to be a consequence of magnetic reconnection but the physics
  involved is not completely understood. We study some recurrent jetting
  events with unprecedented temporal and spatial resolutions.

Title: In situ properties of small and large flux ropes in the
    solar wind
Authors: Janvier, M.; Démoulin, P.; Dasso, S.
Bibcode: 2014JGRA..119.7088J
Altcode: 2014arXiv1408.5520J
  Two populations of twisted magnetic field tubes, or flux ropes
  (hereafter, FRs), are detected by in situ measurements in the solar
  wind. While small FRs are crossed by the observing spacecraft within
  few hours, with a radius typically less than 0.1 AU, larger FRs,
  or magnetic clouds (hereafter, MCs), have durations of about half a
  day. The main aim of this study is to compare the properties of both
  populations of FRs observed by the Wind spacecraft at 1 AU. To do so,
  we use standard correlation techniques for the FR parameters, as well
  as histograms and more refined statistical methods. Although several
  properties seem at first different for small FRs and MCs, we show
  that they are actually governed by the same propagation physics. For
  example, we observe no in situ signatures of expansion for small FRs,
  contrary to MCs. We demonstrate that this result is in fact expected:
  small FRs expand similar to MCs, as a consequence of a total pressure
  balance with the surrounding medium, but the expansion signature is
  well hidden by velocity fluctuations. Next, we find that the FR radius,
  velocity, and magnetic field strength are all positively correlated,
  with correlation factors than can reach a value &gt;0.5. This
  result indicates a remnant trace of the FR ejection process from the
  corona. We also find a larger FR radius at the apex than at the legs
  (up to 3 times larger at the apex), for FR observed at 1 AU. Finally,
  assuming that the detected FRs have a large-scale configuration in
  the heliosphere, we derived the mean axis shape from the probability
  distribution of the axis orientation. We therefore interpret the small
  FR and MC properties in a common framework of FRs interacting with
  the solar wind, and we disentangle the physics present behind their
  common and different features.

Title: Distribution of Electric Currents in Sunspots from Photosphere
    to Corona
Authors: Gosain, Sanjay; Démoulin, Pascal; López Fuentes, Marcelo
Bibcode: 2014ApJ...793...15G
Altcode:
  We present a study of two regular sunspots that exhibit nearly uniform
  twist from the photosphere to the corona. We derive the twist parameter
  in the corona and in the chromosphere by minimizing the difference
  between the extrapolated linear force-free field model field lines
  and the observed intensity structures in the extreme-ultraviolet
  images of the Sun. The chromospheric structures appear more twisted
  than the coronal structures by a factor of two. Further, we derive
  the vertical component of electric current density, j<SUB>z</SUB>
  , using vector magnetograms from the Hinode Solar Optical Telescope
  (SOT). The spatial distribution of j<SUB>z</SUB> has a zebra pattern
  of strong positive and negative values owing to the penumbral fibril
  structure resolved by Hinode/SOT. This zebra pattern is due to the
  derivative of the horizontal magnetic field across the thin fibrils;
  therefore, it is strong and masks weaker currents that might be present,
  for example, as a result of the twist of the sunspot. We decompose
  j<SUB>z</SUB> into the contribution due to the derivatives along
  and across the direction of the horizontal field, which follows the
  fibril orientation closely. The map of the tangential component has
  more distributed currents that are coherent with the chromospheric
  and coronal twisted structures. Moreover, it allows us to map and
  identify the direct and return currents in the sunspots. Finally, this
  decomposition of j<SUB>z</SUB> is general and can be applied to any
  vector magnetogram in order to better identify the weaker large-scale
  currents that are associated with coronal twisted/sheared structures.

Title: Are There Different Populations of Flux Ropes in the Solar
    Wind?
Authors: Janvier, M.; Démoulin, P.; Dasso, S.
Bibcode: 2014SoPh..289.2633J
Altcode: 2014SoPh..tmp...26J; 2014arXiv1401.6812J
  Flux ropes are twisted magnetic structures that can be detected by
  in-situ measurements in the solar wind. However, different properties of
  detected flux ropes suggest different types of flux-rope populations. As
  such, are there different populations of flux ropes? The answer is
  positive and is the result of the analysis of four lists of flux ropes,
  including magnetic clouds (MCs), observed at 1 AU. The in-situ data for
  the four lists were fitted with the same cylindrical force-free field
  model, which provides an estimate of the local flux-rope parameters
  such as its radius and orientation. Since the flux-rope distributions
  have a broad dynamic range, we went beyond a simple histogram analysis
  by developing a partition technique that uniformly distributes the
  statistical fluctuations across the radius range. By doing so, we found
  that small flux ropes with radius R&lt;0.1 AU have a steep power-law
  distribution in contrast to the larger flux ropes (identified as MCs),
  which have a Gaussian-like distribution. Next, from four CME catalogs,
  we estimated the expected flux-rope frequency per year at 1 AU. We
  found that the predicted numbers are similar to the frequencies of MCs
  observed in-situ. However, we also found that small flux ropes are at
  least ten times too abundant to correspond to CMEs, even to narrow
  ones. Investigating the different possible scenarios for the origin
  of these small flux ropes, we conclude that these twisted structures
  can be formed by blowout jets in the low corona or in coronal streamers.

Title: Electric Currents in Flare Ribbons: Observations and
    Three-dimensional Standard Model
Authors: Janvier, M.; Aulanier, G.; Bommier, V.; Schmieder, B.;
   Démoulin, P.; Pariat, E.
Bibcode: 2014ApJ...788...60J
Altcode: 2014arXiv1402.2010J
  We present for the first time the evolution of the photospheric electric
  currents during an eruptive X-class flare, accurately predicted by the
  standard three-dimensional (3D) flare model. We analyze this evolution
  for the 2011 February 15 flare using Helioseismic and Magnetic
  Imager/Solar Dynamics Observatory magnetic observations and find
  that localized currents in J-shaped ribbons increase to double their
  pre-flare intensity. Our 3D flare model, developed with the OHM code,
  suggests that these current ribbons, which develop at the location of
  extreme ultraviolet brightenings seen with Atmospheric Imaging Assembly
  imagery, are driven by the collapse of the flare's coronal current
  layer. These findings of increased currents restricted in localized
  ribbons are consistent with the overall free energy decrease during a
  flare, and the shapes of these ribbons also give an indication of how
  twisted the erupting flux rope is. Finally, this study further enhances
  the close correspondence obtained between the theoretical predictions
  of the standard 3D model and flare observations, indicating that the
  main key physical elements are incorporated in the model.

Title: Topological Analysis of Emerging Bipole Clusters Producing
    Violent Solar Events
Authors: Mandrini, C. H.; Schmieder, B.; Démoulin, P.; Guo, Y.;
   Cristiani, G. D.
Bibcode: 2014SoPh..289.2041M
Altcode: 2013arXiv1312.3359M
  During the rising phase of Solar Cycle 24 tremendous activity occurred
  on the Sun with rapid and compact emergence of magnetic flux leading
  to bursts of flares (C to M and even X-class). We investigate the
  violent events occurring in the cluster of two active regions (ARs),
  NOAA numbers 11121 and 11123, observed in November 2010 with instruments
  onboard the Solar Dynamics Observatory and from Earth. Within one day
  the total magnetic flux increased by 70 % with the emergence of new
  groups of bipoles in AR 11123. From all the events on 11 November,
  we study, in particular, the ones starting at around 07:16 UT in GOES
  soft X-ray data and the brightenings preceding them. A magnetic-field
  topological analysis indicates the presence of null points,
  associated separatrices, and quasi-separatrix layers (QSLs) where
  magnetic reconnection is prone to occur. The presence of null points
  is confirmed by a linear and a non-linear force-free magnetic-field
  model. Their locations and general characteristics are similar in both
  modelling approaches, which supports their robustness. However, in order
  to explain the full extension of the analysed event brightenings,
  which are not restricted to the photospheric traces of the null
  separatrices, we compute the locations of QSLs. Based on this more
  complete topological analysis, we propose a scenario to explain the
  origin of a low-energy event preceding a filament eruption, which is
  accompanied by a two-ribbon flare, and a consecutive confined flare in
  AR 11123. The results of our topology computation can also explain the
  locations of flare ribbons in two other events, one preceding and one
  following the ones at 07:16 UT. Finally, this study provides further
  examples where flare-ribbon locations can be explained when compared
  to QSLs and only, partially, when using separatrices.

Title: The evolution of writhe in kink-unstable flux ropes and
    erupting filaments
Authors: Török, T.; Kliem, B.; Berger, M. A.; Linton, M. G.;
   Démoulin, P.; van Driel-Gesztelyi, L.
Bibcode: 2014PPCF...56f4012T
Altcode: 2014arXiv1403.1565T
  The helical kink instability of a twisted magnetic flux tube has been
  suggested as a trigger mechanism for solar filament eruptions and
  coronal mass ejections (CMEs). In order to investigate if estimations
  of the pre-emptive twist can be obtained from observations of writhe
  in such events, we quantitatively analyze the conversion of twist into
  writhe in the course of the instability, using numerical simulations. We
  consider the line tied, cylindrically symmetric Gold-Hoyle flux rope
  model and measure the writhe using the formulae by Berger and Prior
  which express the quantity as a single integral in space. We find that
  the amount of twist converted into writhe does not simply scale with
  the initial flux rope twist, but depends mainly on the growth rates
  of the instability eigenmodes of higher longitudinal order than the
  basic mode. The saturation levels of the writhe, as well as the shapes
  of the kinked flux ropes, are very similar for considerable ranges of
  initial flux rope twists, which essentially precludes estimations of
  pre-eruptive twist from measurements of writhe. However, our simulations
  suggest an upper twist limit of ∼6π for the majority of filaments
  prior to their eruption.

Title: Coronal Magnetic Reconnection Driven by CME Expansion—the
    2011 June 7 Event
Authors: van Driel-Gesztelyi, L.; Baker, D.; Török, T.; Pariat, E.;
   Green, L. M.; Williams, D. R.; Carlyle, J.; Valori, G.; Démoulin,
   P.; Kliem, B.; Long, D. M.; Matthews, S. A.; Malherbe, J. -M.
Bibcode: 2014ApJ...788...85V
Altcode: 2014arXiv1406.3153V
  Coronal mass ejections (CMEs) erupt and expand in a magnetically
  structured solar corona. Various indirect observational pieces of
  evidence have shown that the magnetic field of CMEs reconnects with
  surrounding magnetic fields, forming, e.g., dimming regions distant
  from the CME source regions. Analyzing Solar Dynamics Observatory
  (SDO) observations of the eruption from AR 11226 on 2011 June 7, we
  present the first direct evidence of coronal magnetic reconnection
  between the fields of two adjacent active regions during a CME. The
  observations are presented jointly with a data-constrained numerical
  simulation, demonstrating the formation/intensification of current
  sheets along a hyperbolic flux tube at the interface between the CME
  and the neighboring AR 11227. Reconnection resulted in the formation of
  new magnetic connections between the erupting magnetic structure from
  AR 11226 and the neighboring active region AR 11227 about 200 Mm from
  the eruption site. The onset of reconnection first becomes apparent
  in the SDO/AIA images when filament plasma, originally contained
  within the erupting flux rope, is redirected toward remote areas in
  AR 11227, tracing the change of large-scale magnetic connectivity. The
  location of the coronal reconnection region becomes bright and directly
  observable at SDO/AIA wavelengths, owing to the presence of down-flowing
  cool, dense (10<SUP>10</SUP> cm<SUP>-3</SUP>) filament plasma in its
  vicinity. The high-density plasma around the reconnection region is
  heated to coronal temperatures, presumably by slow-mode shocks and
  Coulomb collisions. These results provide the first direct observational
  evidence that CMEs reconnect with surrounding magnetic structures,
  leading to a large-scale reconfiguration of the coronal magnetic field.

Title: Mean shape of interplanetary shocks deduced from in situ
    observations and its relation with interplanetary CMEs
Authors: Janvier, M.; Démoulin, P.; Dasso, S.
Bibcode: 2014A&A...565A..99J
Altcode:
  Context. Shocks are frequently detected by spacecraft in the
  interplanetary space. However, the in situ data of a shock do
  not provide direct information on its overall properties even
  when a following interplanetary coronal mass ejection (ICME) is
  detected. <BR /> Aims: The main aim of this study is to constrain
  the general shape of ICME shocks with a statistical study of shock
  orientations. <BR /> Methods: We first associated a set of shocks
  detected near Earth over 10 years with a sample of ICMEs over the
  same period. We then analyzed the correlations between shock and
  ICME parameters and studied the statistical distributions of the
  local shock normal orientation. Supposing that shocks are uniformly
  detected all over their surface projected on the 1 AU sphere, we
  compared the shock normal distribution with synthetic distributions
  derived from an analytical shock shape model. Inversely, we derived
  a direct method to compute the typical general shape of ICME shocks
  by integrating observed distributions of the shock normal. <BR />
  Results: We found very similar properties between shocks with and
  without an in situ detected ICME, so that most of the shocks detected
  at 1 AU are ICME-driven even when no ICME is detected. The statistical
  orientation of shock normals is compatible with a mean shape having a
  rotation symmetry around the Sun-apex line. The analytically modeled
  shape captures the main characteristics of the observed shock normal
  distribution. Next, by directly integrating the observed distribution,
  we derived the mean shock shape, which is found to be comparable for
  shocks with and without a detected ICME and weakly affected by the
  limited statistics of the observed distribution. We finally found a
  close correspondence between this statistical result and the leading
  edge of the ICME sheath that is observed with STEREO imagers. <BR />
  Conclusions: We have derived a mean shock shape that only depends on
  one free parameter. This mean shape can be used in various contexts,
  such as studies for high-energy particles or space weather forecasts.

Title: Highlights of Interplanetary Coronal Mass Ejections and its
    impact on the terrestrial environment
Authors: Dasso, Sergio; Janvier, Miho; Demoulin, Pascal; Masías
   Meza, Jimmy
Bibcode: 2014cosp...40E.637D
Altcode:
  Interplanetary Coronal Mass Ejections (ICMEs) are meso-scale transient
  objects in the heliosphere, ejected by the Sun from the destabilisation
  of a portion of coronal magnetic field. They imply large modifications
  of the heliospheric plasma and magnetic field properties. Then, an
  ICME passing nearby Earth generates strong variations of the input of
  energy, momentum and particles, from the interplanetary medium to the
  terrestrial environment. The study of ICMEs has greatly advanced in the
  last few years, thanks to multi-spacecraft observations of the solar
  corona and the solar wind, combined with high performance numerical
  modelling. The comparisons between models and recent observations
  now answer several open questions, such as the typical configuration
  (internal and global) of ICMEs, as well as how they are affected
  due to their interaction with the ambient solar wind during their
  propagation in the interplanetary medium. This talk will provide a
  summary of recent advances in the field of ICMEs, and will present
  several aspects of the interaction with the ambient solar wind that
  have serious consequences on the level of Sun-Earth coupling.

Title: Structure of ICMEs and their driven shocks at 1 AU, and
    consequences on Forbush decreases
Authors: Dasso, Sergio; Janvier, Miho; Demoulin, Pascal; Masias-Meza,
   Jimmy J.
Bibcode: 2014cosp...40E.636D
Altcode:
  Solar wind structures, such as interplanetary (IP) shocks, can affect
  the transport of energetic particles in the heliosphere. In particular,
  the presence of IP shocks driven by interplanetary coronal mass
  ejections (ICMEs) is typically associated with a transient variation
  of the energetic particles flux (e.g., Forbush decreases, FDs). A FD
  can present two steps: one of them produced by a diffusive barrier
  associated with the turbulent region behind the shock, and the another
  one produced by the ICME itself. However, not every IP shock driven
  by an ICME is followed by a two-step FD, and it is under debate what
  are the properties of the solar wind for determining the presence of a
  two-step Forbush decrease, the presence of a single-step FD, or even
  the absence of a FD after the passage of the ICME. Magnetic clouds
  (MCs) are a subset of ICMEs, which present clear evidence in favor
  of the presence of an interplanetary flux rope in the solar wind. We
  recently found constraints to the geometrical shape of ICME shocks from
  a statistical study of shock orientations, and found constraints to the
  global shape of MCs from a statistical study of main axis orientation
  of a large sample of magnetic clouds, both at one astronomical unit
  from the Sun. The main aim of this study is to establish the link
  between Forbush decreases and the MC/shock properties, taking into
  account these geometrical shapes of MC axis and shocks surfaces. We
  present here a combined analysis of events MC-shock-FD, in order to
  better understand the effects of interplanetary structures on the
  propagation of energetic particles in the heliosphere.

Title: Constraining magnetic flux emergence from a timeseries of
    helicitigrams
Authors: Dalmasse, Kévin; Pariat, Etienne; Green, Lucie M.; Aulanier,
   Guillaume; Demoulin, Pascal; Valori, Gherardo
Bibcode: 2014cosp...40E.612D
Altcode:
  Magnetic helicity quantifies how globally twisted and/or sheared is
  the magnetic field in a volume. Observational studies have reported
  the injection of large amounts of magnetic helicity associated with
  the emergence of magnetic flux into the solar atmosphere. Because
  magnetic helicity is conserved in the convection zone, the injection of
  magnetic helicity into the solar corona reflects the helicity content
  of emerging magnetic flux tubes. Mapping the photospheric injection
  of magnetic helicity thus seems to be a key tool for constraining the
  parameters of the emerging flux tubes in numerical case-studies of
  observed active regions. We recently developed a method to compute the
  distribution of magnetic helicity flux. Contrary to previous proxies,
  this method takes into account the 3D nature of magnetic helicity, and
  is thus, better-suited to study the distribution of helicity flux. After
  introducing this method, we will present the results of its application
  to the NOAA AR 11158. We will show that, the distribution of helicity
  flux is complex, with patterns of real mixed signals of helicity flux
  related to the specific topology of the active region's magnetic
  field. Finally, we will discuss the implications of our results on
  the evolution and dynamics of this active region.

Title: Magnetic flux emergence, flares, and coronal mass ejections
Authors: Mandrini, Cristina H.; Schmieder, Brigitte; Cristiani,
   Germán; Demoulin, Pascal; Guo, Yang
Bibcode: 2014cosp...40E1980M
Altcode:
  We study the violent events occurring in the cluster of two active
  regions (ARs), NOAA numbers 11121 and 11123, observed in November
  2010 with instruments onboard the Solar Dynamics Observatory and from
  Earth. Within one day the total magnetic flux increased by 70 per
  cent with the emergence of new groups of bipoles in AR 11123. These
  emergences led to a very complex magnetic configuration in which around
  ten solar flares, some of them accompanied by coronal mass ejections
  (CMEs), occurred. A magnetic-field topology somputation indicates the
  presence of null points, associated separatrices and quasi-separatrix
  layers (QSLs) where magnetic reconnection is prone to occur. Based
  on this analysis, we propose a scenario to explain the origin of a
  low-energy event preceding a filament eruption, which is accompanied
  by a two-ribbon flare and CME, and a consecutive confined flare in AR
  11123. The results of our topology computation can also explain the
  locations of flare ribbons in two other events, one preceding and one
  following the ones just mentioned.

Title: Electric current variations and 3D magnetic configuration of
    coronal jets
Authors: Schmieder, Brigitte; Harra, Louise K.; Aulanier, Guillaume;
   Guo, Yang; Demoulin, Pascal; Moreno-Insertis, Fernando, , Prof
Bibcode: 2014cosp...40E2928S
Altcode:
  Coronal jets (EUV) were observed by SDO/AIA on September 17, 2010. HMI
  and THEMIS measured the vector magnetic field from which we derived the
  magnetic flux, the phostospheric velocity and the vertical electric
  current. The magnetic configuration was computed with a non linear
  force-free approach. The phostospheric current pattern of the recurrent
  jets were associated with the quasi-separatrix layers deduced from the
  magnetic extrapolation. The large twisted near-by Eiffel-tower-shape
  jet was also caused by reconnection in current layers containing a
  null point. This jet cannot be classified precisely within either the
  quiescent or the blowout jet types. We will show the importance of
  the existence of bald patches in the low atmosphere

Title: Flux rope axis geometry of magnetic clouds deduced from in
    situ data
Authors: Janvier, Miho; Démoulin, Pascal; Dasso, Sergio
Bibcode: 2014IAUS..300..265J
Altcode:
  Magnetic clouds (MCs) consist of flux ropes that are ejected from the
  low solar corona during eruptive flares. Following their ejection, they
  propagate in the interplanetary medium where they can be detected by in
  situ instruments and heliospheric imagers onboard spacecraft. Although
  in situ measurements give a wide range of data, these only depict the
  nature of the MC along the unidirectional trajectory crossing of a
  spacecraft. As such, direct 3D measurements of MC characteristics are
  impossible. From a statistical analysis of a wide range of MCs detected
  at 1 AU by the Wind spacecraft, we propose different methods to deduce
  the most probable magnetic cloud axis shape. These methods include
  the comparison of synthetic distributions with observed distributions
  of the axis orientation, as well as the direct integration of observed
  probability distribution to deduce the global MC axis shape. The overall
  shape given by those two methods is then compared with 2D heliospheric
  images of a propagating MC and we find similar geometrical features.

Title: FIP bias in a sigmoidal active region
Authors: Baker, D.; Brooks, D. H.; Démoulin, P.; van Driel-Gesztelyi,
   Lidia; Green, L. M.; Steed, K.; Carlyle, J.
Bibcode: 2014IAUS..300..222B
Altcode:
  We investigate first ionization potential (FIP) bias levels in
  an anemone active region (AR) - coronal hole (CH) complex using an
  abundance map derived from Hinode/EIS spectra. The detailed, spatially
  resolved abundance map has a large field of view covering 359'' ×
  485''. Plasma with high FIP bias, or coronal abundances, is concentrated
  at the footpoints of the AR loops whereas the surrounding CH has a low
  FIP bias, ~1, i.e. photospheric abundances. A channel of low FIP bias
  is located along the AR's main polarity inversion line containing a
  filament where ongoing flux cancellation is observed, indicating a
  bald patch magnetic topology characteristic of a sigmoid/flux rope
  configuration.

Title: Active region helicity properties from magnetic tongues.
Authors: Poisson, Mariano; Mandrini, Cristina H.; Lopez Fuentes,
   Marcelo; Demoulin, Pascal
Bibcode: 2014cosp...40E2579P
Altcode:
  We study the evolution of photospheric magnetic tongues to infer
  the magnetic helicity sign of a large set of active regions (ARs)
  observed during Solar Cycle 23. Magnetic tongues appear during the
  emergence of twisted toroidal magnetic flux tubes that form ARs due to
  contribution of the azimuthal component of the magnetic field around
  the torus axis. The method to compute the helicity sign is based
  on the determination of the polarity inversion line (PIL) and its
  relative orientation respect to the direction of the AR main bipolar
  axis (the AR's tilt), as well as the analysis of its evolution during
  the AR emergence. We analyze a set of 150 bipolar ARs observed with
  SOHO/MDI between 1996 and 2010. The PIL method, as tested in previous
  works, needs ARs with simple bipolar structures and devoid of backgroud
  magnetic remnants in order to provide reliable computations. Therefore,
  the low number of sunspots registered along the mínimum between Cycles
  23 and 24 is a favourable period to find simple isolated ARs. We
  determine a series of statistical properties of the studied ARs,
  such as the latitudinal and hemispherical dependence of the magnetic
  helicity sign, the AR tilt, the total unsigned magnetic flux, and the
  presence of asymmetries between the main polarities.

Title: Electric currents in solar active regions
Authors: Dalmasse, Kévin; Pariat, Etienne; Kliem, Bernhard; Aulanier,
   Guillaume; Demoulin, Pascal; Torok, Tibor
Bibcode: 2014cosp...40E.613D
Altcode:
  There is a recurring question in solar physics about whether or not
  photospheric vertical electric currents are neutralized in solar active
  regions, i.e. if the total electric current integrated over a single
  photospheric magnetic polarity of an active region vanishes. Different
  arguments have been proposed in favor of, or against, the neutralization
  of electric currents, but both theory and observations are still not
  fully conclusive. The answer to this question has implications for
  eruption models. Indeed, if currents are neutralized in active regions,
  then any eruption model based on non-neutralized electric currents,
  such as the torus instability, would need to be further analyzed. We
  addressed the question of electric currents neutralization in active
  regions using 3D zero-beta, line-tied, slow driving motions of an
  initially potential magnetic field. We compared our results to a recent
  study of electric currents build-up in a MHD numerical simulation of the
  emergence of a current-neutralized twisted flux tube. Our parametric
  analyses show that, as for the emergence, photospheric motions are
  associated with the formation of both direct and return currents. It
  further shows that both processes can lead to the formation of strong
  net currents in the solar corona, and that the non-neutralization of
  electric currents is related to the presence of magnetic shear at the
  polarity inversion line. We will discuss the implications of our results
  for the observations and for the different solar eruption models.

Title: Evolution of interplanetary coronal mass ejections and magnetic
    clouds in the heliosphere
Authors: Démoulin, Pascal
Bibcode: 2014IAUS..300..245D
Altcode:
  Interplanetary Coronal Mass Ejections (ICMEs), and more specifically
  Magnetic Clouds (MCs), are detected with in situ plasma and magnetic
  measurements. They are the continuation of the CMEs observed with
  imagers closer to the Sun. A review of their properties is presented
  with a focus on their magnetic configuration and its evolution. Many
  recent observations, both in situ and with imagers, point to a key
  role of flux ropes, a conclusion which is also supported by present
  coronal eruptive models. Then, is a flux rope generically present
  in an ICME? How to quantify its 3D physical properties when it is
  detected locally as a MC? Is it a simple flux rope? How does it evolve
  in the solar wind? This paper reviews our present answers and limited
  understanding to these questions.

Title: Photospheric Injection of Magnetic Helicity: Connectivity-Based
    Flux Density Method
Authors: Dalmasse, K.; Pariat, E.; Démoulin, P.; Aulanier, G.
Bibcode: 2014SoPh..289..107D
Altcode: 2013arXiv1307.2829D
  Magnetic helicity quantifies the degree to which the magnetic field
  in a volume is globally sheared and/or twisted. This quantity is
  believed to play a key role in solar activity due to its conservation
  property. Helicity is continuously injected into the corona during
  the evolution of active regions (ARs). To better understand and
  quantify the role of magnetic helicity in solar activity, the
  distribution of magnetic helicity flux in ARs needs to be studied. The
  helicity distribution can be computed from the temporal evolution of
  photospheric magnetograms of ARs such as the ones provided by SDO/HMI
  and Hinode/SOT. Most recent analyses of photospheric helicity flux
  derived a proxy to the helicity-flux density based on the relative
  rotation rate of photospheric magnetic footpoints. Although this
  proxy allows a good estimate of the photospheric helicity flux, it is
  still not a true helicity flux density because it does not take into
  account the connectivity of the magnetic field lines. For the first
  time, we implement a helicity density that takes this connectivity
  into account. To use it for future observational studies, we tested
  the method and its precision on several types of models involving
  different patterns of helicity injection. We also tested it on more
  complex configurations - from magnetohydrodynamics (MHD) simulations
  - containing quasi-separatrix layers. We demonstrate that this
  connectivity-based proxy is best-suited to map the true distribution
  of photospheric helicity injection.

Title: Active region upflow plasma: its relation to small activity
    and the solar wind
Authors: Mandrini, Cristina H.; Culhane, J. Leonard; Cristiani,
   Germán; Vásquez, Alberto; Van Driel-Gesztelyi, Lidia; Baker, Deborah;
   Pick, Monique; Demoulin, Pascal; Nuevo, Federico
Bibcode: 2014cosp...40E1979M
Altcode:
  Recent studies show that active region (AR) upflowing plasma,
  observed by the Hinode EUV Imaging Spectrometer (EIS), can gain
  access to open field lines and be released into the solar wind via
  magnetic interchange reconnection occurring below the source surface
  at magnetic null-points in pseudo-streamer configurations. When only
  one simple bipolar AR is present on the Sun and it is fully covered by
  the separatrix of a streamer, like AR 10978 on December 2007, it seems
  unlikely that the upflowing AR plasma could find its way into the slow
  solar wind. However, signatures of plasma with AR composition at 1 AU
  that appears to originate from the West of AR 10978 were recently found
  by Culhane and coworkers. We present a detailed topology analysis of
  AR 10978 based on a linear force-free magnetic field model at the AR
  scale, combined with a global PFSS model. This allows us, on one hand,
  to explain the variations observed in the upflows to the West of the
  AR as the result of magnetic reconnection at quasi-separatrix layers
  (QSLs). While at a global scale, we show that reconnection, occurring
  in at least two main steps, first at QSLs and later at a high-altitude
  coronal null-point, allows the AR plasma to get around the topological
  obstacle of the streamer separatrix and be released into the solar wind.

Title: Magnetic reconnection driven by filament eruption in the 7
    June 2011 event
Authors: van Driel-Gesztelyi, L.; Baker, D.; Török, T.; Pariat, E.;
   Green, L. M.; Williams, D. R.; Carlyle, J.; Valori, G.; Démoulin,
   P.; Matthews, S. A.; Kliem, B.; Malherbe, J. -M.
Bibcode: 2014IAUS..300..502V
Altcode:
  During an unusually massive filament eruption on 7 June 2011,
  SDO/AIA imaged for the first time significant EUV emission around a
  magnetic reconnection region in the solar corona. The reconnection
  occurred between magnetic fields of the laterally expanding CME
  and a neighbouring active region. A pre-existing quasi-separatrix
  layer was activated in the process. This scenario is supported by
  data-constrained numerical simulations of the eruption. Observations
  show that dense cool filament plasma was re-directed and heated in
  situ, producing coronal-temperature emission around the reconnection
  region. These results provide the first direct observational evidence,
  supported by MHD simulations and magnetic modelling, that a large-scale
  re-configuration of the coronal magnetic field takes place during
  solar eruptions via the process of magnetic reconnection.

Title: Recurrent filament eruptions and associated CMEs
Authors: Schmieder, Brigitte; Cremades, Hebe; Mandrini, Cristina;
   Démoulin, Pascal; Guo, Yang
Bibcode: 2014IAUS..300..489S
Altcode:
  We investigate the violent events in the cluster of two active regions
  (ARs), NOAA numbers 11121 and 11123, observed on 11 November 2010
  by the Solar Dynamics Observatory (SDO). Within one day the magnetic
  field intensity increased by 70% with the emergence of new groups of
  bipoles in AR 11123, where three filaments are seen along the complex
  inversion line. The destabilization of the filaments led to flares
  and CMEs. The CMEs around 08:24 UT and 17:00 UT are directly related
  to the partial eruption of one filament in the new AR, as shown by a
  topology computation and analysis. The other CMEs on this day are due
  to either other ARs or to the destabilization of the global magnetic
  configuration of the two ARs. This conclusion can be only reached by
  using the three eyes of SOHO, STEREO and SDO.

Title: Plasma Composition in a Sigmoidal Anemone Active Region
Authors: Baker, D.; Brooks, D. H.; Démoulin, P.; van Driel-Gesztelyi,
   L.; Green, L. M.; Steed, K.; Carlyle, J.
Bibcode: 2013ApJ...778...69B
Altcode: 2013arXiv1310.0999B
  Using spectra obtained by the EUV Imaging Spectrometer (EIS) instrument
  onboard Hinode, we present a detailed spatially resolved abundance map
  of an active region (AR)-coronal hole (CH) complex that covers an area
  of 359'' × 485''. The abundance map provides first ionization potential
  (FIP) bias levels in various coronal structures within the large EIS
  field of view. Overall, FIP bias in the small, relatively young AR
  is 2-3. This modest FIP bias is a consequence of the age of the AR,
  its weak heating, and its partial reconnection with the surrounding
  CH. Plasma with a coronal composition is concentrated at AR loop
  footpoints, close to where fractionation is believed to take place in
  the chromosphere. In the AR, we found a moderate positive correlation
  of FIP bias with nonthermal velocity and magnetic flux density, both
  of which are also strongest at the AR loop footpoints. Pathways of
  slightly enhanced FIP bias are traced along some of the loops connecting
  opposite polarities within the AR. We interpret the traces of enhanced
  FIP bias along these loops to be the beginning of fractionated plasma
  mixing in the loops. Low FIP bias in a sigmoidal channel above the
  AR's main polarity inversion line, where ongoing flux cancellation is
  taking place, provides new evidence of a bald patch magnetic topology
  of a sigmoid/flux rope configuration.

Title: Global axis shape of magnetic clouds deduced from the
    distribution of their local axis orientation
Authors: Janvier, M.; Démoulin, P.; Dasso, S.
Bibcode: 2013A&A...556A..50J
Altcode: 2013arXiv1305.4039J
  Context. Coronal mass ejections (CMEs) are routinely tracked with
  imagers in the interplanetary space, while magnetic clouds (MCs)
  properties are measured locally by spacecraft. However, both imager
  and in situ data do not provide any direct estimation of the general
  flux rope properties. <BR /> Aims: The main aim of this study
  is to constrain the global shape of the flux rope axis from local
  measurements and to compare the results from in-situ data with imager
  observations. <BR /> Methods: We performed a statistical analysis of the
  set of MCs observed by WIND spacecraft over 15 years in the vicinity
  of Earth. We analyzed the correlation between different MC parameters
  and studied the statistical distributions of the angles defining the
  local axis orientation. With the hypothesis of having a sample of MCs
  with a uniform distribution of spacecraft crossing along their axis,
  we show that a mean axis shape can be derived from the distribution
  of the axis orientation. As a complement, while heliospheric imagers
  do not typically observe MCs but only their sheath region, we analyze
  one event where the flux rope axis can be estimated from the STEREO
  imagers. <BR /> Results: From the analysis of a set of theoretical
  models, we show that the distribution of the local axis orientation
  is strongly affected by the overall axis shape. Next, we derive the
  mean axis shape from the integration of the observed orientation
  distribution. This shape is robust because it is mostly determined
  from the overall shape of the distribution. Moreover, we find no
  dependence on the flux rope inclination on the ecliptic. Finally, the
  derived shape is fully consistent with the one derived from heliospheric
  imager observations of the June 2008 event. <BR /> Conclusions: We have
  derived a mean shape of MC axis that only depends on one free parameter,
  the angular separation of the legs (as viewed from the Sun). This mean
  shape can be used in various contexts, such as studies of high-energy
  particles or space weather forecasts.

Title: The standard flare model in three dimensions. III. Slip-running
    reconnection properties
Authors: Janvier, M.; Aulanier, G.; Pariat, E.; Démoulin, P.
Bibcode: 2013A&A...555A..77J
Altcode: 2013arXiv1305.4053J
  Context. A standard model for eruptive flares aims at describing
  observational 3D features of the reconnecting coronal magnetic
  field. Extensions to the 2D model require the physical understanding of
  3D reconnection processes at the origin of the magnetic configuration
  evolution. However, the properties of 3D reconnection without null point
  and separatrices still need to be analyzed. <BR /> Aims: We focus on
  magnetic reconnection associated with the growth and evolution of a
  flux rope and associated flare loops during an eruptive flare. We aim
  at understanding the intrinsic characteristics of 3D reconnection in
  the presence of quasi-separatrix layers (QSLs), how QSL properties are
  related to the slip-running reconnection mode in general, and how this
  applies to eruptive flares in particular. <BR /> Methods: We studied
  the slip-running reconnection of field lines in a magnetohydrodynamic
  simulation of an eruptive flare associated with a torus-unstable flux
  rope. The squashing degree and the mapping norm are two parameters
  related to the QSLs. We computed them to investigate their relation
  with the slip-running reconnection speed of selected field lines. <BR />
  Results: Field lines associated with the flux rope and the flare loops
  undergo a continuous series of magnetic reconnection, which results
  in their super-Alfvénic slipping motion. The time profile of their
  slippage speed and the space distribution of the mapping norm are shown
  to be strongly correlated. We find that the motion speed is proportional
  to the mapping norm. Moreover, this slip-running motion becomes faster
  as the flux rope expands, since the 3D current layer evolves toward a
  current sheet, and QSLs to separatrices. <BR /> Conclusions: The present
  analysis extends our understanding of the 3D slip-running reconnection
  regime. We identified a controlling parameter of the apparent velocity
  of field lines while they slip-reconnect, enabling the interpretation
  of the evolution of post flare loops. This work completes the standard
  model for flares and eruptions by giving its 3D properties.

Title: Recurrent coronal jets induced by repetitively accumulated
    electric currents
Authors: Guo, Y.; Démoulin, P.; Schmieder, B.; Ding, M. D.; Vargas
   Domínguez, S.; Liu, Y.
Bibcode: 2013A&A...555A..19G
Altcode: 2013arXiv1305.0902G
  Context. Jets of plasma are frequently observed in the solar corona. A
  self-similar recurrent behavior is observed in a fraction of them. <BR
  /> Aims: Jets are thought to be a consequence of magnetic reconnection;
  however, the physics involved is not fully understood. Therefore,
  we study some jet observations with unprecedented temporal and
  spatial resolutions. <BR /> Methods: The extreme-ultraviolet (EUV)
  jets were observed by the Atmospheric Imaging Assembly on board the
  Solar Dynamics Observatory (SDO). The Helioseismic and Magnetic Imager
  (HMI) on board SDO measured the vector magnetic field, from which
  we derive the magnetic flux evolution, the photospheric velocity
  field, and the vertical electric current evolution. The magnetic
  configuration before the jets is derived by the nonlinear force-free
  field extrapolation. <BR /> Results: Three EUV jets recurred in about
  one hour on 17 September 2010 in the following magnetic polarity
  of active region 11106. We derive that the jets are above a pair of
  parasitic magnetic bipoles that are continuously driven by photospheric
  diverging flows. The interaction drove the buildup of electric currents,
  which we observed as elongated patterns at the photospheric level. For
  the first time, the high temporal cadence of the HMI allows the
  evolution of such small currents to be followed. In the jet region,
  we found that the integrated absolute current peaks repetitively in
  phase with the 171 Å flux evolution. The current buildup and its
  decay are both fast, about ten minutes each, and the current maximum
  precedes the 171 Å also by about ten minutes. Then, the HMI temporal
  cadence is marginally fast enough to detect such changes. <BR />
  Conclusions: The photospheric current pattern of the jets is found to
  be associated with the quasi-separatrix layers deduced from the magnetic
  extrapolation. From previous theoretical results, the observed diverging
  flows are expected to continuously build such currents. We conclude
  that the magnetic reconnection occurs periodically, in the current
  layer created between the emerging bipoles and the large-scale active
  region field. The periodic magnetic reconnection induced the observed
  recurrent coronal jets and the decrease of the vertical electric
  current magnitude. <P />Two movies are available in electronic form
  at <A href="http://www.aanda.org">http://www.aanda.org</A>

Title: First observational application of a connectivity-based
    helicity flux density
Authors: Dalmasse, K.; Pariat, E.; Valori, G.; Démoulin, P.; Green,
   L. M.
Bibcode: 2013A&A...555L...6D
Altcode: 2013arXiv1307.2838D
  Context. Measuring the magnetic helicity distribution in the solar
  corona can help in understanding the trigger of solar eruptive
  events because magnetic helicity is believed to play a key role in
  solar activity due to its conservation property. <BR /> Aims: A new
  method for computing the photospheric distribution of the helicity
  flux was recently developed. This method takes into account the
  magnetic field connectivity whereas previous methods were based
  on photospheric signatures only. This novel method maps the true
  injection of magnetic helicity in active regions. We applied this
  method for the first time to an observed active region, NOAA 11158,
  which was the source of intense flaring activity. <BR /> Methods: We
  used high-resolution vector magnetograms from the SDO/HMI instrument
  to compute the photospheric flux transport velocities and to perform
  a nonlinear force-free magnetic field extrapolation. We determined
  and compared the magnetic helicity flux distribution using a purely
  photospheric as well as a connectivity-based method. <BR /> Results:
  While the new connectivity-based method confirms the mixed pattern
  of the helicity flux in NOAA 11158, it also reveals a different, and
  more correct, distribution of the helicity injection. This distribution
  can be important for explaining the likelihood of an eruption from the
  active region. <BR /> Conclusions: The connectivity-based approach is
  a robust method for computing the magnetic helicity flux, which can
  be used to study the link between magnetic helicity and eruptivity of
  observed active regions.

Title: Solar filament eruptions and their physical role in triggering
    coronal mass ejections
Authors: Schmieder, B.; Démoulin, P.; Aulanier, G.
Bibcode: 2013AdSpR..51.1967S
Altcode: 2012arXiv1212.4014S
  Solar filament eruptions play a crucial role in triggering coronal
  mass ejections (CMEs). More than 80% of eruptions lead to a CME. This
  correlation has been studied extensively during the past solar cycles
  and the last long solar minimum. The statistics made on events occurring
  during the rising phase of the new solar cycle 24 is in agreement with
  this finding. Both filaments and CMEs have been related to twisted
  magnetic fields. Therefore, nearly all the MHD CME models include
  a twisted flux tube, called a flux rope. Either the flux rope is
  present long before the eruption, or it is built up by reconnection
  of a sheared arcade from the beginning of the eruption.

Title: Study of magnetic flux emergence and related activity in
    active region NOAA 10314
Authors: Poisson, Mariano; López Fuentes, Marcelo; Mandrini, Cristina
   H.; Démoulin, Pascal; Pariat, Etienne
Bibcode: 2013AdSpR..51.1834P
Altcode:
  We study the extremely complex active region (AR) NOAA 10314, that
  was observed from March 13-19, 2003. This AR was the source of several
  energetic events, among them two major (X class) flares, along a few
  days. We follow the evolution of this AR since the very first stages
  of its emergence. From the photospheric evolution of the magnetic
  polarities observed with SOHO/MDI we infer the morphology of the
  flux tube that originates the AR. Using a computation technique that
  combines Local Correlation Tracking with magnetic induction constrains,
  we compute the rate of magnetic helicity injection at the photosphere
  during the observed evolution. From our results we conclude that the
  AR originated by the emergence of a severely deformed magnetic flux
  tube having a dominantly positive magnetic helicity.

Title: Statistical analysis of magnetic cloud erosion by magnetic
    reconnection
Authors: Ruffenach, A.; Lavraud, B.; Farrugia, C. J.; Démoulin, P.;
   Dasso, S.; Sauvaud, J.; Kajdic, P.; Rouillard, A. P.; Lynnyk, A.;
   Foullon, C.; Owens, M. J.; Savani, N. P.; Luhmann, J. G.
Bibcode: 2013AGUSMSH33A..03R
Altcode:
  Magnetic clouds (MCs), described as large-scale toroidal magnetic
  structures, interact with the surrounding interplanetary medium
  during propagation. It has been suggested in particular that magnetic
  reconnection may peel off their outer magnetic structure. Recently,
  Ruffenach et al. (2012) confirmed the occurrence of MC erosion thanks
  to a multi-spacecraft study combining a set of key signatures expected
  from this process. The aim of the present study is to extend previous
  works on the topic to all MCs of solar cycle 23 in order to quantify
  this phenomenon. This statistical analysis, primarily carried out
  with WIND and complemented with recent STEREO data, focuses on three
  signatures. First, based on careful determination of the MCs main
  axes, we estimate the amount of magnetic flux eroded for each event
  by analysing the azimuthal flux imbalance during the spacecraft
  sampling of the flux rope. We also search for magnetic reconnection
  signatures at the front boundary of the MCs. Finally, we investigate
  the characteristics of suprathermal electrons in the back region of
  the MCs. Those electrons are considered to signal potential large-scale
  topological changes expected from the erosion process.

Title: Accuracy of magnetic energy computations
Authors: Valori, G.; Démoulin, P.; Pariat, E.; Masson, S.
Bibcode: 2013A&A...553A..38V
Altcode: 2013arXiv1303.6773V
  Context. For magnetically driven events, the magnetic energy of
  the system is the prime energy reservoir that fuels the dynamical
  evolution. In the solar context, the free energy (i.e., the energy in
  excess of the potential field energy) is one of the main indicators
  used in space weather forecasts to predict the eruptivity of active
  regions. A trustworthy estimation of the magnetic energy is therefore
  needed in three-dimensional (3D) models of the solar atmosphere, e.g.,
  in coronal fields reconstructions or numerical simulations. <BR /> Aims:
  The expression of the energy of a system as the sum of its potential
  energy and its free energy (Thomson's theorem) is strictly valid when
  the magnetic field is exactly solenoidal. For numerical realizations on
  a discrete grid, this property may be only approximately fulfilled. We
  show that the imperfect solenoidality induces terms in the energy that
  can lead to misinterpreting the amount of free energy present in a
  magnetic configuration. <BR /> Methods: We consider a decomposition
  of the energy in solenoidal and nonsolenoidal parts which allows
  the unambiguous estimation of the nonsolenoidal contribution to the
  energy. We apply this decomposition to six typical cases broadly used
  in solar physics. We quantify to what extent the Thomson theorem is
  not satisfied when approximately solenoidal fields are used. <BR />
  Results: The quantified errors on energy vary from negligible to
  significant errors, depending on the extent of the nonsolenoidal
  component of the field. We identify the main source of errors and
  analyze the implications of adding a variable amount of divergence to
  various solenoidal fields. Finally, we present pathological unphysical
  situations where the estimated free energy would appear to be negative,
  as found in some previous works, and we identify the source of this
  error to be the presence of a finite divergence. <BR /> Conclusions:
  We provide a method of quantifying the effect of a finite divergence in
  numerical fields, together with detailed diagnostics of its sources. We
  also compare the efficiency of two divergence-cleaning techniques. These
  results are applicable to a broad range of numerical realizations of
  magnetic fields. <P />Appendices are available in electronic form at
  <A href="http://www.aanda.org">http://www.aanda.org</A>

Title: The 3D Geometry of Active Region Upflows Deduced from Their
    Limb-to-Limb Evolution
Authors: Démoulin, P.; Baker, D.; Mandrini, C. H.; van
   Driel-Gesztelyi, L.
Bibcode: 2013SoPh..283..341D
Altcode: 2012arXiv1211.5962D
  We analyze the evolution of coronal plasma upflows from the edges of
  AR 10978, which has the best limb-to-limb data coverage with Hinode's
  EUV Imaging Spectrometer (EIS). We find that the observed evolution is
  largely due to the solar rotation progressively changing the viewpoint
  of nearly stationary flows. From the systematic changes in the upflow
  regions as a function of distance from disc center, we deduce their
  3D geometrical properties as inclination and angular spread in three
  coronal lines (Si VII, Fe XII, and Fe XV). In agreement with magnetic
  extrapolations, we find that the flows are thin, fan-like structures
  rooted in quasi separatrix layers (QSLs). The fans are tilted away
  from the AR center. The highest plasma velocities in these three
  spectral lines have similar magnitudes and their heights increase with
  temperature. The spatial location and extent of the upflow regions
  in the Si VII, Fe XII, and Fe XV lines are different owing to i)
  temperature stratification and ii) line of sight integration of the
  spectral profiles with significantly different backgrounds. We conclude
  that we sample the same flows at different temperatures. Further,
  we find that the evolution of line widths during the disc passage is
  compatible with a broad range of velocities in the flows. Everything
  considered, our results are compatible with the AR upflows originating
  from reconnections along QSLs between over-pressure AR loops and
  neighboring under-pressure loops. The flows are driven along magnetic
  field lines by a pressure gradient in a stratified atmosphere. Our
  interpretation of the above results is that, at any given time, we
  observe the superposition of flows created by successive reconnections,
  leading to a broad velocity distribution.

Title: Does spacecraft trajectory strongly affect detection of
    magnetic clouds?
Authors: Démoulin, P.; Dasso, S.; Janvier, M.
Bibcode: 2013A&A...550A...3D
Altcode: 2012arXiv1211.5343D
  Context. Magnetic clouds (MCs) are a subset of interplanetary coronal
  mass ejections (ICMEs). One property of MCs is the presence of a
  magnetic flux rope. Is the difference between ICMEs with and without
  MCs intrinsic or rather due to an observational bias? <BR /> Aims:
  As the spacecraft has no relationship with the MC trajectory, the
  frequency distribution of MCs versus the spacecraft distance to the
  MCs' axis is expected to be approximately flat. However, Lepping &amp;
  Wu (2010, Ann. Geophys., 28, 1539) confirmed that it is a strongly
  decreasing function of the estimated impact parameter. Is a flux rope
  more frequently undetected for larger impact parameter? <BR /> Methods:
  In order to answer the questions above, we explore the parameter space
  of flux rope models, especially the aspect ratio, boundary shape,
  and current distribution. The proposed models are analyzed as MCs
  by fitting a circular linear force-free field to the magnetic field
  computed along simulated crossings. <BR /> Results: We find that the
  distribution of the twist within the flux rope and the non-detection
  due to too low field rotation angle or magnitude only weakly affect the
  expected frequency distribution of MCs versus impact parameter. However,
  the estimated impact parameter is increasingly biased to lower values
  as the flux rope cross section is more elongated orthogonally to the
  crossing trajectory. The observed distribution of MCs is a natural
  consequence of a flux rope cross section flattened on average by a
  factor 2 to 3 depending on the magnetic twist profile. However, the
  faster MCs at 1 AU, with V &gt; 550 km s<SUP>-1</SUP>, present an almost
  uniform distribution of MCs vs. impact parameter, which is consistent
  with round-shaped flux ropes, in contrast with the slower ones. <BR />
  Conclusions: We conclude that the sampling of MCs at various distances
  from the axis does not significantly affect their detection. The large
  part of ICMEs without MCs could be due to a too strict criteria for
  MCs or to the fact that these ICMEs are encountered outside their flux
  rope or near the leg region, or they do not contain a flux rope.

Title: The standard flare model in three dimensions. II. Upper limit
    on solar flare energy
Authors: Aulanier, G.; Démoulin, P.; Schrijver, C. J.; Janvier, M.;
   Pariat, E.; Schmieder, B.
Bibcode: 2013A&A...549A..66A
Altcode: 2012arXiv1212.2086A
  Context. Solar flares strongly affect the Sun's atmosphere as well as
  the Earth's environment. Quantifying the maximum possible energy of
  solar flares of the present-day Sun, if any, is thus a key question in
  heliophysics. <BR /> Aims: The largest solar flares observed over the
  past few decades have reached energies of a few times 10<SUP>32</SUP>
  erg, possibly up to 10<SUP>33</SUP> erg. Flares in active Sun-like
  stars reach up to about 10<SUP>36</SUP> erg. In the absence of direct
  observations of solar flares within this range, complementary methods
  of investigation are needed to assess the probability of solar flares
  beyond those in the observational record. <BR /> Methods: Using
  historical reports for sunspot and solar active region properties
  in the photosphere, we scaled to observed solar values a realistic
  dimensionless 3D MHD simulation for eruptive flares, which originate
  from a highly sheared bipole. This enabled us to calculate the magnetic
  fluxes and flare energies in the model in a wide paramater space. <BR />
  Results: Firstly, commonly observed solar conditions lead to modeled
  magnetic fluxes and flare energies that are comparable to those
  estimated from observations. Secondly, we evaluate from observations
  that 30% of the area of sunspot groups are typically involved in
  flares. This is related to the strong fragmentation of these groups,
  which naturally results from sub-photospheric convection. When the
  model is scaled to 30% of the area of the largest sunspot group ever
  reported, with its peak magnetic field being set to the strongest value
  ever measured in a sunspot, it produces a flare with a maximum energy of
  ~6 × 10<SUP>33</SUP> erg. <BR /> Conclusions: The results of the model
  suggest that the Sun is able to produce flares up to about six times as
  energetic in total solar irradiance fluence as the strongest directly
  observed flare of Nov. 4, 2003. Sunspot groups larger than historically
  reported would yield superflares for spot pairs that would exceed tens
  of degrees in extent. We thus conjecture that superflare-productive
  Sun-like stars should have a much stronger dynamo than in the Sun.

Title: Statistical analysis of magnetic cloud erosion by magnetic
    reconnection
Authors: Ruffenach, A.; Lavraud, B.; Farrugia, C. J.; Démoulin, P.;
   Dasso, S.; Sauvaud, J.; Rouillard, A. P.; Lynnyk, A.; Foullon, C.;
   Owens, M. J.; Savani, N. P.; Luhmann, J. G.
Bibcode: 2012AGUFMSH31A2203R
Altcode:
  Magnetic clouds (MCs), described as large-scale toroidal magnetic
  structures, interact with the surrounding interplanetary medium
  during propagation. It has been suggested in particular that magnetic
  reconnection may peel off their outer magnetic structure. Recently,
  Ruffenach et al. (2012) confirmed the occurrence of MC erosion thanks
  to a multi-spacecraft study combining a set of key signatures expected
  from this process. The aim of the present study is to extend previous
  works on the topic to all MCs of solar cycle 23 in order to quantify
  this phenomenon. This statistical analysis, primarily carried out
  with WIND and complemented with recent STEREO data, focuses on three
  signatures. First, based on careful determination of the MCs main
  axes, we estimate the amount of magnetic flux eroded for each event
  by analysing the azimuthal flux imbalance during the spacecraft
  sampling of the flux rope. We also search for magnetic reconnection
  signatures at the front boundary of the MCs. Finally, we investigate
  the characteristics of suprathermal electrons in the back region of
  the MCs. Those electrons are considered to signal potential large-scale
  topological changes expected from the erosion process.

Title: Magnetic Topology of Active Regions and Coronal Holes:
    Implications for Coronal Outflows and the Solar Wind
Authors: van Driel-Gesztelyi, L.; Culhane, J. L.; Baker, D.; Démoulin,
   P.; Mandrini, C. H.; DeRosa, M. L.; Rouillard, A. P.; Opitz, A.;
   Stenborg, G.; Vourlidas, A.; Brooks, D. H.
Bibcode: 2012SoPh..281..237V
Altcode: 2012SoPh..tmp..228V
  During 2 - 18 January 2008 a pair of low-latitude opposite-polarity
  coronal holes (CHs) were observed on the Sun with two active regions
  (ARs) and the heliospheric plasma sheet located between them. We use
  the Hinode/EUV Imaging Spectrometer (EIS) to locate AR-related outflows
  and measure their velocities. Solar-Terrestrial Relations Observatory
  (STEREO) imaging is also employed, as are the Advanced Composition
  Explorer (ACE) in-situ observations, to assess the resulting impacts on
  the solar wind (SW) properties. Magnetic-field extrapolations of the two
  ARs confirm that AR plasma outflows observed with EIS are co-spatial
  with quasi-separatrix layer locations, including the separatrix of a
  null point. Global potential-field source-surface modeling indicates
  that field lines in the vicinity of the null point extend up to the
  source surface, enabling a part of the EIS plasma upflows access
  to the SW. We find that similar upflow properties are also observed
  within closed-field regions that do not reach the source surface. We
  conclude that some of plasma upflows observed with EIS remain confined
  along closed coronal loops, but that a fraction of the plasma may be
  released into the slow SW. This suggests that ARs bordering coronal
  holes can contribute to the slow SW. Analyzing the in-situ data, we
  propose that the type of slow SW present depends on whether the AR is
  fully or partially enclosed by an overlying streamer.

Title: Multispacecraft observation of magnetic cloud erosion by
    magnetic reconnection during propagation
Authors: Ruffenach, A.; Lavraud, B.; Owens, M. J.; Sauvaud, J. -A.;
   Savani, N. P.; Rouillard, A. P.; Démoulin, P.; Foullon, C.; Opitz,
   A.; Fedorov, A.; Jacquey, C. J.; Génot, V.; Louarn, P.; Luhmann,
   J. G.; Russell, C. T.; Farrugia, C. J.; Galvin, A. B.
Bibcode: 2012JGRA..117.9101R
Altcode: 2012JGRA..11709101R
  During propagation, Magnetic Clouds (MC) interact with their
  environment and, in particular, may reconnect with the solar wind
  around it, eroding away part of its initial magnetic flux. Here we
  quantitatively analyze such an interaction using combined, multipoint
  observations of the same MC flux rope by STEREO A, B, ACE, WIND and
  THEMIS on November 19-20, 2007. Observation of azimuthal magnetic flux
  imbalance inside a MC flux rope has been argued to stem from erosion
  due to magnetic reconnection at its front boundary. The present study
  adds to such analysis a large set of signatures expected from this
  erosion process. (1) Comparison of azimuthal flux imbalance for the
  same MC at widely separated points precludes the crossing of the MC
  leg as a source of bias in flux imbalance estimates. (2) The use of
  different methods, associated errors and parametric analyses show that
  only an unexpectedly large error in MC axis orientation could explain
  the azimuthal flux imbalance. (3) Reconnection signatures are observed
  at the MC front at all spacecraft, consistent with an ongoing erosion
  process. (4) Signatures in suprathermal electrons suggest that the
  trailing part of the MC has a different large-scale magnetic topology,
  as expected. The azimuthal magnetic flux erosion estimated at ACE
  and STEREO A corresponds respectively to 44% and 49% of the inferred
  initial azimuthal magnetic flux before MC erosion upon propagation. The
  corresponding average reconnection rate during transit is estimated to
  be in the range 0.12-0.22 mV/m, suggesting most of the erosion occurs
  in the inner parts of the heliosphere. Future studies ought to quantify
  the influence of such an erosion process on geo-effectiveness.

Title: Identifying the Main Driver of Active Region Outflows
Authors: Baker, D.; van Driel-Gesztelyi, L.; Mandrini, C. H.;
   Démoulin, P.; Murray, M. J.
Bibcode: 2012ASPC..454..425B
Altcode:
  Hinode's EUV Imaging Spectrometer (EIS) has discovered ubiquitous
  outflows of a few to 50 km s<SUP>-1</SUP> from active regions (ARs). The
  characteristics of these outflows are very curious in that they are
  most prominent at the AR boundary and appear over monopolar magnetic
  areas. They are linked to strong non-thermal line broadening and
  are stronger in hotter EUV lines. The outflows persist for at least
  several days. Whereas red-shifted down flows observed in AR closed
  loops are well understood, to date there is no general consensus
  for the mechanism(s) driving blue-shifted AR-related outflows. We
  use Hinode EIS and X-Ray Telescope observations of AR 10942 coupled
  with magnetic modeling to demonstrate for the first time that the
  outflows originate from specific locations of the magnetic topology
  where field lines display strong gradients of magnetic connectivity,
  namely quasi-separatrix layers (QSLs), or in the limit of infinitely
  thin QSLs, separatrices. The strongest AR outflows were found to be
  in the vicinity of QSL sections located over areas of strong magnetic
  field. We argue that magnetic reconnection at QSLs, separating closed
  field lines of the AR and either large-scale externally connected or
  ‘open’ field lines, is a viable mechanism for driving AR outflows
  which are potentially sources of the slow solar wind. In fact, magnetic
  reconnection along QSLs (including separatricies) is the first theory
  to explain the most puzzling characteristics of the outflows, namely
  their occurrence over monopolar areas at the periphery of ARs and
  their longevity.

Title: Does Magnetic Helicity Affect Active Region Evolution and
    Energetics?
Authors: Wallace, A. J.; Green, L. M.; Mandrini, C. H.; Démoulin,
   P.; van Driel-Gesztelyi, L.; Matthews, S. A.
Bibcode: 2012ASPC..454..281W
Altcode:
  The purpose of this investigation is to determine whether there is a
  difference between the evolution of an active region with additional new
  flux emergence if the new flux has either the same or the opposite sign
  of magnetic helicity from the active region. Of these two scenarios, the
  one that produces the most energetics is still a topic for debate. We
  present a study of two active regions following the emergence of a
  bipole, one with the same and one with the opposite sign of helicity
  from the active region. We discover that while there is less flaring
  in the mixed helicity active region the EUV flux normalised to the
  magnetic field is three times higher than that of the same helicity
  active region. We propose that reconnection is more likely to occur
  between opposite helicity structures and thus, the energy can never
  build up to the levels required for flaring.

Title: Erratum: "Initiation and Development of the White-light
    and Radio Coronal Mass Ejection on 2001 April 15" <A
    href="/abs/2012ApJ...750..147D">(2012, ApJ, 750, 147)</A>
Authors: Démoulin, P.; Vourlidas, A.; Pick, M.; Bouteille, A.
Bibcode: 2012ApJ...754..156D
Altcode:
  No abstract at ADS

Title: Reconstruction of 3D Coronal Magnetic Structures from
    THEMIS/MTR and Hinode/SOT Vector Maps
Authors: Schmieder, B.; Guo, Y.; Aulanier, G.; Démoulin, P.; Török,
   T.; Bommier, V.; Wiegelmann, T.; Gosain, S.
Bibcode: 2012ASPC..454..363S
Altcode:
  Coordinated campaigns using THEMIS, Hinode, and other instruments have
  allowed us to study the magnetic fields of faculae, filaments, and
  active regions. In a first case, we modelled the 3D magnetic field in a
  flaring active region with a nonlinear force-free field extrapolation,
  using magnetic vectors observed by THEMIS/MTR as boundary condition. In
  order to construct a consistent bottom boundary for the model, we
  first removed the 180 degree ambiguity of the transverse fields and
  minimized the force and torque in the observed vector fields. We found
  a twisted magnetic flux rope, well aligned with the polarity inversion
  line and a part of an Hα filament, and located where a large flare is
  initiated about two hours later. In a second case, Hinode/SOT allowed
  us to detect fine flux concentrations in faculae, while MTR provided us
  with magnetic information at different levels in the atmosphere. The
  polarimetry analysis of the MTR and SOT data gave consistent results,
  using both UNNOFIT and MELANIE inversion codes.

Title: Expansion of magnetic clouds in the outer heliosphere
Authors: Gulisano, A. M.; Démoulin, P.; Dasso, S.; Rodriguez, L.
Bibcode: 2012A&A...543A.107G
Altcode: 2012arXiv1206.1532G
  Context. A large amount of magnetized plasma is frequently ejected from
  the Sun as coronal mass ejections (CMEs). Some of these ejections are
  detected in the solar wind as magnetic clouds (MCs) that have flux rope
  signatures. <BR /> Aims: Magnetic clouds are structures that typically
  expand in the inner heliosphere. We derive the expansion properties of
  MCs in the outer heliosphere from one to five astronomical units to
  compare them with those in the inner heliosphere. <BR /> Methods: We
  analyze MCs observed by the Ulysses spacecraft using in situ magnetic
  field and plasma measurements. The MC boundaries are defined in the
  MC frame after defining the MC axis with a minimum variance method
  applied only to the flux rope structure. As in the inner heliosphere,
  a large fraction of the velocity profile within MCs is close to
  a linear function of time. This is indicative of a self-similar
  expansion and a MC size that locally follows a power-law of the solar
  distance with an exponent called ζ. We derive the value of ζ from
  the in situ velocity data. <BR /> Results: We analyze separately the
  non-perturbed MCs (cases showing a linear velocity profile almost for
  the full event), and perturbed MCs (cases showing a strongly distorted
  velocity profile). We find that non-perturbed MCs expand with a similar
  non-dimensional expansion rate (ζ = 1.05 ± 0.34), i.e. slightly
  faster than at the solar distance and in the inner heliosphere (ζ =
  0.91 ± 0.23). The subset of perturbed MCs expands, as in the inner
  heliosphere, at a significantly lower rate and with a larger dispersion
  (ζ = 0.28 ± 0.52) as expected from the temporal evolution found in
  numerical simulations. This local measure of the expansion also agrees
  with the distribution with distance of MC size, mean magnetic field,
  and plasma parameters. The MCs interacting with a strong field region,
  e.g. another MC, have the most variable expansion rate (ranging from
  compression to over-expansion).

Title: Magnetic clouds along the solar cycle: expansion and magnetic
    helicity
Authors: Dasso, Sergio; Démoulin, Pascal; Gulisano, Adriana M.
Bibcode: 2012IAUS..286..139D
Altcode:
  Magnetic clouds (MCs) are objects of extreme importance in the
  heliosphere. They have a major role on releasing magnetic helicity
  from the Sun (with crucial consequences on the solar dynamo), they
  are the hugest transient object in the interplanetary medium, and the
  main actors for the Sun-Earth coupling. The comparison between models
  and observations is beginning to clarify several open questions on MCs,
  such as their internal magnetic configuration and their interaction with
  the ambient solar wind. Due to the decay of the solar wind pressure with
  the distance to the Sun, MCs are typically in expansion. However, their
  detailed and local expansion properties depend on their environment
  plasma properties. On the other hand, while it is well known that
  the solar cycle determines several properties of the heliosphere, the
  effects of the cycle on MC properties are not so well understood. In
  this work we review two major properties of MCs: (i) their expansion,
  and (ii) the magnetic flux and helicity that they transport through
  the interplanetary medium. We find that the amount of magnetic flux
  and helicity released via MCs during the last solar minimum (years
  2007-2009) was significantly lower than in the previous one (years
  1995-1997). Moreover, both MC size and mean velocity are in phase with
  the solar cycle while the expansion rate is weakly variable and has
  no relationship with the cycle.

Title: Evolution of a very complex active region during the decay
    phase of Cycle 23
Authors: Poisson, Mariano; Fuentes, Marcelo López; Mandrini, Cristina
   H.; Démoulin, Pascal; Pariat, Etienne
Bibcode: 2012IAUS..286..246P
Altcode:
  We study the emergence and evolution of AR NOAA 10314, observed on
  the solar disk during March 13-19, 2003. This extremely complex AR is
  of particular interest due to its unusual magnetic flux distribution
  and the clear rotation of the polarities of a δ-spot within the
  AR. Using SOHO/MDI magnetograms we follow the evolution of the
  photospheric magnetic flux to infer the morphology of the structure
  that originates the AR. We determine the tilt angle variation for
  the δ-spot and find a counter-clockwise rotation corresponding to a
  positive writhed flux tube. We compute the magnetic helicity injection
  and the total accumulated helicity in the AR and find a correlation
  with the observed rotation.

Title: Magnetic topology, coronal outflows, and the solar wind
Authors: Mandrini, Cristina H.; Culhane, J. Leonard; Vourlidas,
   Angelos; Demoulin, Pascal; Stenborg, Guillermo; Opitz, Andrea;
   Rouillard, Alexis; Van Driel-Gesztelyi, Lidia; Baker, Deborah; DeRosa,
   Marc; Brooks, David
Bibcode: 2012cosp...39.1173M
Altcode: 2012cosp.meet.1173M
  During 2-18 January 2008 a pair of low-latitude opposite polarity
  coronal holes were observed on the Sun flanked by two ARs with
  the heliospheric plasma sheet between them. Hinode/EUV Imaging
  Telescope (EIS) is used to locate AR-related outflows and measure their
  velocities. The Advanced Composition Explorer (ACE) in-situ observations
  are employed to assess the resulting impacts on the interplanetary solar
  wind (SW). Magnetic field extrapolations of the two ARs confirm that AR
  plasma outflows observed with EIS are co-spatial with quasi-separatrix
  layer locations, including the separatrix of a null point. Global
  potential field source-surface modeling indicates that field lines
  in the vicinity of the null point extend up to the source-surface,
  enabling a part of the EIS plasma upflows access to the SW. Similar
  upflow magnitude is also observed within closed field regions. Though
  part of the plasma upflows observed with EIS remain confined along
  closed coronal loops, a subset of them are indeed able to make their
  imprint in the slow SW, making ARs bordering coronal holes a slow
  SW contributor.

Title: Photospheric injection of magnetic helicity: implementation
    of a new density estimate
Authors: Dalmasse, Kévin; Pariat, Etienne; Demoulin, Pascal
Bibcode: 2012cosp...39..393D
Altcode: 2012cosp.meet..393D
  Magnetic helicity quantifies how globally sheared and/or twisted is
  the magnetic field, and thus, is a tracer of the non--potentiality
  of the magnetic field in a volume. In the conditions of the solar
  corona, magnetic helicity is a conserved quantity, and thus, imposes
  a high constraint on the evolution of the magnetic field. Helicity
  is continuously injected into the corona during the evolution of
  active regions (ARs), and CMEs are possibly the manifestation of the
  ejection of helicity excess. To better understand and quantify the role
  of magnetic helicity in solar activity, the distribution of magnetic
  helicity flux in ARs needs to be studied. The helicity distribution can
  be computed from the temporal evolution of photospheric magnetograms
  of ARs such as the ones provided by SDO/HMI and Hinode/SOT. Most of
  previous analyses of photospheric helicity flux derive helicity flux
  density proxies such as the so-called G_{A}, and recently G_{θ}. The
  proxy G_{θ} had been developed in order to reduce the fake signals
  observed using G_{A}. Although G_{θ} allows a better estimate of the
  photospheric helicity flux, it is still not a true helicity flux density
  because it does not account for the connectivity of the magnetic field
  lines. For the first time, we implement the helicity density G_{Φ}
  which takes into account such connectivity. In order to use G_{Φ}
  for future observational studies, we test the method and its precision
  on several models involving different types of helicity injection (by
  rotation and relative motions of two opposite magnetic polarities). We
  show that G_{Φ} is a much better proxy to estimate the photospheric
  helicity flux than G_{A} and G_{θ}. We discuss how it could be
  implemented from the dataset provided by SDO/HMI.

Title: Topology analysis of emerging bipole clusters producing
    violent solar events observed by SDO
Authors: Schmieder, Brigitte; Demoulin, Pascal; Mandrini, Cristina H.;
   Guo, Yang
Bibcode: 2012cosp...39.1724S
Altcode: 2012cosp.meet.1724S
  During the rising phase of Solar Cycle 24, tremendous magnetic solar
  activity occurs on the Sun with fast and compact emergence of magnetic
  flux leading to burts of flares (C to M and even X class) . We have
  investigated the violent events occuring in the cluster of two active
  regions AR 11121 and AR11123 observed in November by SDO. In less
  than two days the magnetic field increases by a factor of 10 with
  the emergence of groups of bipoles. A topology analysis demonstrates
  the formation of multiple separatrices and quasi-separatrix layers
  explaining possible mechanisms for destabilization of the magnetic
  structures such as filaments and coronal loops.

Title: Comparing Values of the Relative Magnetic Helicity in Finite
    Volumes
Authors: Valori, G.; Démoulin, P.; Pariat, E.
Bibcode: 2012SoPh..278..347V
Altcode: 2012SoPh..tmp..271G
  Relative magnetic helicity, as a conserved quantity of ideal
  magnetohydrodynamics, has been highlighted as an important quantity to
  study in plasma physics. Due to its nonlocal nature, its estimation
  is not straightforward in both observational and numerical data. In
  this study we derive expressions for the practical computation of the
  gauge-independent relative magnetic helicity in three-dimensional
  finite domains. The derived expressions are easy to implement and
  rapid to compute. They are derived in Cartesian coordinates, but can
  be easily written in other coordinate systems. We apply our method to
  a numerical model of a force-free equilibrium containing a flux rope,
  and compare the results with those obtained employing known half-space
  equations. We find that our method requires a much smaller volume
  than half-space expressions to derive the full helicity content. We
  also prove that values of relative magnetic helicity of different
  magnetic fields can be compared with each other in the same sense as
  free-energy values can. Therefore, relative magnetic helicity can
  be meaningfully and directly compared between different datasets,
  such as those from different active regions, but also within the
  same dataset at different times. Typical applications of our formulae
  include the helicity computation in three-dimensional models of the
  solar atmosphere, e.g., coronal-field reconstructions by force-free
  extrapolation and discretized magnetic fields of numerical simulations.

Title: Implications of Non-cylindrical Flux Ropes for Magnetic
    Cloud Reconstruction Techniques and the Interpretation of Double
    Flux Rope Events
Authors: Owens, M. J.; Démoulin, P.; Savani, N. P.; Lavraud, B.;
   Ruffenach, A.
Bibcode: 2012SoPh..278..435O
Altcode:
  Magnetic clouds (MCs) are a subset of interplanetary coronal mass
  ejections (ICMEs) which exhibit signatures consistent with a magnetic
  flux rope structure. Techniques for reconstructing flux rope orientation
  from single-point in situ observations typically assume the flux
  rope is locally cylindrical, e.g., minimum variance analysis (MVA)
  and force-free flux rope (FFFR) fitting. In this study, we outline a
  non-cylindrical magnetic flux rope model, in which the flux rope radius
  and axial curvature can both vary along the length of the axis. This
  model is not necessarily intended to represent the global structure
  of MCs, but it can be used to quantify the error in MC reconstruction
  resulting from the cylindrical approximation. When the local flux
  rope axis is approximately perpendicular to the heliocentric radial
  direction, which is also the effective spacecraft trajectory through
  a magnetic cloud, the error in using cylindrical reconstruction
  methods is relatively small (≈ 10<SUP>∘</SUP>). However, as the
  local axis orientation becomes increasingly aligned with the radial
  direction, the spacecraft trajectory may pass close to the axis at
  two separate locations. This results in a magnetic field time series
  which deviates significantly from encounters with a force-free flux
  rope, and consequently the error in the axis orientation derived from
  cylindrical reconstructions can be as much as 90<SUP>∘</SUP>. Such
  two-axis encounters can result in an apparent `double flux rope'
  signature in the magnetic field time series, sometimes observed in
  spacecraft data. Analysing each axis encounter independently produces
  reasonably accurate axis orientations with MVA, but larger errors with
  FFFR fitting.

Title: Initiation and Development of the White-light and Radio
    Coronal Mass Ejection on 2001 April 15
Authors: Démoulin, P.; Vourlidas, A.; Pick, M.; Bouteille, A.
Bibcode: 2012ApJ...750..147D
Altcode:
  The 2001 April 15 event was one of the largest of the last solar
  cycle. A former study established that this event was associated
  with a coronal mass ejection (CME) observed both at white light
  and radio frequencies. This radio CME is illuminated by synchrotron
  emission from relativistic electrons. In this paper, we investigate
  the relation of the radio CME to its extreme-ultraviolet (EUV) and
  white-light counterpart and reach four main conclusions. (1) The radio
  CME corresponds to the white-light flux rope cavity. (2) The presence
  of a reconnecting current sheet behind the erupting flux rope is framed,
  both from below and above, by bursty radio sources. This reconnection is
  the source of relativistic radiating electrons which are injected down
  along the reconnected coronal arches and up along the flux rope border
  forming the radio CME. (3) Radio imaging reveals an important lateral
  overexpansion in the low corona; this overexpansion is at the origin of
  compression regions where type II and III bursts are imaged. (4) Already
  in the initiation phase, radio images reveal large-scale interactions
  of the source active region (AR) with its surroundings, including
  another AR and open magnetic fields. Thus, these complementary radio,
  EUV, and white-light data validate the flux rope eruption model of CMEs.

Title: Nonlinear Force-Free Extrapolation of Emerging Flux with a
    Global Twist and Serpentine Fine Structures
Authors: Valori, G.; Green, L. M.; Démoulin, P.; Vargas Domínguez,
   S.; van Driel-Gesztelyi, L.; Wallace, A.; Baker, D.; Fuhrmann, M.
Bibcode: 2012SoPh..278...73V
Altcode:
  We study the flux emergence process in NOAA active region 11024, between
  29 June and 7 July 2009, by means of multi-wavelength observations
  and nonlinear force-free extrapolation. The main aim is to extend
  previous investigations by combining, as much as possible, high spatial
  resolution observations to test our present understanding of small-scale
  (undulatory) flux emergence, whilst putting these small-scale events
  in the context of the global evolution of the active region. The
  combination of these techniques allows us to follow the whole process,
  from the first appearance of the bipolar axial field on the east limb,
  until the buoyancy instability could set in and raise the main body
  of the twisted flux tube through the photosphere, forming magnetic
  tongues and signatures of serpentine field, until the simplification
  of the magnetic structure into a main bipole by the time the active
  region reaches the west limb. At the crucial time of the main emergence
  phase high spatial resolution spectropolarimetric measurements of the
  photospheric field are employed to reconstruct the three-dimensional
  structure of the nonlinear force-free coronal field, which is then
  used to test the current understanding of flux emergence processes. In
  particular, knowledge of the coronal connectivity confirms the identity
  of the magnetic tongues as seen in their photospheric signatures,
  and it exemplifies how the twisted flux, which is emerging on small
  scales in the form of a sea-serpent, is subsequently rearranged by
  reconnection into the large-scale field of the active region. In
  this way, the multi-wavelength observations combined with a nonlinear
  force-free extrapolation provide a coherent picture of the emergence
  process of small-scale magnetic bipoles, which subsequently reconnect
  to form a large-scale structure in the corona.

Title: Estimation of the squashing degree within a three-dimensional
    domain
Authors: Pariat, E.; Démoulin, P.
Bibcode: 2012A&A...541A..78P
Altcode:
  Context. The study of the magnetic topology of magnetic
  fields aims at determining the key sites for the development of
  magnetic reconnection. Quasi-separatrix layers (QSLs), regions of
  strong connectivity gradients, are topological structures where
  intense-electric currents preferentially build-up, and where,
  later on, magnetic reconnection occurs. <BR /> Aims: QSLs are
  volumes of intense squashing degree, Q; the field-line invariant
  quantifying the deformation of elementary flux tubes. QSL are complex
  and thin three-dimensional (3D) structures difficult to visualize
  directly. Therefore Q maps, i.e. 2D cuts of the 3D magnetic domain, are
  a more and more common features used to study QSLs. <BR /> Methods:
  We analyze several methods to derive 2D Q maps and discuss their
  analytical and numerical properties. These methods can also be used to
  compute Q within the 3D domain. <BR /> Results: We demonstrate that
  while analytically equivalent, the numerical implementation of these
  methods can be significantly different. We derive the analytical formula
  and the best numerical methodology that should be used to compute
  Q inside the 3D domain. We illustrate this method with two twisted
  magnetic configurations: a theoretical case and a non-linear force
  free configuration derived from observations. <BR /> Conclusions: The
  representation of QSL through 2D planar cuts is an efficient procedure
  to derive the geometry of these structures and to relate them with other
  quantities, e.g. electric currents and plasma flows. It will enforce
  a more direct comparison of the role of QSL in magnetic reconnection.

Title: Long-term series of tropospheric water vapour amounts and
    HDO/H2O ratio profiles above Jungfraujoch.
Authors: Lejeune, B.; Mahieu, E.; Schneider, M.; Hase, F.; Servais,
   C.; Demoulin, P.
Bibcode: 2012EGUGA..14.7923L
Altcode:
  Water vapour is a crucial climate variable involved in many processes
  which widely determine the energy budget of our planet. In particular,
  water vapour is the dominant greenhouse gas in the Earth's atmosphere
  and its radiative forcing is maximum in the middle and upper
  troposphere. Because of the extremely high variability of water
  vapour concentration in time and space, it is challenging for the
  available relevant measurement techniques to provide a consistent
  data set useful for trend analyses and climate studies. Schneider et
  al. (2006a) showed that ground-based Fourier Transform Infrared (FTIR)
  spectroscopy, performed from mountain observatories, allows for the
  detection of H2O variabilities up to the tropopause. Furthermore, the
  FTIR measurements allow the retrieval of HDO amounts and therefore the
  monitoring of HDO/H2O ratio profiles whose variations act as markers
  for the source and history of the atmospheric water vapour. In the
  framework of the MUSICA European project (Multi-platform remote Sensing
  of Isotopologues for investigating the Cycle of Atmospheric water,
  http://www.imk-asf.kit.edu/english/musica.php), a new approach has
  been developed and optimized by M. Schneider and F. Hase, using the
  PROFFIT algorithm, to consistently retrieve tropospheric water vapour
  profiles from high-resolution ground-based infrared solar spectra and
  so taking benefit from available long-term data sets of ground-based
  observations. The retrieval of the water isotopologues is performed on
  a logarithmic scale from 14 micro-windows located in the 2600-3100 cm-1
  region. Other important features of this new retrieval strategy are:
  a speed dependant Voigt line shape model, a joint temperature profile
  retrieval and an interspecies constraint for the HDO/H2O profiles. In
  this contribution, we will combine the quality of the MUSICA strategy
  and of our observations, which are recorded on a regular basis
  with FTIR spectrometers, under clear-sky conditions, at the NDACC
  site (Network for the Detection of Atmospheric Composition Change,
  http://www.ndacc.org) of the Jungfraujoch International Scientific
  Station (Swiss Alps, 46.5° N, 8.0° E, 3580m asl). Information
  content analysis of the retrieved H2O products allows us to produce
  a long-term trend from 1996 to 2011 for different tropospheric
  levels. We will compare the annual cycle of tropospheric HDO/H2O ratio
  profiles with those already produced at other sites (Schneider et al.,
  2010). We will also focus on the diurnal variability of water vapour
  to determine a time limit in the inter-comparison of different water
  vapour measurement techniques. Acknowledgments The University of Liège
  involvement has primarily been supported by the PRODEX program funded
  by the Belgian Federal Science Policy Office, Brussels and by the Swiss
  GAW-CH program. The FRS-FNRS and the Fédération Wallonie-Bruxelles are
  further acknowledged for observational activities support. We thank the
  International Foundation High Altitude Research Stations Jungfraujoch
  and Gornergrat (HFSJG, Bern) for supporting the facilities needed to
  perform the observations. MUSICA is funded by the European Research
  Council under the European Community's Seventh Framework Programme
  (FP7/2007-2013) / ERC Grant agreement n° 256961.

Title: The interplanetary magnetic structure that guides solar
    relativistic particles
Authors: Masson, S.; Démoulin, P.; Dasso, S.; Klein, K. -L.
Bibcode: 2012A&A...538A..32M
Altcode: 2011arXiv1110.6811M
  Context. Relating in-situ measurements of relativistic solar particles
  to their parent activity in the corona requires understanding the
  magnetic structures that guide them from their acceleration site to the
  Earth. Relativistic particle events are observed at times of high solar
  activity, when transient magnetic structures such as interplanetary
  coronal mass ejections (ICMEs) often shape the interplanetary magnetic
  field (IMF). They may introduce interplanetary paths that are longer
  than nominal, and magnetic connections rooted far from the nominal
  Parker spiral. <BR /> Aims: We present a detailed study of the IMF
  configurations during ten relativistic solar particle events of
  the 23rd activity cycle to elucidate the actual IMF configuration
  that guides the particles to the Earth, where they are measured by
  neutron monitors. <BR /> Methods: We used magnetic field (MAG) and
  plasma parameter measurements (SWEPAM) from the ACE spacecraft and
  determined the interplanetary path lengths of energetic particles
  through a modified version of the velocity dispersion analysis based
  on energetic particle measurements with SoHO/ERNE. <BR /> Results:
  We find that the majority (7/10) of the events is detected in the
  vicinity of an ICME. Their interplanetary path lengths are found to be
  longer (1.5-2.6 AU) than those of the two events propagating in the
  slow solar wind (1.3 AU). The longest apparent path length is found
  in an event within the fast solar wind, probably caused by enhanced
  pitch angle scattering. The derived path lengths imply that the first
  energetic and relativistic protons are released at the Sun at the
  same time as electron beam emitting type III radio bursts. <BR />
  Conclusions: The timing of the first high-energy particle arrival on
  Earth is mainly determined by the type of IMF in which the particles
  propagate. Initial arrival times are as expected from Parker's model
  in the slow solar wind, and significantly longer in or near transient
  structures such as ICMEs.

Title: Evolution of Hard X-Ray Sources and Ultraviolet Solar Flare
    Ribbons for a Confined Eruption of a Magnetic Flux Rope
Authors: Guo, Y.; Ding, M. D.; Schmieder, B.; Démoulin, P.; Li, H.
Bibcode: 2012ApJ...746...17G
Altcode: 2011arXiv1111.1790G
  We study the magnetic field structures of hard X-ray (HXR) sources and
  flare ribbons of the M1.1 flare in active region NOAA 10767 on 2005 May
  27. We have found in a nonlinear force-free field extrapolation over the
  same polarity inversion line, a small pre-eruptive magnetic flux rope
  located next to sheared magnetic arcades. RHESSI and the Transition
  Region and Coronal Explorer (TRACE) observed this confined flare in
  the X-ray bands and ultraviolet (UV) 1600 Å bands, respectively. In
  this event magnetic reconnection occurred at several locations. It
  first started at the location of the pre-eruptive flux rope. Then,
  the observations indicate that magnetic reconnection occurred between
  the pre-eruptive magnetic flux rope and the sheared magnetic arcades
  more than 10 minutes before the flare peak. This implies the formation
  of the larger flux rope, as observed with TRACE. Next, HXR sources
  appeared at the footpoints of this larger flux rope at the peak of the
  flare. The associated high-energy particles may have been accelerated
  below the flux rope in or around a reconnection region. Still, the close
  spatial association between the HXR sources and the flux rope footpoints
  favors an acceleration within the flux rope. Finally, a topological
  analysis of a large solar region, including active regions NOAA 10766
  and 10767, shows the existence of large-scale Quasi-Separatrix Layers
  (QSLs) before the eruption of the flux rope. No enhanced emission was
  found at these QSLs during the flare, but the UV flare ribbons stopped
  at the border of the closest large-scale QSL.

Title: Magnetic tongues properties in solar active regions
Authors: Poisson, M.; López Fuentes, M.; Mandrini, C. H.; Démoulin,
   P.
Bibcode: 2012BAAA...55..147P
Altcode:
  We study the emergence of solar active regions (ARs) to determine
  how their magnetic helicity properties affect the evolution of the
  photospheric flux observed in longitudinal magnetograms. We characterize
  the so called ``magnetic tongues'', which appear due to the line of
  sight projection of the azimuthal component of the magnetic field
  in twisted emerging flux-tubes forming ARs. We determine and study
  the evolution of a series of parameters, such as: the tilt angle,
  the polarity inversion line (PIL) orientation, the magnetic flux,
  the size and shape of the polarities and of their tongues for 25 ARs
  observed between 2004 and 2010. We model the emergence of a toroidal
  flux-tube with different amounts of twist and we test different methods
  to determine the PIL. Finally, from the obtained PIL evolution we are
  able to infer the sign of the flux-tube twist by comparing the results
  with our model predictions.

Title: Dynamical evolution of a magnetic cloud from the Sun to 5.4 AU
Authors: Nakwacki, M. S.; Dasso, S.; Démoulin, P.; Mandrini, C. H.;
   Gulisano, A. M.
Bibcode: 2011A&A...535A..52N
Altcode: 2011arXiv1108.0951N
  Context. Significant quantities of magnetized plasma are transported
  from the Sun to the interstellar medium via interplanetary coronal
  mass ejections (ICMEs). Magnetic clouds (MCs) are a particular subset
  of ICMEs, forming large-scale magnetic flux ropes. Their evolution in
  the solar wind is complex and mainly determined by their own magnetic
  forces and the interaction with the surrounding solar wind. <BR /> Aims:
  Magnetic clouds are strongly affected by the surrounding environment as
  they evolve in the solar wind. We study expansion of MCs, its consequent
  decrease in magnetic field intensity and mass density, and the possible
  evolution of the so-called global ideal-MHD invariants. <BR /> Methods:
  In this work we analyze the evolution of a particular MC (observed
  in March 1998) using in situ observations made by two spacecraft
  approximately aligned with the Sun, the first one at 1 AU from the Sun
  and the second one at 5.4 AU. We describe the magnetic configuration of
  the MC using different models and compute relevant global quantities
  (magnetic fluxes, helicity, and energy) at both heliodistances. We
  also tracked this structure back to the Sun, to find out its solar
  source. <BR /> Results: We find that the flux rope is significantly
  distorted at 5.4 AU. From the observed decay of magnetic field and
  mass density, we quantify how anisotropic is the expansion and the
  consequent deformation of the flux rope in favor of a cross section
  with an aspect ratio at 5.4 AU of ≈1.6 (larger in the direction
  perpendicular to the radial direction from the Sun). We quantify the
  ideal-MHD invariants and magnetic energy at both locations, and find
  that invariants are almost conserved, while the magnetic energy decays
  as expected with the expansion rate found. <BR /> Conclusions: The use
  of MHD invariants to link structures at the Sun and the interplanetary
  medium is supported by the results of this multi-spacecraft study. We
  also conclude that the local dimensionless expansion rate, which is
  computed from the velocity profile observed by a single-spacecraft,
  is very accurate for predicting the evolution of flux ropes in the
  solar wind.

Title: A filament supported by different magnetic field configurations
Authors: Guo, Y.; Schmieder, B.; Démoulin, P.; Wiegelmann, T.;
   Aulanier, G.; Török, T.; Bommier, V.
Bibcode: 2011IAUS..273..328G
Altcode:
  A nonlinear force-free magnetic field extrapolation of vector
  magnetogram data obtained by THEMIS/MTR on 2005 May 27 suggests the
  simultaneous existence of different magnetic configurations within
  one active region filament: one part of the filament is supported by
  field line dips within a flux rope, while the other part is located
  in dips within an arcade structure. Although the axial field chirality
  (dextral) and the magnetic helicity (negative) are the same along the
  whole filament, the chiralities of the filament barbs at different
  sections are opposite, i.e., right-bearing in the flux rope part and
  left-bearing in the arcade part. This argues against past suggestions
  that different barb chiralities imply different signs of helicity of
  the underlying magnetic field. This new finding about the chirality of
  filaments will be useful to associate eruptive filaments and magnetic
  cloud using the helicity parameter in the Space Weather Science.

Title: Solar activity due to magnetic complexity of active regions
Authors: Schmieder, Brigitte; Mandrini, Cristina; Chandra, Ramesh;
   Démoulin, Pascal; Török, Tibor; Pariat, Etienne; Uddin, Wahab
Bibcode: 2011IAUS..273..164S
Altcode:
  Active regions (ARs), involved in the Halloween events during
  October-November 2003, were the source of unusual activity during
  the following solar rotation. The flares on 18-20 November 2003 that
  occur in the AR NOAA10501 were accompanied by coronal mass ejections
  associated to some particularly geoeffective magnetic clouds. <P />Our
  analysis of the magnetic flux and helicity injection revealed that
  a new emerging bipole and consequent shearing motions continuously
  energized the region during its disk passage. The stored energy was
  eventually released through the interaction of the various systems
  of magnetic loops by several magnetic reconnection events. Active
  events on November 18 (filament eruptions and CMEs) were originated by
  shearing motions along a section of the filament channel that injected
  magnetic helicity with sign opposite to that of the AR. Two homologous
  flares, that occurred on November 20, were apparently triggered by
  different mechanisms as inferred from the flare ribbons evolution
  (filament eruption and CMEs). We studied in detail the behaviour of
  two North-South oriented filaments on November 20 2003. They merged
  and split following a process suggestive of `sling-shot' reconnection
  between two coronal flux ropes. We successfully tested this scenario
  in a 3D MHD simulation that is presented in this paper.

Title: Twist and writhe of δ-island active regions
Authors: López Fuentes, M. C.; Mandrini, C. H.; Démoulin, P.
Bibcode: 2011IAUS..273..153L
Altcode:
  We study the magnetic helicity properties of a set of peculiar
  active regions (ARs) including δ-islands and other high-tilt bipolar
  configurations. These ARs are usually identified as the most active in
  terms of flare and CME production. Due to their observed structure,
  they have been associated with the emergence of magnetic flux tubes
  that develop a kink instability. Our main goal is to determine the
  chirality of the twist and writhe components of the AR magnetic helicity
  in order to set constrains on the possible mechanisms producing the
  flux tube deformations. We determine the magnetic twist comparing
  observations of the AR coronal structure with force-free models of
  the magnetic field. We infer the flux-tube writhe from the rotation
  of the main magnetic bipole during the observed evolution. From the
  relation between the obtained twist and writhe signs we conclude that
  the development of the kink instability cannot be the single mechanism
  producing deformed flux-tubes.

Title: On Asymmetry of Magnetic Helicity in Emerging Active Regions:
    High Resolution Observations
Authors: Alexander, David; Tian, Lirong; Demoulin, Pascal; Zhu,
   Chunming
Bibcode: 2011shin.confE..11A
Altcode:
  We employ the DAVE (differential affine velocity estimator, Schuck
  2005; 2006) tracking technique on a time series of MDI/1m high spatial
  resolution lineof- sight magnetograms to measure the photospheric
  flow velocity for three newly emerging bipolar active regions. We
  separately calculate the magnetic helicity injection rate of the
  leading and following polarities to confirm or refute the magnetic
  helicity asymmetry, found by Tian &amp; Alexander (2009) using MDI/96m
  low spatial resolution magnetograms. Our results demonstrate that the
  magnetic helicity asymmetry is robust being present in the three active
  regions studied, two of which have an observed balance of the magnetic
  flux. The magnetic helicity injection rate measured is found to depend
  little on the window size selected, but does depend on the time interval
  used between the two successive magnetograms tracked. It is found
  that the measurement of the magnetic helicity injection rate performs
  well for a window size between 12-10 and 18-15 pixels, and at a time
  interval ∼t=10 minutes. Moreover, the short-lived magnetic structures,
  10-60 minutes, are found to contribute 30-50% of the magnetic helicity
  injection rate. Comparing with the results calculated by MDI/96m data,
  we find that the MDI/96m data, in general, can outline the main trend
  of the magnetic properties, but they significantly underestimate
  the magnetic flux in strong field region and are not appropriate for
  quantitative tracking studies, so provide a poor estimate of the amount
  of magnetic helicity injected into the corona.

Title: Interplanetary magnetic structure guiding relativistic
    particles
Authors: Masson, Sophie; Démoulin, P.; Dasso, S.; Klein, K. -L.
Bibcode: 2011shin.confE..77M
Altcode:
  The origin and the propagation of relativistic solar particles (0.5 to
  few GeV) in the interplanetary medium remains a debated topic. These
  relativistic particles, detected at the Earth by neutron monitors have
  been previously accelerated close to the Sun and are guided by the
  interplanetary magnetic field (IMF) lines, connecting the acceleration
  site and the Earth. Usually, the nominal Parker spiral is considered
  for ensuring the magnetic connection to the Earth. However, in most
  GLEs the IMF is highly disturbed, and the active regions associated to
  the GLEs are not always located close to the solar footprint of the
  nominal Parker spiral. A possible explanation is that relativistic
  particles are propagating in transient magnetic structures, such as
  Interplanetary Coronal Mass Ejections (ICMEs). <P />In order to check
  this interpretation, we studied in detail the interplanetary medium
  where the particles propagate for 10 GLEs of the last solar cycle. Using
  the magnetic field and the plasma parameter measurements (ACE/MAG
  and ACE/SWEPAM), we found widely different IMF configurations. In
  an independent approach we develop and apply an improved method of
  the velocity dispersion analysis to energetic protons measured by
  SoHO/ERNE. We determined the effective path length and the solar release
  time of protons from these data and also combined them with the neutron
  monitor data. <P />We found that in most of the GLEs, protons propagate
  in transient magnetic structures. Moreover, the comparison between
  the interplanetary magnetic structure and the interplanetary length
  suggest that the timing of particle arrival at Earth is dominantly
  determined by the type of IMF in which high energetic particles are
  propagating. Finally we find that these energetic protons are not
  significantly scattered during their transport to Earth.

Title: Actors of the main activity in large complex centres during
    the 23 solar cycle maximum
Authors: Schmieder, B.; Démoulin, P.; Pariat, E.; Török, T.;
   Molodij, G.; Mandrini, C. H.; Dasso, S.; Chandra, R.; Uddin, W.;
   Kumar, P.; Manoharan, P. K.; Venkatakrishnan, P.; Srivastava, N.
Bibcode: 2011AdSpR..47.2081S
Altcode:
  During the maximum of Solar Cycle 23, large active regions had a long
  life, spanning several solar rotations, and produced large numbers of
  X-class flares and CMEs, some of them associated to magnetic clouds
  (MCs). This is the case for the Halloween active regions in 2003. The
  most geoeffective MC of the cycle (Dst = -457) had its source during
  the disk passage of one of these active regions (NOAA 10501) on
  18 November 2003. Such an activity was presumably due to continuous
  emerging magnetic flux that was observed during this passage. Moreover,
  the region exhibited a complex topology with multiple domains of
  different magnetic helicities. The complexity was observed to reach
  such unprecedented levels that a detailed multi-wavelength analysis
  is necessary to precisely identify the solar sources of CMEs and
  MCs. Magnetic clouds are identified using in situ measurements and
  interplanetary scintillation (IPS) data. Results from these two
  different sets of data are also compared.

Title: Twisted Flux Tube Emergence Evidenced in Longitudinal
Magnetograms: Magnetic Tongues
Authors: Luoni, M. L.; Démoulin, P.; Mandrini, C. H.; van
   Driel-Gesztelyi, L.
Bibcode: 2011SoPh..270...45L
Altcode: 2011SoPh..tmp...66L
  Bipolar active regions (ARs) are thought to be formed by twisted flux
  tubes, as the presence of such twist is theoretically required for a
  cohesive rise through the whole convective zone. We use longitudinal
  magnetograms to demonstrate that a clear signature of a global magnetic
  twist is present, particularly, during the emergence phase when the AR
  is forming in a much weaker pre-existing magnetic field environment. The
  twist is characterised by the presence of elongated polarities, called
  "magnetic tongues", which originate from the azimuthal magnetic field
  component. The tongues first extend in size before retracting when the
  maximum magnetic flux is reached. This implies an apparent rotation of
  the magnetic bipole. Using a simple half-torus model of an emerging
  twisted flux tube having a uniform twist profile, we derive how the
  direction of the polarity inversion line and the elongation of the
  tongues depend on the global twist in the flux rope. Using a sample of
  40 ARs, we verify that the helicity sign, determined from the magnetic
  polarity distribution pattern, is consistent with the sign derived from
  the photospheric helicity flux computed from magnetogram time series,
  as well as from other proxies such as sheared coronal loops, sigmoids,
  flare ribbons and/or the associated magnetic cloud observed in situ
  at 1 AU. The evolution of the tongues observed in emerging ARs is
  also closely similar to the evolution found in recent MHD numerical
  simulations. We also found that the elongation of the tongue formed
  by the leading magnetic polarity is significantly larger than that of
  the following polarity. This newly discovered asymmetry is consistent
  with an asymmetric Ω-loop emergence, trailing the solar rotation,
  which was proposed earlier to explain other asymmetries in bipolar ARs.

Title: Pulsed Flows Along a Cusp Structure Observed with SDO/AIA
Authors: Thompson, Barbara; Démoulin, P.; Mandrini, C.; Mays, M.;
   Ofman, L.; Van Driel-Gesztelyi, L.; Viall, N.
Bibcode: 2011SPD....42.2117T
Altcode: 2011BAAS..43S.2117T
  We present observations of a cusp-shaped structure that formed after
  a flare and coronal mass ejection on 14 February 2011. Throughout
  the evolution of the cusp structure, blob features up to a few Mm in
  size were observed flowing along the legs and stalk of the cusp at
  projected speeds ranging from 50 to 150 km/sec. Around two dozen blob
  features, on order of 1 - 3 minutes apart, were tracked in multiple
  AIA EUV wavelengths. The blobs flowed outward (away from the Sun)
  along the cusp stalk, and most of the observed speeds were either
  constant or decelerating. We attempt to reconstruct the 3-D magnetic
  field of the evolving structure, discuss the possible drivers of the
  flows (including pulsed reconnection and tearing mode instability),
  and compare the observations to studies of pulsed reconnection and
  blob flows in the solar wind and the Earth's magnetosphere.

Title: Homologous Flares and Magnetic Field Topology in Active Region
    NOAA 10501 on 20 November 2003
Authors: Chandra, R.; Schmieder, B.; Mandrini, C. H.; Démoulin, P.;
   Pariat, E.; Török, T.; Uddin, W.
Bibcode: 2011SoPh..269...83C
Altcode: 2010arXiv1011.1187C; 2010SoPh..tmp..249C
  We present and interpret observations of two morphologically homologous
  flares that occurred in active region (AR) NOAA 10501 on 20 November
  2003. Both flares displayed four homologous Hα ribbons and were
  both accompanied by coronal mass ejections (CMEs). The central flare
  ribbons were located at the site of an emerging bipole in the centre
  of the active region. The negative polarity of this bipole fragmented
  in two main pieces, one rotating around the positive polarity by
  ≈ 110° within 32 hours. We model the coronal magnetic field and
  compute its topology, using as boundary condition the magnetogram
  closest in time to each flare. In particular, we calculate the
  location of quasi-separatrix layers (QSLs) in order to understand the
  connectivity between the flare ribbons. Though several polarities were
  present in AR 10501, the global magnetic field topology corresponds
  to a quadrupolar magnetic field distribution without magnetic null
  points. For both flares, the photospheric traces of QSLs are similar
  and match well the locations of the four Hα ribbons. This globally
  unchanged topology and the continuous shearing by the rotating bipole
  are two key factors responsible for the flare homology. However, our
  analyses also indicate that different magnetic connectivity domains
  of the quadrupolar configuration become unstable during each flare,
  so that magnetic reconnection proceeds differently in both events.

Title: Initiation and Early Development of the 2008 April 26 Coronal
    Mass Ejection
Authors: Huang, J.; Démoulin, P.; Pick, M.; Auchère, F.; Yan, Y. H.;
   Bouteille, A.
Bibcode: 2011ApJ...729..107H
Altcode:
  We present a detailed study of a coronal mass ejection (CME) with
  high temporal cadence observations in radio and extreme-ultraviolet
  (EUV). The radio observations combine imaging of the low corona with
  radio spectra in the outer corona and interplanetary space. The EUV
  observations combine the three points of view of the STEREO and SOHO
  spacecraft. The beginning of the CME initiation phase is characterized
  by emissions that are signatures of the reconnection of the outer part
  of the erupting configuration with surrounding magnetic fields. Later
  on, a main source of emission is located in the core of the active
  region. It is an indirect signature of the magnetic reconnection
  occurring behind the erupting flux rope. Energetic particles are also
  injected in the flux rope and the corresponding radio sources are
  detected. Other radio sources, located in front of the EUV bright
  front, trace the interaction of the flux rope with the surrounding
  fields. Hence, the observed radio sources enable us to detect the main
  physical steps of the CME launch. We find that imaging radio emissions
  in the metric range permits us to trace the extent and orientation of
  the flux rope which is later detected in interplanetary space. Moreover,
  combining the radio images at various frequencies with fast EUV imaging
  permits us to characterize in space and time the processes involved
  in the CME launch.

Title: Filament Interaction Modeled by Flux Rope Reconnection
Authors: Török, T.; Chandra, R.; Pariat, E.; Démoulin, P.;
   Schmieder, B.; Aulanier, G.; Linton, M. G.; Mandrini, C. H.
Bibcode: 2011ApJ...728...65T
Altcode:
  Hα observations of solar active region NOAA 10501 on 2003 November
  20 revealed a very uncommon dynamic process: during the development
  of a nearby flare, two adjacent elongated filaments approached each
  other, merged at their middle sections, and separated again, thereby
  forming stable configurations with new footpoint connections. The
  observed dynamic pattern is indicative of "slingshot" reconnection
  between two magnetic flux ropes. We test this scenario by means
  of a three-dimensional zero β magnetohydrodynamic simulation,
  using a modified version of the coronal flux rope model by Titov
  and Démoulin as the initial condition for the magnetic field. To
  this end, a configuration is constructed that contains two flux
  ropes which are oriented side-by-side and are embedded in an ambient
  potential field. The choice of the magnetic orientation of the flux
  ropes and of the topology of the potential field is guided by the
  observations. Quasi-static boundary flows are then imposed to bring
  the middle sections of the flux ropes into contact. After sufficient
  driving, the ropes reconnect and two new flux ropes are formed,
  which now connect the former adjacent flux rope footpoints of opposite
  polarity. The corresponding evolution of filament material is modeled
  by calculating the positions of field line dips at all times. The dips
  follow the morphological evolution of the flux ropes, in qualitative
  agreement with the observed filaments.

Title: On Asymmetry of Magnetic Helicity in Emerging Active Regions:
    High-resolution Observations
Authors: Tian, Lirong; Démoulin, Pascal; Alexander, David; Zhu,
   Chunming
Bibcode: 2011ApJ...727...28T
Altcode: 2011arXiv1101.1068T
  We employ the DAVE (differential affine velocity estimator) tracking
  technique on a time series of Michelson Doppler Imager (MDI)/1 minute
  high spatial resolution line-of-sight magnetograms to measure the
  photospheric flow velocity for three newly emerging bipolar active
  regions (ARs). We separately calculate the magnetic helicity injection
  rate of the leading and following polarities to confirm or refute the
  magnetic helicity asymmetry, found by Tian &amp; Alexander using MDI/96
  minute low spatial resolution magnetograms. Our results demonstrate
  that the magnetic helicity asymmetry is robust, being present in
  the three ARs studied, two of which have an observed balance of the
  magnetic flux. The magnetic helicity injection rate measured is found to
  depend little on the window size selected, but does depend on the time
  interval used between the two successive magnetograms being tracked. It
  is found that the measurement of the magnetic helicity injection rate
  performs well for a window size between 12 × 10 and 18 × 15 pixels
  and at a time interval Δt = 10 minutes. Moreover, the short-lived
  magnetic structures, 10-60 minutes, are found to contribute 30%-50%
  of the magnetic helicity injection rate. Comparing with the results
  calculated by MDI/96 minute data, we find that the MDI/96 minute data,
  in general, can outline the main trend of the magnetic properties,
  but they significantly underestimate the magnetic flux in strong field
  regions and are not appropriate for quantitative tracking studies,
  so provide a poor estimate of the amount of magnetic helicity injected
  into the corona.

Title: Investigating the observational signatures of magnetic cloud
    substructure
Authors: Steed, K.; Owen, C. J.; Démoulin, P.; Dasso, S.
Bibcode: 2011JGRA..116.1106S
Altcode:
  Magnetic clouds (MCs) represent a subset of interplanetary coronal mass
  ejections (ICMEs) that exhibit a magnetic flux rope structure. They
  are primarily identified by smooth, large-scale rotations of the
  magnetic field. However, both small- and large-scale fluctuations of
  the magnetic field are observed within some magnetic clouds. We analyzed
  the magnetic field in the frames of the flux ropes, approximated using
  a minimum variance analysis (MVA), and have identified a small number
  of MCs within which multiple reversals of the gradient of the azimuthal
  magnetic field are observed. We herein use the term “substructure”
  to refer to regions that exhibit this signature. We examine, in detail,
  one such MC observed on 13 April 2006 by the ACE and WIND spacecraft
  and show that substructure has distinct signatures in both the magnetic
  field and plasma observations. We identify two thin current sheets
  within the substructure and find that they bound the region in which the
  observations deviate most significantly from those typically expected
  in MCs. The majority of these clouds are followed by fast solar wind
  streams, and a comparison of the properties of this magnetic cloud
  with five similar events reveals that they have lower nondimensional
  expansion rates than nonovertaken magnetic clouds. We discuss and
  evaluate several possible explanations for this type of substructure,
  including the presence of multiple flux ropes and warping of the MC
  structure, but we conclude that none of these scenarios is able to
  fully explain all of the aspects of the substructure observations.

Title: Study of solar flares and filament interaction in NOAA 10501
    on 20 November, 2003
Authors: Chandra, R.; Schmieder, B.; Mandrini, C. H.; Démoulin, P.;
   Pariat, E.; Török, T.; Aulanier, G.; Uddin, W.; Linton, M. G.
Bibcode: 2011ASInC...2..323C
Altcode:
  We analyze the observations of two flares from NOAA AR 10501 on 20
  November, 2003. The flares are homologous, exhibit four ribbons and
  are located in a quadrupolar magnetic configuration. The evolution
  of the ribbons suggests that the first eruption is triggered by
  "tether cutting" (with subsequent quadrupolar reconnection as in the
  "magnetic breakout" model), whereas the second one is consistent
  with the "magnetic breakout" model. Another interesting feature of
  our observations is the interaction of two filaments elongated in the
  north-south direction. The filaments merge at their central parts and
  afterwards change their orientation to the east-west direction. This
  merging and splitting is closely related to the evolution found in an
  MHD simulation as a result of reconnection between two flux ropes.

Title: Evolution of geoeffective ICMEs in the inner heliosphere
    (Invited)
Authors: Dasso, S.; Demoulin, P.; Gulisano, A. M.; Nakwacki, M.
Bibcode: 2010AGUFMSH43C..05D
Altcode:
  Over recent years, the new generation of space observations using
  multispacecraft fleets combined with high performance MHD numerical
  simulations and with new theoretical interpretations, have led to
  a very fruitful advance on our knowledge about the evolution of
  geoeffective transient structures of solar origin, from their birth
  in the low corona to their arrival at Earth. Interplanetary Coronal
  Mass Ejections (ICMEs) are the most geoeffective transients in the
  solar wind (SW), and the comparison between models and observations
  is one of the keys to clarify their dynamical evolution, mainly given
  by interaction with the environment. In this presentation we will
  examine some important physical processes, which can take place during
  the interaction ICME-SW and ICME-ICME, as drag, deviation from radial
  propagation, distortion of their inner configuration, and compression
  or expansion with the consequent intensification or weakening of the
  internal magnetic field. All these processes are crucial to determine
  the geoeffectiveness of an ICME reaching Earth.

Title: Expansion rate of Magnetic Clouds beyond Earth
Authors: Gulisano, A. M.; Dasso, S.; Demoulin, P.
Bibcode: 2010AGUFMSH43A1813G
Altcode:
  Magnetic Clouds (MCs) are interplanetary manifestations of transient
  structures erupted from the Sun. They are formed by strong helical
  magnetic field lines, and their configuration evolve accordingly to
  their interaction with the surrounding plasma. Due to the decay of the
  solar wind pressure for increasing heliodistance, and because their
  magnetic configuration remains as an entity during their evolution,
  MCs are objects in global expansion. When the MC is not perturbed by
  fast streams or other interplanetary transients, its expansion rate is
  expected to be in agreement with the rate of decay of total solar wind
  pressure, as it was recently confirmed by observations at the ecliptic
  plane in the inner heliosphere and near Earth. In this work we present
  results of the local expansion of MCs observed at heliodistances between
  one and five AUs. In particular, we compute the dimensionless expansion
  rate (ζ [Démoulin et al., Solar Physics, 2008]) using the MC bulk
  velocity profile in-situ observed by Ulysses. We analyze the dependence
  of ζ with heliodistance, MC size and other MC properties. As it was
  done previously for the inner heliosphere, we find now that when the MC
  is not perturbed by the environment (and thus it shows a linear bulk
  velocity profile) ζ is in a very good agreement with the expected
  global expansion.

Title: Tracking ICMEs from combining modeling, remote-sensing,
    and in-situ observations (Invited)
Authors: Dasso, S.; Demoulin, P.
Bibcode: 2010AGUFMSH52B..04D
Altcode:
  Remote-sensing and in-situ techniques can be used to model and
  track the evolution of a Coronal Mass Ejection (CME) from its solar
  eruption to its interplanetary manifestation (ICME), including the
  travel through the low corona and the solar wind (SW). The synergy
  from combining these different observational techniques have produced
  very important progresses in our understanding of these astrophysical
  objects, with important consequences on Sun-Earth connection and space
  weather. In particular, major advances have been obtained on identifying
  different substructures inside ICMEs, some times forming multiple flux
  ropes. Recent results obtained from these combined techniques will be
  given in this presentation, with special focus on new insights about
  magnetic properties and expansion of ICMEs, and physical processes
  that can take place during the interaction ICME-SW and ICME-ICME.

Title: Criteria for Flux Rope Eruption: Non-equilibrium Versus
    Torus Instability
Authors: Démoulin, P.; Aulanier, G.
Bibcode: 2010ApJ...718.1388D
Altcode: 2010arXiv1006.1785D
  The coronal magnetic configuration of an active region typically
  evolves quietly for a few days before becoming suddenly eruptive and
  launching a coronal mass ejection (CME). The precise origin of the
  eruption is still under debate. The loss of equilibrium, or an ideal
  magnetohydrodynamic (MHD) instability such as torus instability are
  among the several mechanisms that have proposed to be responsible for
  the sudden eruptions. Distinct approaches have also been formulated
  for limited cases having circular or translation symmetry. We
  revisit the previous theoretical approaches setting them in the same
  analytical framework. The coronal field results from the contribution
  of a non-neutralized current channel added to a background magnetic
  field, which in our model is the potential field generated by two
  photospheric flux concentrations. The evolution on short Alfvénic
  timescale is governed by ideal MHD. We first show analytically that
  the loss of equilibrium and the stability analysis are two different
  views of the same physical mechanism. Second, we identify that the
  same physics is involved in the instabilities of circular and straight
  current channels. Indeed, they are just two particular limiting cases
  of more general current paths. A global instability of the magnetic
  configuration is present when the current channel is located at
  a coronal height, h, large enough so that the decay index of the
  potential field, ∂ln |B <SUB>p</SUB>|/∂ln h, is larger than a
  critical value. At the limit of very thin current channels, previous
  analysis has found critical decay indices of 1.5 and 1 for circular
  and straight current channels, respectively. However, with current
  channels being deformable and as thick as that expected in the corona,
  we show that this critical index has similar values for circular and
  straight current channels, and is typically in the range [1.1,1.3].

Title: Long-Term Trend of Carbon Tetrachloride (CCl<SUB>4</SUB>)
    from Ground-Based High Resolution Infrared Solar Spectra Recroded
    at the Jungfraujoch
Authors: Rinsland, C.; Mahieu, E.; Demoulin, P.; Zander, R.; Chiou,
   L.; Hartmann, J. -M.
Bibcode: 2010mss..confEMJ10R
Altcode:
  The long-term trend of carbon tetrachloride (CCl<SUB>4</SUB>)
  has been retrieved from infrared high resolution solar absorption
  spectra encompassing the 1999 to 2010 time period. The measurements
  were recorded with a Fourier transform spectrometer at the northern
  mid-latitude, high altitude Jungfraujoch station in Switzerland
  (46.5°N latitude, 8.0°E longitude, 3580 m altitude). Total
  columns were derived from the region of the strong CCl<SUB>4</SUB>
  \upsilon<SUB>3</SUB> band at 794 cm<SUP>-1</SUP> accounting for all
  interfering molecules (e.g. H<SUB>2</SUB>O, O<SUB>3</SUB>) with
  significant improvement in the residuals obtained by also taking
  into account the line mixing in a nearby CO<SUB>2</SUB> Q branch, a
  procedure not implemented in previous remote sensing CCl<SUB>4</SUB>
  retrievals though its importance has been noted in several papers. The
  time series shows a statistically-significant long-term decrease in
  the CCl<SUB>4</SUB> total atmospheric burden of (-1.18 ±0.10 %/yr),
  at the 95% confidence level, using 2005 as reference. Furthermore,
  fit to the total column data set also reveals a seasonal cycle with
  a peak-to-peak amplitude of 10.2%, with minimum and maximum values
  found in mid-February and early August, respectively. This seasonal
  modulation can however be attributed to tropopause height changes
  throughout the season. The results quantify the continued impact of the
  regulations implemented by the Montreal Protocol and its strengthening
  amendments and adjustments for a molecule with high global warming
  potential. Although a statistically significant decrease in the total
  column is inferred, the CCl<SUB>4</SUB> molecule remains an important
  contributor to the stratospheric chlorine budget and burden.

Title: Coexisting Flux Rope and Dipped Arcade Sections Along One
    Solar Filament
Authors: Guo, Y.; Schmieder, B.; Démoulin, P.; Wiegelmann, T.;
   Aulanier, G.; Török, T.; Bommier, V.
Bibcode: 2010ApJ...714..343G
Altcode:
  We compute the three-dimensional magnetic field of an active
  region in order to study the magnetic configuration of active region
  filaments. The nonlinear force-free field model is adopted to compute
  the magnetic field above the photosphere, where the vector magnetic
  field was observed by THEMIS/MTR on 2005 May 27. We propose a new
  method to remove the 180° ambiguity of the transverse field. Next, we
  analyze the implications of the preprocessing of the data by minimizing
  the total force and torque in the observed vector fields. This step
  provides a consistent bottom boundary condition for the nonlinear
  force-free field model. Then, using the optimization method to compute
  the coronal field, we find a magnetic flux rope along the polarity
  inversion line. The magnetic flux rope aligns well with part of an Hα
  filament, while the total distribution of the magnetic dips coincides
  with the whole Hα filament. This implies that the magnetic field
  structure in one section of the filament is a flux rope, while the
  other is a sheared arcade. The arcade induced a left-bearing filament
  in the magnetic field of negative helicity, which is opposite to the
  chirality of barbs that a flux rope would induce in a magnetic field
  of the same helicity sign. The field strength in the center of the flux
  rope is about 700 G, and the twist of the field lines is ~1.4 turns.

Title: Evolution of magnetic clouds in the inner heliosphere
Authors: Gulisano, Adriana Maria; Démoulin, Pascal; Dasso, Sergio;
   Ruiz, Maria Emilia; Marsch, Eckart
Bibcode: 2010AIPC.1216..391G
Altcode:
  Magnetic clouds (MCs) are objects in expansion during their travel
  through the heliosphere. In situ observations indicate that their front
  travel faster than their back, showing a clear empirical signature
  of expansion. With the aim of quantifying the expansion rate of MCs
  in the inner heliosphere (0.3 to 1 AU), we present here a statistical
  study of events observed by the spacecraft Helios 1 and 2, during their
  complete period of operations. From the analysis of the profile of the
  MC magnetic field components in its local frame, which is obtained
  from a rotation of the observed magnetic field vectors to a system
  of reference oriented as the main axis of the flux rope, we revise a
  list of events identified in previous works and redefine improved MC
  boundaries/orientation for each event. We then split the sample into two
  subsets according to the characteristics of their velocity profiles,
  (a) those MCs with a significantly perturbed velocity profile due to
  the interaction with their surrounding solar wind (i.e. overtaken
  by streams) and (b) those that are not perturbed. We compute the
  dimensionless local expansion rate (ζ) for MCs defined by several
  works [e.g. Démoulin et al., Solar Phys, 250, 347-374 (2008)]. We find
  significantly different distribution of values for ζ when perturbed
  and non perturbed events are considered. Non perturbed MCs expand at
  rates ζ consistent with the expected value from the global pressure
  decay in the surrounding solar wind for increasing helio-distances,
  while perturbed ones may present strong departures from that global
  rule. We interpret these departures of ζ for perturbed MCs as a
  consequence of interaction with streams on their expansion.

Title: Interaction of ICMEs with the Solar Wind
Authors: Démoulin, Pascal
Bibcode: 2010AIPC.1216..329D
Altcode:
  Interplanetary Coronal Mass Ejections (ICMEs) are formed of plasma and
  magnetic field launched from the Sun into the Solar Wind (SW). These
  coherent magnetic structures, frequently formed by a flux rope,
  interact strongly with the SW. This interaction is reviewed by
  comparing the results obtained from in situ observations and numerical
  simulations. Like fast ships in the ocean, fast ICMEs drive an extended
  shock in front. ICMEs expand in all directions while traveling away
  from the Sun, a sheath of SW plasma and magnetic field accumulates in
  front of the ICME, which partially reconnects with the ICME magnetic
  field. Furthermore, not only do ICMEs have a profound impact on the
  heliosphere, but the type of SW encountered by an ICME has an important
  impact on its evolution (e.g. increase of mass, global deceleration,
  lost of magnetic flux and helicity, distortion of the configuration).

Title: Why proton temperature and velocity are correlated in the SW
    and not in ICMEs?
Authors: Démoulin, Pascal
Bibcode: 2010AIPC.1216..231D
Altcode:
  The in situ correlation of the proton temperature with the bulk plasma
  velocity of the solar wind (SW) is a firm result confirmed by several
  spacecraft, while in interplanetary coronal mass ejections (ICMEs)
  the proton temperature is both cooler and not correlated with the
  velocity. For some specific heating mechanism, the internal energy
  equation alone could provide a temperature increasing with velocity,
  but the increase remains much weaker than observed in the SW. In fact,
  it is shown here that the observed correlation is generically obtained
  from a global energy conservation in thermally driven winds. It results
  from the conversion of thermal to kinetic energy close to the Sun. The
  absence (or even anti-) correlation observed in situ between electron
  temperature and SW velocity, together with the correlation found for
  proton temperature, show that protons have a dominant role in the SW
  acceleration. In contrast, in ICMEs the plasma is contained by the
  magnetic field since ICMEs have both a closed configuration and a low
  plasma β. It implies no significant correlation between temperature and
  velocity, as observed. In conclusion, a different dominating term in the
  impulsion equation is the main origin of the different relation observed
  between the proton temperature and the bulk velocity in SW and ICMEs.

Title: Study of helicity properties of peculiar active regions
Authors: López Fuentes, M. C.; Mandrini, C. H.; Démoulin, P.
Bibcode: 2010IAUS..264..102L
Altcode: 2010IAUS..264..102F
  Peculiar solar active regions (ARs), such as δ-islands and other high
  tilt bipoles, are commonly associated with the emergence of severely
  deformed magnetic flux tubes. Therefore, the study of these ARs provides
  valuable information on the origin and evolution of magnetic structures
  in the solar interior. Here, we infer the magnetic helicity properties
  of the flux tubes associated to a set of peculiar ARs by studying
  the evolution of photospheric magnetograms (SOHO/MDI) and coronal
  observations (SOHO/EIT and TRACE) in combination with force-free models
  of the magnetic field. We discuss how our results relate to different
  models of the evolution of emerging magnetic flux tubes.

Title: Formation of Torus-Unstable Flux Ropes and Electric Currents
    in Erupting Sigmoids
Authors: Aulanier, G.; Török, T.; Démoulin, P.; DeLuca, E. E.
Bibcode: 2010ApJ...708..314A
Altcode:
  We analyze the physical mechanisms that form a three-dimensional
  coronal flux rope and later cause its eruption. This is achieved by a
  zero-β magnetohydrodynamic (MHD) simulation of an initially potential,
  asymmetric bipolar field, which evolves by means of simultaneous slow
  magnetic field diffusion and sub-Alfvénic, line-tied shearing motions
  in the photosphere. As in similar models, flux-cancellation-driven
  photospheric reconnection in a bald-patch (BP) separatrix transforms the
  sheared arcades into a slowly rising and stable flux rope. A bifurcation
  from a BP to a quasi-separatrix layer (QSL) topology occurs later on in
  the evolution, while the flux rope keeps growing and slowly rising,
  now due to shear-driven coronal slip-running reconnection, which
  is of tether-cutting type and takes place in the QSL. As the flux
  rope reaches the altitude at which the decay index -∂ln B/∂ln z
  of the potential field exceeds ~3/2, it rapidly accelerates upward,
  while the overlying arcade eventually develops an inverse tear-drop
  shape, as observed in coronal mass ejections (CMEs). This transition
  to eruption is in accordance with the onset criterion of the torus
  instability. Thus, we find that photospheric flux-cancellation and
  tether-cutting coronal reconnection do not trigger CMEs in bipolar
  magnetic fields, but are key pre-eruptive mechanisms for flux ropes to
  build up and to rise to the critical height above the photosphere at
  which the torus instability causes the eruption. In order to interpret
  recent Hinode X-Ray Telescope observations of an erupting sigmoid, we
  produce simplified synthetic soft X-ray images from the distribution
  of the electric currents in the simulation. We find that a bright
  sigmoidal envelope is formed by pairs of J-shaped field lines in the
  pre-eruptive stage. These field lines form through the BP reconnection
  and merge later on into S-shaped loops through the tether-cutting
  reconnection. During the eruption, the central part of the sigmoid
  brightens due to the formation of a vertical current layer in the wake
  of the erupting flux rope. Slip-running reconnection in this layer
  yields the formation of flare loops. A rapid decrease of currents due
  to field line expansion, together with the increase of narrow currents
  in the reconnecting QSL, yields the sigmoid hooks to thin in the early
  stages of the eruption. Finally, a slightly rotating erupting loop-like
  feature (ELLF) detaches from the center of the sigmoid. Most of this
  ELLF is not associated with the erupting flux rope, but with a current
  shell that develops within expanding field lines above the rope. Only
  the short, curved end of the ELLF corresponds to a part of the flux
  rope. We argue that the features found in the simulation are generic
  for the formation and eruption of soft X-ray sigmoids.

Title: The interplanetary magnetic field associated with the
    propagation of solar relativistic particles
Authors: Masson, Sophie; Dasso, Sergio; Demoulin, Pascal
Bibcode: 2010cosp...38.3009M
Altcode: 2010cosp.meet.3009M
  The origin and the propagation of relativistic solar particles
  (450 MeV-few GeV) in the inter-planetary medium remains a complex
  topic. These particles, detected at the Earth by neutron monitors
  (called Ground level enhancement, GLE), have been previously accelerated
  close to the Sun. Before being detected at the Earth, these relativistic
  particles have to travel along an interplanetary magnetic field (IMF)
  connecting the acceleration site and the Earth. Generally, the nominal
  Parker spiral (SP), is considered for ensuring the magnetic connection
  to the Earth. However, in most GLEs the IMF is highly disturbed,
  and the active regions (ARs) associated to the GLEs are not always
  located close to the footprint of the nominal Parker spiral. If it is
  not the nominal Parker spiral, which IMF connects the acceleration site
  and the Earth during the GLEs? A possible explanation of relativistic
  particles propagation under these circumstances are transient magnetic
  structures, travelling in the IMF as Interplanetary coronal mass
  ejections (ICMEs). In order to check this interpretation, we studied
  in detail the interplanetary medium in which 10 GLEs of the last solar
  cycle propagate. Using the magnetic field and the plasma parameter
  measurements (ACE/MAG and ACE/SWEPAM), we found widely different
  IMF configurations. Those included obvious cases of propagation in
  an ICME, as well as some cases consistent with a Parker Spiral. But,
  we also found cases correponding to the propagation of relativistic
  particles in a highly disturbed Parker like IMF. In an independant
  approach we applied the velocity dispersion method (VDA) to energetic
  protons measured by SoHO/ERNE and relativistic particles measured by
  the neutron monitor network. We determined the path length travelled by
  energetic particles. These lengths are fully consistent with the IMF
  shape determined previously. Thus, the length associated to particles
  propagating along the nominal Parker spiral is of the order of 1-1.2
  AU, contrary to the length associated with a distrubed interplanetary
  magnetic filed which is of order of 1.3-1.8 AU. For particles in
  an ICME, the velocity dispersion analysis gives a length approching
  2 AU. This is an important element when one want use the timing of
  particle arrival at Earth to identify type of solar activity that
  leads to the acceleration of these particles.

Title: Magnetic Flux Rope Eruption: Non Equilibrium versus Torus
    Instability
Authors: Demoulin, Pascal; Aulanier, Guillaume; Toeroek, Tibor;
   Deluca, Edward
Bibcode: 2010cosp...38.1855D
Altcode: 2010cosp.meet.1855D
  The coronal magnetic configuration of an active region typically
  evolves quietly during few days before becoming suddenly eruptive
  and launching a CME. The precise origin of the eruption is still
  debated. Among other mechanisms, it has been long proposed that a
  loss of equilibrium, or an ideal MHD instability such as the torus
  instability, could be responsible for the sudden eruptivity. We first
  revisit both approaches with simple analytical models as well as with
  a 3D MHD simulation of an initially potential bipolar field, which
  evolves by means of simultaneous slow magnetic field diffusion and
  shearing motions in the photosphere. Reconnection of sheared arcade
  leads to the formation of a twisted flux rope, which corresponds to an
  electric current channel. We find that the electric current distribution
  and the field-line organization present in the MHD simulation provide
  an explanation for the recent X-rays Hinode observations of erupting
  sigmoidal regions. Next, we show analytically that the loss of
  equilibrium and the torus instability are two different views of the
  same physical mechanism. We compare the instability thresholds in the
  limit of straight and circular current channels, finding that they are
  closely comparable for thick current channels (as present in the MHD
  simulation and as expected in the corona) while these thresholds are
  well distinct at the limit of very thin current channels (as typically
  found in previous studies). Finally, including photospheric line tying
  of the current channel in the analytical models permits to have a
  closer comparison between instability thresholds found analytically
  and by the MHD simulation.

Title: Magnetic reconnection along QSLs -a major driver of active
    region outflows
Authors: Baker, Deborah; van Driel-Gesztelyi, Lidia; Mandrini,
   Cristina H.; Demoulin, Pascal
Bibcode: 2010cosp...38.2926B
Altcode: 2010cosp.meet.2926B
  The relationship between quasi-separatrix layers (QSLs), or in the limit
  of infinitely thin QSLs, separatrices, and various activity phenomena
  has been explored in many different solar magnetic configurations
  across all scales in recent years. In the absence of magnetic nulls,
  fast reconnec-tion along QSLs, which are specific locations in the
  magnetic topology where field lines display strong gradients of
  magnetic connectivity, was identified as the main physical process
  at the origin of flares. Recently, it was shown that fast (tens of
  km/s) persistent hot plasma upflows in active regions (ARs) can also
  be linked to locations of QSLs. It is likely that these upflows that
  occur at the edges of ARs over unipolar magnetic field concentrations
  are accelerated by magnetic reconnection along QSLs. We will show
  multi-temperature spectral scan observations from Hinode's EIS combined
  with magnetic modeling of QSLs in two ARs observed on 20-21 February
  2007 and 11 January 2008. The latter AR is observed and modeled when
  it is in the vicinity of the solar central meridian where there are no
  projection effects, thereby eliminating ambiguity linking the origin
  of multi-temperature observations of AR upflows to QSLs. We use the
  Potential Source Surface Model to look for open field lines in the
  vicinity of upflows and QSL locations in order to demonstrate whether
  these upflows become outflows and can contribute to the solar wind.

Title: Global and local expansion of magnetic clouds in the inner
    heliosphere
Authors: Gulisano, A. M.; Démoulin, P.; Dasso, S.; Ruiz, M. E.;
   Marsch, E.
Bibcode: 2010A&A...509A..39G
Altcode: 2012arXiv1206.1112G
  Context. Observations of magnetic clouds (MCs) are consistent with the
  presence of flux ropes detected in the solar wind (SW) a few days after
  their expulsion from the Sun as coronal mass ejections (CMEs). <BR />
  Aims: Both the in situ observations of plasma velocity profiles and the
  increase of their size with solar distance show that MCs are typically
  expanding structures. The aim of this work is to derive the expansion
  properties of MCs in the inner heliosphere from 0.3 to 1 AU. <BR />
  Methods: We analyze MCs observed by the two Helios spacecraft using in
  situ magnetic field and velocity measurements. We split the sample in
  two subsets: those MCs with a velocity profile that is significantly
  perturbed from the expected linear profile and those that are not. From
  the slope of the in situ measured bulk velocity along the Sun-Earth
  direction, we compute an expansion speed with respect to the cloud
  center for each of the analyzed MCs. <BR /> Results: We analyze how
  the expansion speed depends on the MC size, the translation velocity,
  and the heliocentric distance, finding that all MCs in the subset of
  non-perturbed MCs expand with almost the same non-dimensional expansion
  rate (ζ). We find departures from this general rule for ζ only for
  perturbed MCs, and we interpret the departures as the consequence of
  a local and strong SW perturbation by SW fast streams, affecting the
  MC even inside its interior, in addition to the direct interaction
  region between the SW and the MC. We also compute the dependence of
  the mean total SW pressure on the solar distance and we confirm that
  the decrease of the total SW pressure with distance is the main origin
  of the observed MC expansion rate. We found that ζ was 0.91 ± 0.23
  for non-perturbed MCs while ζ was 0.48 ± 0.79 for perturbed MCs,
  the larger spread in the last ones being due to the influence of the
  solar wind local environment conditions on the expansion.

Title: Ejective events from a complex active region
Authors: Mandrini, Cristina H.; Chandra, Ramesh; Pariat, Etienne;
   Schmieder, Brigitte; Demoulin, Pascal; Toeroek, Tibor; Uddin, Wahab
Bibcode: 2010cosp...38.1886M
Altcode: 2010cosp.meet.1886M
  On 18 and 20 November 2003 active region (AR) 10501 produced a series of
  M flares all of them associated with coronal mass ejections (CMEs). The
  particularity of this AR is that while observational tracers of the
  magnetic helicity sign indicate that the large scale field in the
  region had a negative magnetic helicity sign, the MC associated
  to the most intense flare/CME on November 18 showed the opposite
  sign. Furthermore, the filaments observed on November 20 present
  morphological characteristics that correspond to a negative magnetic
  helicity sign, the rotation of the polarities of an emerging bipole
  indicate negative magnetic helicity sign injection; however, the flare
  ribbons observed after two homologous events can be connected either
  by field lines computed using a positive or a negative helicity sign
  magnetic field. We combine Hα, EUV, hard X-rays, and magnetic field
  data analysis with magnetic field modelling, and magnetic helicity
  injection computations to understand the origin of the helicity
  sign discrepancies discussed above. On November 20 magnetic field
  modeling and topology computations (in particular, the location of
  quasi-separatrix layers in relation to flare ribbons and evolution)
  give us clues about the CME initiation process.

Title: Actors of the main activity of large complex centres during
    the 23 Solar Cycle maximum
Authors: Schmieder, Brigitte; Chandra, Ramesh; Demoulin, Pascal;
   Mandrini, Cristina H.; Venkatakrishnan, P.; Manoharan, P. K.; Uddin,
   Wahab; Pariat, Etienne; Toeroek, Tibor; Molodij, Guillaume; Kumar, P.
Bibcode: 2010cosp...38.1861S
Altcode: 2010cosp.meet.1861S
  During the maximum of the last Solar Cycle solar cycle 23, large
  active regions had a long life spanning several solar rotations and
  produced a large number of X-ray class flares, CMEs and Magnetic
  clouds (MC). This was the case for the Halloween active regions in
  2003. The most geoeffective magnetic cloud of the cycle (Dst=-457)
  has its source in one passage of the active region (NOAA 10501) on
  November 18, 2003. Such an activity is presumably due to continuous
  emerging magnetic flux that was observed during this passage. Moreover,
  the region exhibited a complex topology with multiple domains of
  distinct magnetic helicities. The complexity is observed to reach
  such unprecedented levels that a detailed multi wavelength analysis
  is necessary to precisely identify the sources of CMEs and MCs.

Title: Analysis of Magnetic Clouds Evolution from 0.3 to 5
    Astronomical Units
Authors: Dasso, Sergio; Gulisano, Adriana Maria; Demoulin, Pascal;
   Marsch, Eckart
Bibcode: 2010cosp...38.1922D
Altcode: 2010cosp.meet.1922D
  Magnetic clouds (MCs) are transient structures in the solar wind,
  formed by large scale magnetic flux ropes as deduced from in situ
  observations of magnetic field. Moreover, in situ observations of
  the plasma velocity frequently show a clear evidence of an expansion
  in the radial direction from the Sun, unlike in the solar wind. This
  expansion has important consequences on the MC evolution, such as on
  the rates of decrease of mass density or magnetic field intensity. The
  aim of this work is to show properties of the evolution of MCs in
  the inner and outer heliosphere from 0.3 to 5 AUs. We present here an
  analysis of MCs observed by the Helios and Ulysses spacecraft, using
  in situ magnetic field and bulk plasma measurements. We analyze the
  dependence of several properties of MCs with the distance to the Sun,
  and in particular we analyze the dimensionless local expansion rate
  (ζ) [e.g. Démoulin et al., 2008]. We explore the dependence of
  the expansion speed on the MC size, the translation velocity, and
  the heliocentric distance, finding that there is a subset of MCs with
  almost the same non-dimensional expansion rate (ζ). The time velocity
  profile observed in this subset of MCs is almost linear, then we call
  them non perturbed MCs. These MCs expand at rates ζ consistent with
  the expected value from the global pressure decay in the surrounding
  solar wind for increasing helio-distances, while perturbed ones may
  present strong departures from that global rule. We interpret these
  departures of ζ for perturbed MCs as a consequence of the interaction
  of MCs with fast streams on their expansion.

Title: Magnetic Reconnection along Quasi-separatrix Layers as a
    Driver of Ubiquitous Active Region Outflows
Authors: Baker, D.; van Driel-Gesztelyi, L.; Mandrini, C. H.;
   Démoulin, P.; Murray, M. J.
Bibcode: 2009ApJ...705..926B
Altcode: 2009arXiv0909.4738B
  Hinode's EUV Imaging Spectrometer (EIS) has discovered ubiquitous
  outflows of a few to 50 km s<SUP>-1</SUP> from active regions
  (ARs). These outflows are most prominent at the AR boundary and
  appear over monopolar magnetic areas. They are linked to strong
  non-thermal line broadening and are stronger in hotter EUV lines. The
  outflows persist for at least several days. Using Hinode EIS and X-Ray
  Telescope observations of AR 10942 coupled with magnetic modeling,
  we demonstrate that the outflows originate from specific locations
  of the magnetic topology where field lines display strong gradients
  of magnetic connectivity, namely quasi-separatrix layers (QSLs),
  or in the limit of infinitely thin QSLs, separatrices. We found the
  strongest AR outflows to be in the vicinity of QSL sections located over
  areas of strong magnetic field. We argue that magnetic reconnection at
  QSLs separating closed field lines of the AR and either large-scale
  externally connected or "open" field lines is a viable mechanism for
  driving AR outflows which are likely sources of the slow solar wind.

Title: Magnetic cloud models with bent and oblate cross-section
    boundaries
Authors: Démoulin, P.; Dasso, S.
Bibcode: 2009A&A...507..969D
Altcode:
  Context: Magnetic clouds (MCs) are formed by magnetic flux ropes that
  are ejected from the Sun as coronal mass ejections. These structures
  generally have low plasma beta and travel through the interplanetary
  medium interacting with the surrounding solar wind. Thus, the dynamical
  evolution of the internal magnetic structure of a MC is a consequence
  of both the conditions of its environment and of its own dynamical laws,
  which are mainly dominated by magnetic forces. <BR />Aims: With in-situ
  observations the magnetic field is only measured along the trajectory
  of the spacecraft across the MC. Therefore, a magnetic model is needed
  to reconstruct the magnetic configuration of the encountered MC. The
  main aim of the present work is to extend the widely used cylindrical
  model to arbitrary cross-section shapes. <BR />Methods: The flux rope
  boundary is parametrized to account for a broad range of shapes. Then,
  the internal structure of the flux rope is computed by expressing the
  magnetic field as a series of modes of a linear force-free field. <BR
  />Results: We analyze the magnetic field profile along straight cuts
  through the flux rope, in order to simulate the spacecraft crossing
  through a MC. We find that the magnetic field orientation is only
  weakly affected by the shape of the MC boundary. Therefore, the MC
  axis can approximately be found by the typical methods previously used
  (e.g., minimum variance). The boundary shape affects the magnetic
  field strength most. The measurement of how much the field strength
  peaks along the crossing provides an estimation of the aspect ratio
  of the flux-rope cross-section. The asymmetry of the field strength
  between the front and the back of the MC, after correcting for the
  time evolution (i.e., its aging during the observation of the MC),
  provides an estimation of the cross-section global bending. A flat
  or/and bent cross-section requires a large anisotropy of the total
  pressure imposed at the MC boundary by the surrounding medium. <BR
  />Conclusions: The new theoretical model developed here relaxes
  the cylindrical symmetry hypothesis. It is designed to estimate the
  cross-section shape of the flux rope using the in-situ data of one
  spacecraft. This allows a more accurate determination of the global
  quantities, such as magnetic fluxes and helicity. These quantities
  are especially important for both linking an observed MC to its solar
  source and for understanding the corresponding evolution.

Title: Signatures of interchange reconnection: STEREO, ACE and Hinode
    observations combined
Authors: Baker, D.; Rouillard, A. P.; van Driel-Gesztelyi, L.;
   Démoulin, P.; Harra, L. K.; Lavraud, B.; Davies, J. A.; Opitz, A.;
   Luhmann, J. G.; Sauvaud, J. -A.; Galvin, A. B.
Bibcode: 2009AnGeo..27.3883B
Altcode: 2009arXiv0909.5624B
  Combining STEREO, ACE and Hinode observations has presented an
  opportunity to follow a filament eruption and coronal mass ejection
  (CME) on 17 October 2007 from an active region (AR) inside a coronal
  hole (CH) into the heliosphere. This particular combination of
  "open" and closed magnetic topologies provides an ideal scenario for
  interchange reconnection to take place. With Hinode and STEREO data
  we were able to identify the emergence time and type of structure
  seen in the in-situ data four days later. On the 21st, ACE observed
  in-situ the passage of an ICME with "open" magnetic topology. The
  magnetic field configuration of the source, a mature AR located
  inside an equatorial CH, has important implications for the solar and
  interplanetary signatures of the eruption. We interpret the formation of
  an "anemone" structure of the erupting AR and the passage in-situ of the
  ICME being disconnected at one leg, as manifested by uni-directional
  suprathermal electron flux in the ICME, to be a direct result of
  interchange reconnection between closed loops of the CME originating
  from the AR and "open" field lines of the surrounding CH.

Title: Why Do Temperature and Velocity Have Different Relationships
    in the Solar Wind and in Interplanetary Coronal Mass Ejections?
Authors: Démoulin, P.
Bibcode: 2009SoPh..257..169D
Altcode:
  In-situ observations of the solar wind (SW) show temperature increasing
  with the wind speed, whereas such a dependence is not observed in
  interplanetary coronal mass ejections (ICMEs). The aim of this paper
  is to understand the main origin of this correlation in the SW and its
  absence in ICMEs. For that purpose both the internal-energy and momentum
  equations are solved analytically with various approximations. The
  internal-energy equation does not provide a strong link between
  temperature and velocity, but the momentum equation does. Indeed, the
  observed correlation in the open magnetic-field configuration of the
  SW is the result of its acceleration and heating close to the Sun. In
  contrast, the magnetic configuration of ICMEs is closed, and moreover
  the momentum equation is dominated by magnetic forces. This implies no
  significant correlation between temperature and velocity, as observed.

Title: Causes and consequences of magnetic cloud expansion
Authors: Démoulin, P.; Dasso, S.
Bibcode: 2009A&A...498..551D
Altcode:
  Context: A magnetic cloud (MC) is a magnetic flux rope in the solar
  wind (SW), which, at 1 AU, is observed ~2-5 days after its expulsion
  from the Sun. The associated solar eruption is observed as a coronal
  mass ejection (CME). <BR />Aims: Both the in situ observations of
  plasma velocity distribution and the increase in their size with solar
  distance demonstrate that MCs are strongly expanding structures. The
  aim of this work is to find the main causes of this expansion and
  to derive a model to explain the plasma velocity profiles typically
  observed inside MCs. <BR />Methods: We model the flux rope evolution
  as a series of force-free field states with two extreme limits: (a)
  ideal magneto-hydrodynamics (MHD) and (b) minimization of the magnetic
  energy with conserved magnetic helicity. We consider cylindrical
  flux ropes to reduce the problem to the integration of ordinary
  differential equations. This allows us to explore a wide variety
  of magnetic fields at a broad range of distances to the Sun. <BR
  />Results: We demonstrate that the rapid decrease in the total SW
  pressure with solar distance is the main driver of the flux-rope
  radial expansion. Other effects, such as the internal over-pressure,
  the radial distribution, and the amount of twist within the flux rope
  have a much weaker influence on the expansion. We demonstrate that any
  force-free flux rope will have a self-similar expansion if its total
  boundary pressure evolves as the inverse of its length to the fourth
  power. With the total pressure gradient observed in the SW, the radial
  expansion of flux ropes is close to self-similar with a nearly linear
  radial velocity profile across the flux rope, as observed. Moreover,
  we show that the expansion rate is proportional to the radius and to
  the global velocity away from the Sun. <BR />Conclusions: The simple
  and universal law found for the radial expansion of flux ropes in the
  SW predicts the typical size, magnetic structure, and radial velocity
  of MCs at various solar distances.

Title: Coronal loops, flare ribbons and aurora during slip-running
Authors: Schmieder, Brigitte; Aulanier, Guillaume; Démoulin, Pascal;
   Pariat, Etienne
Bibcode: 2009EP&S...61..565S
Altcode: 2009EP&S...61L.565S
  Solar two ribbon flares are commonly explained by magnetic field
  reconnections in the low corona. During the reconnection energetic
  particles (electrons and protons) are accelerated from the reconnection
  site. These particles are following the magnetic field lines down
  to the chromosphere. As the plasma density is higher in these lower
  layers, there are collisions and emission of radiation. Thus bright
  ribbons are observed at both ends of flare loops. These ribbons are
  typically observed in Hα and in EUV with SoHO and TRACE. As the
  time is going, these ribbons are expanding away of each other. In
  most studied models, the reconnection site is a separator line,
  where two magnetic separatrices intersect. They define four distinct
  connectivity domains, across which the magnetic connectivity changes
  discontinuously. In this paper, we present a generalization of this
  model to 3D complex magnetic topologies where there are no null points,
  but quasi-separatrices layers instead. In that case, while the ribbons
  spread away during reconnection, we show that magnetic field lines
  can quickly slip along them. We propose that this new phenomenon could
  explain fast extension of Hα and TRACE 1600 Å ribbons, fast moving
  HXR footpoints along the ribbons as observed by RHESSI, and that it
  is observed in soft X rays with Hinode/XRT.

Title: Modelling and observations of photospheric magnetic helicity
Authors: Démoulin, P.; Pariat, E.
Bibcode: 2009AdSpR..43.1013D
Altcode:
  Mounting observational evidence of the emergence of twisted magnetic
  flux tubes through the photosphere have now been published. Such flux
  tubes, formed by the solar dynamo and transported through the convection
  zone, eventually reach the solar atmosphere. Their accumulation in
  the solar corona leads to flares and coronal mass ejections. Since
  reconnections occur during the evolution of the flux tubes, the concepts
  of twist and magnetic stress become inappropriate. Magnetic helicity,
  as a well preserved quantity, in particular in plasma with high magnetic
  Reynolds number, is a more suitable physical quantity to use, even
  if reconnection is involved. <P />Only recently, it has been realized
  that the flux of magnetic helicity can be derived from magnetogram time
  series. This paper reviews the advances made in measuring the helicity
  injection rate at the photospheric level, mostly in active regions. It
  relates the observations to our present theoretical understanding of
  the emergence process. Most of the helicity injection is found during
  magnetic flux emergence, whereas the effect of differential rotation
  is small, and the long-term evolution of active regions is still
  puzzling. The photospheric maps of the injection of magnetic helicity
  provide new spatial information about the basic properties of the link
  between the solar activity and its sub-photospheric roots. Finally,
  the newest techniques to measure photospheric flows are reviewed.

Title: The link between CME-associated dimmings and interplanetary
    magnetic clouds
Authors: Mandrini, Cristina H.; Nakwacki, María S.; Attrill, Gemma;
   van Driel-Gesztelyi, Lidia; Dasso, Sergio; Démoulin, Pascal
Bibcode: 2009IAUS..257..265M
Altcode:
  Coronal dimmings often develop in the vicinity of erupting magnetic
  configurations. It has been suggested that they mark the location of
  the footpoints of ejected flux ropes and, thus, their magnetic flux can
  be used as a proxy for the ejected flux. If so, this quantity can be
  compared to the flux in the associated interplanetary magnetic cloud
  (MC) to find clues about the origin of the ejected flux rope. In the
  context of this interpretation, we present several events for which
  we have done a comparative solar-interplanetary analysis. We combine
  SOHO/Extreme Ultraviolet Imaging Telescope (EIT) data and Michelson
  Doppler Imager (MDI) magnetic maps to identify and measure the flux
  in the dimmed regions. We model the associated MCs and compute their
  magnetic flux using in situ observations. We find that the magnetic
  fluxes in the dimmings and MCs are compatible in some events; though
  this is not the case for large-scale and intense eruptions that occur in
  regions that are not isolated from others. We conclude that, in these
  particular cases, a fraction of the dimmed regions can be formed by
  reconnection between the erupting field and the surrounding magnetic
  structures, via a stepping process that can also explain other CME
  associated events.

Title: Linking two consecutive nonmerging magnetic clouds with their
    solar sources
Authors: Dasso, S.; Mandrini, C. H.; Schmieder, B.; Cremades, H.; Cid,
   C.; Cerrato, Y.; Saiz, E.; Démoulin, P.; Zhukov, A. N.; Rodriguez,
   L.; Aran, A.; Menvielle, M.; Poedts, S.
Bibcode: 2009JGRA..114.2109D
Altcode: 2009JGRA..11402109D; 2012arXiv1212.5546D
  On 15 May 2005, a huge interplanetary coronal mass ejection (ICME) was
  observed near Earth. It triggered one of the most intense geomagnetic
  storms of solar cycle 23 (Dst <SUB> peak </SUB> = -263 nT). This
  structure has been associated with the two-ribbon flare, filament
  eruption, and coronal mass ejection originating in active region 10759
  (NOAA number). We analyze here the sequence of events, from solar wind
  measurements (at 1 AU) and back to the Sun, to understand the origin
  and evolution of this geoeffective ICME. From a detailed observational
  study of in situ magnetic field observations and plasma parameters
  in the interplanetary (IP) medium and the use of appropriate models
  we propose an alternative interpretation of the IP observations,
  different to those discussed in previous studies. In our view, the
  IP structure is formed by two extremely close consecutive magnetic
  clouds (MCs) that preserve their identity during their propagation
  through the interplanetary medium. Consequently, we identify two
  solar events in Hα and EUV which occurred in the source region
  of the MCs. The timing between solar and IP events, as well as the
  orientation of the MC axes and their associated solar arcades are in
  good agreement. Additionally, interplanetary radio type II observations
  allow the tracking of the multiple structures through inner heliosphere
  and pin down the interaction region to be located midway between the
  Sun and the Earth. The chain of observations from the photosphere to
  interplanetary space is in agreement with this scenario. Our analysis
  allows the detection of the solar sources of the transients and explains
  the extremely fast changes of the solar wind due to the transport of
  two attached (though nonmerging) MCs which affect the magnetosphere.

Title: Flux Rope Eruption From the Sun to the Earth: What do Reversals
    in the Azimuthal Magnetic Field Gradient Tell us About the Evolution
    of the Magnetic Structure?
Authors: Steed, K.; Owen, C. J.; Harra, L. K.; Green, L. M.; Dasso,
   S.; Walsh, A. P.; Démoulin, P.; van Driel-Gesztelyi, L.
Bibcode: 2008AGUFMSH23B1638S
Altcode:
  Using ACE in situ data we identify and describe an interplanetary
  magnetic cloud (MC) observed near Earth on 13 April 2006. We also use
  multi-instrument and multi-wavelength observations from SOHO, TRACE and
  ground-based solar observatories to determine the solar source of this
  magnetic cloud. A launch window for the MC between 9 and 11 April 2006
  was estimated from the propagation time of the ejecta observed near
  Earth. A number of large active regions were present on the Sun during
  this period, which were initially considered to be the most likely
  candidate source regions of the MC. However, it was determined that
  the solar source of the MC was a small, spotless active region observed
  in the Northern Hemisphere. Following an eruption from this region on
  11 April 2006, the ACE spacecraft detected, 59 h later, the passage of
  the MC, preceded by the arrival of a weak, forward fast shock. The link
  between the eruption in this active region and the interplanetary MC is
  supported by several pieces of evidence, including the location of the
  solar source near to the disk centre and to the east of the central
  meridian (in agreement with the spacecraft trajectory through the
  western leg of the magnetic cloud), the propagation time of the ejecta,
  the agreement between the amount of flux in the magnetic cloud and in
  the active region, and the agreement between the signs of helicity of
  the magnetic cloud and the active region (which differs from the sign
  of helicity of each of the other active regions on the Sun at this
  time). In addition, the active region is located on the boundary of
  a coronal hole, and a high speed solar wind stream originating from
  this region is observed near Earth shortly after the passage of the
  magnetic cloud. This event highlights the complexities associated
  with locating the solar source of an ICME observed near Earth, and
  serves to emphasise that it is the combination of a number of physical
  characteristics and signatures that is important for successfully
  tying together the Earth-end and the Sun-end of an event. Further
  investigation of this MC has revealed some sub-structure towards its
  centre, observed as a small scale reversal of the azimuthal magnetic
  field of the MC, similar to that reported by Dasso et al., 2007. We
  explore several possible explanations for this signature, including
  the occurrence of multiple flux ropes and/or warping of the magnetic
  cloud. We also consider whether magnetic reconnection plays a role in
  creating the geometry that would explain these observations.

Title: The Recovery of CME-Related Dimmings and the ICME's Enduring
    Magnetic Connection to the Sun
Authors: Attrill, G. D. R.; van Driel-Gesztelyi, L.; Démoulin, P.;
   Zhukov, A. N.; Steed, K.; Harra, L. K.; Mandrini, C. H.; Linker, J.
Bibcode: 2008SoPh..252..349A
Altcode: 2008SoPh..tmp..158A
  It is generally accepted that transient coronal holes (TCHs, dimmings)
  correspond to the magnetic footpoints of CMEs that remain rooted in
  the Sun as the CME expands out into the interplanetary space. However,
  the observation that the average intensity of the 12 May 1997 dimmings
  recover to their pre-eruption intensity in SOHO/EIT data within 48
  hours, whilst suprathermal unidirectional electron heat fluxes are
  observed at 1 AU in the related ICME more than 70 hours after the
  eruption, leads us to question why and how the dimmings disappear
  whilst the magnetic connectivity is maintained. We also examine two
  other CME-related dimming events: 13 May 2005 and 6 July 2006. We study
  the morphology of the dimmings and how they recover. We find that, far
  from exhibiting a uniform intensity, dimmings observed in SOHO/EIT data
  have a deep central core and a more shallow extended dimming area. The
  dimmings recover not only by shrinking of their outer boundaries but
  also by internal brightenings. We quantitatively demonstrate that the
  model developed by Fisk and Schwadron (Astrophys. J.560, 425, 2001)
  of interchange reconnections between "open" magnetic field and small
  coronal loops is a strong candidate for the mechanism facilitating the
  recovery of the dimmings. This process disperses the concentration of
  "open" magnetic field (forming the dimming) out into the surrounding
  quiet Sun, thus recovering the intensity of the dimmings whilst still
  maintaining the magnetic connectivity to the Sun.

Title: A review of the quantitative links between CMEs and magnetic
    clouds
Authors: Démoulin, P.
Bibcode: 2008AnGeo..26.3113D
Altcode:
  Magnetic clouds (MCs), and more generally, interplanetary coronal mass
  ejections (ICMEs), are believed to be the interplanetary counterparts
  of CMEs. The link has usually been shown by taking into account the CME
  launch position on the Sun, the expected time delay and by comparing the
  orientation of the coronal and interplanetary magnetic field. Making
  such a link more quantitative is challenging since it requires a
  relation between very different kinds of magnetic field measurements:
  (i) photospheric magnetic maps, which are observed from a distant
  vantage point (remote sensing) and (ii) in-situ measurements of MCs,
  which provide precise, directly measured, magnetic field data merely
  from one-dimensional linear samples. The association between events
  in these different domains can be made using adequate coronal and MC
  models. Then, global quantities like magnetic fluxes and helicity can
  be derived and compared. This review paper describes all the general
  trends found in the above association criteria. A special focus is
  given for the cases which do not follow the earlier derived mean laws
  since interesting physics is usually involved.

Title: Why are CMEs large-scale coronal events: nature or nurture?
Authors: van Driel-Gesztelyi, L.; Attrill, G. D. R.; Démoulin, P.;
   Mandrini, C. H.; Harra, L. K.
Bibcode: 2008AnGeo..26.3077V
Altcode:
  The apparent contradiction between small-scale source regions of,
  and large-scale coronal response to, coronal mass ejections (CMEs)
  has been a long-standing puzzle. For some, CMEs are considered to
  be inherently large-scale events eruptions in which a number of flux
  systems participate in an unspecified manner, while others consider
  magnetic reconnection in special global topologies to be responsible
  for the large-scale response of the lower corona to CME events. Some
  of these ideas may indeed be correct in specific cases. However,
  what is the key element which makes CMEs large-scale? Observations
  show that the extent of the coronal disturbance matches the angular
  width of the CME an important clue, which does not feature strongly
  in any of the above suggestions. We review observational evidence
  for the large-scale nature of CME source regions and find them
  lacking. Then we compare different ideas regarding how CMEs evolve
  to become large-scale. The large-scale magnetic topology plays an
  important role in this process. There is amounting evidence, however,
  that the key process is magnetic reconnection between the CME and other
  magnetic structures. We outline a CME evolution model, which is able
  to account for all the key observational signatures of large-scale
  CMEs and presents a clear picture how large portions of the Sun become
  constituents of the CME. In this model reconnection is driven by the
  expansion of the CME core resulting from an over-pressure relative to
  the pressure in the CME's surroundings. This implies that the extent of
  the lower coronal signatures match the final angular width of the CME.

Title: Locating the solar source of 13 April 2006 magnetic cloud
Authors: Steed, K.; Owen, C. J.; Harra, L. K.; Green, L. M.; Dasso,
   S.; Walsh, A. P.; Démoulin, P.; van Driel-Gesztelyi, L.
Bibcode: 2008AnGeo..26.3159S
Altcode:
  Using Advanced Composition Explorer (ACE) in situ data we identify and
  describe an interplanetary magnetic cloud (MC) observed near Earth
  on 13 April 2006. We also use multi-instrument and multi-wavelength
  observations from the Solar and Heliospheric Observatory (SOHO), the
  Transition Region and Coronal Explorer (TRACE) and ground-based solar
  observatories to determine the solar source of this magnetic cloud. A
  launch window for the MC between 9 and 11 April 2006 was estimated from
  the propagation time of the ejecta observed near Earth. A number of
  large active regions (ARs) were present on the Sun during this period,
  which were initially considered to be the most likely candidate source
  regions of the MC. However, it was determined that the solar source
  of the MC was a small, spotless active region observed in the Northern
  Hemisphere. Following an eruption from this region on 11 April 2006, the
  ACE spacecraft detected, 59 h later, the passage of the MC, preceded by
  the arrival of a weak, forward fast shock. The link between the eruption
  in this active region and the interplanetary MC is supported by several
  pieces of evidence, including the location of the solar source near to
  the disk centre and to the east of the central meridian (in agreement
  with the spacecraft trajectory through the western leg of the magnetic
  cloud), the propagation time of the ejecta, the agreement between
  the amount of flux in the magnetic cloud and in the active region,
  and the agreement between the signs of helicity of the magnetic cloud
  and the active region (which differs from the sign of helicity of each
  of the other active regions on the Sun at this time). In addition,
  the active region is located on the boundary of a coronal hole, and a
  high speed solar wind stream originating from this region is observed
  near Earth shortly after the passage of the magnetic cloud.

Title: Multi-scale reconnections in a complex CME
Authors: van Driel-Gesztelyi, L.; Goff, C. P.; Démoulin, P.; Culhane,
   J. L.; Matthews, S. A.; Harra, L. K.; Mandrini, C. H.; Klein, K. -L.;
   Kurokawa, H.
Bibcode: 2008AdSpR..42..858V
Altcode:
  A series of three flares of GOES class M, M and C, and a CME were
  observed on 20 January 2004 occurring in close succession in NOAA
  10540. Types II, III, and N radio bursts were associated. We use
  the combined observations from TRACE, EIT, Hα images from Kwasan
  Observatory, MDI magnetograms, GOES, and radio observations from
  Culgoora and Wind/ WAVES to understand the complex development of this
  event. We reach three main conclusions. First, we link the first two
  impulsive flares to tether-cutting reconnections and the launch of
  the CME. This complex observation shows that impulsive quadrupolar
  flares can be eruptive. Second, we relate the last of the flares, an
  LDE, to the relaxation phase following forced reconnections between
  the erupting flux rope and neighbouring magnetic field lines, when
  reconnection reverses and restores some of the pre-eruption magnetic
  connectivities. Finally, we show that reconnection with the magnetic
  structure of a previous CME launched about 8 h earlier injects electrons
  into open field lines having a local dip and apex (located at about six
  solar radii height). This is observed as an N-burst at decametre radio
  wavelengths. The dipped shape of these field lines is due to large-scale
  magnetic reconnection between expanding magnetic loops and open field
  lines of a neighbouring streamer. This particular situation explains
  why this is the first N-burst ever observed at long radio wavelengths.

Title: Twist, Writhe and Rotation of Magnetic Flux Ropes in Filament
    Eruptions and Coronal Mass Ejections
Authors: Török, T.; Berger, M. A.; Kliem, B.; Démoulin, P.; Linton,
   M.; van Driel-Gesztelyi, L.
Bibcode: 2008ESPM...12.3.54T
Altcode:
  We present the first quantitative analysis of the conversion of twist
  into writhe in the course of ideal MHD instabilities in erupting coronal
  magnetic flux ropes. For our analysis, we consider numerical simulations
  of two instabilities which have been suggested as trigger and initial
  driving mechanisms in filament eruptions and coronal mass ejections,
  namely the helical kink instability and the torus instability. We
  use two different coronal flux rope models as initial conditions
  in the simulations, namely the cylindrical Gold-Hoyle equilibrium
  and the toroidal Titov-Demoulin equilibrium. <P />For each model, we
  perform a series of simulations with different amounts of initial flux
  rope twist. In order to study both confined and ejective eruptions,
  we additionally use different initial potential fields overlying
  the flux rope in the simulations of the Titov-Demoulin model. <P
  />In all simulations, we measure the writhe of the flux rope and the
  corresponding rotation of its axis in vertical projection by making use
  of recently developed expressions which permit us to calculate writhe as
  a single integral in space. We discuss the implications of our results
  for filament eruptions, coronal mass ejections and magnetic clouds.

Title: Expected in Situ Velocities from a Hierarchical Model for
    Expanding Interplanetary Coronal Mass Ejections
Authors: Démoulin, P.; Nakwacki, M. S.; Dasso, S.; Mandrini, C. H.
Bibcode: 2008SoPh..250..347D
Altcode: 2008SoPh..tmp..121D
  In situ data provide only a one-dimensional sample of the plasma
  velocity along the spacecraft trajectory crossing an interplanetary
  coronal mass ejection (ICME). Then, to understand the dynamics of ICMEs
  it is necessary to consider some models to describe it. We derive
  a series of equations in a hierarchical order, from more general to
  more specific cases, to provide a general theoretical basis for the
  interpretation of in situ observations, extending and generalizing
  previous studies. The main hypothesis is a self-similar expansion,
  but with the freedom of possible different expansion rates in three
  orthogonal directions. The most detailed application of the equations is
  though for a subset of ICMEs, magnetic clouds (MCs), where a magnetic
  flux rope can be identified. The main conclusions are the following
  ones. First, we obtain theoretical expressions showing that the observed
  velocity gradient within an ICME is not a direct characteristic of its
  expansion, but that it depends also on other physical quantities such
  as its global velocity and acceleration. The derived equations quantify
  these dependencies for the three components of the velocity. Second,
  using three different types of data we show that the global acceleration
  of ICMEs has, at most, a small contribution to the in situ measurements
  of the velocity. This eliminates practically one contribution to the
  observed velocity gradient within ICMEs. Third, we provide a method to
  quantify the expansion rate from velocity data. We apply it to a set
  of 26 MCs observed by Wind or ACE spacecrafts. They are typical MCs,
  and their main physical parameters cover the typical range observed
  in MCs in previous statistical studies. Though the velocity difference
  between their front and back includes a broad range of values, we find
  a narrow range for the determined dimensionless expansion rate. This
  implies that MCs are expanding at a comparable rate, independently of
  their size or field strength, despite very different magnitudes in
  their velocity profiles. Furthermore, the equations derived provide
  a base to further analyze the dynamics of MCs/ICMEs.

Title: Analysis of large scale MHD quantities in expanding magnetic
    clouds
Authors: Nakwacki, María Soledad; Dasso, Sergio; Mandrini, Cristina
   Hemilse; Démoulin, Pascal
Bibcode: 2008JASTP..70.1318N
Altcode:
  Magnetic clouds (MCs) transport the magnetic flux and helicity released
  by the Sun. They are generally modeled as a static flux rope traveling
  in the solar wind, though they can present signatures of expansion. We
  analyze three expanding MCs using a self-similar free radial expansion
  model with a cylindrical linear force-free field (i.e., Lundquist
  solution) as the initial condition. We derive expressions for the
  magnetic fluxes, the magnetic helicity and the magnetic energy per
  unit length along the flux tube. We find that these quantities do not
  differ more than 25% when using the static or expansion model.

Title: Non-Linear Force-Free Field Modeling of a Solar Active Region
    Around the Time of a Major Flare and Coronal Mass Ejection
Authors: De Rosa, M. L.; Schrijver, C. J.; Metcalf, T. R.; Barnes,
   G.; Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann,
   T.; Wheatland, M.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann,
   M.; Kusano, K.; Régnier, S.; Thalmann, J.
Bibcode: 2008AGUSMSP31A..06D
Altcode:
  Solar flares and coronal mass ejections are associated with rapid
  changes in coronal magnetic field connectivity and are powered by
  the partial dissipation of electrical currents that run through
  the solar corona. A critical unanswered question is whether the
  currents involved are induced by the advection along the photosphere
  of pre-existing atmospheric magnetic flux, or whether these currents
  are associated with newly emergent flux. We address this problem by
  applying nonlinear force-free field (NLFFF) modeling to the highest
  resolution and quality vector-magnetographic data observed by the
  recently launched Hinode satellite on NOAA Active Region 10930 around
  the time of a powerful X3.4 flare in December 2006. We compute 14
  NLFFF models using 4 different codes having a variety of boundary
  conditions. We find that the model fields differ markedly in geometry,
  energy content, and force-freeness. We do find agreement of the best-fit
  model field with the observed coronal configuration, and argue (1)
  that strong electrical currents emerge together with magnetic flux
  preceding the flare, (2) that these currents are carried in an ensemble
  of thin strands, (3) that the global pattern of these currents and
  of field lines are compatible with a large-scale twisted flux rope
  topology, and (4) that the ~1032~erg change in energy associated with
  the coronal electrical currents suffices to power the flare and its
  associated coronal mass ejection. We discuss the relative merits of
  these models in a general critique of our present abilities to model
  the coronal magnetic field based on surface vector field measurements.

Title: Nonlinear Force-free Field Modeling of a Solar Active Region
    around the Time of a Major Flare and Coronal Mass Ejection
Authors: Schrijver, C. J.; DeRosa, M. L.; Metcalf, T.; Barnes, G.;
   Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann, T.;
   Wheatland, M. S.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann,
   M.; Kusano, K.; Régnier, S.; Thalmann, J. K.
Bibcode: 2008ApJ...675.1637S
Altcode: 2007arXiv0712.0023S
  Solar flares and coronal mass ejections are associated with rapid
  changes in field connectivity and are powered by the partial dissipation
  of electrical currents in the solar atmosphere. A critical unanswered
  question is whether the currents involved are induced by the motion of
  preexisting atmospheric magnetic flux subject to surface plasma flows or
  whether these currents are associated with the emergence of flux from
  within the solar convective zone. We address this problem by applying
  state-of-the-art nonlinear force-free field (NLFFF) modeling to the
  highest resolution and quality vector-magnetographic data observed
  by the recently launched Hinode satellite on NOAA AR 10930 around
  the time of a powerful X3.4 flare. We compute 14 NLFFF models with
  four different codes and a variety of boundary conditions. We find
  that the model fields differ markedly in geometry, energy content,
  and force-freeness. We discuss the relative merits of these models in
  a general critique of present abilities to model the coronal magnetic
  field based on surface vector field measurements. For our application
  in particular, we find a fair agreement of the best-fit model field
  with the observed coronal configuration, and argue (1) that strong
  electrical currents emerge together with magnetic flux preceding the
  flare, (2) that these currents are carried in an ensemble of thin
  strands, (3) that the global pattern of these currents and of field
  lines are compatible with a large-scale twisted flux rope topology,
  and (4) that the ~10<SUP>32</SUP> erg change in energy associated with
  the coronal electrical currents suffices to power the flare and its
  associated coronal mass ejection.

Title: CME-related dimmings as a signature of interplanetary magnetic
    cloud footpoints
Authors: Mandrini, Cristina H.; Soledad Nakwacki, Ms Maria; Attrill,
   Gemma; van Driel-Gesztelyi, Lidia; Dasso, Sergio; Demoulin, Pascal
Bibcode: 2008cosp...37.1900M
Altcode: 2008cosp.meet.1900M
  Coronal dimmings are often present on both sides of erupting magnetic
  configurations. It has been suggested that dimmings mark the location
  of the footpoints of ejected flux ropes and, thus, their magnetic
  flux can be used as a proxy for the flux involved in the ejection. If
  so, this quantity can be compared to the flux in the associated
  interplanetary magnetic cloud to find clues about the origin of the
  ejected flux rope. In the context of this physical interpretation,
  we analyse several events, flares and coronal mass ejections (CMEs),
  for which we can find their interplanetary counterpart. We combine
  SOHO/Extreme Ultraviolet Imaging Telescope data and Michelson Doppler
  Imager magnetic maps to identify and measure the flux in the dimming
  regions. We model the associated clouds and compute their magnetic
  flux using in situ observations. We find that the magnetic fluxes of
  the dimmings and magnetic clouds are compatible in some cases; though
  this is not the case for large-scale events and eruptions that occur
  in regions that are not isolated from other flux concentrations. We
  conclude that the interpretation of dimmings requires a deeper analysis
  of the global magnetic field configuration, since at least a fraction
  of the dimmed regions could be formed by reconnection between the
  erupting field and the surrounding magnetic structures.

Title: Interaction between emerging flux and coronal hole -
    observations and simulations
Authors: van Driel-Gesztelyi, Lidia; Baker, Deborah; Murray, Michelle;
   Demoulin, Pascal; Attrill, Gemma; Matthews, Sarah A.; Mandrini,
   Cristina H.; Toeroek, Tibor
Bibcode: 2008cosp...37.3288V
Altcode: 2008cosp.meet.3288V
  Flux emergence in the vicinity of or inside a coronal hole (CH) is
  expected to induce magnetic reconnection between the closed emerging
  and open CH magnetic field lines, resulting in an evolution of the
  CH as formerly closed field lines become topologically open, while at
  the same time, open field lines close down. Through two case studies
  we show observational signatures of this (interchange) reconnection
  process and discuss its implications. First, using SOHO EIT and MDI
  data, we study a small active region (AR10869) emerging in the close
  vicinity of a low-latitude coronal hole in April 2006. The interfacing
  magnetic polarities between the AR and the CH were opposite, favourable
  for magnetic reconnection. We indeed observe the coupled formation of
  bright closed loops between the CH and the AR and coronal dimming on
  the far side of the AR, which we interpret as evidence of interchange
  reconnection. This process effectively modifies the CH boundary
  (making it retreat), while simultaneously displacing open field lines
  to the far side of the AR. In order to study this process in detail,
  we perform 2.5D MHD simulations, which qualitatively reproduce important
  aspects of the observations. We expect to find upflows of plasma at the
  location where previously closed field lines are opening up as well as
  on the reconnecting side, but since we had no spectroscopic data for
  this event, we can not verify this. Therefore we analyze Hinode/EIS
  line-of-sight velocity maps of another low-latitude CH with a small AR
  in its midst observed on 18 Oct. 2007. We find that while closed loops
  of the bipole are dominated by downflows in the Fe XII, Fe XIII and
  Fe XV lines, the strongest coronal plasma upflows are indeed located
  around and particularly at the "far side" of the bipolar AR, i.e. having
  the same polarity as the dominant polarity of the CH. The emerging
  biplole and the series of interchange reconnections it induces create
  a significant additional plasma upflow in the CH, thus we identify
  this outflow must contribute to the acceleration of the fast solar wind.

Title: Magnetic Clouds: Global and local expansion
Authors: Gulisano, Adriana; Demoulin, Pascal; Soledad Nakwacki,
   Ms Maria; Dasso, Sergio; Emilia Ruiz, Maria
Bibcode: 2008cosp...37.1113G
Altcode: 2008cosp.meet.1113G
  Magnetic clouds (MCs) are magnetized objects forming flux ropes,
  which are expelled from the Sun and travel through the heliosphere,
  transporting important amounts of energy, mass, magnetic flux, and
  magnetic helicity from the Sun to the interplanetary medium. To know
  the detailed dynamical evolution of MCs is very useful to improve the
  knowledge of solar processes, for instance from linking a transient
  solar source with its interplanetary manifestation. During its
  travel, and mainly due to the decrease of the total (magnetic plus
  thermal) pressure in the surrounding solar wind, MCs are objects in
  expansion. However, the detailed magnetic structure and the dynamical
  evolution of MCs is still not fully known. Even the identification of
  their boundaries is an open question in some cases. In a previous work
  we have shown that from onepoint observations of the bulk velocity
  profile, it is possible to infer the 'local' expansion rate for a
  given MC, i.e., the expansion rate while the MC is observed by the
  spacecraft. By the another hand, and from the comparison of sizes for
  different MCs observed at different heliodistances, it is possible
  to quantify an 'average' expansion law (i.e., a global expansion). In
  this work, in order to study the variability of the 'local' expansion
  with respect to the 'average' expansion of MCs during their travel,
  we present results and a comparison between both approaches. We make a
  detailed study of one-point observations (magnetic and bulk velocity)
  using a set of MCs and we get the 'local' expansion rate for each
  studied event. We compare the obtained 'local' expansion rates with
  the 'average' expansion law, and also with the expansion rates for
  the stationary solar wind.

Title: Modelling and observations of photospheric helicity
Authors: Demoulin, Pascal
Bibcode: 2008cosp...37..694D
Altcode: 2008cosp.meet..694D
  There is mounting observational evidence of the emergence of twisted
  magnetic flux tubes through the photosphere. Such flux tubes are formed
  by the solar dynamo, then transported through the convection zone and
  eventually reach the solar atmosphere. Their accumulation in the solar
  corona leads to flares and coronal mass ejections. Since a series of
  reconnections occur during the evolution of the flux tubes, the notions
  of twist and magnetic stress become inappropriate. However, since
  magnetic helicity is a well preserved quantity, even in the presence of
  reconnection, it is a suitable physical quantity to use. Until recently,
  the main difficulty was that its observational estimations involved
  the determination of the vector potential of the magnetic field, a
  quantity which cannot be deduced from observations. Only relatively
  recently it has been realized that the magnetic helicity flux can be
  derived from magnetogram time series. In addition, only the vertical
  component of the magnetic field and the photospheric flux-tube motions
  are needed to obtain a good estimation of the total helicity flux. The
  photospheric maps for the injection of magnetic helicity provide a
  new spatial information about the basic properties of the link between
  the solar activity and its sub-photospheric roots.

Title: Are Constant Loop Widths an Artifact of the Background and
    the Spatial Resolution?
Authors: López Fuentes, M. C.; Démoulin, P.; Klimchuk, J. A.
Bibcode: 2008ApJ...673..586L
Altcode: 2007arXiv0704.0637L
  We study the effect of the coronal background in the determination
  of the diameter of EUV loops, and we analyze the suitability of
  the procedure followed in a previous paper for characterizing their
  expansion properties. For the analysis we create different synthetic
  loops, and we place them on real backgrounds from data obtained
  with the Transition Region and Coronal Explorer (TRACE). We apply to
  these loops the same procedure followed in our previous works, and we
  compare the results with real loop observations. We demonstrate that
  the procedure allows us to distinguish constant width loops from loops
  that expand appreciably with height, as predicted by simple force-free
  field models. This holds even for loops near the resolution limit. The
  procedure can easily determine when loops are below the resolution
  limit and therefore not reliably measured. We find that small-scale
  variations in the measured loop width are likely due to imperfections
  in the background subtraction. The greatest errors occur in especially
  narrow loops and in places where the background is especially bright
  relative to the loop. We stress, however, that these effects do not
  impact the ability to measure large-scale variations. The result that
  observed loops do not expand systematically with height is robust.

Title: Acceleration and expansion of interplanetary coronal mass
    ejections
Authors: Soledad Nakwacki, Maria; Demoulin, Pascal; Dasso, Sergio;
   Mandrini, Cristina H.
Bibcode: 2008cosp...37.2171S
Altcode: 2008cosp.meet.2171S
  Coronal mass ejections (CMEs) are solar eruptions that release huge
  amounts of magnetized plasma into the interplanetary medium. When
  a CME is observed in the interplanetary space, it is called an ICME
  (interplanetary coronal mass ejection). These heliospheric counterparts
  can be identified from the surrounding solar wind because of their
  particular characteristics. In their travel from the Sun, ICMEs expand
  and accelerate. However, from single spacecraft observations, expansion
  and acceleration cannot be distinguished from each other. In this work,
  we take a new approach to study the acceleration and expansion of
  ICMEs, which is based on the assumption of a self-similar expansion
  with a different rate in each direction. To decouple the effects of
  expansion and acceleration, we use multi-spacecraft observations.

Title: Breaking or maintaining magnetic connection of CMEs to the
    Sun - solar vs. interplanetary signatures tested
Authors: van Driel-Gesztelyi, Lidia; Attrill, Gemma; Demoulin, Pascal;
   Mandrini, Cristina H.; Harra, Louise K.
Bibcode: 2008cosp...37.3287V
Altcode: 2008cosp.meet.3287V
  Though their relationship is complex, the presence of suprathermal
  unior bi-directional electron streams in ICMEs are treated as
  signatures of magnetic field lines with one or both ends being
  connected to the Sun, respectively, while their absence is
  interpreted as disconnection. However, do we have any reliable
  signature in the solar corona distinguishing between maintained
  connection and disconnection? We test two solar signatures against
  interplanetary suprathermal electron signatures in order to establish
  their relevance. We test the hypothesis that the recovery of Transient
  Coronal Holes (TCHs, dimming regions corresponding to the footpoints of
  CMEs) is a signature of magnetic disconnection from the Sun. Through
  three case studies we quantitatively demonstrate that magnetic
  reconnections between field lines of the expanded CME magnetic field
  and small coronal loops can act to disperse the concentration of
  CME footpoints (forming the dimming region) out into the surrounding
  quiet Sun, thus recovering the intensity of the dimming region whilst
  still maintaining the magnetic connectivity to the Sun. This analysis
  provides evidence that the recovery of coronal dimming regions can,
  in fact, be simply reconciled with maintained magnetic connectivity
  to the Sun. However, disconnection can occur when open field lines are
  involved in reconnection with CMEs. We show through two well-observed
  case studies that magnetic reconnection between the expanding CME and
  a nearby coronal hole (CH) is indeed able to disconnect one leg of
  the expanding CME magnetic structure, as indicated by uni-directional
  electron streams in their respective ICMEs. Therefore we suggest that
  brightenings (signatures of reconnection) appearing along a coronal
  hole boundary in the wake of a CME can be treated as a signature of
  (at least partial) disconnection of one of the CME legs from the Sun.

Title: Coronal ``wave'': A signature of the mechanism making CMEs
    large-scale in the low corona?
Authors: Attrill, G. D. R.; Harra, L. K.; van Driel-Gesztelyi, L.;
   Démoulin, P.; Wülser, J. -P.
Bibcode: 2007AN....328..760A
Altcode:
  We analyse one of the first coronal waves observed by STEREO/EUVI
  associated with a source region just behind the limb, NOAA 10940. We
  apply the coronal ``wave'' model proposed by Attrill et al. (2007) to
  explain the evolution of the observed bright fronts, thereby arguing
  that the bright fronts and dimmings are due to magnetic reconnections
  between the expanding CME core and surrounding magnetic structures. We
  offer a discussion showing that this model provides a mechanism via
  which CMEs, expanding from a small source region can naturally become
  large-scale in the low corona.

Title: Progressive Transformation of a Flux Rope to an
    ICME. Comparative Analysis Using the Direct and Fitted Expansion
    Methods
Authors: Dasso, S.; Nakwacki, M. S.; Démoulin, P.; Mandrini, C. H.
Bibcode: 2007SoPh..244..115D
Altcode: 2007arXiv0706.2889D
  The solar wind conditions at one astronomical unit (AU) can be strongly
  disturbed by interplanetary coronal mass ejections (ICMEs). A subset,
  called magnetic clouds (MCs), is formed by twisted flux ropes that
  transport an important amount of magnetic flux and helicity, which
  is released in CMEs. At 1 AU from the Sun, the magnetic structure
  of MCs is generally modeled by neglecting their expansion during
  the spacecraft crossing. However, in some cases, MCs present a
  significant expansion. We present here an analysis of the huge
  and significantly expanding MC observed by the Wind spacecraft
  during 9 - 10 November 2004. This MC was embedded in an ICME. After
  determining an approximate orientation for the flux rope using the
  minimum variance method, we obtain a precise orientation of the cloud
  axis by relating its front and rear magnetic discontinuities using a
  direct method. This method takes into account the conservation of the
  azimuthal magnetic flux between the inbound and outbound branches and
  is valid for a finite impact parameter (i.e., not necessarily a small
  distance between the spacecraft trajectory and the cloud axis). The
  MC is also studied using dynamic models with isotropic expansion. We
  have found (6.2±1.5)×10<SUP>20</SUP> Mx for the axial flux and
  (78±18)×10<SUP>20</SUP> Mx for the azimuthal flux. Moreover, using
  the direct method, we find that the ICME is formed by a flux rope (MC)
  followed by an extended coherent magnetic region. These observations
  are interpreted by considering the existence of a previously larger
  flux rope, which partially reconnected with its environment in the
  front. We estimate that the reconnection process started close to the
  Sun. These findings imply that the ejected flux rope is progressively
  peeled by reconnection and transformed to the observed ICME (with a
  remnant flux rope in the front part).

Title: Erratum: ``Identification of a Peculiar Radio Source
    in the Aftermath of Large Coronal Mass Ejection Events'' (<A
    href="/abs/2007ApJ...656L.105V">ApJ, 656, L105 [2007]</A>)
Authors: Vourlidas, Angelos; Pick, Monique; Hoang, Sang; Démoulin,
   Pascal
Bibcode: 2007ApJ...665L.179V
Altcode:
  In our recent Letter (A. Vourlidas et al. [<A
  href="/abs/2007ApJ...656L.105V">ApJ, 656, L105 [2007]</A>], hereafter
  Paper I), we determined the azimuth and elevation of our radio source
  with a direction-finding algorithm (Paper I, Fig. 4) assuming that
  the source emission dominates over the galactic background. This is
  generally true for type III emissions that are mainly used for these
  analyses. However, this condition does not necessarily hold for weaker
  emissions such as the broadband continuum source in our Letter. As the
  source intensity decreases to near the Galactic background level, the
  source direction shifts toward the direction of the Galactic center. It
  is therefore important to subtract the background before deriving
  source directions, which we did not do in Paper I. This correction
  has now been applied to the WIND WAVES data reported in Figure 4
  of Paper I. As a result, there is no more significant drift in the
  source elevation or azimuth. The radio continuum source remains along
  the ecliptic plane as do other radio bursts observed in association
  with this coronal mass ejection (CME) event. <P />This correction
  does not significantly alter our proposed scenarios for the origin of
  the broadband source. The emission could still arise from electrons
  injected in nearby structures originating from interactions between
  the expanding CME and closed coronal loops or from the closing down of
  previously opened loops. Our velocity estimations are also unaffected
  by the corrections on the source location. They still suggest that
  the continuum propagates too slowly to be the CME shock. However, we
  must point out that M. J. Reiner, M. L. Kaiser, &amp; J.-L. Bougeret
  (<A href="/abs/2007ApJ...656L.105V">ApJ, 656, L105 [2007]</A>) modeled
  this event as a type II source deriving an initial speed of 3000 km
  s<SUP>-1</SUP>, a strong deceleration of 41 ms<SUP>-2</SUP> lasting
  for about 15 hr, followed by an almost constant propagation to the
  Earth. As the authors acknowledge in their paper, these parameters
  were obtained using a simple generic speed profile. Currently, there
  are no independent observations or theoretical predictions that
  show such a velocity profile for interplanetary CMEs. On the other
  hand, patchy, drifting structures that are typical signatures of
  interplanetary type II bursts are clearly seen in the radio spectrum
  after 14:30 UT but at a higher frequency than that of our continuum
  source. Similar patchy emissions are seen until a shock signature at
  Earth on September 24 at 21:00 UT. So a type II source is present in
  the spectrum. <P />Our initial intention with this work was to bring
  attention to the possibility that the conventional interpretation,
  as type II emission from a CME-driven shock, for low-frequency
  drifting continua might not hold true for all cases. We suggested
  in Paper I that the emission mechanism of this continuum could be
  gyrosynchrotron from nonthermal electrons. Recently, T. S. Bastian
  (ApJ, 665, 805 [2007]) proposed incoherent synchrotron emission from
  electrons entrained in the CME as an alternative explanation for such
  smooth type II-like sources. Therefore, we may be confronted with
  a new phenomenon, and we clearly need more studies to pin down the
  physical mechanism. <P />We are grateful to M. Reiner for pointing
  out the need for correction of our direction-finding results and for
  providing a preprint of M. J. Reiner, M. L. Kaiser, &amp; J.-L. Bougeret
  (<A href="/abs/2007ApJ...656L.105V">ApJ, 656, L105 [2007]</A>).

Title: Are CME-Related Dimmings Always a Simple Signature of
    Interplanetary Magnetic Cloud Footpoints?
Authors: Mandrini, C. H.; Nakwacki, M. S.; Attrill, G.; van
   Driel-Gesztelyi, L.; Démoulin, P.; Dasso, S.; Elliott, H.
Bibcode: 2007SoPh..244...25M
Altcode:
  Coronal dimmings are often present on both sides of erupting magnetic
  configurations. It has been suggested that dimmings mark the location
  of the footpoints of ejected flux ropes and, thus, their magnetic
  flux can be used as a proxy for the flux involved in the ejection. If
  so, this quantity can be compared to the flux in the associated
  interplanetary magnetic cloud to find clues about the origin of the
  ejected flux rope. In the context of this physical interpretation,
  we analyze the event, flare, and coronal mass ejection (CME) that
  occurred in active region 10486 on 28 October 2003. The CME on this
  day is associated with large-scale dimmings, located on either side of
  the main flaring region. We combine SOHO/Extreme Ultraviolet Imaging
  Telescope data and Michelson Doppler Imager magnetic maps to identify
  and measure the flux in the dimming regions. We model the associated
  cloud and compute its magnetic flux using in situ observations from
  the Magnetometer Instrument and the Solar Wind Electron Proton Alpha
  Monitor aboard the Advance Composition Explorer. We find that the
  magnetic fluxes of the dimmings and magnetic cloud are incompatible, in
  contrast to what has been found in previous studies. We conclude that,
  in certain cases, especially in large-scale events and eruptions that
  occur in regions that are not isolated from other flux concentrations,
  the interpretation of dimmings requires a deeper analysis of the global
  magnetic configuration, since at least a fraction of the dimmed regions
  is formed by reconnection between the erupting field and the surrounding
  magnetic structures.

Title: Coronal "wave": Magnetic Footprint Of A Cme?
Authors: Attrill, Gemma; Harra, L. K.; van Driel-Gesztelyi, L.;
   Demoulin, P.; Wuelser, J.
Bibcode: 2007AAS...210.2921A
Altcode: 2007BAAS...39..141A
  We propose a new mechanism for the generation of "EUV coronal
  waves". This work is based on new analysis of data from SOHO/EIT,
  SOHO/MDI &amp; STEREO/EUVI. Although first observed in 1997, the
  interpretation of coronal waves as flare-induced or CME-driven remains
  a debated topic. We investigate the properties of two "classical"
  SOHO/EIT coronal waves in detail. The source regions of the associated
  CMEs possess opposite helicities &amp; the coronal waves display
  rotations in opposite senses. We observe deep dimmings near the
  flare site &amp; also widespread diffuse dimming, accompanying the
  expansion of the EIT wave. We report a new property of these EIT
  waves, namely, that they display dual brightenings: persistent ones
  at the outermost edge of the core dimming regions &amp; simultaneously
  diffuse brightenings constituting the leading edge of the coronal wave,
  surrounding the expanding diffuse dimmings. We show that such behaviour
  is consistent with a diffuse EIT wave being the magnetic footprint of
  a CME. We propose a new mechanism where driven magnetic reconnections
  between the skirt of the expanding CME &amp; quiet-Sun magnetic loops
  generate the observed bright diffuse front. The dual brightenings &amp;
  widespread diffuse dimming are identified as innate characteristics
  of this process. In addition we present some of the first analysis
  of a STEREO/EUVI limb coronal wave. We show how the evolution of the
  diffuse bright front &amp; dimmings can be understood in terms of the
  model described above. We show that an apparently stationary part of
  the bright front can be understood in terms of magnetic interchange
  reconnections between the expanding CME &amp; the "open" magnetic
  field of a low-latitude coronal hole. We use both the SOHO/EIT &amp;
  STEREO/EUVI events to demonstrate that through successive reconnections,
  this new model provides a natural mechanism via which CMEs can become
  large-scale in the lower corona.

Title: Slip running reconnection in the Sun's atmosphere observed
    by RHESSI, SOHO, TRACE and Hinode
Authors: Schmieder, B.; Aulanier, G.; Démoulin, P.; Pariat, E.;
   Golub, L.
Bibcode: 2007AGUSMSH22A..01S
Altcode:
  Solar double ribbon flares are commonly explained by magnetic field
  reconnections in the high corona. The bright ribbons, typically
  observed in Halpha, in EUV with SoHO, TRACE correspond to the ends
  of the reconnected loops. In most studied cases, the reconnection
  site is an X-point, where two magnetic separatrices intersect. In
  this presentation, we show a generalization of this model to 3D
  complex magnetic topologies where there are no null points, but
  quasi-separatrices layers instead. In that case, while the ribbons
  spread away during reconnection, we show that magnetic field lines
  can quickly slip along them. We propose that this new phenomenon
  could explain also fast moving HXR footpoints as observed by RHESSI,
  and that it may be observed in soft X rays with XRT.

Title: Coronal Loops Really Do Have Constant Cross Sections!
Authors: Klimchuk, James A.; Lopez Fuentes, M.; Demoulin, P.
Bibcode: 2007AAS...210.9111K
Altcode: 2007BAAS...39..205K
  The observation that coronal loops do not expand systematically
  with height has been one of the more intriguing puzzles in solar
  physics. Simple force-free magnetic field models based on extrapolated
  magnetograms predict a much larger expansion than is observed. It
  has been suggested that the cross section uniformity is an artifact
  of inadequate spatial resolution, complex background emission, or
  both. For example, loops that are everywhere thinner than the instrument
  point spread function (PSF) would be seen to have a nearly constant
  thickness even if they actually expand. We have argued previously
  that actual loops are wide enough to rule out this possibility. Our
  present work also rules out the background emission as a possible
  explanation. We have simulated TRACE observations in the following
  manner. We constructed synthetic loops with both uniform and expanding
  cross sections, convolved them with the PSF, and placed them on actual
  TRACE images. We then measured the widths of the loops using the same
  technique used in our earlier studies of real observations. We find
  that expanding loops can be readily distinguished from loops with
  a constant cross section. Thus, the enigma remains! We tentatively
  suggest that constant cross sections are a consequence of the complex
  internal structure of loops (e.g., loops as bundles of tangled elemental
  strands). We are confident that this can explain the observed symmetry
  of loops, but whether it can also explain the lack of systematic
  expansion with height is not at all clear.

Title: A Multiple Flare Scenario where the Classic Long-Duration
    Flare Was Not the Source of a CME
Authors: Goff, C. P.; van Driel-Gesztelyi, L.; Démoulin, P.; Culhane,
   J. L.; Matthews, S. A.; Harra, L. K.; Mandrini, C. H.; Klein, K. L.;
   Kurokawa, H.
Bibcode: 2007SoPh..240..283G
Altcode:
  A series of flares (GOES class M, M and C) and a CME were observed in
  close succession on 20 January 2004 in NOAA 10540. Radio observations,
  which took the form of types II, III and N bursts, were associated with
  these events. We use the combined observations from TRACE, EIT, Hα
  images from Kwasan, MDI magnetograms and GOES to understand the complex
  development of this event. Contrary to a standard interpretation,
  we conclude that the first two impulsive flares are part of the CME
  launch process while the following long-duration event flare represents
  simply the recovery phase. Observations show that the flare ribbons
  not only separate but also shift along the magnetic inversion line
  so that magnetic reconnection progresses stepwise to neighboring flux
  tubes. We conclude that "tether cutting" reconnection in the sheared
  arcade progressively transforms it to a twisted flux tube, which
  becomes unstable, leading to a CME. We interpret the third flare,
  a long-duration event, as a combination of the classical two-ribbon
  flare with the relaxation process following forced reconnection between
  the expanding CME structure and neighboring magnetic fields.

Title: Decametric N Burst: A Consequence of the Interaction of Two
    Coronal Mass Ejections
Authors: Démoulin, P.; Klein, K. -L.; Goff, C. P.; van
   Driel-Gesztelyi, L.; Culhane, J. L.; Mandrini, C. H.; Matthews, S. A.;
   Harra, L. K.
Bibcode: 2007SoPh..240..301D
Altcode:
  Radio emissions of electron beams in the solar corona and interplanetary
  space are tracers of the underlying magnetic configuration and of
  its evolution. We analyse radio observations from the Culgoora and
  WIND/WAVES spectrographs, in combination with SOHO/LASCO and SOHO/MDI
  data, to understand the origin of a type N burst originating from NOAA
  AR 10540 on January 20, 2004, and its relationship with type II and
  type III emissions. All bursts are related to the flares and the CME
  analysed in a previous paper (Goff et al., 2007). A very unusual feature
  of this event was a decametric type N burst, where a type III-like
  burst, drifting towards low frequencies (negative drift), changes drift
  first to positive, then again to negative. At metre wavelengths, i.e.,
  heliocentric distances ≲1.5R<SUB>⊙</SUB>, these bursts are ascribed
  to electron beams bouncing in a closed loop. Neither U nor N bursts are
  expected at decametric wavelengths because closed quasi-static loops
  are not thought to extend to distances ≫1.5R<SUB>⊙</SUB>. We take
  the opportunity of the good multi-instrument coverage of this event to
  analyse the origin of type N bursts in the high corona. Reconnection
  of the expanding ejecta with the magnetic structure of a previous CME,
  launched about 8 hours earlier, injects electrons in the same manner as
  with type III bursts but into open field lines having a local dip and
  apex. The latter shape was created by magnetic reconnection between
  the expanding CME and neighbouring (open) streamer field lines. This
  particular flux tube shape in the high corona, between 5R<SUB>⊙</SUB>
  and 10R<SUB>⊙</SUB>, explains the observed type N burst. Since the
  required magnetic configuration is only a transient phenomenon formed
  by reconnection, severe timing and topological constraints are present
  to form the observed decametric N burst. They are therefore expected
  to be rare features.

Title: Identification of a Peculiar Radio Source in the Aftermath
    of Large Coronal Mass Ejection Events
Authors: Vourlidas, Angelos; Pick, Monique; Hoang, Sang; Démoulin,
   Pascal
Bibcode: 2007ApJ...656L.105V
Altcode:
  We report the discovery of a new radio feature associated with coronal
  mass ejection (CME) events. The feature is a low-frequency (&lt;1 MHz),
  relatively wide (~300 kHz) continuum that appears just after the main
  phase of the eruptive event, lasts for several hours, and exhibits a
  slow negative frequency drift. So far, we have identified this radio
  signature in a handful of CME events and suspect it might be a common
  occurrence. The radio continuum starts almost simultaneously with the
  commonly observed decimetric type IV stationary continuum (also called
  flare continuum), but the two seem unrelated. The emission mechanism,
  whether plasma emission or gyroresonance, is unclear at the moment. On
  the basis of our preliminary analysis, we interpret this radio continuum
  as the lateral interaction of the CME with magnetic structures. Another
  possibility is that this continuum traces the reconfiguration of
  large-scale loop systems, such as streamers. In other words, it could
  be the large-scale counterpart of the post-CME arcades seen over active
  region neutral lines after big CME events. This Letter aims to bring
  attention to this feature and attract more research into its nature.

Title: Coronal ``Wave'': Magnetic Footprint of a Coronal Mass
    Ejection?
Authors: Attrill, Gemma D. R.; Harra, Louise K.; van Driel-Gesztelyi,
   Lidia; Démoulin, Pascal
Bibcode: 2007ApJ...656L.101A
Altcode:
  We investigate the properties of two ``classical'' EUV Imaging Telescope
  (EIT) coronal waves. The two source regions of the associated coronal
  mass ejections (CMEs) possess opposite helicities, and the coronal waves
  display rotations in opposite senses. We observe deep core dimmings
  near the flare site and also widespread diffuse dimming, accompanying
  the expansion of the EIT wave. We also report a new property of these
  EIT waves, namely, that they display dual brightenings: persistent ones
  at the outermost edge of the core dimming regions and simultaneously
  diffuse brightenings constituting the leading edge of the coronal wave,
  surrounding the expanding diffuse dimmings. We show that such behavior
  is consistent with a diffuse EIT wave being the magnetic footprint of
  a CME. We propose a new mechanism where driven magnetic reconnections
  between the skirt of the expanding CME magnetic field and quiet-Sun
  magnetic loops generate the observed bright diffuse front. The dual
  brightenings and the widespread diffuse dimming are identified as
  innate characteristics of this process.

Title: Estimation of the bias of the Minimum Variance technique in
    the determination of magnetic clouds global quantities and orientation
Authors: Gulisano, A. M.; Dasso, S.; Mandrini, C. H.; Démoulin, P.
Bibcode: 2007AdSpR..40.1881G
Altcode:
  Magnetic clouds (MCs) are highly magnetized plasma structures that
  have a low proton temperature and a magnetic field vector that
  rotates when seen by a heliospheric observer. More than 25 years of
  observations of magnetic and plasma properties of MCs at 1 AU have
  provided significant knowledge of their magnetic structure. However,
  because in situ observations only give information along the trajectory
  of the spacecraft, their real 3D magnetic configuration remains still
  partially unknown. We generate a set of synthetic clouds, exploring
  the space of parameters that represents the possible orientations
  and minimum distances of the satellite trajectory to the cloud axis,
  p. The synthetic clouds have a local cylindrical symmetry and a linear
  force-free magnetic configuration. From the analysis of synthetic
  clouds, we quantify the errors introduced in the determination of the
  orientation/size (and, consequently, of the global magnetohydrodynamic
  quantities) by the Minimum Variance method when p is not zero.

Title: From The Photosphere to the Interplanetary Medium: The Magnetic
    Helicity Sign from Observations
Authors: Luoni, M. L.; Mandrini, C. H.; Dasso, S.; Démoulin, P.;
   Van Driel-Gesztelyi, L.
Bibcode: 2007BAAA...50...43L
Altcode:
  The helicity sign of the solar magnetic field exhibits a hemispheric
  preference. On a certain statistical base, it is negative (positive)
  in the northern (southern) hemisphere. In this work we study a set of
  active regions, observed from 1997 to 2001, for which we can determine
  the magnetic helicity sign from the evolution of their polarities during
  flux emergence. We confirm this sign analyzing the coronal field of
  the studied regions. Then, we combine this analysis with ``in situ''
  observations of the magnetic clouds associated with the coronal mass
  ejections that occurred in those regions. Finally, we find that the
  helicity sign predicted by the distribution of the photospheric flux
  agrees with the one observed at coronal and interplanetary level.

Title: What is the role of magnetic null points in large flares?
Authors: Schmieder, B.; Mandrini, C. H.; Démoulin, P.; Aulanier,
   G.; Li, H.; Berlicki, A.
Bibcode: 2007AdSpR..39.1840S
Altcode:
  We have performed the analysis of the magnetic topology of active
  region NOAA 10486 before two large flares occurring on October 26
  and 28, 2003. The 3D extrapolation of the photospheric magnetic field
  shows the existence of magnetic null points when using two different
  methods. We use TRACE 1600 Å and 195 Å brightenings as tracers of
  the energy release due to magnetic reconnections. We conclude on the
  three following points: The small events observed before the flares are
  related to low lying null points. They are long lasting and associated
  with low energy release. They are not triggering the large flares. <P
  />On October 26, a high altitude null point is found. We look for
  bright patches that could correspond to the signatures of coronal
  reconnection at the null point in TRACE 1600 Å images. However,
  such bright patches are not observed before the main flare, they are
  only observed after it. <P />On October 28, four ribbons are observed
  in TRACE images before the X17 flare. We interpret them as due to a
  magnetic breakout reconnection in a quadrupolar configuration. There
  is no magnetic null point related to these four ribbons, and this
  reconnection rather occurs at quasi-separatrix layers (QSLs). <P />We
  conclude that the existence of a null point in the corona is neither
  a sufficient nor a necessary condition to give rise to large flares.

Title: Computing magnetic energy and helicity fluxes from series of
    magnetograms .
Authors: Démoulin, P.; Pariat, E.
Bibcode: 2007MmSAI..78..136D
Altcode:
  Magnetic energy and helicity fluxes can now be derived from measurements
  of the photospheric magnetic and velocity fields. We show that
  only photospheric flux-tube motions are needed to estimate the full
  fluxes. The derived maps of flux densities permit to localize where
  energy and helicity input occurs in active regions (ARs). The precision
  of the energy flux density is dominantly limited by the precision
  obtained on the transverse component of the magnetic field. On the
  contrary, the helicity flux density requires only the measurement of
  the vertical component of the magnetic field. Previously, the magnetic
  helicity maps were strongly affected by a false definition of the
  helicity flux density involving the magnetic vector potential. Applied
  to observations, this approach introduces important fake polarities. We
  define a better helicity flux density; it reduces the fake polarities by
  more than an order of magnitude. The spatial distribution of helicity
  injected into the studied ARs is much more coherent than previously
  thought, and presents a dominant sign in each AR. Finally, the correct
  helicity flux density could be derived from magnetograms if coronal
  connectivities are known.

Title: The magnetic field topology associated with two M flares
Authors: Luoni, M. L.; Mandrini, C. H.; Cristiani, G. D.; Démoulin, P.
Bibcode: 2007AdSpR..39.1382L
Altcode: 2007arXiv0706.0242L
  On 27 October, 2003, two GOES M-class flares occurred in an interval
  of 3 h in active region NOAA 10486. The two flares were confined and
  their associated brightenings appeared at the same location, displaying
  a very similar shape both at the chromospheric and coronal levels. We
  focus on the analysis of magnetic field (SOHO/MDI), chromospheric
  (HASTA, Kanzelhöhe Solar Observatory, TRACE) and coronal (TRACE)
  observations. By combining our data analysis with a model of the coronal
  magnetic field, we compute the magnetic field topology associated with
  the two M flares. We find that both events can be explained in terms
  of a localized magnetic reconnection process occurring at a coronal
  magnetic null point. This null point is also present at the same
  location one day later, on 28 October, 2003. Magnetic energy release
  at this null point was proposed as the origin of a localized event
  that occurred independently with a large X17 flare on 28 October, 2003
  [Mandrini, C.H., Démoulin, P., Schmieder, B., Deluca, E., Pariat,
  E., Uddin, W. Companion event and precursor of the X17 flare on 28
  October, 2003. Solar Physics, 238, 293-312, 2006], at 11:01 UT. The
  three events, those on 27 October and the one on 28 October, are
  homologous. Our results show that coronal null points can be stable
  topological structures where energy release via magnetic reconnection
  can happen, as proposed by classical magnetic reconnection models.

Title: How to improve the maps of magnetic helicity injection in
    active regions?
Authors: Pariat, Etienne; Démoulin, Pascal; Nindos, Alexander
Bibcode: 2007AdSpR..39.1706P
Altcode:
  Magnetic helicity, a topological quantity which measures the twist,
  the writhe and the shear of a magnetic field, has recently appeared
  as a key quantity to understand some mechanisms of the solar activity
  such as Coronal Mass Ejections and flare onset. It is thus becoming
  of major importance to be able to compute magnetic helicity in active
  regions. Computing photospheric maps of the injection of magnetic
  helicity provides new spatial information that helps us to understand
  basic properties of solar activity, such as where and how magnetic
  helicity is injected. Several helicity flux density maps have been
  published for different active regions. Unfortunately, the classical
  helicity flux density is not a correct physical quantity and it does
  induce spurious signals (fake polarities) which mask the real injection
  of helicity. To map the real helicity injection, the knowledge of
  the complete connectivity of the field lines is fundamental. Even
  without the connectivity, improved helicity flux density maps can
  be derived. They have fake polarities which are lower by more than a
  factor 10 than the previous incorrect maps. Rather than a mixture of
  negative and positive injection patterns, they show almost unipolar
  injection on the active region scale. This leads to a completely new
  way of understanding the dynamics of active regions, in the frame of
  magnetic helicity studies.

Title: Recent theoretical and observational developments in magnetic
    helicity studies
Authors: Démoulin, P.
Bibcode: 2007AdSpR..39.1674D
Altcode:
  Magnetic helicity quantifies how the magnetic field is sheared and
  twisted compared to its lowest energy state (potential field). Such
  stressed magnetic fields are usually observed in association with
  flares, eruptive filaments, and coronal mass ejections (CMEs). Magnetic
  helicity plays a key role in magnetohydrodynamics because it is almost
  preserved on a timescale less than the global diffusion time scale. Its
  conservation defines a constraint to the magnetic field evolution. Only
  relatively recently, scientists have realized that magnetic helicity
  can be computed from observations, and methods have been derived to
  bridge the gap between theory and observations. At the photospheric
  level, the rate (or flux) of magnetic helicity can be computed from
  the evolution of longitudinal magnetograms. The coronal helicity is
  estimated from magnetic extrapolation, while the helicity ejected
  in magnetic clouds (interplanetary counter-part of CMEs) is derived
  through modelling of in situ magnetic field measurements. Using its
  conserved property, a quantitative link between phenomena observed in
  the corona and then in the interplanetary medium has been achieved.

Title: Where will efficient energy release occur in 3-D magnetic
    configurations?
Authors: Démoulin, P.
Bibcode: 2007AdSpR..39.1367D
Altcode:
  The energy needed to power flares is thought to be stored in the coronal
  magnetic field. However, the energy release is efficient only at very
  small scales. Magnetic configurations with a complex topology, i.e. with
  separatrices, are the most obvious configurations where current
  sheets can form, and then, reconnection can efficiently occur. This
  has been confirmed for several flares computing the coronal field and
  comparing the locations of the flare loops and ribbons to the deduced
  3-D magnetic topology. However, this view is too restrictive taking into
  account the variety of observed solar flaring configurations. Indeed,
  "Quasi-Separatrix Layers" (QSLs), which are regions where there is
  a drastic change in field-line linkage, generalize the definition of
  separatrices. They let us understand where reconnection occurs in a
  broader variety of flares than separatrices do. The strongest electric
  field and current are generated at, or close to where the QSLs are
  thinnest. This defines the region where particle acceleration can
  efficiently occur. A new feature of 3-D reconnection is the natural
  presence of fast field-line slippage along the QSLs, a process called
  "slip-running reconnection". This is a plausible origin for the motions
  of the X-ray sources along flare ribbons.

Title: Companion Event and Precursor of the X17 Flare on 28 October
    2003
Authors: Mandrini, C. H.; Demoulin, P.; Schmieder, B.; Deluca, E. E.;
   Pariat, E.; Uddin, W.
Bibcode: 2006SoPh..238..293M
Altcode: 2006SoPh..tmp...79M
  A major two-ribbon X17 flare occurred on 28 October 2003, starting
  at 11:01 UT in active region NOAA 10486. This flare was accompanied
  by the eruption of a filament and by one of the fastest halo coronal
  mass ejections registered during the October-November 2003 strong
  activity period. We focus on the analysis of magnetic field (SOHO/MDI),
  chromospheric (NainiTal observatory and TRACE), and coronal (TRACE) data
  obtained before and during the 28 October event. By combining our data
  analysis with a model of the coronal magnetic field, we concentrate
  on the study of two events starting before the main flare. One
  of these events, evident in TRACE images around one hour prior to
  the main flare, involves a localized magnetic reconnection process
  associated with the presence of a coronal magnetic null point. This
  event extends as long as the major flare and we conclude that it is
  independent from it. A second event, visible in Hα and TRACE images,
  simultaneous with the previous one, involves a large-scale quadrupolar
  reconnection process that contributes to decrease the magnetic field
  tension in the overlaying field configuration; this allows the filament
  to erupt in a way similar to that proposed by the breakout model,
  but with magnetic reconnection occurring at Quasi-Separatrix Layers
  (QSLs) rather than at a magnetic null point.

Title: Slip-Running Reconnection in Quasi-Separatrix Layers
Authors: Aulanier, G.; Pariat, E.; Démoulin, P.; Devore, C. R.
Bibcode: 2006SoPh..238..347A
Altcode: 2006SoPh..tmp...62A; 2006SoPh..tmp...81A
  Using time dependent MHD simulations, we study the nature of
  three-dimensional magnetic reconnection in thin quasi-separatrix layers
  (QSLs), in the absence of null points. This process is believed to
  take place in the solar atmosphere, in many solar flares and possibly
  in coronal heating. We consider magnetic field configurations which
  have previously been weakly stressed by asymmetric line-tied twisting
  motions and whose potential fields already possessed thin QSLs. When the
  line-tied driving is suppressed, magnetic reconnection is solely due to
  the self-pinching and dissipation of narrow current layers previously
  formed along the QSLs. A generic property of this reconnection process
  is the continuous slippage of magnetic field lines along each other,
  while they pass through the current layers. This is contrary to standard
  null point reconnection, in which field lines clearly reconnect by
  pair and abruptly exchange their connectivities. For sufficiently
  thin QSLs and high resistivities, the field line footpoints slip-run
  at super-Alfvénic speeds along the intersection of the QSLs with the
  line-tied boundary, even though the plasma velocity and resistivity
  are there fixed to zero. The slip-running velocities of a given
  footpoint have a well-defined maximum when the field line crosses the
  thinnest regions of the QSLs. QSLs can then physically behave as true
  separatrices on MHD time scales, since magnetic field lines can change
  their connections on time scales far shorter than the travel-time of
  Alfvén waves along them. Since particles accelerated in the diffusive
  regions travel along the field much faster than the Alfvén speed,
  slip-running reconnection may also naturally account for the fast
  motion of hard X-ray sources along chromospheric ribbons, as observed
  during solar flares.

Title: Build-up of a CME and its Interaction with Large-Scale
    Magnetic Structures
Authors: van Driel-Gesztelyi, L.; Goff, C. P.; Demoulin, P.; Culhane,
   J. L.; Klein, K. L.; Mandrini, C. H.; Matthews, S. A.; Harra, K. L.;
   Kurokawa, H.
Bibcode: 2006IAUJD...3E..86V
Altcode:
  Introduction: A series of flares (GOES class M, M and C) and a
  CME were observed on 20-JAN-2004 occurring in close succession in
  NOAA 10540. Types II, III and a N radio bursts were associated. We
  investigate the link between the flares (two impulsive flares followed
  by an LDE) and the CME as well as the origin of the rare decametric
  N-burst. Methods: We use the combined observations from TRACE, SOHO/EIT,
  H-alpha images from Kwasan Observatory, SOHO/MDI magnetograms, GOES
  and radio observations from Culgoora and Wind/WAVES as well as magnetic
  modelling to understand the complex development of this event. Results:
  We link the first two impulsive flares to tether-cutting reconnections
  and the launch of the CME, while the last of the flares, an LDE,
  to the relaxation phase following forced reconnections between the
  erupting flux rope and neighbouring magnetic field lines. We show
  that reconnection with the magnetic structure of a previous CME,
  launched about 8 hours earlier, injects electrons into open field
  lines having a local dip and apex of about 6 solar radii height. The
  dipped shape of these field lines was due to large-scale magnetic
  reconnection between expanding magnetic loops and open field lines of a
  neighbouring streamer. This particular situation explains the observed
  decametric N burst. Discussion: This complex observation shows that
  impulsive quadrupolar flares can be eruptive, while an LDE may remain
  a confined event. We find that reconnection forced by the expanding CME
  structure is followed by a relaxation phase, when reconnection reverses
  and restores some of the pre-eruption magnetic connectivities. The
  observed decametric N-burst was caused by the interaction of two CMEs
  and reconnection of their expanding magnetic field with neighbouring
  streamer field lines - a very particular interplay, which explains
  why N-bursts are so rare.

Title: A new model-independent method to compute magnetic helicity
    in magnetic clouds
Authors: Dasso, S.; Mandrini, C. H.; Démoulin, P.; Luoni, M. L.
Bibcode: 2006A&A...455..349D
Altcode:
  Context: .Magnetic clouds are transient magnetic structures expulsed
  from the Sun that travel toward the external heliosphere carrying a
  significant amount of magnetic flux and helicity.<BR /> Aims: .To
  improve our understanding of magnetic clouds in relation to their
  solar source regions, we need a reliable method to compute magnetic
  flux and helicity in both regions. Here we evaluate the sensitivity
  of the results using different models, methods and magnetic cloud
  boundaries applied to the same magnetic cloud data.<BR /> Methods: .The
  magnetic cloud was observed by the spacecraft Wind on October 18-20,
  1995. We analyze this cloud considering four different theoretical
  configurations (two force free and two non-force free) that have been
  previously proposed to model cloud fields. These four models are applied
  using two methods to determine the orientation of the cloud axis:
  minimum variance and simultaneous fitting. Finally, we present a new
  method to obtain the axial and azimuthal magnetic fluxes and helicity
  directly from the observed magnetic field when rotated to the cloud
  frame.<BR /> Results: .The results from the fitted models have biases
  that we analyze. The new method determines the centre and the rear
  boundary of the flux rope when the front boundary is known. It also
  gives two independent measurements in the front and back parts for the
  fluxes and helicity; they are free of model and boundary biases. We
  deduce that the leading flux of the magnetic cloud had reconnected
  with the overtaken solar wind magnetic field and estimate the fluxes
  and helicity present in the full cloud before this reconnection.<BR />

Title: Linking solar to interplanetary events: A new direct method
    to quantify global MHD magnitudes in magnetic clouds
Authors: Dasso, S.; Mandrini, C. H.; Demoulin, P.
Bibcode: 2006IAUJD...3E..26D
Altcode:
  Magnetic Clouds (MCs) carry a significant amount of magnetic flux
  (MF) and helicity (MH) away from the solar corona as they travel
  to the outer heliosphere. From a theoretical point of view, MH is a
  conserved magnitude in the solar corona and heliosphere; thus, it is
  expected that MH be preserved in MCs during their evolution through the
  interplanetary medium. In this sense, MH plays a key role to link the
  magnetic properties of MCs with their solar active region (AR) sources,
  helping us to improve the knowledge of the ejection mechanisms in the
  corona. We present here a new method to compute MH in clouds, which
  provides values for the helicity per unit length along the flux tube
  axis using the observed interplanetary magnetic field, without assuming
  a given model to describe the twist of magnetic field lines inside the
  MC. This method let us also determine the cloud boundaries with more
  precision, which improves the estimation of MH. We apply this method
  to two MCs, one of the biggest and one of the smallest ever observed,
  and compare our results with the helicity ejected from their respective
  solar sources.

Title: Magnetic Sources of Flares and CMEs from Multi-Wavelength
    Flare Studies
Authors: Schmieder, B.; Mandrini, C.; Berlicki, A.; Démoulin, P.;
   Li, H.
Bibcode: 2006ESASP.617E.145S
Altcode: 2006soho...17E.145S
  No abstract at ADS

Title: Global Magnitudes in Expanding Magnetic Clouds
Authors: Nakwacki, M. S.; Dasso, S.; Mandrini, C. H.; Demoulin, P.
Bibcode: 2006RMxAC..26..155N
Altcode:
  Magnetic clouds (MCs) are the interplanetary counterpart of coronal mass
  ejections (CMEs). They transport the magnetic flux and helicity released
  in CMEs by the Sun. At 1 AU from the Sun, an MC is generally modeled as
  a static flux rope and its magnetic helicity content can be quantified
  (Dasso et al., JGR 108, 1362, 2003). However, an MC can be also modeled
  as an expanding structure when its velocity profile shows evidence of
  a significant expansion. Here we present a quantification of the global
  magnitudes for the expanding MC observed by the spacecraft Wind between
  August 09 (10:48UT) and August 10 (15:48UT), 1999. We use magnetic
  (Magnetic Field Instrument, MFI) and plasma (Solar Wind Experiment,
  SWE) data. We analyze here two cylindrical models: (1) a static model
  that considers the cloud magnetic structure as a linear force free field
  (i.e., the Lundquist's solution), and (2) a radial expanding selfsimilar
  model (Farrugia et al., JGR 98, 7621, 1993). In both cases, we derive
  expressions for magnetic fluxes, helicity, and energy. We apply the
  minimun variance method to find the cloud orientation and compute the
  cloud radius for the static model (R_s). For the dynamic model, we fit
  the initial radius for the expanding model (R_0) and the age of the
  cloud (T_0) from the observed velocity profile. We also fit the free
  parameters of each magnetic model using the magnetic observations,
  and find that the dynamical model better represents the data, since
  it fits the assymetry caused by the expansion in the cloud. Finally,
  for both models, we quantify the magnetic fluxes, helicity and energy,
  as done in Nakwacki et al. (Proc. Solar Wind 11 - SOHO 16, ESA SP-592,
  629, 2005). We find a change in the computed helicity and fluxes of
  less than 30% (comparing static and dynamic models). Considering the
  range of time in which Wind observes the cloud, and the dynamic model,
  we find a magnetic energy decay of less than ≈ 12% and a radial
  expansion of 17%.

Title: Multi-Wavelength Analysis of an M6.7 Flare from AR 10486
Authors: Luoni, M. L.; Raulin, J. -P.; Mandrini, C. H.; Bandeira,
   W.; Demoulin, P.; Kaufmann, P.; Luthi, T.; Giménez de Castro, G. G.
Bibcode: 2006RMxAC..26R.154L
Altcode:
  The most intense flares of Solar Physics history were registered during
  October - November 2003. Here we analyze the M6.7 flare (12:27 UT)
  on October 27, 2003, that occurred in the complex active region (AR)
  10486 (NOAA number). We use data in different wavelengths provided
  by instruments observing from the photosphere to the corona. Using
  the Michelson Doppler Imager (SoHO/MDI) magnetogram at 12:47:03 UT as
  boundary condition, we compute the coronal magnetic field under the
  linear force-free field assumption. We compare the computed magnetic
  field lines with the Extreme ultraviolet Imaging Telescope (SoHO/EIT)
  loops to determine the free parameters of our model. From the model we
  find that a magnetic null point is present in the corona. We propose
  that magnetic reconnection at this null point is responsible for
  the M6.7 flare. Concerning radio wavelengths, we analyze the Solar
  Submillimeter Telescope (SST) data. At 12:31 UT, a short impulsive phase
  (∼ 1 minute) is detected followed by a gradual (∼ 1 hour) emission
  associated with H α radiation observed by the H-Alpha Solar Telescope
  for Argentina (HASTA). The radio spectrum during the impulsive peak
  suggests the presence of energetic electrons radiating through the
  synchrotron process. During the extended phase the radio spectrum is
  flat up to very high frequencies, indicating that the emission is due
  to the thermal radiation of a cool and dense plasma. The radio analysis
  is complemented with patrol data from the Bern Polarimeters and Kosma
  and Bemrak observations.

Title: Why Are Coronal Loops So Symmetric?
Authors: Klimchuk, James A.; Lopez Fuentes, M. C.; Demoulin, P.
Bibcode: 2006SPD....37.1706K
Altcode: 2006BAAS...38..246K
  Coronal loops are observed to be very symmetric in the sense that the
  two legs have a comparable thickness. Magnetic flux tubes in magnetic
  field extrapolation models are typically much less symmetric. We
  have quantified these differences using 171 A images from TRACE and
  magnetograms from MDI/SOHO. For a sample of 20 different loops, we found
  the linear force-free field that best matches the observed loop. We
  then measured the plane-of-the-sky widths of the loops and corresponding
  flux tubes and computed footpoint-to-footpoint expansion factors (i.e.,
  asymmetry ratios). The mean expansion factor of the flux tubes is 2.62,
  whereas the mean expansion factor of the loops is only 1.35. Note that
  these expansion factors are different from the footpoint-to-midpoint
  expansion factors that we have presented previously.Evidence suggests
  that the coronal magnetic field is comprised elemental flux strands
  that are tangled by turbulent convection. These strands are so small
  that many tens of them are contained within a single TRACE loop. We
  suggest that this fine structure is a critical missing ingredient of
  the extrapolation models and that a combination of footpoint shuffling
  and coronal reconnection can explain the observed loop symmetry. This
  has important implications for coronal heating.Research supported by
  NASA and the Office of Naval Research.

Title: A new concept for magnetic reconnection : slip-running
    reconnection
Authors: Pariat, E.; Aulanier, G.; Démoulin, P.
Bibcode: 2006sf2a.conf..559P
Altcode:
  In magnetohydrodynamics (MHD), most models of magnetic reconnection
  suppose that this mechanism takes places when the magnetic field
  configuration contains separatrices. Separatrices are surfaces
  through which the magnetic field connectivity is discontinuous. But
  such topological structures are not always present when solar flares
  takes place. Quasi-separatrix layers (QSLs), which are regions of
  strong variations of magnetic connectivity, are a generalisation
  of separatrices. Using a 3D MHD simulation of several solar-like
  magnetic configurations containing QSLs, we investigated the link
  between the build-up of current layers and the location of QSLs. Thin
  current sheets are naturally formed along QSLs whatever the line-tied
  boundary driven motions are. When the line-tied driving is suppressed,
  magnetic reconnection is solely due to the self-pinching and dissipation
  of narrow current layers. In this reconnection process, field line
  continuously slip along each other while they pass through the current
  layers. This slip-running reconnection may naturally account for
  the fast motion of hard X-ray sources along chromospheric ribbons,
  as observed during solar flares.

Title: What is the spatial distribution of magnetic helicity injected
    in a solar active region?
Authors: Pariat, E.; Nindos, A.; Démoulin, P.; Berger, M. A.
Bibcode: 2006A&A...452..623P
Altcode:
  Context: .Magnetic helicity is suspected to play a key role in
  solar phenomena such as flares and coronal mass ejections. Several
  investigations have recently computed the photospheric flux of
  magnetic helicity in active regions. The derived spatial maps of the
  helicity flux density, called G_A, have an intrinsic mixed-sign patchy
  distribution. <BR /> Aims: . Pariat et al. (2005) recently showed
  that G<SUB>A</SUB> is only a proxy of the helicity flux density,
  which tends to create spurious polarities. They proposed a better
  proxy, G<SUB>θ</SUB>. We investigate here the implications of this
  new approach on observed active regions.<BR /> Methods: . The magnetic
  data are from MDI/SoHO instrument and the photospheric velocities are
  computed by local correlation tracking. Maps and temporal evolution of
  G<SUB>A</SUB> and G<SUB>θ</SUB> are compared using the same data set
  for 5 active regions.<BR /> Results: . Unlike the usual G<SUB>A</SUB>
  maps, most of our G<SUB>θ</SUB> maps show almost unipolar spatial
  structures because the nondominant helicity flux densities are
  significantly suppressed. In a few cases, the G<SUB>θ</SUB> maps still
  contain spurious bipolar signals. With further modelling we infer that
  the real helicity flux density is again unipolar. On time-scales larger
  than their transient temporal variations, the time evolution of the
  total helicity fluxes derived from G<SUB>A</SUB> and G<SUB>θ</SUB>
  show small differences. However, unlike G_A, with G<SUB>θ</SUB>
  the time evolution of the total flux is determined primarily by the
  predominant-signed flux while the nondominant-signed flux is roughly
  stable and probably mostly due to noise. <BR /> Conclusions: .Our
  results strongly support the conclusion that the spatial distribution
  of helicity injected into active regions is much more coherent than
  previously thought: on the active region scale the sign of the injected
  helicity is predominantly uniform. These results have implications for
  the generation of the magnetic field (dynamo) and for the physics of
  both flares and coronal mass ejections.

Title: Magnetic Sources of flares and CMEs in October 2003
Authors: Schmieder, B.; Démoulin, P.; Berlicki, A.; Mandrini, C.;
   Hui, Li
Bibcode: 2006sf2a.conf..565S
Altcode:
  We present the data analysis of an observing campaign on October 2003
  with the objective of understanding the onset of Coronal Mass Ejections
  (CME) and solar flares. The magnetic field was observed with THEMIS
  and MDI, the chromosphere with the MSDP operating on THEMIS, the EUV
  images with SOHO/EIT and TRACE, the X-rays with RHESSI. Two examples
  of flares will be presented: the 28 Oct 2003 X17 flare and the 20
  October 2003 M1.9 flare. The magnetic field analysis of the active
  regions is done using a linear-force-free field code. The X17 flare is
  at the origin of a halo CME while the M1.9 flare has no corresponding
  CME. Before the X17 flare there was a pre-flare event which allowed
  to change the connectivities in a first phase and to destabilize the
  stressed field in a second phase producing the X17 flare. A compact
  twisted emerging flux was responsible of the M1.9 flare, which remains
  a compact flare due to very tied overlaying loops. These two examples
  illustrate the major role of the magnetic configuration involved on
  the flare physical characteristics.

Title: The Magnetic Structure of Coronal Loops Observed by TRACE
Authors: López Fuentes, M. C.; Klimchuk, J. A.; Démoulin, P.
Bibcode: 2006ApJ...639..459L
Altcode: 2006ApJ...639..459F; 2005astro.ph..7462L
  Previous studies have found that coronal loops have a nearly uniform
  thickness, which seems to disagree with the characteristic expansion
  of active region magnetic fields. This is one of the most intriguing
  enigmas in solar physics. We here report on the first comprehensive
  one-to-one comparison of observed loops with corresponding magnetic flux
  tubes obtained from cotemporal magnetic field extrapolation models. We
  use EUV images from TRACE, magnetograms from the MDI instrument on
  SOHO, and linear force-free field extrapolations satisfying b.nabla
  XB=αB, with α equal to a constant. For each loop, we find the
  particular value of α that best matches the observed loop axis and
  then construct flux tubes using different assumed cross sections at
  one footpoint (circle and ellipses with different orientations). We
  find that the flux tubes expand with height by typically twice as much
  as the corresponding loops. We also find that many flux tubes are much
  wider at one footpoint than the other, whereas the corresponding loops
  are far more symmetric. It is clear that the actual coronal magnetic
  field is more complex than the models we have considered. We suggest
  that the observed symmetry of loops is related to the tangling of
  elemental magnetic flux strands produced by photospheric convection.

Title: The magnetic field topology associated to an M6.7 flare
Authors: Luoni, M.; Mandrini, C.; Cristiani, G.; Démoulin, P.
Bibcode: 2006cosp...36.1657L
Altcode: 2006cosp.meet.1657L
  We study an M6 7 solar flare that occurred on October 27 2003 12 27 UT
  We use data in different wavelenghts magnetograms from the Michelson
  Doppler Imager SoHO MDI images from the H alpha Solar Telescope for
  Argentina HASTA and Extreme Ultraviolet Imaging Telescope SoHO EIT We
  analyze the magnetic field evolution and compute the coronal field to
  identify the energy release site From this study we find evidence of
  a magnetic null point in the corona We relate the chromospheric and
  EUV brightenings to the magnetic field topology in its neighborhood A
  null point at about the same location is also found in the magnetogram
  closest in time to the X17 flare observed on October 28 2003 The shape
  of bright loops observed by the Transition Region and Coronal Explorer
  TRACE in 195 AA during a secondary confined event accompayning the X-ray
  flare agrees with those of EIT during the M6 7 flare We especulate that
  this null point is a stable topological structure where reconnection
  occurred giving raise to two sympathetic events

Title: Magnetic structure and observed width of coronal loops
Authors: Lopez-Fuentes, M. C.; Klimchuk, J. A.; Demoulin, P.
Bibcode: 2006cosp...36.2575L
Altcode: 2006cosp.meet.2575L
  Previous studies have found that coronal loops have a nearly uniform
  thickness which seems to disagree with the characteristic expansion
  of active region magnetic fields This is one of the most intriguing
  enigmas in solar physics We here report on the first comprehensive
  one-to-one comparison of observed loops with corresponding magnetic
  flux tubes obtained from cotemporal magnetic field extrapolation models
  We use EUV images from TRACE magnetograms from the MDI instrument
  on SOHO and linear force-free field extrapolations For each loop we
  find the particular value of the force-free parameter alpha that best
  matches the observed loop axis and then construct flux tubes using
  different assumed cross sections at one footpoint circle and ellipses
  with different orientations We find that the flux tubes expand with
  height by typically twice as much as the corresponding loops We also
  find that many flux tubes are much wider at one footpoint than the
  other whereas the corresponding loops are far more symmetric It is
  clear that the actual coronal magnetic field is more complex than the
  models we have considered We suggest that the observed symmetry of
  loops is related to the tangling of elemental magnetic flux strands
  produced by photospheric convection

Title: Basic Properties of Mutual Magnetic Helicity
Authors: Demoulin, P.; Pariat, E.; Berger, M. A.
Bibcode: 2006SoPh..233....3D
Altcode:
  We derive the magnetic helicity for configurations formed by flux tubes
  contained fully or only partially in the spatial domain considered
  (called closed and open configurations, respectively). In both cases,
  magnetic helicity is computed as the sum of mutual helicity over
  all possible pairs of magnetic flux tubes weighted by their magnetic
  fluxes. We emphasize that these mutual helicities have properties which
  are not those of mutual inductances in classical circuit theory. For
  closed configurations, the mutual helicity of two closed flux tubes is
  their relative winding around each other (known as the Gauss linkage
  number). For open configurations, the magnetic helicity is derived
  directly from the geometry of the interlaced flux tubes so it can
  be computed without reference to a ground state (such as a potential
  field). We derive the explicit expression in the case of a planar and
  spherical boundary. The magnetic helicity has two parts. The first
  one is given only by the relative positions of the flux tubes on the
  boundary. It is the only part if all flux tubes are arch-shaped. The
  second part counts the integer number of turns each pair of flux tubes
  wind about each other. This provides a general method to compute
  the magnetic helicity with discrete or continuous distributions of
  magnetic field. The method sets closed and open configurations on an
  equal level within the same theoretical framework.

Title: Extending the concept of separatrices to QSLs for magnetic
    reconnection
Authors: Démoulin, P.
Bibcode: 2006AdSpR..37.1269D
Altcode:
  Magnetic reconnection is usually thought to be linked to the
  presence of magnetic null points and to be accompanied by the
  transport of magnetic field lines across separatrices, the set of
  field lines where the field-line linkage is discontinuous. However,
  this view is too restrictive taking into account the variety of
  observed solar flaring configurations. Indeed “quasi-separatrix
  layers” (QSLs), which are regions where there is a drastic change in
  field-line linkage, generalize the definition of separatrices. Magnetic
  reconnection is expected to occur preferentially at QSLs in 3-D magnetic
  configurations. This paper surveys the evolution of the QSL concept from
  the beginning to its recent status. The theory was successfully tested
  with multi-wavelength observations of solar flares. This validates the
  reconnection scenario as the main physical process at the origin of
  flares. The confrontation of observations with the state-of-the-art
  theory gives us also hints how to further develop our understanding
  of 3-D magnetic reconnection.

Title: Multi-scale reconnections in a complex CME
Authors: van Driel-Gesztelyi, L.; Goff, C.; Demoulin, P.; Culhane,
   J. L.; Matthews, S. A.; Harra, L. K.; Mandrini, C. H.; Klein, K. L.;
   Kurokawa, H.
Bibcode: 2006cosp...36.2371V
Altcode: 2006cosp.meet.2371V
  A series of flares GOES class M M and C and a CME were observed on
  20-JAN-2004 occurring in close succession in NOAA 10540 Types II III
  and an N radio bursts were associated We use the combined observations
  from TRACE EIT H-alpha images from Kwasan Observatory MDI magnetograms
  GOES and radio observations from Culgoora and Wind WAVES to understand
  the complex development of this event We link the first two impulsive
  flares to tether-cutting reconnections and the launch of the CME while
  the last of the flares an LDE to the relaxation phase following forced
  reconnections between the erupting flux rope and neighbouring magnetic
  field lines We show that reconnection with the magnetic structure of
  a previous CME launched about 8 hours earlier injects electrons into
  open field lines having a local dip and apex of about 6 solar radii
  height The dipped shape of these field lines was due to large-scale
  magnetic reconnection between expanding magnetic loops and open field
  lines of a neighbouring streamer This particular situation explains
  the observed decametric N burst and why N-bursts are so rare

Title: Magnetic reconfiguration before the X 17 Solar flare of
    October 28 2003
Authors: Schmieder, B.; Mandrini, C. H.; Démoulin, P.; Pariat, E.;
   Berlicki, A.; Deluca, E.
Bibcode: 2006AdSpR..37.1313S
Altcode:
  An active region (AR) NOAA 10486, which produced a large number of
  X-ray flares during October November 2003, was observed during a
  multi-wavelength campaign with ground based and space instruments. We
  focus our analysis on the observations of October 28, 2003. The
  magnetic field was observed with THEMIS (Na D1) and MDI (Ni I), the
  chromosphere with THEMIS (Ca II 8542 Å) and with the Meudon heliograph
  in Hα, the EUV images with SOHO/EIT and TRACE. Two pre-events started
  just before the major X 17 flare. One was related to localized flux
  emergence and lasted until the decay phase of the X flare; while the
  second one involved a large scale quadrupolar reconnection, that we
  infer by modeling the AR magnetic field. Extended dimming areas across
  the equator (EIT), large arcades of post-flare loops (TRACE 195 Å)
  and a halo CME (LASCO) were observed consequently after the flare. We
  perform an extrapolation of the magnetic field above the photosphere
  using a linear force-free-field approximation that allows us to find
  the connectivity among the four polarities that would be involved
  in the quadrupolar reconnection event. The X 17 flare is plausibly
  due to the destabilisation of a twisted flux tube, the bottom part
  of this magnetic structure can be visualized by the presence of a
  filament. The destabilization is caused by converging and shearing
  photospheric motions towards the main magnetic inversion line. The
  large scale quadrupolar reconnection related to the second pre-event
  would favour the opening of the field above the twisted flux tube and,
  consequently, the coronal mass ejection.

Title: Magnetic clouds: An statistical study of their global
    magnetohydrodynamic magnitudes
Authors: Gulisano, A. M.; Dasso, S.; Mandrini, C. H.; Demoulin, P.
Bibcode: 2006cosp...36.2971G
Altcode: 2006cosp.meet.2971G
  Magnetic clouds MCs are highly magnetized plasma structures that have
  a low proton temperature and a magnetic field vector that rotates when
  seen by a heliospheric observer More than 20 years of observations
  of magnetic and plasma properties of MCs at 1 AU have provided
  significant knowledge on their magnetic structure However because
  in situ observations only give information along the one-dimensional
  trajectory of the spacecraft its real 3D magnetic configuration remains
  still unknown We study a set of 20 magnetic clouds observed by the
  Wind spacecraft at 1 AU during a solar minimum We explore different
  models force free and non-force free fields and two different methods
  one is a simultaneous fitting that let us take the minimum distance
  from the cloud axis to the spacecraft the impact parameter p different
  from zero to reconstruct the magnetic structure of clouds from in situ
  observations Thus for each cloud and for each model method we determine
  the cloud axis orientation p and the two physical free parameters
  of each model the twist and the magnetic field intensity both at the
  cloud axis Then for every cloud we analyze the variation of the computed
  amounts of magnetic flux and helicity using the different approaches We
  generate a set of synthetic clouds by changing the space of parameter
  that represents the possible orientations and p values for real clouds
  and then we model them using our code to check the validity of our
  numerical tools Finally from the analysis of the synthetic clouds we

Title: On the origin of the 28 October 2003 X17 event and its
    companion event
Authors: Mandrini, C. H.; Demoulin, P.; Schmieder, B.; de Luca, E. E.;
   Pariat, E.; Uddin, W.
Bibcode: 2006BAAA...49..109M
Altcode:
  An X17 flare started at 11:01 UT on 28 October, 2003, in active region
  (AR) NOAA 10486. This event was accompanied by a filament eruption
  and one of the fastest coronal mass ejections (CMEs) observed during
  the extreme activity period of October-November 2003. Combining
  chromospheric, coronal and magnetic field data with modeling, we
  concentrate in the study of two events that started before the X17
  flare. One of them, which appears in UV images one hour before the major
  event, is associated with localized magnetic reconnection occurring at
  a magnetic mull point. T his event lasts as long as the X17 flare and
  our analysis indicates that it is independent of it. The other one,
  visible in Hα and UV images and simultaneous with the previous one,
  is related to a large scale quadrupolar reconnection process. This
  process is similar to the one proposed by the breakout model for the
  initiation of CMEs, but it takes place at quasiseparatrices and not
  in null points. These results will be published in Solar Physics.

Title: Recent theoretical and observational developments in magnetic
    helicity studies
Authors: Demoulin, P.
Bibcode: 2006cosp...36..117D
Altcode: 2006cosp.meet..117D
  Magnetic helicity quantifies how the magnetic field is sheared and
  twisted compared to its lowest energy state potential field Such
  stressed magnetic fields are usually observed in association with
  flares eruptive filaments and coronal mass ejections CMEs Magnetic
  helicity plays a key role in magnetohydrodynamics because it is almost
  preserved on a timescale less than the global diffusion time scale
  Its conservation defines a constraint to the magnetic field evolution
  Only relatively recently it has been realized that magnetic helicity
  can be computed from observations and methods have been derived to
  bridge the gap between theory and observations At the photospheric
  level the flux of magnetic helicity can be computed from the evolution
  of longitudinal magnetograms The coronal helicity is estimated from
  magnetic extrapolation while the helicity ejected in magnetic clouds
  interplanetary counter-part of CMEs is derived through modelling the
  in-situ magnetic field measurements Using its conserved property a
  quantitative link between phenomena observed in the corona and then
  in the inter-planetary medium has been achieved

Title: A new method to determine the boundary of magnetic clouds
Authors: Dasso, S.; Démoulin, P.; Mandrini, C. H.; Luoni, M. L.
Bibcode: 2006cosp...36.2390D
Altcode: 2006cosp.meet.2390D
  Magnetic clouds MCs are transient structures formed by magnetic flux
  ropes with low proton temperature and strongly enhanced magnetic field
  intensity with respect to ambient values The identification of the MC
  boundaries is an open question for some clouds mainly because different
  proxies can provide different positions In this paper we analyze the
  magnetic cloud observed by the spacecraft Wind on October 18-20 1995
  a cloud previously studied by several authors The front of this cloud
  seems to be relatively well determined from plasma and magnetic data
  However different authors set the rear boundary at different times We
  present a new method that determines the centre and the rear boundary
  of a flux rope when the front boundary is well known It is based on
  the azimuthal magnetic flux conservation We deduce that the leading
  flux of the analyzed magnetic cloud had reconnected with the overtaken
  solar-wind magnetic field Then we estimate the magnetic flux associated
  with the full cloud before it reconnects with the solar wind Finally we
  evaluate the sensitivity of our results using different models methods
  and magnetic-cloud boundaries applied to the same magnetic cloud data

Title: Where will efficient energy release occur in 3D magnetic
    configurations?
Authors: Demoulin, P.
Bibcode: 2006cosp...36..118D
Altcode: 2006cosp.meet..118D
  The energy needed to power flares is thought to be stored in the coronal
  magnetic field However the energy release which results in thermal
  energy brightenings is efficient only at very small scales Magnetic
  configurations with a complex topology i e with separatrices are the
  most obvious configurations where current layers then reconnection
  can efficiently occur This has been confirmed for several flares by
  computing the coronal field and by comparing the locations of the
  flare loops and ribbons to the deduced 3D magnetic topology However
  this view is too restrictive taking into account the variety of
  observed solar flaring configurations Indeed Quasi-Separatrix Layers
  QSLs which are regions where there is a drastic change in field-line
  linkage generalize the definition of separatrices They permit us to
  understand where reconnection occurs in a broader variety of flares
  than separatrices do The location where the QSL are the thinnest called
  Hyperbolic Flux Tube HFT is the location for the strongest electric
  field and current being generated This is a good candidate for the
  region where particle acceleration can occur efficiently

Title: How to derive the real pattern of magnetic helicity injection
    in an active region?
Authors: Pariat, E.; Nindos, A.; Démoulin, P.; Berger, M.
Bibcode: 2006cosp...36..851P
Altcode: 2006cosp.meet..851P
  Magnetic helicity a topological quantity which measures the twist the
  writhe and the shear of a magnetic field has recently appeared as
  a key quantity to understand some mechanisms of the solar activity
  such as Coronal Mass Ejections and flare onset It is thus becoming
  of major importance to be able to compute magnetic helicity in active
  regions Looking at the pattern of the photospheric injection of magnetic
  helicity may provide new useful pieces of information to understand the
  basic properties of solar activity If several helicity flux density
  maps were published no one yet wondered if helicity flux density is
  a correct physical quantity Unfortunately the classical helicity flux
  density do induce spurious signal fake polarities which mask the real
  injection of helicity To map the real helicity injection the knowledge
  of the complete connectivity of the field lines is fundamental Even
  without the connectivity improved helicity flux density maps can be
  derived which present strong differences with the previous incorrect
  maps This leads to a complete new way of understanding the dynamics
  of the active region in the frame of the magnetic helicity study

Title: The role of null points in large flares
Authors: Schmieder, B.; Mandrini, C.; Démoulin, P.; Aulanier, G.;
   Li, H.
Bibcode: 2006cosp...36..156S
Altcode: 2006cosp.meet..156S
  We have performed the analysis of the magnetic topology of the active
  region NOAA 10486 before two large flares occurring on October 26 and
  28 2003 The 3D extrapolation of photospheric magnetic field show the
  existence of magnetic null points We used TRACE 1600 A brightenings
  as tracers of the energy release during magnetic reconnections We
  conclude on the three following points 1 The observed small pre-events
  observed before the flares were related to low lying null points They
  were long lasting and associated with low energy release They were not
  triggering of the large flares 2 On October 26 a high altitude null
  point was detected We looked at the TRACE 1600 A images for bright
  patches corresponding to a possible coronal reconnection at the null
  point However no bright patch was observed before the main flare 3
  On October 28 a breakout of the large scale overlaying magnetic field
  lines occurred but without the presence of a null point in the corona
  So the existence of a null point in the corona is not a sufficient
  and or necessary condition for getting large flares

Title: Tracing magnetic helicity from the solar corona to the
    interplanetary space
Authors: Luoni, M. L.; Mandrini, C. H.; Dasso, Sergio; van
   Driel-Gesztelyi, L.; Démoulin, P.
Bibcode: 2005JASTP..67.1734L
Altcode: 2005JATP...67.1734L
  On October 14, 1995, a C1.6 long duration event (LDE) started in active
  region (AR) NOAA 7912 at approximately 5:00 UT and lasted for about
  15 h. On October 18, 1995, the Solar Wind Experiment and the Magnetic
  Field Instrument (MFI) on board the Wind spacecraft registered a
  magnetic cloud (MC) at 1 AU, which was followed by a strong geomagnetic
  storm. We identify the solar source of this phenomenon as AR 7912. We
  use magnetograms obtained by the Imaging Vector Magnetograph at Mees
  Solar Observatory, as boundary conditions to the linear force-free
  model of the coronal field, and, we determine the model in which the
  field lines best fit the loops observed by the Soft X-ray Telescope on
  board Yohkoh. The computations are done before and after the ejection
  accompanying the LDE. We deduce the loss of magnetic helicity from AR
  7912. We also estimate the magnetic helicity of the MC from in situ
  observations and force-free models. We find the same sign of magnetic
  helicity in the MC and in its solar source. Furthermore, the helicity
  values turn out to be quite similar considering the large errors that
  could be present. Our results are a first step towards a quantitative
  confirmation of the link between solar and interplanetary phenomena
  through the study of magnetic helicity.

Title: a Series of Compact Flares with AN Associated CME
Authors: Goff, C. P.; van Driel-Geszrelyi, L.; Culhane, J. L.;
   Matthews, S. A.; Harra, L. K.; Démoulin, P.; Mandrini, C. H.;
   Kurokawa, H.
Bibcode: 2005ESASP.600E.157G
Altcode: 2005ESPM...11..157G; 2005dysu.confE.157G
  No abstract at ADS

Title: Magnetic clouds: A statistical study of magnetic helicity
Authors: Gulisano, A. M.; Dasso, S.; Mandrini, C. H.; Démoulin, P.
Bibcode: 2005JASTP..67.1761G
Altcode: 2005JATP...67.1761G
  We select a set of 20 magnetic clouds (MCs) observed by the spacecraft
  Wind and reconstruct their local magnetic structure from in situ
  observations under different models. In particular, we quantify
  their relative magnetic helicity per unit length (H<SUB>r</SUB>/L)
  under the assumption of a cylindrical geometry. We investigate how
  model-dependent are the results using four models (two force-free and
  two non-force-free) with a significantly different twist distribution in
  their magnetic field: (a) a linear force-free field, (b) a uniformly
  twisted field, (c) a non-force-free field with constant current
  (J) and (d) a non-force-free field with an azimuthal component of J
  depending linearly on the radius and with a constant axial component
  of J. We find that the dispersion of the mean H<SUB>r</SUB>/L for the
  20 MCs is one order of magnitude larger than the dispersion of the
  H<SUB>r</SUB>/L value using different models for a given event. In
  this sense, magnetic helicity per unit length is a well-determined
  magnitude considering these four models.

Title: Current sheet formation in quasi-separatrix layers and
    hyperbolic flux tubes
Authors: Aulanier, G.; Pariat, E.; Démoulin, P.
Bibcode: 2005A&A...444..961A
Altcode:
  In 3D magnetic field configurations, quasi-separatrix layers (QSLs) are
  defined as volumes in which field lines locally display strong gradients
  of connectivity. Considering QSLs both as the preferential locations for
  current sheet development and magnetic reconnection, in general, and as
  a natural model for solar flares and coronal heating, in particular,
  has been strongly debated issues over the past decade. In this paper,
  we perform zero-β resistive MHD simulations of the development of
  electric currents in smooth magnetic configurations which are, strictly
  speaking, bipolar though they are formed by four flux concentrations,
  and whose potential fields contain QSLs. The configurations are driven
  by smooth and large-scale sub-Alfvénic footpoint motions. Extended
  electric currents form naturally in the configurations, which evolve
  through a sequence of quasi non-linear force-free equilibria. Narrow
  current layers also develop. They spontaneously form at small scales
  all around the QSLs, whatever the footpoint motions are. For long
  enough motions, the strongest currents develop where the QSLs are the
  thinnest, namely at the Hyperbolic Flux Tube (HFT), which generalizes
  the concept of separator. These currents progressively take the shape
  of an elongated sheet, whose formation is associated with a gradual
  steepening of the magnetic field gradients over tens of Alfvén times,
  due to the different motions applied to the field lines which pass
  on each side of the HFT. Our model then self-consistently accounts
  for the long-duration energy storage prior to a flare, followed by a
  switch-on of reconnection when the currents reach the dissipative scale
  at the HFT. In configurations whose potential fields contain broader
  QSLs, when the magnetic field gradients reach the dissipative scale,
  the currents at the HFT reach higher magnitudes. This implies that
  major solar flares which are not related to an early large-scale ideal
  instability, must occur in regions whose corresponding potential fields
  have broader QSLs. Our results lead us to conjecture that physically,
  current layers must always form on the scale of the QSLs. This implies
  that electric currents around QSLs may be gradually amplified in time
  only if the QSLs are broader than the dissipative length-scale. We
  also discuss the potential role of QSLs in coronal heating in bipolar
  configurations made of a continuous distribution of flux concentrations.

Title: Quantitative Link Between Solar Ejecta and Interplanetary
Magnetic Clouds: Magnetic Helicity
Authors: Mandrini, C. H.; Dasso, S.; Luoni, M. L.; Pohjolainen, S.;
   Démoulin, P.; van Driel-Gesztelyi, L.
Bibcode: 2005ESASP.596E..29M
Altcode: 2005ccmf.confE..29M
  No abstract at ADS

Title: Erratum: Photospheric flux density of magnetic helicity
Authors: Pariat, E.; Démoulin, P.; Berger, M. A.
Bibcode: 2005A&A...442.1105P
Altcode:
  No abstract at ADS

Title: Magnetic Topologies: where Will Reconnection Occur ?
Authors: Démoulin, P.
Bibcode: 2005ESASP.596E..22D
Altcode: 2005ccmf.confE..22D
  No abstract at ADS

Title: Helicity Analysis for Expanding Magnetic Clouds: A Case Study
Authors: Nakwacki, M. S.; Dasso, S.; Mandrini, C. H.; Démoulin, P.
Bibcode: 2005ESASP.592..629N
Altcode: 2005soho...16E.123N; 2005ESASP.592E.123N
  No abstract at ADS

Title: Large Scale Properties of Magnetic Clouds: Different Approaches
    to Estimate their Orientation and Impact Parameter
Authors: Gulisano, A. M.; Dasso, S.; Mandrini, C. H.; Démoulin, P.
Bibcode: 2005ESASP.592..621G
Altcode: 2005ESASP.592E.121G; 2005soho...16E.121G
  No abstract at ADS

Title: Photospheric flux density of magnetic helicity
Authors: Pariat, E.; Démoulin, P.; Berger, M. A.
Bibcode: 2005A&A...439.1191P
Altcode:
  Several recent studies have developed the measurement of magnetic
  helicity flux from the time evolution of photospheric magnetograms. The
  total flux is computed by summing the flux density over the analyzed
  region. All previous analyses used the density G<SUB>A</SUB> (=-2
  ( A\cdot {u}) B_n) which involves the vector potential A of the
  magnetic field. In all the studied active regions, the density
  G<SUB>A</SUB> has strong polarities of both signs with comparable
  magnitude. Unfortunately, the density G<SUB>A</SUB> can exhibit spurious
  signals which do not provide a true helicity flux density. The main
  objective of this study is to resolve the above problem by defining the
  flux of magnetic helicity per unit surface. In a first step, we define a
  new density, G<SUB>θ</SUB>, which reduces the fake polarities by more
  than an order of magnitude in most cases (using the same photospheric
  data as G_A). In a second step, we show that the coronal linkage needs
  to be provided in order to define the true helicity flux density. It
  represents how all the elementary flux tubes move relatively to a
  given elementary flux tube, and the helicity flux density is defined
  per elementary flux tube. From this we define a helicity flux per unit
  surface, G<SUB>Φ</SUB>. We show that it is a field-weighted average
  of G<SUB>θ</SUB> at both photospheric feet of coronal connections. We
  compare these three densities (G_A, G<SUB>θ</SUB>, G<SUB>Φ</SUB>)
  using theoretical examples representing the main cases found in
  magnetograms (moving magnetic polarities, separating polarities, one
  polarity rotating around another one and emergence of a twisted flux
  tube). We conclude that G<SUB>θ</SUB> is a much better proxy of the
  magnetic helicity flux density than G<SUB>A</SUB> because most fake
  polarities are removed. Indeed G<SUB>θ</SUB> gives results close to
  G<SUB>Φ</SUB> and should be used to monitor the photospheric injection
  of helicity (when coronal linkages are not well known). These results
  are applicable to the results of any method determining the photospheric
  velocities. They can provide separately the flux density coming from
  shearing and advection motions if plasma motions are known.

Title: Linking Coronal to Heliospheric Magnetic Helicity: A New
    Model-Independent Technique to Compute Helicity in Magnetic Clouds
Authors: Dasso, Sergio; Mandrini, Cristina H.; Luoni, Maria L.;
   Gulisano, Adriana M.; Nakwacki, Maria S.; Pohjolainen, Silja; van
   Driel-Gesztelyi, Lidia; Démoulin, Pascal
Bibcode: 2005ESASP.592..605D
Altcode: 2005soho...16E.117D; 2005ESASP.592E.117D
  No abstract at ADS

Title: Flows in the solar atmosphere due to the eruptions on the
    15th July, 2002
Authors: Harra, L. K.; Démoulin, P.; Mandrini, C. H.; Matthews,
   S. A.; van Driel-Gesztelyi, L.; Culhane, J. L.; Fletcher, L.
Bibcode: 2005A&A...438.1099H
Altcode:
  Which kind of flows are present during flares? Are they compatible
  with the present understanding of energy release and which model
  best describes the observations? We analyze successive flare events
  in order to answer these questions. The flares were observed in the
  magnetically complex NOAA active region (AR) 10030 on 15 July 2002. One
  of them is of GOES X-class. The description of these flares and how
  they relate to the break-out model is presented in Gary &amp; Moore
  (2004). The Coronal Diagnostic Spectrometer on board SOHO observed
  this active region for around 14 h. The observed emission lines
  provided data from the transition region to the corona with a field
  of view covering more than half of the active region. In this paper
  we analyse the spatially resolved flows seen in the atmosphere from
  the preflare to the flare stages. We find evidence for evaporation
  occurring before the impulsive phase. During the main phase, the
  ongoing magnetic reconnection is demonstrated by upflows located at
  the edges of the flare loops (while downflows are found in the flare
  loops themselves). We also report the impact of a filament eruption
  on the atmosphere, with flows up to 300 km s<SUP>-1</SUP> observed at
  transition-region temperatures in regions well away from the location
  of the pre-eruptive filament. Our results are consistent with the
  predictions of the break out model before the impulsive phase of the
  flare; while, as the flare progresses, the directions of the flows are
  consistent with flare models invoking evaporation followed by cooling
  and downward plasma motions in the flare loops.

Title: Eruption of a Kink-unstable Filament in NOAA Active Region
    10696
Authors: Williams, David R.; Török, Tibor; Démoulin, Pascal;
   van Driel-Gesztelyi, Lidia; Kliem, Bernhard
Bibcode: 2005ApJ...628L.163W
Altcode: 2005astro.ph..7661W
  We present rapid-cadence Transition Region and Coronal Explorer (TRACE)
  observations that show evidence of a filament eruption from NOAA active
  region 10696, accompanied by an X2.5 flare, on 2004 November 10. The
  eruptive filament, which manifests as a fast coronal mass ejection
  some minutes later, rises as a kinking structure with an apparently
  exponential growth of height within TRACE's field of view. We compare
  the characteristics of this filament eruption with MHD numerical
  simulations of a kink-unstable magnetic flux rope, finding excellent
  qualitative agreement. We suggest that while tether weakening by
  breakout-like quadrupolar reconnection may be the release mechanism
  for the previously confined flux rope, the driver of the expansion is
  most likely the MHD helical kink instability.

Title: Radio and X-Ray Signatures of Magnetic Reconnection behind
    an Ejected Flux Rope
Authors: Pick, M.; Démoulin, P.; Krucker, S.; Malandraki, O.; Maia, D.
Bibcode: 2005ApJ...625.1019P
Altcode:
  We present a detailed study of a complex solar event observed on
  2002 June 2. Joint imaging EUV, X-ray, and multiwavelength radio
  observations allow us to trace the development of the magnetic structure
  involved in this solar event up to a radial distance of the order of 2
  R<SUB>solar</SUB>. The event involves type II, III, and IV bursts. The
  type IV burst is formed by two sources: a fast-moving one (M) and a
  ``quasi-stationary'' one (S). The time coincidence in the flux peaks
  of these radio sources and the underlying hard X-ray sources implies
  a causal link. In the first part of our paper we provide a summary
  of the observations without reference to any coronal mass ejection
  (CME) model. The experimental results impose strong constraints on
  the physical processes. In the second part of our paper, we find that
  a model with an erupting twisted flux rope, with the formation of a
  current sheet behind, best relates the different observations in a
  coherent physical evolution (even if there is no direct evidence of
  the twisted flux rope). Our results show that multiwavelength radio
  imaging represents a powerful tool to trace the dynamical evolution of
  the reconnecting current sheet behind ejected flux ropes (in between
  sources M and S) and over an altitude range not accessible by X-ray
  observations.

Title: Interplanetary flux rope ejected from an X-ray bright
    point. The smallest magnetic cloud source-region ever observed
Authors: Mandrini, C. H.; Pohjolainen, S.; Dasso, S.; Green, L. M.;
   Démoulin, P.; van Driel-Gesztelyi, L.; Copperwheat, C.; Foley, C.
Bibcode: 2005A&A...434..725M
Altcode:
  Using multi-instrument and multi-wavelength observations (SOHO/MDI and
  EIT, TRACE and Yohkoh/SXT), as well as computing the coronal magnetic
  field of a tiny bipole combined with modelling of Wind in situ data,
  we provide evidences for the smallest event ever observed which links
  a sigmoid eruption to an interplanetary magnetic cloud (MC). The
  tiny bipole, which was observed very close to the solar disc centre,
  had a factor one hundred less flux than a classical active region
  (AR). In the corona it had a sigmoidal structure, observed mainly
  in EUV, and we found a very high level of non-potentiality in the
  modelled magnetic field, 10 times higher than we have ever found in
  any AR. From May 11, 1998, and until its disappearance, the sigmoid
  underwent three intense impulsive events. The largest of these events
  had extended EUV dimmings and a cusp. The Wind spacecraft detected 4.5
  days later one of the smallest MC ever identified (about a factor one
  hundred times less magnetic flux in the axial component than that of an
  average MC). The link between this last eruption and the interplanetary
  magnetic cloud is supported by several pieces of evidence: good timing,
  same coronal loop and MC orientation, same magnetic field direction
  and magnetic helicity sign in the coronal loops and in the MC. We
  further quantify this link by estimating the magnetic flux (measured
  in the dimming regions and in the MC) and the magnetic helicity (pre-
  to post-event change in the solar corona and helicity content of the
  MC). Within the uncertainties, both magnetic fluxes and helicities
  are in reasonable agreement, which brings further evidences of their
  link. These observations show that the ejections of tiny magnetic flux
  ropes are indeed possible and put new constraints on CME models.

Title: Equilibrium and observational properties  of line-tied twisted
    flux tubes
Authors: Aulanier, G.; Démoulin, P.; Grappin, R.
Bibcode: 2005A&A...430.1067A
Altcode:
  We describe a new explicit three-dimensional magnetohydrodymanic code,
  which solves the standard zero-β MHD equations in Cartesian geometry,
  with line-tied conditions at the lower boundary and open conditions at
  the other ones. Using this code in the frame of solar active regions,
  we simulate the evolution of an initially potential and concentrated
  bipolar magnetic field, subject to various sub-Alfvénic photospheric
  twisting motions which preserve the initial photospheric vertical
  magnetic field. Both continuously driven and relaxation runs are
  performed. Within the numerical domain, a steep equilibrium curve is
  found for the altitude of the apex of the field line rooted in the
  vortex centers as a function of the twist. Its steepness strongly
  depends on the degree of twist in outer field lines rooted in weak
  field regions. This curve fits the analytical expression for the
  asymptotic behaviour of force-free fields of spherical axisymmetric
  dipoles subject to azimuthal shearing motions, as well as the curve
  derived for other line-tied twisted flux tubes reported in previous
  works. This suggests that it is a generic property of line-tied
  sheared/twisted arcades. However, contrary to other studies we never
  find a transition toward a non-equilibrium within the numerical domain,
  even for twists corresponding to steep regions of the equilibrium
  curve. The calculated configurations are analyzed in the frame of solar
  observations. We discuss which specific conditions are required for
  the steepness of the generic equilibrium curve to result in dynamics
  which are typical of both fast and slow CMEs observed below 3 R_⊙. We
  provide natural interpretations for the existence of asymmetric and
  multiple concentrations of electric currents in homogeneoulsy twisted
  sunspots, due to the twisting of both short and long field lines. X-ray
  sigmoids are reproduced by integrating the Joule heating term along the
  line-of-sight. These sigmoids have inverse-S shapes associated with
  negative force-free parameters α, which is consistent with observed
  rules in the northern solar hemisphere. We show that our sigmoids are
  not formed in the main twisted flux tube, but rather in an ensemble of
  low-lying sheared and weakly twisted field lines, which individually
  never trace the whole sigmoid, and which barely show their distorded
  shapes when viewed in projection. We find that, for a given bipolar
  configuration and a given twist, neither the α nor the altitude of
  the lines whose envelope is a sigmoid depends on the vortex size.

Title: Analysis of 20 magnetic clouds at 1 AU during a solar minimum
Authors: Gulisano, A. M.; Dasso, S.; Mandrini, C. H.; Démoulin, P.
Bibcode: 2005BAAA...48...79G
Altcode:
  We study 20 magnetic clouds, observed in situ by the spacecraft Wind, at
  the Lagrangian point L1, from 22 August, 1995, to 7 November, 1997. In
  previous works, assuming a cylindrical symmetry for the local magnetic
  configuration and a satellite trajectory crossing the axis of the cloud,
  we obtained their orientations using a minimum variance analysis. In
  this work we compute the orientations and magnetic configurations using
  a non-linear simultaneous fit of the geometric and physical parameters
  for a linear force-free model, including the possibility of a not null
  impact parameter. We quantify global magnitudes such as the relative
  magnetic helicity per unit length and compare the values found with
  both methods (minimum variance and the simultaneous fit). FULL TEXT
  IN SPANISH

Title: Magnetic topology analysis of an M6.7 solar flare
Authors: Luoni, M. L.; Mandrini, C. H.; Démoulin, P.
Bibcode: 2005BAAA...48...84L
Altcode:
  We study an M6.7 solar flare that occurred on October 27, 2003
  (12:27 UT). We use data in different wavelenghts: magnetograms from
  the Michelson Doppler Imager (SoHO/MDI), images from the Halpha
  Solar Telescope for Argentina (HASTA) and Extreme Ultraviolet Imaging
  Telescope (SoHO/EIT).We analyze the magnetic field evolution and compute
  the coronal field to identify the energy release site. From this study,
  we find evidence of a magnetic null point in the corona. We relate the
  chromospheric and EUV brightenings to the magnetic field topology in
  its neighborhood. FULL TEXT IN SPANISH

Title: A Direct Method to Estimate Magnetic Helicity in Magnetic
    Clouds
Authors: Dasso, S.; Mandrini, C. H.; Gulisano, A. M.; Démoulin, P.
Bibcode: 2005IAUS..226..403D
Altcode:
  Magnetic clouds are extended and magnetized plasma structures that
  travel from the Sun toward the outer heliosphere, carrying an important
  amount of magnetic helicity. The magnetic helicity quantifies several
  aspects of a given magnetic structure, such as the twist, kink, and
  the number of knots between magnetic field lines, the linking between
  magnetic flux tubes, etc. Since the helicity is practically conserved
  in the solar atmosphere and the heliosphere, it is a useful quantity
  to compare the physical properties of magnetic clouds to those of
  their solar source regions. In this work we describe a method that,
  assuming a cylindrical geometry for the magnetic cloud structures,
  allows us to calculate their helicity (per unit length) content directly
  from the observed magnetic field values. We apply the method to a
  set of 20 magnetic clouds observed by the WIND spacecraft. To test
  its reliability we compare our results with the helicity computed
  using a linear force-free field model under cylindrical geometry
  (i.e. Lundquist's solution).

Title: The smallest source region of an interplanetary magnetic cloud:
    A mini-sigmoid
Authors: Mandrini, C. H.; Pohjolainen, S.; Dasso, S.; Green, L. M.;
   Démoulin, P.; van Driel-Gesztelyi, L.; Foley, C.; Copperwheat, C.
Bibcode: 2005AdSpR..36.1579M
Altcode:
  We provide evidence for the smallest sigmoid eruption - CME -
  interplanetary magnetic cloud event ever observed by combining
  multi-wavelength remote sensing and in situ observations, as well as
  computing the coronal and interplanetary magnetic fields. The tiny
  bipole had 100 times less flux than an average active region (AR). It
  had a sigmoidal structure in the corona and we detected a very high
  level of twist in its magnetic field. On 11 May 1998, at about 8 UT, the
  sigmoid underwent eruption evidenced by expanding elongated EUV loops,
  dimmings and formation of a cusp. The Wind spacecraft, 4.5 days later,
  detected one of the smallest magnetic clouds (MC) ever identified
  (100 times less magnetic flux than an average MC). The link between
  the EUV bright point eruption and the interplanetary MC is supported by
  several pieces of evidence: timing, same coronal loop and MC orientation
  relative to the ecliptic, same magnetic field direction and magnetic
  helicity sign in the coronal loops and in the MC, comparable magnetic
  flux measured in the dimming regions and in the interplanetary MC and,
  most importantly, the pre- to post-event change of magnetic helicity
  in the solar corona is found to be comparable to the helicity content
  of the cloud.

Title: Linking Coronal to Interplanetary Magnetic Helicity
Authors: Luoni, M. L.; Dasso, S.; Mandrini, C. H.; Van Driel-Gesztelyi,
   L.; Démoulin, P.
Bibcode: 2005ASSL..320..243L
Altcode: 2005smp..conf..243L
  No abstract at ADS

Title: Large scale MHD properties of interplanetary magnetic clouds
Authors: Dasso, S.; Mandrini, C. H.; Démoulin, P.; Luoni, M. L.;
   Gulisano, A. M.
Bibcode: 2005AdSpR..35..711D
Altcode:
  Magnetic Clouds (MCs) are the interplanetary manifestation of
  Coronal Mass Ejections. These huge astrophysical objects travel
  from the Sun toward the external heliosphere and can reach the
  Earth environment. Depending on their magnetic field orientation,
  they can trigger intense geomagnetic storms. The details of the
  magnetic configuration of clouds and the typical values of their
  magnetohydrodynamic magnitudes are not yet well known. One of the
  most important magnetohydrodynamic quantities in MCs is the magnetic
  helicity. The helicity quantifies several aspects of a given magnetic
  structure, such as the twist, kink, number of knots between magnetic
  field lines, linking between magnetic flux tubes, etc. The helicity is
  approximately conserved in the solar atmosphere and the heliosphere,
  and it is very useful to link solar phenomena with their interplanetary
  counterpart. Since a magnetic cloud carries an important amount of
  helicity when it is ejected from the solar corona, estimations of the
  helicity content in clouds can help us to understand its evolution
  and its coronal origin. In situ observations of magnetic clouds at
  one astronomical unit are in agreement with a local helical magnetic
  structure. However, since spacecrafts only register data along a unique
  direction, several aspects of the global configuration of clouds
  cannot be observed. In this paper, we review the general properties
  of magnetic clouds and different models for their magnetic structure
  at one astronomical unit. We describe the corresponding techniques to
  analyze in situ measurements. We also quantify their magnetic helicity
  and compare it with the release of helicity in their solar source for
  some of the analyzed cases.

Title: Study of an expanding magnetic cloud
Authors: Nakwacki, M. S.; Dasso, S.; Mandrini, C. H.; Démoulin, P.
Bibcode: 2005BAAA...48...93N
Altcode:
  Magnetic Clouds (MCs) transport into the interplanetary medium the
  magnetic flux and helicity released in coronal mass ejections by the
  Sun. At 1 AU from the Sun, MCs are generally modelled as static flux
  ropes. However, the velocity profile of some MCs presents signatures
  of expansion. We analise here the magnetic structure of an expanding
  magnetic cloud observed by Wind spacecraft. We consider a dynamical
  model, based on a self-similar behaviour for the cloud radial
  velocity. We assume a free expansion for the cloud, and a cylindrical
  linear force free field (i.e., the Lundquist's field) as the initial
  condition for its magnetic configuration. We derive theoretical
  expressions for the magnetic flux across a surface perpendicular to
  the cloud axis, for the magnetic helicity and magnetic energy per unit
  length along the tube using the self-similar model. Finally, we compute
  these magntitudes with the fitted parameters. FULL TEXT IN SPANISH

Title: Solar and Interplanetary Magnetic Helicity Balance of Active
    Regions
Authors: Mandrini, Cristina H.; Démoulin, Pascal; van Driel-Gesztelyi,
   Lidia; Dasso, Sergio; Green, Lucinda M.; López Fuentes, Marcelo
Bibcode: 2005HiA....13..122M
Altcode:
  No abstract at ADS

Title: Model-independent large-scale magnetohydrodynamic quantities
    in magnetic clouds
Authors: Dasso, S.; Gulisano, A. M.; Mandrini, C. H.; Démoulin, P.
Bibcode: 2005AdSpR..35.2172D
Altcode:
  Magnetic clouds are the interplanetary manifestation of coronal
  mass ejections, which are transient expulsions of major quantities
  of magnetized plasma, from the Sun toward the heliosphere. The
  magnetic flux and helicity are two key physical magnitudes to track
  solar structures from the photosphere-corona to the interplanetary
  medium. To determine the content of flux and helicity in magnetic
  clouds, we have to know their 3D structure. However, since spacecrafts
  register data along a unique direction, several aspects of their global
  configuration cannot be observed. We present a method to estimate the
  magnetic flux and the magnetic helicity per unit length in magnetic
  clouds, directly from in situ magnetic observations, assuming only
  a cylindrical symmetry for the magnetic field configuration in the
  observed cross-section of the cloud. We select a set of 20 magnetic
  clouds observed by the spacecraft Wind and estimate their magnetic flux
  and their helicity per unit length. We compare the results obtained
  from our direct method with those obtained under the assumption of a
  helical linear force-free field. This direct method improves previous
  estimations of helicity in clouds.

Title: Observational Consequences of a Magnetic Flux Rope Emerging
    into the Corona
Authors: Gibson, S. E.; Fan, Y.; Mandrini, C.; Fisher, G.; Demoulin, P.
Bibcode: 2004ApJ...617..600G
Altcode:
  We show that a numerical simulation of a magnetic flux rope emerging
  into a coronal magnetic field predicts solar structures and dynamics
  consistent with observations. We first consider the structure,
  evolution, and relative location and orientation of S-shaped, or
  sigmoid, active regions and filaments. The basic assumptions are that
  (1) X-ray sigmoids appear at the regions of the flux rope known as
  ``bald-patch-associated separatrix surfaces (BPSSs), where, under
  dynamic forcing, current sheets can form, leading to reconnection
  and localized heating, and that (2) filaments are regions of enhanced
  density contained within dips in the magnetic flux rope. We demonstrate
  that the shapes and relative orientations and locations of the BPSS
  and dipped field are consistent with observations of X-ray sigmoids and
  their associated filaments. Moreover, we show that current layers indeed
  form along the sigmoidal BPSS as the flux rope is driven by the kink
  instability. Finally, we consider how apparent horizontal motions of
  magnetic elements at the photosphere caused by the emerging flux rope
  might be interpreted. In particular, we show that local correlation
  tracking analysis of a time series of magnetograms for our simulation
  leads to an underestimate of the amount of magnetic helicity transported
  into the corona by the flux rope, largely because of undetectable
  twisting motions along the magnetic flux surfaces. Observations of
  rotating sunspots may provide better information about such rotational
  motions, and we show that if we consider the separated flux rope legs as
  proxies for fully formed sunspots, the amount of rotation that would
  be observed before the region becomes kink unstable would be in the
  range 40°-200° per leg/sunspot, consistent with observations.

Title: Comparisons Between SCIAMACHY Scientific Products and
    Ground-Based FTIR Data for Total Columns of CO, CH4 and N2O.
Authors: de Mazière, M.; Barret, B.; Blumenstock, T.; Buchwitz, M.;
   de Beek, R.; Demoulin, P.; Fast, H.; Gloudemans, A.; Griesfeller,
   A.; Griffith, D.; Ionov, D.; Janssens, K.; Jones, N.; Mahieu,
   E.; Mellqvist, J.; Mittermeier, R. L.; Notholt, J.; Rinsland, C.;
   Schrijver, H.; Schultz, A.; Smale, D.; Strandberg, A.; Strong, K.;
   Sussmann, R.; Warneke, T.; Wood, S.
Bibcode: 2004ESASP.562E..12D
Altcode: 2004acve.conf...12D
  Total column amounts of CO, CH4 and N2O retrieved from SCIAMACHY nadir
  observations in its near-infrared channels have been compared to data
  from a ground-based network of Fourier-transform infrared (FTIR)
  spectrometers as well as to data obtained with an FTIR instrument
  during a ship cruise in January-February 2003, along the African West
  Coast. The SCIAMACHY data considered here have been produced by two
  different scientific retrieval algorithms, wfm-doas (version 4.0)
  and IMLM (version 5.1), and cover different time periods, making the
  number of reliable coincidences that satisfy the temporal and spatial
  collocation criteria rather limited and different for both. Also the
  quality of the SCIAMACHY Level 1 data, and thus of the Level 2 data
  for the different time periods is very different. Still the comparisons
  demonstrate the capability of SCIAMACHY, using one of both algorithms,
  to deliver geophysically valuable products for the target species
  under consideration, on a global scale

Title: Geophysical Validation of SCIAMACHY NO2 Vertical Columns:
    Overview of Early 2004 Results
Authors: Lambert, J. -C.; Blumenstock, T.; Boersma, F.; Bracher, A.;
   de Mazière, M.; Demoulin, P.; de Smedt, I.; Eskes, H.; Gil, M.;
   Goutail, F.; Granville, J.; Hendrick, F.; Ionov, D. V.; Johnston,
   P. V.; Kostadinov, I.; Kreher, K.; Kyr, E.; Martin, R.; Meier, A.;
   Navarro-Comas, M.; Petritoli, A.; Pommereau, J. -P.; Richter, A.;
   Roscoe, H. K.; Sioris, C.; Sussmann, R.; van Roozendael, M.; Wagner,
   T.; Wood, S.; Yela, M.
Bibcode: 2004ESASP.562E...6L
Altcode: 2004acve.conf....6L
  Following the recommendations drawn after the Commissioning Phase of
  the ENVISAT satellite in 2002, SCIAMACHY near real time data processors
  were upgraded to version 5.01 in early 2004. Before public release of
  the new SCIAMACHY nitrogen dioxide (NO2) vertical column data product,
  several validation teams investigated its improvement and assessed
  its geophysical consistency by means of correlative studies involving
  NDSC-affiliated groundbased networks of DOAS UV-visible and FTIR
  spectrometers and the ERS-2 GOME satellite. In parallel, preliminary
  SCIAMACHY NO2 column data products generated by research processors
  under development at scientific institutes were also tested, using the
  same correlative data and validation procedures. Digesting the results
  obtained by a list of validation teams and SCIAMACHY data processing
  teams, this overview paper draws a preliminary quality assessment of
  the SCIAMACHY NO2 column data sets available in spring 2004.

Title: First Ground-Based Validation of SCIAMACHY V5.01 Ozone Column
Authors: Lambert, J. -C.; Allaart, M.; Andersen, S. B.; Blumenstock,
   T.; Bodeker, G.; Brinksma, E.; Cambridge, C.; de Mazière, M.;
   Demoulin, P.; Gerard, P.; Gil, M.; Goutail, F.; Granville, J.; Ionov,
   D. V.; Kyrö, E.; Navarro-Comas, M.; Piters, A.; Pommereau, J. -P.;
   Richter, A.; Roscoe, H. K.; Schets, H.; Shanklin, J. D.; Suortti,
   T.; Sussmann, R.; van Roozendael, M.; Varotsos, C.; Wagner, T.; Wood,
   S.; Yela, M.
Bibcode: 2004ESASP.562E...3L
Altcode: 2004acve.conf....3L
  In early 2004, the near real-time data processor of ENVISAT SCIAMACHY
  (SCI_NL) was upgraded to version 5.01. Based on the correlative
  measurements acquired and collected during the commissioning phase
  of the satellite in 2002, a preliminary validation was organised to
  verify the improvement and assess the geophysical consistency of the
  new SCIAMACHY o z o n e vertical column data product. The present
  overview summarises the results obtained by a list of v a l i d a
  t i o n teams and involving ground-based data acquired from pole to
  pole by complementary groundbased sensors. The studies conclude to an
  improvement compared to previous versions 3.5x. They also confirm the
  presence of expected errors (e.g. dependence on solar elevation and
  on ozone column) inherited from the G O M E Data Processor GDP 2.4,
  on which the SCIAMACHY processor SCI_NL is based

Title: Solar Origin of Interplanetary Impulsive Electron Events
Authors: Pick, M.; Maia, D. J.; Malandraki, O.; Krucker, S.;
   Demoulin, P.
Bibcode: 2004AGUSMSH22A..03P
Altcode:
  Many solar impulsive electron events have been traditionally associated
  with type III radio emissions. Several recent studies however showed
  that, in the majority of the events, the solar release of electrons at
  high energies can present delays of up-to-half an hour with respect of
  the onset of type III bursts. We have revisited the origin of a large
  number of events using multiwave-length observations. For each event,
  we investigated the coronal restructuring using EUV, white-light,
  radio imaging and spectral observations in a wide frequency range that
  allows us to follow the evolution of the corona from a few tenths above
  the solar limb up to a few solar radii. Radio observations revealed
  direct energetic electron signatures, close in time with the electron
  release. The release time for the delayed events always coincides with
  the onset or major changes in the complex of radio emissions. This
  close association indicates that the coronal processes involved in the
  radio emissions are at the origin of the electron acceleration. We
  illustrate our results by presenting, more particularly, one recent
  event for which the observations were also coupled with imaging
  spectroscopy measurements obtained by the RHESSI mission (from 3 keV to
  17 MeV). RHESSI observed a hard X-ray emission, which lasted for more
  than fifteen minutes. This emission was closely associated in time and
  space with the radio emission imaged by the Nançay Radioheliograph. The
  results suggest that, for this event, both electrons detected in the
  corona and those injected in the interplanetary medium are due to a
  similar process involving coronal magnetic field interactions. Their
  respective sites of acceleration/injection are however distinct in
  space and time. The energetic electrons detected in the interplanetary
  medium are not released during the X-ray burst.

Title: Magnetic Helicity Budget of Solar-Active Regions from the
    Photosphere to Magnetic Clouds
Authors: Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.;
   van Driel-Gesztelyi, L.; van Driel-Gesztelyi, L.; van Driel-Gesztelyi,
   L. L. M.; López Fuentes, M. C.
Bibcode: 2004Ap&SS.290..319M
Altcode:
  We have analyzed the long-term evolution of two active regions (ARs)
  from their emergence through their decay using observations from several
  instruments on board SoHO (MDI, EIT and LASCO) and Yohkoh/SXT. We
  have computed the evolution of the relative coronal magnetic helicity
  combining data from MDI and SXT with a linear force-free model of
  the coronal magnetic field. Next, we have computed the injection of
  helicity by surface differential rotation using MDI magnetic maps. To
  estimate the depletion of helicity we have counted all the CMEs of which
  these ARs have been the source, and we have evaluated their magnetic
  helicity assuming a one to one correspondence with magnetic clouds
  with an average helicity contain. When these three values (variation
  of coronal magnetic helicity, injection by differential rotation and
  ejection via CMEs) are compared, we find that surface differential
  rotation is a minor contributor to the helicity budget since CMEs carry
  away at least 10 times more helicity than the one differential rotation
  can provide. Therefore, the magnetic helicity flux needed in the global
  balance should come from localized photospheric motions that, at least
  partially, reflect the emergence of twisted flux tubes. We estimate
  that the total helicity carried away in CMEs can be provided by the
  end-to-end helicity of the flux tubes forming these ARs. Therefore,
  we conclude that most of the helicity ejected in CMEs is generated
  below the photosphere and emerges with the magnetic flux.

Title: The long-term evolution of active regions, multi-wavelength
flux and heating studies: observations and theory
Authors: Démoulin, P.
Bibcode: 2004IAUS..223...13D
Altcode: 2005IAUS..223...13D
  Analyzing the long-term evolution of active regions (ARs) permits to
  quantify the link between their atmospheric emission (from optical to
  X-rays) and the magnetic field. Multi-wavelength studies provide the
  full story, and not just a snapshot, of the phenomena and they allow
  us analyze how the atmosphere changes as the field strength decreases
  (with the dispersion of the AR).

Title: An Observational Test for Coronal Heating Models
Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Mandrini, C. H.;
   Harra, L. K.; Klimchuk, J. A.
Bibcode: 2004IAUS..219..473V
Altcode: 2003IAUS..219E..97V
  We correlate the evolution of the mean X-ray flux emission measure
  and temperature (Yohkoh SXT &amp; BCS) with the magnetic flux density
  (SOHO/MDI) in active region NOAA 7978 from its birth throughout its
  decay for five solar rotations. We show that these plasma parameters
  together with other quantities deduced from them such as the density
  and the pressure follow power-law relationships with the mean magnetic
  flux density (bar{B}). We derive the dependence of the mean coronal
  heating rate on the magnetic flux density. We use the obtained scaling
  laws of coronal loops in thermal equilibrium to derive observational
  estimates of the scaling of the coronal heating with bar{B}. These
  results are used to test the validity of coronal heating models. We
  find that models invoking stochastic buildup of energy current layers
  and MHD turbulence are in best agreement with the observations. This
  narrows down the range of possible models retained by previous results
  obtained for individual coronal loops as well as for the global coronal
  emission of the Sun and cool stars.

Title: Magnetohydrodinamic properties of solar origin magnetic clouds:
    an statistical study
Authors: Gulisano, A. M.; Dasso, S.; Mandrini, C. H.; Démoulin, P.
Bibcode: 2004BAAA...47...28G
Altcode:
  Magnetic Clouds (MCs) are the interplanetary manifestation of transient
  expulsions of solar mass, the so-called coronal mass ejections. Despite
  several statistical works that have been done studying diverse
  properties of MCs, systematic studies of their magnetohydrodynamic
  (MHD) global magnitudes, such as their magnetic helicity (MH) and
  energy, have not yet been undertaken. In this work we present a study
  of 20 MCs observed by the spacecraft Wind and quantify their MHD
  properties. The study is performed exploring 4 helical models with
  substantial differences in the magnetic field twist distribution. We
  find that the values of the MH content are almost independent from the
  analyzed models, in the sense that their dispersion when considering
  different models for a given event is smaller than the dispersion when
  considering different events.

Title: Emerging Flux and the Heating of Coronal Loops
Authors: Schmieder, B.; Rust, D. M.; Georgoulis, M. K.; Démoulin,
   P.; Bernasconi, P. N.
Bibcode: 2004ApJ...601..530S
Altcode:
  We use data collected by a multiwavelength campaign of observations
  to describe how the fragmented, asymmetric emergence of magnetic flux
  in NOAA active region 8844 triggers the dynamics in the active-region
  atmosphere. Observations of various instruments on board Yohkoh, SOHO,
  and TRACE complement high-resolution observations of the balloon-borne
  Flare Genesis Experiment obtained on 2000 January 25. We find that
  coronal loops appeared and evolved rapidly ~6+/-2 hr after the first
  detection of emerging magnetic flux. In the low chromosphere, flux
  emergence resulted in intense Ellerman bomb activity. Besides the
  chromosphere, we find that Ellerman bombs may also heat the transition
  region, which showed ``moss'' ~100% brighter in areas with Ellerman
  bombs as compared to areas without Ellerman bombs. In the corona,
  we find a spatiotemporal anticorrelation between the soft X-ray (SXT)
  and the extreme ultraviolet (TRACE) loops. First, SXT loops preceded
  the appearance of the TRACE loops by 30-40 minutes. Second, the TRACE
  and SXT loops had different shapes and different footpoints. Third,
  the SXT loops were longer and higher than the TRACE loops. We conclude
  that the TRACE and the SXT loops were formed independently. TRACE loops
  were mainly heated at their footpoints, while SXT loops brightened in
  response to coronal magnetic reconnection. In summary, we observed a
  variety of coupled activity, from the photosphere to the active-region
  corona. Links between different aspects of this activity lead to
  a unified picture of the evolution and the energy release in the
  active region.

Title: Multi-wavelength flare study and magnetic configuration
Authors: Schmieder, Brigitte; Berlicki, A.; Vilmer, N.; Aulanier,
   G.; Démoulin, P.; Mein, P.; Mandrini, C.; Deluca, E.
Bibcode: 2004IAUS..223..397S
Altcode: 2005IAUS..223..397S
  Recent results of two observation campaigns (October 2002 and October
  2003) are presented with the objective of understanding the onset
  of flares and CMEs. The magnetic field was observed with THEMIS and
  MDI, the chromosphere with the MSDP operating on the German telescope
  VTT and on THEMIS, the EUV images with SOHO/CDS and TRACE, the X-ray
  with RHESSI. We show how important is the magnetic configuration of
  the active region to produce CMEs using two examples: the October 28
  2003 X 17 flare and the October 22 2002 M 1.1 flare. The X 17 flare
  gave a halo CME while the M 1.1 flare has no corresponding CME. The
  magnetic topology analysis of the active regions is processed with a
  linear-force-free field configuration.

Title: Linking coronal observations of a `miniÂ´active region with
    its interplanetary manifestation
Authors: Dasso, S.; Mandrini, C. H.; Pohjolainen, S.; Green, L. M.;
   Démoulin, P.; van Driel-Gesztelyi, L.; Foley, C.; Copperwheat, C.
Bibcode: 2004BAAA...47...18D
Altcode:
  We analyze the smallest 'sigmoidal eruption - CME - interplanetary
  magnetic cloud' event even observed before. We find: (a) the same
  magnetic helicity sign and (b) similar magnetic flux values in the
  coronal source region and associated cloud, and (c) that the magnetic
  helicity changes, before and after the ejection, in approximately the
  same amount as the helicity content in the interplanetary cloud. These
  results stress the importance of complementary solar and interplanetary
  studies, to achieve a better understanding of the origin of eruptive
  phenomena.

Title: Emerging Flux and the Heating of Coronal Loops
Authors: Schmieder, B.; Démoulin, P.; Rust, D. M.; Georgoulis, M. K.;
   Bernasconi, P. N.
Bibcode: 2004IAUS..219..483S
Altcode: 2003IAUS..219E..18S
  We suggest that coronal loop heating is caused by dissipation of
  magnetic energy as new magnetic flux emerges from the photosphere. Based
  on data from a multi wavelength campaign of observations during the
  flight of the Flare Genesis Experiment we describe how emergence
  of flux from the photosphere appears directly to heat the corona
  to 2-3 MK. Following intense heating the loops cool and become
  visible through the filters of the TRACE (Transition Region and
  Coronal Explorer)instrument at one million degrees. We determine the
  relaxation time of the cooling and compare it withtheoretical heating
  functions. The proposed mechanism is well accepted in flare loops but
  we suggest that the mechanism is generally valid and helps to explain
  the visibility of active region loops in transition region lines.

Title: Can we determine the magnetic helicity sign of the solar
    active regions?
Authors: Luoni, M. L.; Mandrini, C. H.; Démoulin, P.; van
   Diel-Gesztelyi, L.; Kövári, Zs.
Bibcode: 2004BAAA...47...14L
Altcode:
  To improve space weather prediction it is important to know the
  characteristics of the solar active event responsable for the observed
  disturbances in the interplanetary (IP)medium. The comparison of the
  magnetic helicity sign of the active region (AR) and the interplanetary
  magnetic cloud, observed after a coronal mass ejection (CME), is a
  useful tool to link solar and interplanetary events. However, the
  determination of the coronal helicity sign requires the analysis of
  loop observations which is not promptly available (and, sometimes,
  non-conclusive), vector magnetograms that are not obtained in a routine
  way, and/or coronal magnetic field modeling. In this preliminary work,
  we show that it is possible to determine the magnetic helicity sign
  of an AR using only observations of the photospheric line of sight
  component of the magnetic field (Bl) during its emergence and early
  life-time stages.

Title: The smallest source region of an interplanetary magnetic cloud:
    a mini-sigmoid
Authors: Mandrini, C.; Pohjolainen, S.; Dasso, S.; Green, L.; Demoulin,
   P.; van Driel-Gesztelyi, L.; Copperwheat, C.; Foley, C.
Bibcode: 2004cosp...35..290M
Altcode: 2004cosp.meet..290M
  Using multi-instrument and multi-wavelength observations (SOHO/MDI
  and EIT, TRACE and Yohkoh/SXT), as well as computing the coronal
  magnetic field of a tiny bipole combined with modelling of WIND in situ
  data, we provide evidence for the smallest sigmoid eruption - CME -
  interplanetary magnetic cloud event ever observed. The tiny bipole,
  which was observed very close to the solar disc centre, had 100 times
  less flux than an average active region (AR). In the corona it had a
  sigmoidal structure and we detected a very high level of twist. On 11
  May 1998, at about 8 UT, the sigmoid underwent eruption evidenced by
  expanding elongated EUV loops, dimmings and formation of a cusp. The
  WIND spacecraft detected 4.5 days later one of the smallest magnetic
  clouds (MC) ever identified (100 times less flux and radius than an
  average MC). The link between the sigmoidal EUV bright point eruption
  and the interplanetary magnetic cloud is supported by several pieces of
  evidence: good timing, same coronal loop and MC orientation relative
  to the ecliptic, same magnetic field direction and magnetic helicity
  sign in the coronal loops and in the MC, comparable magnetic flux
  measured in the dimming regions and in the interplanetary MC and,
  most importantly, the pre- to post-event change of magnetic helicity
  in the solar corona is found to be similar to the helicity content of
  the cloud, when assuming a length compatible with the fact that the
  cloud can be detached from the Sun one day after its ejection. These
  observations are a challenge to present theoretical CME models, and show
  us the need of missions such us Solar B and Stereo to contribute to our
  understanding of the broad spectrum covered by solar eruptive phenomena.

Title: How small can an interplanetary magnetic cloud source-region
    be?
Authors: Mandrini, C.; Pohjolainen, S.; Dasso, S.; Green, L.; Demoulin,
   P.; van Driel-Gesztelyi, L.; Copperwheat, C.; Foley, C.
Bibcode: 2004cosp...35..282M
Altcode: 2004cosp.meet..282M
  Using multi-instrument and multi-wavelength observations (SOHO/MDI
  and EIT, TRACE and Yohkoh/SXT), as well as computing the coronal
  magnetic field of a tiny bipole combined with modelling of WIND in situ
  data, we provide evidence for the smallest sigmoid eruption - CME -
  interplanetary magnetic cloud event ever observed. The tiny bipole,
  which was observed very close to the solar disc centre, had 100 times
  less flux than an average active region (AR). In the corona it had a
  sigmoidal structure and we detected a very high level of twist. On 11
  May 1998, at about 8 UT, the sigmoid underwent eruption evidenced by
  expanding elongated EUV loops, dimmings and formation of a cusp. The
  WIND spacecraft detected 4.5 days later one of the smallest magnetic
  clouds (MC) ever identified (100 times less flux and radius than an
  average MC). The link between the sigmoidal EUV bright point eruption
  and the interplanetary magnetic cloud is supported by several pieces of
  evidence: good timing, same coronal loop and MC orientation relative
  to the ecliptic, same magnetic field direction and magnetic helicity
  sign in the coronal loops and in the MC, comparable magnetic flux
  measured in the dimming regions and in the interplanetary MC and,
  most importantly, the pre- to post-event change of magnetic helicity
  in the solar corona is found to be similar to the helicity content
  of the cloud, when assuming a length compatible with the fact that
  thecloud can be dettached from the Sun one day after its ejection. These
  observations are a challenge to present theoretical CME models, and show
  us the need of missions such us Solar B and Stereo to contribute to our
  understandig of the broad spectrum covered by solar eruptive phenomena.

Title: Extending the concept of separatrices to QSLs for magnetic
    reconnection
Authors: Demoulin, P.
Bibcode: 2004cosp...35.1084D
Altcode: 2004cosp.meet.1084D
  Magnetic reconnection is usually thought to be linked to the presence
  of magnetic null points and to be accompanied by the transport of
  magnetic field lines across separatrices, the set of field lines where
  the mapping of field lines is discontinuous. However, this view is
  too restrictive taking into account the variety of observed solar
  flaring configurations. Indeed ``quasi-separatrix layers" (QSLs),
  which are regions where there is drastic change in field-line linkage
  generalize the definition of separatrices. The use of this broader
  concept allows us to localize these thin regions where magnetic
  reconnection can preferentially occur in three-dimensional magnetic
  configurations. I will survey the evolution of the QSL concept from
  the beginning to the recent developments. The application to solar
  observations requires first the computation of the coronal magnetic
  field from photospheric data. Then, the determination of the QSLs allows
  us to understand the observed location of flare kernels and loops and
  so to validate the reconnection scenario as the main physical process
  at the origin of flares. On the theoretical side, locating the QSLs
  let us predict where strong current layers will form as a consequence
  of boundary evolution. Numerical simulations broadly confirm this,
  with direct implications for coronal heating. This QSL approach is
  also compatible with an MHD turbulence scenario for coronal heating
  as numerical simulations show the development of MHD turbulence when
  reconnection starts in QSLs.

Title: Direct observation of large scale magnetohydrodynamic
    quantities in magnetic clouds
Authors: Dasso, S.; Gulisano, A.; Mandrini, C. H.; Démoulin, P.
Bibcode: 2004cosp...35..530D
Altcode: 2004cosp.meet..530D
  Magnetic Clouds (MCs) are the interplanetary manifestation of Coronal
  Mass Ejections (CMEs). Despite these astrophysical objects have been
  observed for more than 20 years, several details of their magnetic
  configuration at 1AU, as consequence of their dynamical evolution
  through the inner heliosphere, are not well known. The magnetic flux
  (F) and helicity (MH) are very important magnetohydrodynamic (MHD)
  quantities characterizing the magnetic configuration in these objects,
  and there are very few studies quantifying their typical values. MH
  measures several aspects of a given magnetic structure, and it is
  practically conserved in the solar atmosphere and the heliosphere. MCs
  travel from the Sun toward the external heliosphere carrying an
  important amount of MH. In situ observations of MCs at 1 AU agree
  with a local helical magnetic structure. However, since spacecrafts
  only register data along a unique direction, several aspects of the
  global configuration are not observed. We select a set of MCs observed
  by the spacecraft Wind and we analyze them, obtaining values for F and
  MH directly from the observations. We apply first the Minimum Variance
  method to obtain the components of the magnetic field in the coordinates
  of the cloud, then we apply a method to calculate the MH and the F from
  these components, assuming only a cylindrical symmetry for the magnetic
  field configuration in the cloud. We compare the results obtained from
  our direct method with that obtained under the assumption of a helical
  linear force-free field (i.e., the Lundquist's solution). Our direct
  method is useful to compare the MH content in a given MC, with the MH
  variation in the solar corona before and after the associated CME.

Title: 3D MHD models for XUV sigmoids
Authors: Aulanier, G.; Démoulin, P.; Grappin, R.; Marqué, C.
Bibcode: 2004cosp...35.3011A
Altcode: 2004cosp.meet.3011A
  Solar sigmoids observed in XUV wavelengths have recently been identified
  as good probes of current-carrying magnetic fields which can precede
  the launch of a CME. However, the amplitude and the distribution of
  these pre-eruptive currents are yet very poorly known, since several
  3D magnetostatic models are able to produce S-shaped field lines
  projected onto the photospheric plane, most of them implying that
  more or less twisted field lines trace the whole sigmoid. We will
  show two new families of magnetic models for XUV sigmoids: a generic
  model based on MHD calculations of line-tied twisted flux tubes,
  and a model for one observed sigmoid based on linear force-free
  field extrapolations. Both models predict that XUV sigmoids do not
  trace the central twisted flux tube, also that no single field line
  can ever trace the whole sigmoid, and finally that sigmoids may only
  show an ensemble of low-lying sheared field lines of various lengths,
  with several interruptions of connectivities all along the sigmoid
  depending on the shear distribution and on the local complexity of
  the photospheric field. So, these new models predict that sigmoids may
  not have a magnetic topology as simple as what is predicted by classic
  models, and that the derivation of the degree of twist from the shape
  of the sigmoid may not be directly doable, so that it may require
  the use of models. The 3D characteristic of these new XUV sigmoid
  models, combined with their synthetic transverse photospheric fields,
  provide new predictions and tools which will be very well suited for
  the analyzis of the upcoming STEREO and SOLAR-B combined observations
  of these structures.

Title: Magnetic configuration reorganisation before the X 17 flare
    of October28 2003
Authors: Schmieder, B.; Mandrini, C.; Demoulin, P.; Mein, P.
Bibcode: 2004cosp...35.1528S
Altcode: 2004cosp.meet.1528S
  The active region NOAA 0486 was observed during a multi-wavelength
  campaign with ground based and space instruments. We analyse the
  magnetic configuration of the region during a pre-event, which
  reorganizes the magnetic connectivities of the field lines before the
  occurence of a X17 flare of October 28 2003. The magnetic field was
  observed with THEMIS and MDI, the chromosphere with the MSDP operating
  on on THEMIS and with the Meudon heliograph, the EUV images with
  SOHO/CDS and TRACE. The X17 flare gave a halo CME while the M1.9 flare
  has no corresponding CME. The magnetic field analysis of the active
  regions is performed by using a linear-force-free field code. The
  pre-flare event before the X17 flare change the connectivities in a
  first phase and allows the stressed field to relax in a second phase
  producing the X17 flare.

Title: Observational consequences of a magnetic flux rope topology
Authors: Gibson, S.; Barnes, G.; Demoulin, P.; Fan, Y.; Fisher, G.;
   Leka, K.; Longcope, D.; Mandrini, C.; Metcalf, T.
Bibcode: 2003AGUFMSH42B0516G
Altcode:
  We consider the implications of a magnetic flux rope topology for
  the interpretation of observations of sigmoidal active regions. A
  region of tangential magnetic discontinuities can be identified
  using techniques that determine a bald patch (BP) and corresponding
  separatrices or a quasi-separatrix layer (QSL) -- for a flux rope this
  region can be S-shaped, or sigmoidal. If such a region is physically
  driven, current sheets can form yielding conditions appropriate for
  reconnective heating. Using a numerical simulation of an emerging
  flux rope driven by the kink instability, Fan and Gibson (ApJL, 2003)
  showed that current sheets indeed formed a sigmoidal surface. In this
  poster we will demonstrate that the current sheets formed on the BP and
  BP separatrices. Moreover, we will use the results of the numerical
  simulation as proxies for observations: specifically the simulated
  field at the photosphere as proxy for the magnetic boundary condition,
  the sigmoidal current sheets as proxy for the X-ray active region
  emission, and the location of dipped magnetic field lines as proxy
  for a filament. We will then consider to what extent such observations
  might be used to understand and constrain the basic properties of the
  coronal field.

Title: Magnetic helicity analysis of an interplanetary twisted
    flux tube
Authors: Dasso, S.; Mandrini, C. H.; DéMoulin, P.; Farrugia, C. J.
Bibcode: 2003JGRA..108.1362D
Altcode:
  We compute the magnetic flux and helicity of an interplanetary flux tube
  observed by the spacecraft Wind on 24-25 October 1995. We investigate
  how model-dependent are the results by determining the flux-tube
  orientation using two different methods (minimum variance and a
  simultaneous fit), and three different models: a linear force-free
  field, a uniformly twisted field, and a nonforce-free field with
  constant current. We have fitted the set of free parameters for
  the six cases and have found that the two force-free models fit
  the data with very similar quality for both methods. Then, both the
  comparable computed parameters and global quantities, magnetic flux and
  helicity per unit length, agree to within 10% for the two force-free
  models. These results imply that the magnetic flux and helicity of the
  tube are well-determined quantities, nearly independent of the model
  used, provided that the fit to the data is good enough.

Title: The Magnetic Helicity of an Interplanetary Hot Flux Rope
Authors: Dasso, S.; Mandrini, C. H.; Démoulin, P.
Bibcode: 2003AIPC..679..786D
Altcode:
  In the last years, interest in the study of the relationship between
  the magnetic helicity of solar active regions and the one contained
  in the interplanetary structures has grown. This has lead us to
  compute the helicity content of an interplanetary hot tube observed
  by Wind on October 24-25, 1995, applying three different approaches
  in cylindrical geometry: a linear force-free field, a constant twist
  angle, and a non force-free model with constant current. We have fitted
  the set of free parameters for each of the three models, finding that
  the determined magnetic helicity values are very similar when using
  the same orientation for the flux tube. From our point of view, these
  results imply that, whatever be the model used, magnetic helicity is a
  well-determined quantity and, thus, it is worth using it to understand
  the link between solar and interplanetary phenomena.

Title: Magnetic Energy and Helicity Fluxes at the Photospheric Level
Authors: Démoulin, P.; Berger, M. A.
Bibcode: 2003SoPh..215..203D
Altcode:
  The source of coronal magnetic energy and helicity lies below the
  surface of the Sun, probably in the convective zone dynamo. Measurements
  of magnetic and velocity fields can capture the fluxes of both
  magnetic energy and helicity crossing the photosphere. We point out the
  ambiguities which can occur when observations are used to compute these
  fluxes. In particular, we show that these fluxes should be computed
  only from the horizontal motions deduced by tracking the photospheric
  cut of magnetic flux tubes. These horizontal motions include the effect
  of both the emergence and the shearing motions whatever the magnetic
  configuration complexity is. We finally analyze the observational
  difficulties involved in deriving such fluxes, in particular the
  limitations of the correlation tracking methods.

Title: How are Emerging Flux, Flares and CMEs Related to Magnetic
    Polarity Imbalance in Midi Data?
Authors: Green, L. M.; Démoulin, P.; Mandrini, C. H.; Van
   Driel-Gesztelyi, L.
Bibcode: 2003SoPh..215..307G
Altcode: 2003astro.ph..4092G
  In order to understand whether major flares or coronal mass ejections
  (CMEs) can be related to changes in the longitudinal photospheric
  magnetic field, we study 4 young active regions during seven days of
  their disk passage. This time period precludes any biases which may
  be introduced in studies that look at the field evolution during the
  short-term flare or CME period only. Data from the Michelson Doppler
  Imager (MDI) with a time cadence of 96 min are used. Corrections are
  made to the data to account for area foreshortening and angle between
  line of sight and field direction, and also the underestimation of
  the flux densities. We make a systematic study of the evolution of the
  longitudinal magnetic field, and analyze flare and CME occurrence in
  the magnetic evolution. We find that the majority of CMEs and flares
  occur during or after new flux emergence. The flux in all four active
  regions is observed to have deviations from polarity balance both on
  the long term (solar rotation) and on the short term (few hours). The
  long-term imbalance is not due to linkage outside the active region; it
  is primarily related to the east-west distance from central meridian,
  with the sign of polarity closer to the limb dominating. The sequence
  of short-term imbalances are not closely linked to CMEs and flares and
  no permanent imbalance remains after them. We propose that both kinds
  of imbalance are due to the presence of a horizontal field component
  (parallel to the photospheric surface) in the emerging flux.

Title: Hyperbolic Flux Tubes in Flaring Magnetic Configurations
Authors: Titov, Vyacheslav S.; Démoulin, Pascal; Hornig, Gunnar
Bibcode: 2003ANS...324...17T
Altcode: 2003ANS...324..B16T
  No abstract at ADS

Title: Amplitude and orientation of prominence magnetic fields from
    constant-alpha  magnetohydrostatic models
Authors: Aulanier, G.; Démoulin, P.
Bibcode: 2003A&A...402..769A
Altcode:
  We analyze outputs from three-dimensional models for three observed
  filaments, which belong to the quiescent, intermediate and plage
  class respectively. Each model was calculated from a constant-alpha
  magnetohydrostatic extrapolation, assuming that the prominence material
  is located in magnetic dips, so that the field is nearly horizontal
  throughout the prominence body and feet. We calculate the spatial
  distribution of the magnetic field amplitude B and orientation
  theta with respect to the filament axis, neither of which were
  imposed a priori in the models. In accordance with past magnetic
  field measurements within prominence bodies, we also obtain nearly
  homogeneous magnetic fields, respectively of about B ~ 3, 14 and 40 G
  for the quiescent, intermediate and plage prominence, with a systematic
  weak vertical field gradient of partial B / partial z ~ 0.1-1.5 x
  10<SUP>-4</SUP> G km<SUP>-1</SUP>. We also find that the inverse
  polarity configuration is dominant with theta ~ -20<SUP>o</SUP> to
  0<SUP>o</SUP>, which is slightly smaller than in some observations. We
  also report some other properties, which have either rarely or never
  been observed. We find at prominence tops some localized normal polarity
  regions with theta &lt; +10<SUP>o</SUP>. At prominence bottoms below 20
  Mm in altitude, we find stronger field gradients partial B / partial z
  ~ 1-10 x 10<SUP>-4</SUP> G km<SUP>-1</SUP> and a wider range of field
  directions theta ~ -90<SUP>o</SUP> to 0<SUP>o</SUP>. These properties
  can be interpreted by the perturbation of the prominence flux tube
  by strong photospheric polarities located in the neighborhood of the
  prominence. We also report some full portions of prominences that have
  the normal polarity. The latter are simply due to the local curvature
  of the filaments with respect to their average axis, which was used
  to define theta . These results could either be used as predictions
  for further testing of this class of models with new observations,
  or as quantitative tools for the interpretation of observations which
  show complex patterns.

Title: The Long-Term Evolution of AR 7978: The Scalings of the
    Coronal Plasma Parameters with the Mean Photospheric Magnetic Field
Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Mandrini, C. H.;
   Harra, L.; Klimchuk, J. A.
Bibcode: 2003ApJ...586..579V
Altcode:
  We analyze the evolution of the fluxes observed in X-rays and correlate
  them with the magnetic flux density in active region (AR) NOAA 7978
  from its birth throughout its decay, for five solar rotations. We
  use Solar and Heliospheric Observatory Michelson Doppler Imager
  (MDI) data, together with Yohkoh Soft X-Ray Telescope (SXT) and
  Yohkoh Bragg Crystal Spectrometer (BCS) data, to determine the global
  evolution of the temperature and the emission measure of the coronal
  plasma at times when no significant brightenings were observed. We
  show that the mean X-ray flux and derived parameters, temperature
  and emission measure (together with other quantities deduced from
  them, such as the density and the pressure), of the plasma in the AR
  follow power-law relationships with the mean magnetic flux density
  (B). The exponents (b) of these power-law functions (aB<SUP>b</SUP>)
  are derived using two different statistical methods, a classical
  least-squares method in log-log plots and a nonparametric method,
  which takes into account the fact that errors in the data may not be
  normally distributed. Both methods give similar exponents, within
  error bars, for the mean temperature and for both instruments (SXT
  and BCS); in particular, b stays in the range [0.27, 0.31] and [0.24,
  0.57] for full-resolution SXT images and BCS data, respectively. For
  the emission measure, the exponent b lies in the range [0.85, 1.35]
  and [0.45, 1.96] for SXT and BCS, respectively. The determination of
  such power-law relations, when combined with the results from coronal
  heating models, can provide us with powerful tools for determining the
  mechanism responsible for the existence of the high-temperature corona.

Title: The Long-Term Evolution of AR 7978: Testing Coronal Heating
    Models
Authors: Démoulin, P.; van Driel-Gesztelyi, L.; Mandrini, C. H.;
   Klimchuk, J. A.; Harra, L.
Bibcode: 2003ApJ...586..592D
Altcode:
  We derive the dependence of the mean coronal heating rate on the
  magnetic flux density. Our results are based on a previous study of
  the plasma parameters and the magnetic flux density (B) in the active
  region NOAA 7978 from its birth to its decay, throughout five solar
  rotations using the Solar and Heliospheric Observatory Michelson
  Doppler Imager, Yohkoh Soft X-Ray Telescope (SXT), and Yohkoh Bragg
  Crystal Spectrometer (BCS). We use the scaling laws of coronal loops
  in thermal equilibrium to derive four observational estimates of the
  scaling of the coronal heating with B (two from SXT and two from
  BCS observations). These results are used to test the validity of
  coronal heating models. We find that models based on the dissipation
  of stressed, current-carrying magnetic fields are in better agreement
  with the observations than models that attribute coronal heating to
  the dissipation of MHD waves injected at the base of the corona. This
  confirms, with smaller error bars, previous results obtained for
  individual coronal loops, as well as for the global coronal emission
  of the Sun and cool stars. Taking into account that the photospheric
  field is concentrated in thin magnetic flux tubes, both SXT and BCS
  data are in best agreement with models invoking a stochastic buildup
  of energy, current layers, and MHD turbulence.

Title: The large scale magnetic helicity content of the interplanetary
    magnetic cloud of October 18-19, 1995
Authors: Dasso, S.; Mandrini, C. H.; Démoulin, P.; Luoni, M. L.
Bibcode: 2003BAAA...46....3D
Altcode:
  Magnetic helicity (MH) quantifies various aspects of a given magnetic
  structure, such as the twist, kink, and the number of knotts between
  magnetic field lines, the linking between magnetic flux tubes, the
  shear in layers of magnetic flux, etc. MH is practically conserved
  in the solar atmosphere and in the heliosphere. The relation between
  the MH generated in the Sun and that ejected into the interplanetary
  medium is not yet well known. Interplanetary magnetic clouds (MCs) are
  huge objects that travel from the Sun toward the external heliosphere
  carrying an important amount of MH. Despite being expanding systems, in
  situ observations of their magnetic field have been frequently modelled
  using several different magnetohydrostatic solutions. At present,
  it is not at all evident which model gives the best representation of
  their magnetic structure. Interest has grown on both the solar physics
  and the interplanetary communities to study the relation between the
  helicity generated in the Sun and ejected into the interplanetary
  medium. However, detailed studies of the magnetic helicity in MCs do
  not yet exist. In this work we analyse the helicity content of the
  magnetic cloud observed by the spacecraft Wind on October 18-19, 1995;
  we use three different models with cylindrical symmetry (two of them
  are force free and the third one has constant current). We compute the
  free parameters for each of the three models from observations and,
  from the fitted values, we compute the MH and compare the results. These
  multi-approaches allow us to quantify the range of MH contained in the
  MC. We found that even if the distribution of the twist inside the MC
  is very different in every model, the MH is practically independent
  of the model. We also conclude that, due to the sensitivity of the
  helicity content with the radius of the cloud, it is essential to
  use an appropriate method in order to determine, without ambiguity,
  the orientation of the flux tube.

Title: How to test coronal heating models?
Authors: Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.;
   Klimchuk, J. A.; Harra, L. K.
Bibcode: 2003BAAA...46....5M
Altcode:
  We have tested coronal heating models following two different
  approaches. In the first case, we compared the dependence of the
  coronal heating rate predicted by theoretical models with the
  observed one, deriving the scalings of parameters, such as: the
  density, temperature and intensity of the coronal magnetic field,
  with the length of magnetic field lines. To do so, we combined density
  and temperature measurements for 47 coronal loops with magnetic field
  models for 14 active regions. In the second case, we analyzed the long
  term evolution of an active region observed during seven rotations
  on the solar disk and we determined the dependence of the observed
  heating rate with the magnetic field density (bar{B}), after finding
  the scalings of plasma parameters with bar{B}. In both cases, we found
  that models based on the dissipation of stressed, current-carrying
  magnetic fields (called direct current models) are in better agreement
  with observations than models that attribute coronal heating to the
  dissipation of MHD waves injected at the base of the corona (called
  alternate current models). Taking into account that the photospheric
  field is concentrated in thin magnetic flux tubes, observations are
  in best agreement with models invoking a stochastic buildup of energy,
  current layers and MHD turbulence, within direct current models.

Title: Validation of Envisat Level-2 Products Related to Lower
    Atmosphere O3 and NOY Chemistry by a FTIR Quasi-Global Network
    (AOID126)
Authors: De Maziere, M.; Coosemans, T.; Barret, B.; Blumenstock, T.;
   Griesfeller, A.; Demoulin, P.; Fast, H.; Griffith, D.; Jones, N.;
   Mahieu, E.; Mellqvist, J.; Mittermeier, R. L.; Notholt, J.; Rinsland,
   C.; Schulz, A.; Smale, D.; Strandberg, A.; Sussmann, R.; Wood, S.;
   Buchwitz, M.
Bibcode: 2003ESASP.531E..40D
Altcode:
  No abstract at ADS

Title: Active region helicity evolution and related coronal mass
    ejection activity
Authors: Green, L. M.; López Fuentes, M. C.; Mandrini, C. H.; van
   Driel-Gesztelyi, L.; Démoulin, P.
Bibcode: 2003AdSpR..32.1959G
Altcode:
  The computation of magnetic helicity has become increasingly important
  in the studies of solar activity. Observations of helical structures
  in the solar atmosphere, and their subsequent ejection into the
  interplanetary medium, have resulted in considerable interest to find
  the link between the amount of helicity in the coronal magnetic field
  and the origin of coronal mass ejections (CMEs), which provide a natural
  method to remove helicity from the corona. Recent works have endeavored
  to find the source of helicity to explain the observed CME activity
  in specific cases. The main candidates being differential rotation,
  shear motions or a transfer of helicity from below the photosphere
  into the corona. We study an active region for several rotations
  during 1997 and 1998 to investigate the relative importance of these
  mechanisms. We find that photospheric differential rotation cannot
  provide the required magnetic helicity to the corona and the ejected
  CMEs. Localized photospheric motions can provide a larger helicity flux,
  though still not sufficient.

Title: Magnetic twist and writhe of active regions. On the origin
    of deformed flux tubes
Authors: López Fuentes, M. C.; Démoulin, P.; Mandrini, C. H.;
   Pevtsov, A. A.; van Driel-Gesztelyi, L.
Bibcode: 2003A&A...397..305L
Altcode: 2014arXiv1411.5626L
  We study the long term evolution of a set of 22 bipolar active regions
  (ARs) in which the main photospheric polarities are seen to rotate one
  around the other during several solar rotations. We first show that
  differential rotation is not at the origin of this large change in
  the tilt angle. A possible origin of this distortion is the nonlinear
  development of a kink-instability at the base of the convective zone;
  this would imply the formation of a non-planar flux tube which,
  while emerging across the photosphere, would show a rotation of its
  photospheric polarities as observed. A characteristic of the flux tubes
  deformed by this mechanism is that their magnetic twist and writhe
  should have the same sign. From the observed evolution of the tilt of
  the bipoles, we derive the sign of the writhe of the flux tube forming
  each AR; while we compute the sign of the twist from transverse field
  measurements. Comparing the handedness of the magnetic twist and writhe,
  we find that the presence of kink-unstable flux tubes is coherent with
  no more than 35% of the 20 cases for which the sign of the twist can
  be unambiguously determined. Since at most only a fraction of the tilt
  evolution can be explained by this process, we discuss the role that
  other mechanisms may play in the inferred deformation. We find that
  36% of the 22 cases may result from the action of the Coriolis force
  as the flux tube travels through the convection zone. Furthermore,
  because several bipoles overpass in their rotation the mean toroidal
  (East-West) direction or rotate away from it, we propose that a
  possible explanation for the deformation of all these flux tubes
  may lie in the interaction with large-scale vortical motions of the
  plasma in the convection zone, including also photospheric or shallow
  sub-photospheric large scale flows.

Title: Observations of magnetic helicity
Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Mandrini, C. H.
Bibcode: 2003AdSpR..32.1855V
Altcode:
  The first observational signature of magnetic helicity in the solar
  atmosphere (sunspot whirls) was discovered 77 years ago. Since then,
  the existence of a cycle-invariant hemispheric helicity pattern has
  been firmly established through current helicity and morphological
  studies. During the last years, attempts were made to estimate/ measure
  magnetic helicity from solar and interplanetary observations. Magnetic
  helicity (unlike current helicity) is one of the few global quantities
  that is conserved even in resistive magnetohydrodynamics (MHD) on a
  timescale less than the global diffusion timescale, thus magnetic
  helicity studies make it possible to trace helicity as it emerges
  from the sub-photospheric layers to the corona and then is ejected via
  coronal mass ejections (CMEs) into the interplanetary space reaching
  the Earth in a magnetic cloud. We give an overview of observational
  studies on the relative importance of different sources of magnetic
  helicity, i.e. whether photospheric plasma motions (photospheric
  differential rotation and localized shearing motions) or the twist
  of the emerging flux tubes created under the photosphere (presumably
  by the radial shear in the differential rotation in the tachocline)
  is the dominant helicity source. We examine the sources of errors
  present in these early results and try to judge how realistic they are.

Title: Why to determine the magnetic helicity in corona and
    interplanetary medium?
Authors: Luoni, M. L.; Dasso, S.; Mandrini, C. H.; van Driel-Gesztelyi,
   L.; Démoulin, P.
Bibcode: 2003BAAA...46....8L
Altcode:
  Magnetic clouds are huge objects that travel in the interplanetary
  medium, transporting magnetic helicity (MH) produced by the Sun. Since
  the dissipation time of MH is much larger than the typical time
  associated with the dynamical processes in the solar corona and the
  heliosphere, MH is the natural magnetohydrodinamic (MHD) magnitude
  to compare interplanetary manifestations with the associated solar
  processes. In this work we study an active region that produced a
  coronal mass ejection (CME). We model the coronal magnetic field
  using a linear force free approach, and we calculate the magnetic
  flux and the variation of MH, before and after the ejection of
  the CME. We model also the magnetic field configuration of the
  associated interplanetary cloud, using several cylindrical models,
  and estimate the flux and the content of MH. Finally, we compare the
  coronal and the interplanetary values for the flux and the MH, and we
  find a very good agreement. The coronal flux is 10<SUP>22</SUP>Mx,
  while the magnetic flux for the cloud is around 10<SUP>21</SUP>Mx
  (∼ 10% of the coronal flux, as typically observed). The variation
  of the coronal MH turns out to be 3x10<SUP>42</SUP>Mx<SUP>2</SUP>,
  while we obtain that the MH contained in the magnetic cloud is in the
  range (2-8)x10<SUP>42</SUP>Mx<SUP>2</SUP>. Our results indicate that
  MH is a very useful tool to link phenomena in very different regimes
  and can be used to constrain both coronal and interplanetary models.

Title: On the origin of peculiar active regions
Authors: Mandrini, C. H.; López Fuentes, M. C.; Démoulin, P.;
   van Driel-Gesztelyi, L.; Pevtsov, A. A.
Bibcode: 2002ESASP.505..121M
Altcode: 2002solm.conf..121M; 2002IAUCo.188..121M
  We study the long term evolution of a set of bipolar active regions
  (ARs) in which the main photospheric polarities are seen to rotate one
  around the other during several solar rotations. After showing that
  differential rotation cannot produce this large change in the tilt
  angle, we interpret this peculiar evolution as being the result of the
  emergence of magnetic flux tubes that are distorted with respect to
  the classical Ω-loop shape. A possible origin of this distortion is
  the nonlinear development of a kink-instability. Flux tubes deformed
  by this mechanism must have the same sign of twist and writhe. From
  the observed evolution of the tilt of the bipoles, we derive the
  sign of the writhe of the tube forming each AR; while we compute
  the sign of the twist from transverse field measurements. Comparing
  the handedness of the magnetic twist and writhe, we find that the
  presence of kink-unstable flux tubes is coherent with no more than 32%
  of the studied cases; so, a small fraction of these peculiar ARs can
  be explained by this process. Then we discuss the role that other
  mechanisms may play inducing the inferred deformation, such as the
  Coriolis force or external rotational motions of the plasma as the
  tube ascends in the convection zone.

Title: The Structure and Evolution of a Sigmoidal Active Region
Authors: Gibson, S. E.; Fletcher, L.; Del Zanna, G.; Pike, C. D.;
   Mason, H. E.; Mandrini, C. H.; Démoulin, P.; Gilbert, H.; Burkepile,
   J.; Holzer, T.; Alexander, D.; Liu, Y.; Nitta, N.; Qiu, J.; Schmieder,
   B.; Thompson, B. J.
Bibcode: 2002ApJ...574.1021G
Altcode:
  Solar coronal sigmoidal active regions have been shown to be precursors
  to some coronal mass ejections. Sigmoids, or S-shaped structures,
  may be indicators of twisted or helical magnetic structures, having
  an increased likelihood of eruption. We present here an analysis of a
  sigmoidal region's three-dimensional structure and how it evolves in
  relation to its eruptive dynamics. We use data taken during a recent
  study of a sigmoidal active region passing across the solar disk
  (an element of the third Whole Sun Month campaign). While S-shaped
  structures are generally observed in soft X-ray (SXR) emission, the
  observations that we present demonstrate their visibility at a range of
  wavelengths including those showing an associated sigmoidal filament. We
  examine the relationship between the S-shaped structures seen in SXR
  and those seen in cooler lines in order to probe the sigmoidal region's
  three-dimensional density and temperature structure. We also consider
  magnetic field observations and extrapolations in relation to these
  coronal structures. We present an interpretation of the disk passage
  of the sigmoidal region, in terms of a twisted magnetic flux rope
  that emerges into and equilibrates with overlying coronal magnetic
  field structures, which explains many of the key observed aspects of
  the region's structure and evolution. In particular, the evolving flux
  rope interpretation provides insight into why and how the region moves
  between active and quiescent phases, how the region's sigmoidicity is
  maintained during its evolution, and under what circumstances sigmoidal
  structures are apparent at a range of wavelengths.

Title: The role of magnetic bald patches in surges and arch filament
    systems
Authors: Mandrini, C. H.; Démoulin, P.; Schmieder, B.; Deng, Y. Y.;
   Rudawy, P.
Bibcode: 2002A&A...391..317M
Altcode:
  The short-lived active region (AR) NOAA 7968 was thoroughly observed
  all along its disk transit (June 3 to 10, 1996) from space and from
  the ground. During the early stage of its evolution, flux emerged in
  between the two main polarities and arch filament systems (AFS) were
  observed to be linked to this emergence. New bipoles and a related surge
  were observed on June 9. We have modeled the magnetic configuration
  of AR 7968 using a magnetohydrostatic approach and we have analyzed
  its topology on June 6 and June 9 in detail. We have found that some
  of the AFS and the surge were associated with field lines having dips
  tangent to the photosphere (the so called ``bald patches'', BPs). Two
  interacting BP separatrices, defining a separator, have been identified
  in the configuration where these very different events occurred. The
  observed evolution of the AFS and the surge is consistent with the
  expected results of magnetic reconnection occuring in this magnetic
  topology, which is specific to 3D configurations. Previously BPs have
  been found to be related to filament feet, small flares and transition
  region brightenings. Our results are evidence of the importance of
  BPs in a much wider range of phenomena, and show that current layers
  can be formed and efficiently dissipated in the chromosphere.

Title: Theory of magnetic connectivity in the solar corona
Authors: Titov, Vyacheslav S.; Hornig, Gunnar; Démoulin, Pascal
Bibcode: 2002JGRA..107.1164T
Altcode:
  Although the analysis of observational data indicates that
  quasi-separatrix layers (QSLs) of magnetic configurations have to
  play an important role in solar flares, the corresponding theory is
  only at an initial stage so far. In particular, there is still a need
  of a proper definition of QSLs based on a comprehensive mathematical
  description of magnetic connectivity. Such a definition is given here
  by analyzing the mapping produced by the field lines which connect
  photospheric areas of positive and negative magnetic polarities. It
  is shown that magnetic configurations may have regions, where
  cross sections of magnetic flux tubes are strongly squashed by this
  mapping. These are the geometrical features that can be identified
  as the QSLs. The theory is applied to quadrupole configuration
  to demonstrate that it may contain two QSLs combined in a special
  structure called hyperbolic flux tube (HFT). Both theoretical and
  observational arguments indicate that the HFT is a preferred site for
  magnetic reconnection processes in solar flares.

Title: The Magnetic Helicity Budget of a cme-Prolific Active Region
Authors: Green, L. M.; López fuentes, M. C.; Mandrini, C. H.;
   Démoulin, P.; Van Driel-Gesztelyi, L.; Culhane, J. L.
Bibcode: 2002SoPh..208...43G
Altcode:
  Coronal mass ejections (CMEs) are thought to be the way by which the
  solar corona expels accumulated magnetic helicity which is injected
  into the corona via several methods. DeVore (2000) suggests that a
  significant quantity is injected by the action of differential rotation,
  however Démoulin et al. (2002b), based on the study of a simple bipolar
  active region, show that this may not be the case. This paper studies
  the magnetic helicity evolution in an active region (NOAA 8100) in
  which the main photospheric polarities rotate around each other during
  five Carrington rotations. As a result of this changing orientation of
  the bipole, the helicity injection by differential rotation is not a
  monotonic function of time. Instead, it experiences a maximum and even
  a change of sign. In this particular active region, both differential
  rotation and localized shearing motions are actually depleting the
  coronal helicity instead of building it. During this period of five
  solar rotations, a high number of CMEs (35 observed, 65 estimated)
  erupted from the active region and the helicity carried away has
  been calculated, assuming that each can be modeled by a twisted flux
  rope. It is found that the helicity injected by differential rotation
  (≈−7×10<SUP>42</SUP> Mx<SUP>2</SUP>) into the active region cannot
  provide the amount of helicity ejected via CMEs, which is a factor 5
  to 46 larger and of the opposite sign. Instead, it is proposed that
  the ejected helicity is provided by the twist in the sub-photospheric
  part of the magnetic flux tube forming the active region.

Title: The Magnetic Helicity Injected by Shearing Motions
Authors: Démoulin, P.; Mandrini, C. H.; Van Driel-Gesztelyi, L.;
   Lopez Fuentes, M. C.; Aulanier, G.
Bibcode: 2002SoPh..207...87D
Altcode:
  Photospheric shearing motions are one of the possible ways to inject
  magnetic helicity into the corona. We explore their efficiency as
  a function of their particular properties and those of the magnetic
  field configuration. Based on the work of M. A. Berger, we separate
  the helicity injection into two terms: twist and writhe. For shearing
  motions concentrated between the centers of two magnetic polarities
  the helicity injected by twist and writhe add up, while for spatially
  more extended shearing motions, such as differential rotation, twist
  and writhe helicity have opposite signs and partially cancel. This
  implies that the amount of injected helicity can change in sign with
  time even if the shear velocity is time independent. We confirm the
  amount of helicity injected by differential rotation in a bipole
  in the two particular cases studied by DeVore (2000), and further
  explore the parameter space on which this injection depends. For a
  given latitude, tilt and magnetic flux, the generation of helicity is
  slightly more efficient in young active regions than in decayed ones
  (up to a factor 2). The helicity injection is mostly affected by the
  tilt of the AR with respect to the solar equator. The total helicity
  injected by shearing motions, with both spatial and temporal coherence,
  is at most equivalent to that of a twisted flux tube having the same
  magnetic flux and a number of turns of 0.3. In the solar case, where
  the motions have not such global coherence, the injection of helicity
  is expected to be much smaller, while for differential rotation this
  maximum value reduces to 0.2 turns. We conclude that shearing motions
  are a relatively inefficient way to bring magnetic helicity into the
  corona (compared to the helicity carried by a significantly twisted
  flux tube).

Title: Long-term helicity evolution in NOAA active region 8100
Authors: Green, L. M.; López Fuentes, M. C.; Mandrini, C. H.; van
   Driel-Gesztelyi, L.; Démoulin, P.
Bibcode: 2002ESASP.477...43G
Altcode: 2002scsw.conf...43G
  Magnetic helicity is the topological parameter used to describe
  the structure in the magnetic field and has become increasingly
  important in coronal studies. Helicity is well preserved in the
  corona even under non-ideal MHD conditions (see Biskamp 1993), and
  the Sun can avoid endless accumulation of helicity by ejecting it
  via the launch of coronal mass ejections (eg. Rust 1994; Low 1996;
  Devore 2000). Computations are made for NOAA active region 8100 to
  determine the coronal helicity and helicity injected into the region
  by differential rotation. These values are then compared to the total
  amount of helicity lost via coronal mass ejections to test whether
  differential rotation can inject a significant amount of helicity into
  the corona. It is found that differential rotation cannot inject a
  significant amount of helicity to be a viable source for the coronal
  mass ejection activity. Instead, helicity is likely to be brought into
  the corona by the emergence of twisted and distorted flux tubes.

Title: The distribution of peculiar active regions along two solar
    cycles
Authors: Mandrini, C. H.; López Fuentes, M. C.; Démoulin, P.;
   van Driel-Gesztelyi, L.
Bibcode: 2002ESASP.477...27M
Altcode: 2002scsw.conf...27M
  We perform a statistical study of the spatial and temporal distribution
  of "peculiar" active regions (ARs) along solar cycles 21 and 22. ARs
  usually appear in the photosphere in the form of bipolar concentrations
  of magnetic flux, by "peculiar" we mean regions in which the the
  main polarities rotate one around the other along several solar
  rotations. Our results show that these regions are spatially distributed
  as usual ARs when no selection on their magnetic flux is applied. When
  classified according to their flux, the latitudinal distribution of
  ARs above 10<SUP>22</SUP> Mx closely follow the butterfly diagram;
  while those with lower flux are more randomly distributed. The number
  of rotating ARs follow the activity cycle, with a tendency to dual-peak
  maxima.

Title: What is the source of the magnetic helicity shed by CMEs? The
    long-term helicity budget of AR 7978
Authors: Démoulin, P.; Mandrini, C. H.; van Driel-Gesztelyi, L.;
   Thompson, B. J.; Plunkett, S.; Kovári, Zs.; Aulanier, G.; Young, A.
Bibcode: 2002A&A...382..650D
Altcode:
  An isolated active region (AR) was observed on the Sun during seven
  rotations, starting from its birth in July 1996 to its full dispersion
  in December 1996. We analyse the long-term budget of the AR relative
  magnetic helicity. Firstly, we calculate the helicity injected
  by differential rotation at the photospheric level using MDI/SoHO
  magnetograms. Secondly, we compute the coronal magnetic field and
  its helicity selecting the model which best fits the soft X-ray loops
  observed with SXT/Yohkoh. Finally, we identify all the coronal mass
  ejections (CMEs) that originated from the AR during its lifetime using
  LASCO and EIT/SoHO. Assuming a one to one correspondence between CMEs
  and magnetic clouds, we estimate the magnetic helicity which could be
  shed via CMEs. We find that differential rotation can neither provide
  the required magnetic helicity to the coronal field (at least a factor
  2.5 to 4 larger), nor to the field ejected to the interplanetary
  space (a factor 4 to 20 larger), even in the case of this AR for
  which the total helicity injected by differential rotation is close
  to the maximum possible value. However, the total helicity ejected is
  equivalent to that of a twisted flux tube having the same magnetic flux
  as the studied AR and a number of turns in the interval [0.5,2.0]. We
  suggest that the main source of helicity is the inherent twist of the
  magnetic flux tube forming the active region. This magnetic helicity
  is transferred to the corona either by the continuous emergence of the
  flux tube for several solar rotations (i.e. on a time scale much longer
  than the classical emergence phase), or by torsional Alfvén waves.

Title: Properties of bipolar active regions through two and a half
    solar cycles
Authors: Villar, P. I.; López Fuentes, M. C.; Mandrini, C. H.;
   Démoulin, P.
Bibcode: 2002BAAA...45...22V
Altcode:
  Hale's Law (Hale &amp; Nicholson, 1925, ApJ, 62, 270) describes the
  orientation of the bipolar active regions (BARs) that are observed
  in the solar photosphere. Generally, BARs are oriented almost
  parallel to the east-west direction, with the preceeding polarity
  (and, therefore, the following one) having different sign in both
  hemispheres and changing from one solar cycle to the other. Joy's Law
  (Hale et al. 1919, ApJ, 49, 153) states that BARs are generally seen
  with their preceedig polarity closer to the equator; this law defines
  the tilt angle as the angle formed by the principal axis of the bipole
  with the horizontal direction. Furthermore, the tilt angle grows as
  latitude increases. Many numerical models simulating the emergence of
  flux tubes through the convective zone are able of reproducing this
  law. Some of these demonstrate that the tilt of BARs is originated
  by the effect of the Coriolis Force which acts on the flux tubes on
  their way up to the photosphere. Others, predict a relation between the
  tilt angle (ϕ), the latitude (λ) and the magnetic flux (Φ) of BARs
  (Fan, Fisher &amp; McClymont, 1994, ApJ, 436, 907). In this relation
  the tilt is proportional to (Φ)<SUP>α</SUP> with α=0.25. In this
  context, we generated a big database containing values of the most
  relevant parameters of the magnetic field and other characteristics of
  BARs. This was done using the synoptic magnetograms of the Kitt Peak
  National Solar Observatory, which has all the magnetograms from 1975
  to the present year. The database contains information about the flux
  (above different values of the magnetic field), the radius and the
  area of the polarities, the flux weighted mean longitude and latitude
  and the tilt angle of each BAR. Through a statistical analysis, we
  determined the functional dependence of the tilt angle on the latitude
  and tested the law proposed by Fan, Fisher &amp; McClymont for the tilt
  angle, latitude and magnetic flux. Consequently, we found that the
  tilt angle holds a linear dependence with the sin(λ) and the value
  of α is 0.22. Our results constrain the validity of theoretical and
  numerical models of the solar dynamo and flux tube emergence.

Title: Relation between the coronal magnetic helicity to the helicity
    in interplanetary magnetic clouds
Authors: Luoni, M. L.; Mandrini, C. H.; Démoulin, P.; van
   Driel-Gesztelyi, L.; López Fuentes, M. C.
Bibcode: 2002BAAA...45...20L
Altcode:
  On October 18, 1995, the Solar Wind Experiment and the Magnetic
  Field Instrument on board the WIND spacecraft registered a magnetic
  cloud at 1 AU, which was followed by a strong geomagnetic storm. The
  solar source of this phenomenon was located in active region (AR) NOAA
  7912. On October 14, 1995, a C1.6 long duration event (LDE) started at
  approximately 5:00 UT and lasted for around 15 hours. In this work, we
  compute the variation of the coronal magnetic helicity using a linear
  force-free model of the field. We use magnetograms obtained at Kitt
  Peak National Solar Observatory as boundary conditions to extrapolate
  the photospheric magnetic field to the corona. The magnetic helicity
  is calculated at three different times, changing the parameters of the
  magnetic field model to fit the loops observed in soft X-rays by the
  Soft X-ray Telescope on board of Yohkoh (SXT/Yohkoh). The computations
  are done before the LDE, during its maximun and its decay phase. The
  variation of the coronal magnetic helicity is compared to the helicity
  of the interplanetary magnetic cloud observed by WIND. These values
  turn out to be quite similar, considering the errors involved. Our
  results confirm quantitatively the link between solar and interplanetary
  phenomena.

Title: Active region helicity evolution and related coronal mass
    ejection activity.
Authors: Green, L.; Mandrini, C.; van Driel-Gesztelyi, L.; Demoulin, P.
Bibcode: 2002cosp...34E1213G
Altcode: 2002cosp.meetE1213G
  The computation of magnetic helicity has become increasingly important
  in the studies of solar activity. Observations of helical structures
  in the solar atmosphere, and their subsequent ejection into the
  interplanetary medium, have resulted in considerable interest to find
  the link between the amount of helicity in the coronal magnetic field
  and the origin of coronal mass ejections (CMEs). This is reinforced by
  theory which shows magnetic helicity to be a well preserved quantity
  (Berger, 1984), and so with a continued injection into the corona an
  endless accumulation will occur. CMEs therefore provide a natural
  method to remove helicity from the corona. Recent works (DeVore,
  2000, Chae, 2001, Chae et al., 2001, Demoulin et al., 2002, Green et
  al., 2002) have endeavoured to find the source of helicity in the
  corona to explain the observed CME activity in specific cases. The
  main candidates being differential rotation, shear motions or a
  transfer of helicity from below the photosphere into the corona. In
  order to establish a confident relation between CMEs and helicity,
  these works needs to be expanded to include CME source regions with
  different characteristics. A study of a very different active region
  will be presented and the relationship between helicity content and
  CME activity will be discussed in the framework of the previous studies.

Title: Energetics of the 18 May 1994 brightening event
Authors: Tang, Y. H.; Li, Y. N.; Fang, C.; Schmieder, B.; Aulanier,
   G.; Demoulin, P.
Bibcode: 2002AdSpR..30..557T
Altcode:
  By using YOHKOH soft X-ray images, vector magnetograms and Hα
  filtergrams, the energetics of the brightening event of May 18, 1994 has
  been studied. It occurred in a nearly potential magnetic configuration
  as shown by the comparison between the magnetic extrapolation(linear
  force free field) and the large scale soft X-ray loops. This event
  is related to the emergence of a new magnetic flux. The brightening
  points of Hα and soft X-ray are located at computed separatrices
  associated with field lines which are tangent to the photosphere. This
  brightening may be a signature of reconnection taking place between the
  pre-existing non-potential loops and the new emerging small loops. The
  magnetic energy provided by reconnection is likely to be stored in
  the non-potential loops and shearing emerging flux. A phenomenological
  model is offered.

Title: Helicity Loading and Dissipation: The Helicity Budget of AR
    7978 from the Cradle to the Grave
Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Mandrini, C. H.;
   Plunkett, S.; Thompson, B.; Kövári, Zs.; Aulanier, G.; Young, A.;
   López Fuentes, M.; Poedts, S.
Bibcode: 2002mwoc.conf..143V
Altcode:
  An isolated active region was observed on the Sun during seven
  rotations, starting in July 1996. I will present a study of its magnetic
  field, concentrating on its helicity budget. The photospheric field
  is extrapolated into the corona in a linear force-free approach,
  using SOHO/MDI magnetograms and Yohkoh/SXT images, allowing us to
  compute, in a crude way, the relative coronal magnetic helicity of
  the active region. Using the observed magnetic field distribution
  (SOHO/MDI magnetograms) we also calculate the helicity injected by
  the differential rotation during seven solar rotations. Finally, using
  SOHO/LASCO and EIT as well as Yohkoh/SXT observations, we identify all
  the 26 CMEs which originated from this active region during its lifetime
  and using average values of the field and radius of magnetic clouds,
  we estimate the helicity which should be shed via CMEs. We compare
  these three values to evaluate the importance of the differential
  rotation relative to twisted flux emergence as a source of magnetic
  helicity. We find that the differential rotation can neither provide
  enough helicity to account for the diagnosed coronal heicity values,
  nor for the helicity carried away by CMEs. We suggest that the main
  source of the magnetic helicity must be the inherent twist of the
  magnetic flux tube forming the active region. This magnetic helicity is
  transferred to the corona either by a slow continuous emergence of the
  flux tube or by torsional Alfven waves, during several solar rotations.

Title: Surges y Arch Filament Systems: Una topología inusual
Authors: Mandrini, C. H.; Démoulin, P.; Schmieder, B.; Deng, Y. Y.;
   Rudawy, P.
Bibcode: 2002BAAA...45...17M
Altcode:
  Active region (AR) NOAA 7968 was observed during its solar disk transit
  by several instruments on ground and on board satellites (Yohkoh and
  SOHO). During its emergence Arch Filament Systems (AFS) linking the
  polarities of the main bipole were observed. During its decay a surge
  (a chromospheric confined mass ejection) occurred to the South of the
  positive polarity of this bipole. We model the AR magnetic field in the
  magnetohydrostatic approach and compute its topology. We find that the
  evolution of both events, AFS and surge, agrees with magnetic field
  reconnection occurring in field lines that are tangentially touching
  the photosphere. These lines define the so called ``bald patches''
  (BPs). In previous studies these topological structures have been found
  to be related to small flares and transition region brightenings. Our
  results point out the importance of BPs in a wider phenomenological
  context and show that current sheets can develop and efficiently
  dissipate in the chromosphere.

Title: Inferring the Writhe of Emerging Flux Tubes from the Evolution
    of the Orientation of Bipole Axes
Authors: López Fuentes, M. C.; Mandrini, C. H.; Démoulin, P.;
   van Driel-Gesztelyi, L.; Pevtsov, A.
Bibcode: 2002RMxAC..14..108L
Altcode:
  No abstract at ADS

Title: High Resolution Observations of Reconnected Magnetic Loops
Authors: Luoni, M. L.; Mandrini, C. H.; Karim, Y.; Schieder, B.;
   Démoulin, P.
Bibcode: 2002RMxAC..14Q.107L
Altcode:
  No abstract at ADS

Title: Magnetic helicity in interplanetary structures of solar origin
Authors: Dasso, S.; Mandrini, C. H.; Démoulin, P.
Bibcode: 2002BAAA...45...15D
Altcode:
  Interplanetary manifestations of transient coronal mass ejections
  (so called ICMEs) form helical structures of magnetic flux that travel
  through the solar wind from the Sun toward the outer heliosphere. The
  global magnetic helicity (MH) contained in these huge structures,
  whose typical length when pass near Earth is of the order of an
  astronomical unit, plays a very important role in the understanding
  of the solar-terrestrial relationship. Moreover, the study of MH is
  crucial in order to link solar active regions with their corresponding
  interplanetary flux tubes. MH is one of the few global quantities
  conserved even under non-ideal MHD. In spite of its importance
  do not yet exist exhaustive studies that estimate the content of
  MH in ICMEs. In spite of ICMEs are structures out of equilibrium,
  generally ICMEs are modeled using three different MHD models with
  cylindrical geometry: linear force-free field, constant twist angle,
  and non force-free model with constant current. In this work, we derive
  analytically the expressions to calculate the MH for every of the three
  models mentioned before, and also present numerical results for a hot
  flux tube observed by the spacecraft Wind on October 24-25, 1995. We
  have fitted the set of free parameters for every model, finding that
  the derived MHs are very similar. Thus, our results support that the
  MH in ICMEs is a well-determined quantity what do not depend of the
  assumed model, being very valuable in order to get insight of the link
  between solar and interplanetary phenomena.

Title: Peculiar Active Regions during the Last Two Solar Cycles
Authors: López Fuentes, M. C.; Mandrini, C. H.; Démoulin, P.;
   van Driel-Gesztelyi, L.
Bibcode: 2002RMxAC..14R.107L
Altcode:
  No abstract at ADS

Title: Relationships between CME's and prominences
Authors: Schmieder, B.; van Driel-Gesztelyi, L.; Aulanier, G.;
   Démoulin, P.; Thompson, B.; De Forest, C.; Wiik, J. E.; Saint Cyr,
   C.; Vial, J. C.
Bibcode: 2002AdSpR..29.1451S
Altcode:
  We have studied the erupting prominences which were associated with
  coronal mass ejections during a series of campaigns involving both
  spacecraft and ground-based observatories. The evolution of the
  physical conditions within the prominences was established from Hα
  and magnetic field observations. Particular attention ahs been paid
  to the presence of mixed amgnetic polarity in the filament channel,
  the evolution of the shear of the large-scale magnetic field, and
  the existence of multiple magnetic inversion lines. We conclude that
  reconnection of large-scale coronal magnetic fields is responsible
  for both the CME and filament eruption.

Title: A Relationship Between Transition Region Brightenings,
    Abundances, and Magnetic Topology
Authors: Fletcher, Lyndsay; López Fuentes, Marcelo C.; Mandrini,
   Cristina H.; Schmieder, Brigitte; Démoulin, Pascal; Mason, Helen E.;
   Young, Peter R.; Nitta, Nariaki
Bibcode: 2001SoPh..203..255F
Altcode:
  We present multi-instrument observations of active region (AR) 8048,
  made between 3 June and 5 June 1997, as part of the SOHO Joint Observing
  Program 33. This AR has a sigmoid-like global shape and undergoes
  transient brightenings in both soft X-rays and transition region
  (TR) lines. We compute a magneto-hydrostatic model of the AR magnetic
  field, using as boundary condition the photospheric observations of
  SOHO/MDI. The computed large-scale magnetic field lines show that the
  large-scale sigmoid is formed by two sets of coronal loops. Shorter
  loops, associated with the core of the SXT emission, coincide with
  the loops observed in the hotter CDS lines. These loops reveal a
  gradient of temperature, from 2 MK at the top to 1 MK at the ends. The
  field lines most closely matching these hot loops extend along the
  quasi-separatrix layers (QSLs) of the computed coronal field. The TR
  brightenings observed with SOHO/CDS can also be associated with the
  magnetic field topology, both QSL intersections with the photosphere,
  and places where separatrices issuing from bald patches (sites where
  field lines coming from the corona are tangent to the photosphere)
  intersect the photosphere. There are, furthermore, suggestions that
  the element abundances measured in the TR may depend on the type
  of topological structure present. Typically, the TR brightenings
  associated with QSLs have coronal abundances, while those associated
  with BP separatrices have abundances closer to photospheric values. We
  suggest that this difference is due to the location and manner in which
  magnetic reconnection occurs in two different topological structures.

Title: Measurement of coronal magnetic twists during loop emergence
    of NOAA 8069
Authors: Portier-Fozzani, F.; Aschwanden, M.; Démoulin, P.; Neupert,
   W.; EIT Team; Delaboudinière, J. -P.
Bibcode: 2001SoPh..203..289P
Altcode:
  Emerging coronal loops were studied with extreme ultraviolet
  observations performed by SOHO/EIT on 5 and 6 August 1997 for NOAA
  8069. Physical parameters (size and twist) were determined by a new
  stereoscopic method. The flux tubes were measured twisted when first
  observed by EIT. After emerging, they de-twisted as they expanded,
  which corresponds to a minimization of the energy. Different scenarios
  which take into account the conservation of the magnetic helicity are
  discussed in relation with structure and temperature variations.

Title: Long-Term Evolution of Active Regions
Authors: López Fuentes, M.; Mandrini, C. H.; Démoulin, P.; van
   Driel-Gesztelyi, L.
Bibcode: 2001ASPC..248..131L
Altcode: 2001mfah.conf..131L
  No abstract at ADS

Title: CDS UV Brightenings Explained by Quasi-separatrices and Bald
    Patches in an S-shape active region
Authors: Schmieder, B.; Démoulin, P.; Fletcher, L.; López Fuentes,
   M. C.; Mandrini, C. H.; Mason, H. E.; Young, P. R.; Nitta, N.
Bibcode: 2001IAUS..203..314S
Altcode:
  We present multi-instrument observations of AR 8048, made between
  June 3 and June5 1997 as part of SoHO JOP033. This active region
  has a sigmoid-like global shape and undergoes transient erupting
  phenomena which releases the stored energy. Using a force free
  field approach, we defined coronal magnetic field lines which fit
  with the observations. The large-scale magnetic field lines confirms
  the sigmoid characteristics of the active region. The study in 3D of
  the configuration explained where and how the energy is released at
  different places. The Ne VI brightenings correspond to the location
  of tangent to the photosphere field lines, named "bald patch", they
  are localized in the low transition region and represent feet of field
  lines. The Si XII brightenings at coronal temperature are at the top
  of coronal loops joining quasi-separatrices.

Title: An Observational Test for Solar Atmospheric Heating
Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Ireland, J.; Thompson,
   B.; Fludra, A.; Oláh, K.; Kövári, Zs.; Harra, L. K.; Mandrini,
   C. H.; Bocchialini, K.; Orlando, S.
Bibcode: 2001IAUS..203..514V
Altcode:
  We study the evolution of the emissivity and heating correlated with
  magnetic observables of an active region from its birth throughout
  its decay during seven solar rotations (July-Dec. 1996). Taking one
  "snapshot" per g:wq: Command not found. time of flares, we analyse
  multi-wavelength and multi-instrument data obtained from SOHO (MDI,
  EIT, CDS and SUMER), Yohkoh (SXT), GOES, SOLSTICE and 10.7 cm radio
  data from DRAO, Canada. We utilise our results to test the validity
  of coronal heating models. We find that models which are based on
  the dissipation of stressed, current-carrying magnetic fields are in
  better agreement with the observations than the models which attribute
  coronal heating to the dissipation of MHD waves.

Title: Magnetic Evolution of a Long-Lived Active Region: The Sources
    of Magnetic Helicity
Authors: Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.;
   Aulanier, G.; Thompson, B.; Plunkett, S.; Kövári, Zs.
Bibcode: 2001ASPC..248..139M
Altcode: 2001mfah.conf..139M
  No abstract at ADS

Title: Emergence of a U-loop - sub-photospheric link between solar
    active regions
Authors: van Driel-Gesztelyi, L.; Malherbe, J. -M.; Démoulin, P.
Bibcode: 2000A&A...364..845V
Altcode:
  Using SOHO/MDI magnetic maps we present the first direct observational
  evidence for the emergence of a U-loop in the solar photosphere. We
  show that two active regions (ARs), i.e. two adjacent Omega -loops,
  which were emerging at the same time at the same solar latitude,
  about 150000 km distance in longitude from each other, emerged from
  at least partially the same toroidal flux strand, and we bring five
  independent arguments to prove this assertion. The opposite polarity
  legs of the two Omega -loops were connected below the photosphere by a
  U-shaped loop. Following the emergence of the Omega -loops, the U-loop
  started emerging, manifested by the fast proper motion of the leading
  spots of the eastern (smaller) active region, which, after forming an
  elongated channel, collided with the following spots of the westerly
  AR and started cancelling with them. The full cancellation could not be
  followed because the ARs rotated out of sight. The total magnetic flux
  of the two ARs was unequal, the flux in the smaller AR was a quarter of
  that of the larger one. We propose scenarios for the formation of such
  a U-loop and discuss the implications of the confirmed existence of
  U-loops for the solution of such puzzles as the in-situ disappearance
  of magnetic flux from active regions, active nests and the formation
  of inter-AR filaments.

Title: Magnetic reconnection: a common origin for flares and AR
    interconnecting arcs
Authors: Bagalá, L. G.; Mandrini, C. H.; Rovira, M. G.; Démoulin, P.
Bibcode: 2000A&A...363..779B
Altcode:
  We present a study of active region (AR) 7031, where several flares
  occurred throughout the last week of January, 1992. We analyze in
  detail the three largest flares, both in Hα and soft X-rays. During
  its transit across the disk this region interacted with another one
  (AR 7038), as indicated by the recurrent brightening in soft X-rays
  of an interconnecting loop, accompanied by sympathetic flaring. Using
  a linear force free extrapolation of the photospheric magnetic field,
  we compute the locations of Quasi-Separatrix Layers (QSLs), which are
  the likely places where the magnetic field can reconnect. We find that
  flare brightenings can be linked by field lines having footpoints at the
  QSLs. Furthermore, field lines connecting AR 7031 and AR 7038 belong
  to the QSLs computed when magnetograms from both ARs are combined. We
  conclude that both soft X-ray flare loops and interconnecting loops
  result from magnetic reconnection at the QSLs. Which of the many
  QSLs found in the computations are the site of magnetic reconnection
  depends on the magnetic field evolution. In the studied ARs we can
  identify three different drivers for energy release: flux emergence,
  photospheric displacements of the polarities and nearby magnetic
  reconnection. This last process leads to sympathetic flaring and to
  the brightness enhancement of the interconnecting arc.

Title: Initiation of CMEs: the role of magnetic twist
Authors: van Driel-Gesztelyi, L.; Manoharan, P. K.; Démoulin, P.;
   Aulanier, G.; Mandrini, C. H.; Lopez-Fuentes, M.; Schmieder, B.;
   Orlando, S.; Thompson, B.; Plunkett, S.
Bibcode: 2000JASTP..62.1437V
Altcode: 2000JATP...62.1437V
  Recent multiwavelength observations, modelling results and
  theoretical developments indicate the importance of twisted magnetic
  configurations in solar active regions (ARs) in the initiation of
  coronal mass ejections (CMEs). Through multiwavelength analysis of a
  few representative events we make an attempt to provide constraints
  for CME models. The two events presented here in detail start with
  the expansion of sigmoids (S- or inverse S-shaped loops) observed in
  soft X-rays. Both events (on 25 October /1994 and 14 October /1995)
  occurred before the launch of the SOHO spacecraft, but indirect
  evidences (i.e. signatures of an outward propagation traced up to /~20
  solar radii and an associated magnetic cloud) suggest that both of them
  were related to CMEs. We show evidence that sigmoids are the coronal
  manifestations of twisted magnetic flux tubes, which start expanding
  presumably due to a loss of equilibrium. It is noteworthy that the
  analysed CMEs occurred in a complex (not simply bipolar) magnetic
  environment and in all cases we found evidences of the interaction
  (magnetic reconnection) with the surrounding fields. We propose a
  scenario for sigmoid expansion related CME events and suggest that
  twisted magnetic configurations are good candidates for being source
  regions of CMEs.

Title: The Counterkink Rotation of a Non-Hale Active Region
Authors: López Fuentes, M. C.; Demoulin, P.; Mandrini, C. H.; van
   Driel-Gesztelyi, L.
Bibcode: 2000ApJ...544..540L
Altcode: 2014arXiv1412.1456L
  We describe the long-term evolution of a bipolar non-Hale active region
  that was observed from 1995 October to 1996 January. During these
  four solar rotations the sunspots and subsequent flux concentrations,
  during the decay phase of the region, were observed to move in such a
  way that by December their orientation conformed to the Hale-Nicholson
  polarity law. The sigmoidal shape of the observed soft X-ray coronal
  loops allows us to determine the sense of the twist in the magnetic
  configuration. This sense is confirmed by extrapolating the observed
  photospheric magnetic field, using a linear force-free approach,
  and comparing the shape of computed field lines with the observed
  coronal loops. This sense of twist agrees with that of the dominant
  helicity in the solar hemisphere where the region lies, as well as
  with the evolution observed in the longitudinal magnetogram during
  the first rotation. At first sight the relative motions of the
  spots may be misinterpreted as the rising of an Ω loop deformed by
  a kink instability, but we deduce from the sense of their relative
  displacements a handedness for the flux-tube axis (writhe) that is
  opposite to that of the twist in the coronal loops and, therefore,
  to what is expected for a kink-unstable flux tube. After excluding
  the kink instability, we interpret our observations in terms of a
  magnetic flux tube deformed by external motions while rising through
  the convective zone. We compare our results with those of other related
  studies, and we discuss, in particular, whether the kink instability
  is relevant to explain the peculiar evolution of some active regions.

Title: Hα and Soft X-Ray Brightening Events Caused by Emerging Flux
Authors: Tang, Y. H.; Li, Y. N.; Fang, C.; Aulanier, G.; Schmieder,
   B.; Demoulin, P.; Sakurai, T.
Bibcode: 2000ApJ...534..482T
Altcode:
  By using Yohkoh soft X-ray images, vector magnetograms, and Hα
  filtergrams, the brightening event that occurred on 1994 May 18 has
  been studied in detail. It occurred in a nearly potential large-scale
  magnetic configuration as shown by the comparison between the magnetic
  extrapolation (linear force-free field) and the large-scale soft
  X-ray loops. This event is related to the emergence of a new magnetic
  flux of about 3×10<SUP>20</SUP> Mx. The impulsive enhancement of
  the emerging flux occurs about 20 minutes before the peaks of the
  Hα and soft X-ray brightening and lasts for about 10 minutes. This
  brightening may be a signature of reconnection taking place between the
  preexisting nonpotential loops and the new emerging small loops. The
  magnetic energy provided by reconnection is likely to be stored in
  the nonpotential loops and the emerging flux as implied by the vector
  magnetograms. By using the electron temperature and the electron density
  of the brightening event derived from the analysis of the Yohkoh data,
  an energy budget has been estimated. The result indicates that the
  energy needed can be reasonably provided by magnetic reconnection.

Title: Magnetic Activity Associated With Radio Noise Storms
Authors: Bentley, R. D.; Klein, K. -L.; van Driel-Gesztelyi, L.;
   Démoulin, P.; Trottet, G.; Tassetto, P.; Marty, G.
Bibcode: 2000SoPh..193..227B
Altcode:
  As it crossed the solar disk in May and June 1998, AR 8227 was tracked
  by TRACE, Yohkoh, SOHO, and many ground-based observatories. We have
  studied how the evolution of the magnetic field resulted in changes in
  activity in the corona. In particular, we examine how the evolving field
  may have led to the acceleration of electrons which emit noise storms
  observed by the Nançay Radio Heliograph between 30 May and 1 June
  1998, in the absence of any flare. The magnetic changes were related
  to moving magnetic features (MMFs) in the vicinity of the leading
  spot and are related to the decay of this spot. Within the limits of
  the instrumental capabilities, the location in time and space of the
  radio emissions followed the changes observed in the photospheric
  magnetograms. We have extrapolated the photospheric magnetic field
  with a linear force-free approximation and find that the active region
  magnetic field was very close to being potential. These computations
  show a complex magnetic topology associated to the MMFs. The observed
  photospheric evolution is expected to drive magnetic reconnection in
  such complex magnetic topology. We therefore propose that the MMFs
  are at the origin of the observed metric noise-storms.

Title: Magnetic Field and Plasma Scaling Laws: Their Implications
    for Coronal Heating Models
Authors: Mandrini, C. H.; Démoulin, P.; Klimchuk, J. A.
Bibcode: 2000ApJ...530..999M
Altcode:
  In order to test different models of coronal heating, we have
  investigated how the magnetic field strength of coronal flux
  tubes depends on the end-to-end length of the tube. Using
  photospheric magnetograms from both observed and idealized
  active regions, we computed potential, linear force-free, and
  magnetostatic extrapolation models. For each model, we then
  determined the average coronal field strength, &lt;B&gt;, in
  approximately 1000 individual flux tubes with regularly spaced
  footpoints. Scatter plots of &lt;B&gt; versus length, L, are
  characterized by a flat section for small L and a steeply declining
  section for large L. They are well described by a function of the form
  log=C<SUB>1</SUB>+C<SUB>2</SUB>logL+C<SUB>3</SUB>/2log(L<SUP>2</SUP>+S<SUP>2</SUP>),
  where C<SUB>2</SUB>~0, -3&lt;=C<SUB>3</SUB>&lt;=-1, and 40&lt;=S&lt;=240
  Mm is related to the characteristic size of the active region. There
  is a tendency for the magnitude of C<SUB>3</SUB> to decrease as the
  magnetic complexity of the region increases. The average magnetic
  energy in a flux tube, &lt;B<SUP>2</SUP>&gt;, exhibits a similar
  behavior, with only C<SUB>3</SUB> being significantly different. For
  flux tubes of intermediate length, 50&lt;=L&lt;=300 Mm, corresponding
  to the soft X-ray loops in a study by Klimchuk &amp; Porter (1995),
  we find a universal scaling law of the form ~L<SUP>δ</SUP>, where
  δ=-0.88+/-0.3. By combining this with the Klimchuk &amp; Porter result
  that the heating rate scales as L<SUP>-2</SUP>, we can test different
  models of coronal heating. We find that models involving the gradual
  stressing of the magnetic field, by slow footpoint motions, are in
  generally better agreement with the observational constraints than are
  wave heating models. We conclude, however, that the theoretical models
  must be more fully developed and the observational uncertainties must
  be reduced before any definitive statements about specific heating
  mechanisms can be made.

Title: Brightening Event in Hα and Soft X-Ray on May 18, 1994
Authors: Tang, Y. H.; Li, Y. N.; Schmieder, B.; Aulanier, G.; Demoulin,
   P.; Fang, C.; Sakurai, T.
Bibcode: 2000AdSpR..25.1829T
Altcode:
  By using Yohkoh soft X-ray images, vector magnetograms and Hα
  filtergrams, a brightening event that occurred on May 18, 1994 has
  been studied in detail. It occurred in a nearly potential large-scale
  magnetic configuration as shown by the comparisons between the magnetic
  extrapolations (linear force-free field) and the large-scale soft
  X-ray loops. This brightening event observed in Hα line and soft
  X-ray seems to be related to new emerging magnetic flux with an
  amount of photospheric magnetic flux of about 3× 10<SUP>20</SUP>
  Mx. The emerging flux increases obviously about 20 minutes before the
  Hα and soft X-ray brightening, and lasts for about 10<SUP>3</SUP>
  s. This brightening may be a signature of reconnection taking place
  between the pre-existing loop and the new emerging small loops

Title: 3-D Magnetic Configurations for Filaments and Flares: The
    Role of ``Magnetic Dips'' and ``Bald Patches''
Authors: Aulanier, G.; Schmieder, B.; van Driel-Gesztelyi, L.; Kucera,
   T.; Démoulin, P.; Fang, C.; Mein, N.; Vial, J. -C.; Mein, P.; Tang,
   Y. H.; Deforest, C.
Bibcode: 2000AdSpR..26..485A
Altcode:
  The 3-D magnetic configuration of a filament and of a low energy
  flare is reconstructed, using linear mag- netohydrostatic (lmhs)
  extrapolations. In both cases, we find observational signatures
  of energy release at the locations of computed ``bald patches''
  separatrices, characterised by field lines which are tangent to
  the photosphere.The filament was observed on Sept. 25, 1996, in Hα
  with the MSDP on the German VTT, Tenerife, as well as in Si IV with
  SOHO/SUMER. It is modeled as a twisted flux-tube deformed by the
  magnetic polarities observed with SOHO/MDI. The shape and location of
  the computed dipped field lines are in good agreement with the shape of
  the filament and its feet observed in Hα. Some ``bald patches'' (BPs)
  are present where the distribution of dips reaches the photosphere. We
  show that some of the large scale field lines rooted in BPs can be
  related to bright fine structures in Si IV. We propose that the plasma
  there is heated by ohmic dissipation from the currents expected to be
  present along the BP separatrices.The flare was observed on May 18,
  1994, in soft X-rays with Yohkoh/SXT, and in Hα at Mitaka (Japan). The
  magnetic field is directly extrapolated from a photospheric magnetogram
  from Kitt Peak Observatory. The intersections with the photosphere of
  the computed separatrices match well the bright Hα ribbons. The later
  are associated to three BPs, with overlaying dipped field lines. We
  show that enhanced densities are present in these dips, which can be
  correlated with dark Hα fibrils.Both cases show the importance of
  dipped field lines and BPs in the solar atmosphere. Energy release
  via ohmic dissipation as well as reconnection along BP separatrices
  is proposed to provide heating observed as UV brightenings in filament
  channels and even as small flares

Title: Structuring of the Solar Plasma by the Magnetic Field
Authors: Demoulin, Pascal; Klein, Karl-Ludwig
Bibcode: 2000LNP...553...99D
Altcode: 2000tech.conf...99D
  This paper presents a simplified overview of the role of the magnetic
  field in the solar atmosphere. The magnetic field emanating from
  the solar interior governs energy transport and plasma motions in
  the outer solar atmosphere. Thereby it creates structure, such as
  coronal holes, loops and prominences, and the dynamical phenomena
  known as coronal mass ejections and flares. The magnetic field is also
  thought to be at the origin of the coronal heating, so of the corona
  itself. An overview of atmospheric structure is presented, followed
  by illustrations on present ideas on the interaction between plasma
  and magnetic field. The physical conditions in the corona are briefly
  compared to those in the magnetosphere. The emphasis is then put on the
  energetic processes from the largest ones (coronal mass ejections) over
  flares and X-ray bright points to coronal heating. In all cases magnetic
  reconnection is likely to play a key role. Solar prominences are then
  described because their observations provide important information on
  the surrounding coronal magnetic field. Finally the implications of
  processes in the convection zone on the physics of the corona and of
  the interplanetary medium are illustrated for the case of formation,
  storage and ejection of twisted magnetic flux tubes.

Title: What Can we Learn Studying Long-Term Magnetic Evolution of
    Solar Active Regions?
Authors: van Driel-Gesztelyi, L.; Kovari, Zs.; Lopez-Fuentes, M.;
   Mandrini, C. H.; Demoulin, P.
Bibcode: 2000ESASP.463..451V
Altcode: 2000sctc.proc..451V
  No abstract at ADS

Title: Test on the parameter dependence of coronal heating models
Authors: Démoulin, P.; Mandrini, C. H.; Klimchuk, J. A.
Bibcode: 2000ssls.work...85D
Altcode:
  The motivation of this work has been to provide observational
  constraints on coronal heating models by testing their predictions
  for the heating rate as a function of several physical parameters. In
  Mandrini et al. (1999), we have investigated how the magnetic field
  strength, , of coronal flux tubes depends on the end-to-end length,
  L, of the tube. For flux tubes of intermediate length, 50 ≤ L ≤
  300 Mm, corresponding to the soft X-ray loops in a study by Klimchuk
  &amp; Porter (1995), we find a universal scaling law of the form
  ∝L<SUP>δ</SUP>, where δ= -0.88±0.3. By combining this with
  the Klimchuk &amp; Porter result that the heating rate scales as
  L<SUP>-2</SUP>, we can test different models of coronal heating. We
  find that models involving the gradual stressing of the magnetic field,
  by slow footpoint motions, are in generally better agreement with the
  observational constraints than are wave heating models.

Title: Coronal Mass Ejections
Authors: Pick, M.; Démoulin, P.; Maia, D.; Plunkett, S.
Bibcode: 1999ESASP.448..915P
Altcode: 1999ESPM....9..915P; 1999mfsp.conf..915P
  No abstract at ADS

Title: Interpretation of the Activity due to Flux Emergence in an AR
Authors: Mandrini, C. H.; Démoulin, P.; Schmieder, B.; Deng, Y. Y.;
   Rudawy, P.
Bibcode: 1999ESASP.448..617M
Altcode: 1999ESPM....9..617M; 1999mfsp.conf..617M
  No abstract at ADS

Title: Basic topology of twisted magnetic configurations in solar
    flares
Authors: Titov, V. S.; Démoulin, P.
Bibcode: 1999A&A...351..707T
Altcode:
  It is accepted now that flare-like phenomena are the result of
  reconnection of topologically complex magnetic fields. Observations show
  that such fields are often characterized by a twisted structure. This
  is modeled here using a force-free flux tube whose arc-like body is
  embedded into an external potential magnetic field. We study how
  the topological structure of this configuration evolves when the
  flux tube emerges quasi-statically from below the photosphere to a
  certain height in the corona, where the tube becomes unstable and its
  eruption has to occur. During this evolution below the flux tube there
  appears a separator field line, along which two separatrix surfaces
  intersect. This separator is of generalized type because there are
  no magnetic nulls in the configuration. Both the separator and the
  separatrices are topological features, where the connectivity of
  magnetic field lines suffers a jump. We propose that the eruption of
  the flux tube has to stimulate the formation of strong current layers,
  in which the free magnetic energy of configuration is released in
  the form of a flare. The model predicts the formation of hot loops
  of two kinds during the reconnection phase: the long loops which make
  nearly one turn around the twisted flux tube, and short sheared loops
  below. The proposed model provides important clues to the mechanism
  of solar flares in twisted configurations.

Title: Long-Term Evolution Of Emissivity And Heating In A Solar
    Active Region
Authors: van Driel-Gesztelyi, L.; Thompson, B.; Démoulin, P.; Orlando,
   S.; Bocchialini, K.; Oláh, K.; Kövári, Z.; Deforest, C.; Khan,
   J.; Fludra, A.; Mandrini, C.
Bibcode: 1999ESASP.446..663V
Altcode: 1999soho....8..663V
  We study the evolution of the heating and emissivity of an active
  region from its birth throughout its decay during six solar rotations
  (July-Nov. 1996). We analyse multi-wavelength and multi-instrument
  data obtained from SOHO (EIT, SUMER, CDS, MDI), Yohkoh (SXT), GOES
  and 10.7cm radio data from DRAO, Canada. We take one "snapshot" per
  rotation at the time of the central meridian passage (CMP) of the
  AR, outside of time of flares, which appears to be representative
  enough to allow us to make some general conclusions about the
  long-term evolution. Deriving physical parameters like intensity
  (flux), temperature and emission measure of the entire AR vs. time,
  we formulate mathematically the change in radiation emitted by the
  decaying AR at several wavelengths. Combining the emissivity data with
  the evolution of magnetic flux density as the flux is being dispersed
  by small- and larger-scale convective motions, we make an attempt to
  understand the physics behind the emission and heating. We also analyse
  the effects of flaring on the heating of the AR, and study whether and
  how the flare properties evolve during the life of the active region.

Title: The Role of "Magnetic Dips" and "Bald Patches" for a Filament
    Observed by SOHO and GBO
Authors: Aulanier, G.; Schmieder, B.; Kucera, T.; van Driel-Gesztelyi,
   L.; Démoulin, P.; Mein, N.; Vial, J. -C.; Mein, P.
Bibcode: 1999ASPC..184..291A
Altcode:
  The studied filament was observed on Sept. 25, 1996, in Hα with
  the MSDP on the German VTT, Tenerife, as well as in Si IV with
  SOHO/SUMER. The 3-D magnetic configuration of the filament channel is
  reconstructed, using linear magnetohydrostatic (lmhs) extrapolations
  from a SOHO/MDI magnetogram, which is modified by a background magnetic
  component constraining a twisted flux-tube. This flux-tube is deformed
  by the magnetic polarities observed with SOHO/MDI. The shape and
  location of the computed "dipped field lines" are in good agreement
  with the shape of the filament and its feet observed in Hα. Some "bald
  patches" (BPs) are present where the distribution of dips reaches the
  photosphere. We find observational signatures in Si IV brightenings of
  energy release at the locations of computed "bald patch separatrices",
  defined by field lines which are tangent to the photosphere. We propose
  that the plasma is there heated by ohmic dissipation from the expected
  currents in the BP separatrices. The results show the importance of
  "dipped field lines" and "bald patches" in filament channels.

Title: Magnetic Field Evolution and Topology of an AR
Authors: Mandrini, C. H.; Deng, Y. Y.; Schmieder, B.; Démoulin, P.;
   Rudawy, P.; Nitta, N.; Newmark, J.; de Forest, C.
Bibcode: 1999ASPC..184..276M
Altcode:
  Active region 7968 was observed during runs of a coordinated SOHO,
  Yohkoh and ground-based observatory program (Joint Observing Program,
  JOP, 17). The region appeared and decayed in a seven day period (June 3
  to 10, 1996). In this time, mainly during June 6, it presented a very
  dynamical behaviour. Flux emerged in between the two main polarities
  and Arch Filament Systems (AFS) were observed to be linked to this
  emergence. We analyze the evolution of some over dark arches observed
  during flux emergence, forming two systems of AFS. Modelling the
  magnetic field, we find that these systems were associated to field
  lines having dips tangent to the photosphere (the so called "bald
  patches", BPs). We discuss their evolution in terms of emergence of
  the dipped portion of the lines or of magnetic field reconnection.

Title: Long-Term Magnetic Evolution of an AR and its CME Activity
Authors: van Driel-Gesztelyi, L.; Mandrini, C. H.; Thompson, B.;
   Plunkett, S.; Aulanier, G.; Démoulin, P.; Schmieder, B.; de Forest, C.
Bibcode: 1999ASPC..184..302V
Altcode:
  Using SOHO/MDI full-disc magnetic maps, we follow the magnetic
  evolution of a solar active region for several months in the period of
  July-November 1996. We extrapolate the photospheric magnetic fields in
  the linear force-free approximation and match the modelled field lines
  with the soft X-ray loops observed with the Yohkoh/SXT in order to
  diagnose the coronal magnetic shear. We find that while the turbulent
  motions diffuse the flux, the differential rotation, and possibly
  twisted flux emergence, increase the magnetic shear. Flares are observed
  during the first three rotations, while CME events (observed by SOHO/EIT
  and LASCO) originate from this AR from its emergence throughout its
  decay. Several early CMEs, while none of the late CMEs, are related to
  flare events above the GOES B1 level. We find that the late CMEs occur
  when the magnetic shear, after accumulating for four rotations, reaches
  a high level and saturates. We propose that CME activity serves as a
  valve through which the AR could get rid of excess shear and helicity.

Title: The Magnetic Topology of a Twisted Force-Free Configuration
    in an Active Region
Authors: Titov, V. S.; Démoulin, P.
Bibcode: 1999ASPC..184...76T
Altcode:
  It is widely accepted now that flare-like phenomena in active
  regions are due to magnetic reconnection process in configurations
  having a topological complexity. Observations demonstrate that such
  configurations are often characterized by a twisted structure. It is
  modeled here by a force-free flux tube, whose curved arc-like body is in
  equilibrium with an external potential magnetic field. We study how the
  topological structure of this configuration evolves with emerging of the
  flux tube from below the photosphere until it achieves a nonequilibrium
  point, where the eruption of the flux tube must occur. At some moment
  of the emergence process there appears a generalized separator field
  line, which is determined without null points and along which two
  separatrix surfaces intersect. Both the separator and these surfaces
  are topological features, where the magnetic connectivity suffers a
  jump, which may cause the formation of strong current sheets there. The
  obtained results give a good insight into the mechanism of solar flares
  with a twisted magnetic field structure.

Title: The evolution from birth to decay of a short-lived active
    region
Authors: Deng, Yuan Yong; Schmieder, Brigitte; Mandrini, Cristina H.;
   Khan, Josef I.; Démoulin, Pascal; Rudawy, Pawel
Bibcode: 1999A&A...349..927D
Altcode:
  In the following paper we present results of the analysis of NOAA active
  region 7968, which was the target of a coordinated observing campaign
  involving the instruments aboard the Solar and Heliospheric Observatory
  (SOHO), Yohkoh, and ground-based observatories (Bialków, Pic du Midi,
  and Huairou). This active region was relatively short-lived, and thus
  provides a rare example of a region observed continuously from its birth
  to its decay phase. We have extrapolated the SOHO Michelson Doppler
  Imager (MDI) longitudinal magnetograms, and have compared the results of
  the modeled field with loops observed over a wide range of temperatures
  ( ~ 10(5) -3x10(6) K). We find that, throughout the interval of disk
  passage, the global magnetic structure of the active region corresponds
  to a nearly potential-field configuration. Magnetic field shear is
  only seen in isolated patches along the polarity inversion line and is
  associated with the emergence of parasitic polarity regions. Several
  small GOES (B-class) X-ray flares and surge-like ejections were
  observed during the lifetime of the active region. We interpret both
  the heating of the active region loops and the flaring in terms of
  magnetic reconnection. In our scenario, the flares are assumed to be
  due to reconnection between the pre-existing field and newly emerging
  twisted flux tubes (as indicated by observed changes in the transverse
  field and inferred twisting motions of the plasma); while the heating of
  the plasma in quasi-static active region loops is assumed to be due to
  a relaxation process of the magnetic configuration. These loops appear
  anchored at places where the photospheric field is highly fragmented,
  creating a very complex connectivity pattern. This fact, together with
  the continual photospheric motions, provides the favorable conditions
  for current sheet formation and release of magnetic energy.

Title: Some Advances in 3D-Magnetic Field Topology: an Observed Case
    of a "Bald Patch" Flare
Authors: Démoulin, P.; Aulanier, G.; Schmieder, B.
Bibcode: 1999ASPC..184...65D
Altcode:
  The aim of this work is to bring observational evidences of the
  possible role of the "bald patch" topology in flaring events. A bald
  patch (or BP) is present along the photospheric inversion line where
  the field lines are curved-up, so when magnetic dips are present. The
  set of field lines associated to the BP define a separatrix where a
  current sheet may form. We find such configuration in AR 7722 where,
  on May 18, 1994, a sub-flare was observed in X-rays by Yohkoh/SXT and
  in Hα at NAOJ. Using the magnetohydrostatic equations derived by Low
  (1992), we model the magnetic field configuration by extrapolation
  of the Kitt Peak photospheric field, taking into account the effects
  of pressure and gravity. Hα flare kernels are shown to be located at
  the lower parts of the computed separatrices associated to bald patches
  (BPs). This is an evidence that BPs can be involved in flares, and that
  current sheets can be dissipated in low levels of the solar atmosphere.

Title: Quasi-Separatrix Layers in a Reduced Magnetohydrodynamic
    Model of a Coronal Loop
Authors: Milano, Leonardo J.; Dmitruk, Pablo; Mandrini, Cristina H.;
   Gómez, Daniel O.; Démoulin, Pascal
Bibcode: 1999ApJ...521..889M
Altcode:
  We run a pseudospectral magnetohydrodynamic code to simulate
  reconnection between two flux tubes inside a solar coronal loop. We
  apply a stationary velocity field at one of the footpoints consisting
  of two vortices in such a way as to induce the development of a current
  layer and force the field lines to reconnect. During the process we
  find a remarkable coincidence between the location of the current layer
  and the location of quasi-separatrix layers, which are thin magnetic
  volumes where the field line connectivity changes abruptly. This result
  lends support to a scenario in which quasi-separatrix layers are
  the most likely locations for impulsive energy release in the solar
  corona. Another important result of this simulation is the observed
  transient of strong magnetohydrodynamic turbulence characterized by
  a k<SUP>-3/2</SUP> energy spectrum. This transient reaches its peak
  activity in coincidence with a maximum in the energy dissipation rate,
  thus suggesting that the direct energy cascade associated with this
  turbulent transient plays a key role in enhancing energy dissipation
  in magnetic reconnection processes.

Title: A new emerging flux and brightening event.
Authors: Li, Yining; Tang, Yuhua; Aulanier, G.; Schmieder, B.;
   Demoulin, P.; Fang, Cheng
Bibcode: 1999PPMtO..18..131L
Altcode:
  By using Yohkoh soft X-ray images, vector magnetograms and Hα
  filtergrams, a brightening event of Hα and soft X-ray of 18 May, 1994
  has been studied in detail. It is shown that the event is obviously
  caused by new emerging flux. The brightening points of Hα and soft
  X-ray are located at computed separatrices associated to field lines
  which are tangent to the photosphere. This brightening event may be a
  signature of reconnection taking place between the pre-existing loops
  and the new emerging small loops in the lower solar atmosphere.

Title: Magnetic Field Scaling Laws and Their Implications for
    Coronal Heating
Authors: Klimchuk, J. A.; Demoulin, P.; Mandrini, C. H.
Bibcode: 1999AAS...194.2304K
Altcode: 1999BAAS...31..861K
  Ever since it was realized, some 60 years ago, that the solar
  corona is two orders of magnitude hotter than the underlying
  photosphere, scientists have puzzled over the reason for these
  extreme conditions. A number of plausible ideas have been proposed,
  including the dissipation of MHD waves (AC models) and the dissipation
  of stressed, current-carrying magnetic fields (DC models), but it has
  proved difficult to establish which, if any, is correct. One approach
  to answering this fundamental question is to determine scaling laws
  relating the heating rate to observable physical parameters. Klimchuk
  &amp; Porter (1995, Nature, 377, 131) showed that the heating rate
  varies inversely with the square of the length of coronal loops observed
  by Yohkoh. To compare this with the predictions of coronal heating
  theories, it is necessary to know also how the magnetic field strength
  in the loops varies with their length. By computing magnetic field
  extrapolation models based on both observed and synthetic distributions
  of active region surface fields, we have found that B ~ ( L(2) + S(2)
  )(c/2) , where B is the coronal field strength averaged along a loop,
  L is the loop length, S is the characteristic size of the active region,
  and -3 &lt;= c &lt;= -1, depending on the complexity of the region. More
  importantly, for the range of loop lengths studied by Klimchuk &amp;
  Porter, 50 &lt; L &lt; 300 Mm, there is a universal scaling law of
  the form B ~ L(delta ,) where delta = -0.98 +/- 0.3. The details of
  these results will be presented, and their implications for theories
  of coronal heating will be discussed. It will be shown that DC models
  are in better agreement with the observations than are AC models. This
  work was supported in part by NASA grant W-19,200.

Title: New 3-D magnetic model for prominences based on dipped field
    lines and compared with observations
Authors: Aulanier, G.; Demoulin, P.
Bibcode: 1999AAS...194.3103A
Altcode: 1999BAAS...31R.868A
  Despite of the large number of 2D and 3D models for the magnetic
  fields in prominences, none has been succesfully directly compared
  with observational data untill recently, even if many of them still
  satisfied some well established observational results. This has
  led to a never ending controversy between theorists and observers,
  about the relevance of dipped field lines for mass support against
  gravity in these objects. Here we present a new 3D magnetohydrostatic
  model based on dipped field lines. The main body of the filament is
  formed by a twisted flux rope in a bipolar region, and we show how
  small parasitic polarities near the neutral line lead to a local
  perturbation of the magnetic fields in the corona, leading to the
  formation of lateral dips, which appear aside from the flux rope. We
  show that these are formed by local expansions of the fluxe rope,
  as well as by the bending of some surrounding sheared field lines,
  toward the photospheric parasitic polarities. We suggest that these
  lateral dips can form lateral feet of filaments. Moreover the global
  magnetic configuration shows in a natural fashion a very large number
  of typical observational aspects of prominences. Using a magnetogram
  obtained by SOHO/MDI on 09/25/96 as boundary conditions, we extrapolate
  the magnetic field under the assumptions of the model. Comparing the
  3D distribution of dips with the morphology of the filament observed
  in Hα on the German VTT (Tenerife) at the same time, we show a good
  correlation between the dips and the filament body, as well as with its
  lateral feet. All these results suggest that the model is well adapted
  for the description of the magnetic field in filaments and their close
  environement. Furthermore its direct comparison with observations
  provide evidence in favor of dipped field lines in prominences.

Title: 3-D magnetic configurations supporting
    prominences. III. Evolution of fine structures observed in a filament
    channel
Authors: Aulanier, G.; Démoulin, P.; Mein, N.; van Driel-Gesztelyi,
   L.; Mein, P.; Schmieder, B.
Bibcode: 1999A&A...342..867A
Altcode:
  On September 25() th 1996, a quiescent filament located near the
  center disc (S2, E5) was observed on the German VTT (Tenerife)
  with the MSDP instrument, in the Hα line center and wings. SOHO/MDI
  line-of-sight magnetograms were co-aligned with the MSDP images, showing
  the position and evolution of the lateral feet of the filament in the
  vicinity of the parasitic magnetic polarities observed in the filament
  channel. Using the assumptions developed in the previous papers of this
  series related to the reconstruction of the 3-D magnetic configuration
  of filaments, we perform ``linear magnetohydrostatic'' extrapolations
  (taking into account the effects of plasma pressure and gravity) on the
  SOHO/MDI magnetograms. The main hypothesis is the presence of a twisted
  flux-tube located above the photospheric inversion line. Assuming that
  the parameters of the model do not need to be significantly modified
  during the evolution of the configuration for a duration of 1 day,
  we have shown that the 3-D distribution of dipped field lines is well
  correlated with Hα dark absorbing features in the filament channel:
  the filament itself, its lateral feet and some of the surrounding dark
  fibrils. In this way we confirm what was suggested in our earlier
  papers, i.e. that the feet are composed of the dipped portions of
  some field lines, which form a continuous pattern from the corona
  to the photosphere. We propose the same explanation for the magnetic
  configuration of some of the dark Hα fibrils in the channel. We show
  that the plasma effects are not responsible for the existence of most
  of the magnetic dips, however their inclusion helps to get a better
  correspondence between the model and the observations. We find that the
  average Hα Doppler velocities associated with the filament and with
  the chromospheric fibrils is of the order of a few hundred m s(-1)
  (though it can go locally up to 3 km s(-1) in the filament). These
  upward velocities are consistent with a quasi-static evolution of
  the magnetic configuration and with the support of dense plasma in
  magnetic dips.

Title: Results on 3-D solar magnetic field, observations and models
Authors: Démoulin, P.
Bibcode: 1999JASTP..61..101D
Altcode: 1999JATP...61..101D
  This review presents some of the new developments in the
  understanding of coronal magnetic fields in flares and coronal
  mass ejections. The modelling of the coronal magnetic field based
  on observed photospheric field permits to understand the location
  of energy release. Various flare observations are consistent with a
  model where magnetic reconnection occurs between two magnetic fields of
  different connectivity. Because magnetic helicity is almost conserved,
  the stored energy cannot be fully released in confined flares. The
  corona gets rid of the helicity injected by the convection zone only
  by ejecting part of the magnetic field. A severe physical constraint
  (open-field limit) on these ejections has been firmly established for
  force-free fields. It is, however, possible to open partially the field
  or to eject a twisted flux-tube keeping the energy of the field behind
  the open-field limit. New results show that in simply connected fields
  this happen after a finite time without loss of equilibrium, while in
  more complex topology a loss of equilibrium can still be present.

Title: Bright Points and Subflares in Ultraviolet Lines and X-Rays
Authors: Rovira, M.; Schmieder, B.; Démoulin, P.; Simnett, G. M.;
   Hagyard, M. J.; Reichmann, E.; Tandberg-Hanssen, E.
Bibcode: 1999ApJ...510..474R
Altcode:
  We have analyzed an active region which was observed in Hα
  (Multichannel Subtractive Double Pass Spectrograph), in UV lines
  (SMM/UVSP), and in X-rays (SMM/HXIS). In this active region there
  were only a few subflares and many small bright points visible in UV
  and in X-rays. Using an extrapolation based on the Fourier transform,
  we have computed magnetic field lines connecting different photospheric
  magnetic polarities from ground-based magnetograms. Along the magnetic
  inversion lines we find two different zones: (1) a high-shear region
  (&gt;70°) where subflares occur, and (2) a low-shear region along
  the magnetic inversion line where UV bright points are observed. In
  these latter regions the magnetic topology is complex with a mixture
  of polarities. According to the velocity field observed in the Si IV
  λ1402 line and the extrapolation of the magnetic field, we notice that
  each UV bright point is consistent with emission from low-rising loops
  with downflows at both ends. We notice some hard X-ray emissions above
  the bright-point regions with temperatures up to 8 × 10<SUP>6</SUP> K,
  which suggests some induced reconnection due to continuous emergence of
  new flux. This reconnection is also enhanced by neighboring subflares.

Title: Calentamiento de arcos coronales en una región activa por
    reconfiguración topológica del campo magnético.
Authors: López Fuentes, M.; Mandrini, C. H.; Démoulin, P.; Schmieder,
   B.; Fletcher, L.; Mason, H.
Bibcode: 1999BAAA...43...24L
Altcode:
  We study the active region (AR) 8048 observed on June 1997 in several
  wavelenghts. The combined observations obtained using CDS (SOHO)
  and SXT (Yohkoh) show the heating of the coronal magnetic loops at
  different atmospheric altitudes. Extrapolating the magnetic field in the
  corona from longitudinal magnetograms from MDI (SOHO), we determine the
  location of Bald Patches in the surroundings of the leading spot. This
  magnetic feature, the emergence of parasitic magnetic polarities and
  the observed photospheric motions provide the conditions to explain
  the observed heating.

Title: The NOAA AR 6718 magnetic field extrapolation with localized
    current filaments.
Authors: Karlický, M.; Démoulin, P.; Aulanier, G.; van
   Driel-Gesztelyi, L.; Hénoux, J. C.; Jirička, K.
Bibcode: 1999joso.proc...97K
Altcode:
  The 3-D extrapolation of magnetic field lines of the July 11, 1991
  Kitt Peak magnetogram shows a differential magnetic field shear in
  the NOAA 6718 active region. A new combined extrapolation technique,
  which includes localized current filaments is suggested and applied in
  modelling of this shear. First, the potential field extrapolation is
  made and then force-free current paths for several current filaments
  in specific positions are computed. It is shown that with the electric
  current increase the localized magnetic field shear is increasing. The
  total electric current in 16 current filaments is considered up to
  1.2×10<SUP>12</SUP>A.

Title: Magnetohydrostatic Model of a Bald-Patch Flare
Authors: Aulanier, G.; Démoulin, P.; Schmieder, B.; Fang, C.; Tang,
   Y. H.
Bibcode: 1998SoPh..183..369A
Altcode:
  On 18 May, 1994, a subflare was observed in AR 7722 in X-rays by
  Yohkoh/SXT and in Hα at National Astronomical Observatory of Japan. The
  associated brightenings are due to small-scale magnetic energy release,
  triggered by parasitic fluxes emerging and moving at the edge of leading
  sunspots. Using the magnetohydrostatic equations derived by Low (1992),
  we model the magnetic field configuration by extrapolation of the Kitt
  Peak photospheric field, taking into account the effects of pressure
  and gravity. Hα flare kernels are shown to be located at computed
  separatrices associated with field lines which are tangent to the
  photosphere, namely 'bald patches' (BPs). This is evidence that BPs
  can be involved in flares, and that current sheets can be dissipated
  in low levels of the solar atmosphere. The presence of dense plasma
  which is supported against gravity in the magnetic dips above BPs is
  correlated to dark elongated features observed in Hα. Mass flows in
  these flat fibrils are discussed in the context of energy release in
  the BP separatrices. The effect of the plasma on the computed magnetic
  configuration is shown to be of secondary importance with respect to
  the topology of the field.

Title: The Effect of Curvature on Flux-Rope Models of Coronal Mass
    Ejections
Authors: Lin, J.; Forbes, T. G.; Isenberg, P. A.; Démoulin, P.
Bibcode: 1998ApJ...504.1006L
Altcode:
  The large-scale curvature of a flux rope can help propel it outward
  from the Sun. Here we extend previous two-dimensional flux-rope models
  of coronal mass ejections to include the curvature force. To obtain
  analytical results, we assume axial symmetry and model the flux rope as
  a torus that encircles the Sun. Initially, the flux rope is suspended
  in the corona by a balance between magnetic tension, compression,
  and curvature forces, but this balance is lost if the photospheric
  sources of the coronal field slowly decay with time. The evolution of
  the system shows catastrophic behavior as occurred in previous models,
  but, unlike the previous models, flux ropes with large radii are more
  likely to erupt than ones with small radii. The maximum total magnetic
  energy that can be stored before equilibrium is lost is 1.53 times the
  energy of the potential field, and this value is less than the limiting
  value of 1.662 for the fully opened field. As a consequence, the loss
  of ideal MHD equilibrium that occurs in the model cannot completely
  open the magnetic field. However, the loss of equilibrium does lead
  to the sudden formation of a current sheet, and if rapid reconnection
  occurs in this sheet, then the flux rope can escape from the Sun. We
  also find that the field can gradually become opened without suffering
  any loss of equilibrium if the photospheric field strength falls
  below a critical value. This behavior is analogous to the opening of
  a spherically symmetric arcade in response to a finite amount of shear.

Title: 3-D magnetic configurations supporting prominences. II. The
    lateral feet as a perturbation of a twisted flux-tube
Authors: Aulanier, G.; Demoulin, P.; van Driel-Gesztelyi, L.; Mein,
   P.; Deforest, C.
Bibcode: 1998A&A...335..309A
Altcode:
  In a previous paper we have shown that a twisted flux-tube is the
  most probable magnetic configuration supporting prominences. The
  model interprets many observations in a natural way (in particular
  the magnetic measurements in prominences and the chirality
  properties). Moreover, prominence feet appear as a direct consequence
  of the parasitic polarities present in the filament channel. Here we
  investigate further the link between feet and parasitic polarities
  by modelling explicitly these polarities. We show that the prominence
  lateral feet appear naturally, above secondary photospheric inversion
  lines and we describe the morphological change of feet as parasitic
  polarities evolve. This approach is applied to an observed filament
  in Hα with the MSDP on the German VTT (Tenerife) where SOHO/MDI
  magnetograms are available. We show that the shape of the prominence
  is defined by the distribution of the dips in the computed magnetic
  configuration. Then we analyse the topology of the magnetic field using
  the quasi-separatrix layers (QSLs) method. We describe the basic changes
  in the topology as the parasitic polarities evolve, in particular
  how the configuration pass from an OX to an OF topology. We find a
  correspondance between the computed QSLs and some of the chromospheric
  brightenings, observed around the feet of filaments in the y line (Ca
  II, 8542 Angstroms). It confirms the deduced magnetic configuration
  and shows that energy release is present at a low level in the complex
  topology of the filament configuration.

Title: Interactions between nested sunspots. II. A confined X1 flare
    in a delta-type sunspot
Authors: Gaizauskas, V.; Mandrini, C. H.; Demoulin, P.; Luoni, M. L.;
   Rovira, M. G.
Bibcode: 1998A&A...332..353G
Altcode:
  We study the flaring activity in a nest of sunspots in which two bipolar
  regions emerge inside a third one. These bipolar regions belong to
  a large complex of activity (McMath 15314) formed by five bipoles on
  its May 1978 rotation. The usual spreading action during the growth
  of the bipoles leads to the formation of a $Delta lta-configuration:
  the preceding and following spots of the two interior regions overlap
  (p-f collision) into a single penumbra. While Delta lta-configurations
  created in this way normally favor strong flaring activity, only
  very small flares occur during 5 days. Only when the following umbra
  in the Delta lta$-spot breaks into pieces, accompanied by rapid
  photospheric motions, do intense flares occur. The largest and best
  observed one in this sequence, a class 1B/X1 flare on 28 May 1978,
  is remarkable for the absence of ejecta and for the concentration
  of its emission in three widely spaced sites, a pattern which holds
  in general over two days for lesser flares. We take this pattern as
  evidence that the flare is confined to the low corona. We first compute
  the coronal magnetic field using subphotospheric sources to model the
  observed magnetic data and derive the location of separatrices. In
  this case the magnetic field topology is defined by the link between
  these discrete sources. The relevant generalization of separatrices
  in any kind of magnetic configuration are `quasi-separatrix layers'
  (QSLs). We calculate them using the previous model, but also for a
  model obtained with a more classical extrapolation technique based on
  the fast Fourier transform method. We show, with both approaches, that
  the plage brightenings during the quiescent phase of the region and the
  flare kernels are located at the intersection of separatrices and QSLs
  with the photosphere. Moreover, they are magnetically linked. Bright and
  dark `post'-flare loops which form in the maximum and gradual phases
  of the 1B/X1 flare also highlight the location of the separatrices
  and the QSLs. This confirms previous studies on the importance of the
  magnetic field topology for flares and, with this study, we further
  constrain the underlying physical mechanism. We draw some conclusions
  about the role of magnetic reconnection in the solar corona; depending
  on the photospheric conditions that we identify, reconnection can lead
  to steady heating or flaring.

Title: Evolution of the Magnetic Field and Chromospheric Fine
    Structure in a Filament Channel
Authors: van Driel-Gesztelyi, L.; Mein, P.; Mein, N.; Schmieder,
   B.; Malherbe, J. -M.; Aulanier, G.; Démoulin, P.; Deforest, C.;
   Staiger, J.
Bibcode: 1998ASPC..155..321V
Altcode: 1998sasp.conf..321V
  No abstract at ADS

Title: Reorganization of solar magnetic field by a flare event
Authors: Manoharan, P. K.; van Driel-Gesztelyi, L.; Pick, M.;
   Démoulin, P.
Bibcode: 1998BASI...26..319M
Altcode:
  No abstract at ADS

Title: Non potentiality of coronal loops above active regions
Authors: Aulanier, G.; Schmieder, B.; Démoulin, P.; van
   Driel-Gesztelyi, L.; Deforest, C.
Bibcode: 1998ASPC..155..105A
Altcode: 1998sasp.conf..105A
  No abstract at ADS

Title: Filament Disparition Brusque and CME - September 25-26,
    1996 Event
Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Aulanier, G.;
   Demoulin, P.; Martens, P. C. H.; Zarro, D.; Deforest, C.; Thompson,
   B.; St. Cyr, C.; Kucera, T.; Burkepile, J. T.; White, O. R.; Hanaoka,
   Y.; Nitta, N.
Bibcode: 1998ASPC..150..366V
Altcode: 1998IAUCo.167..366V; 1998npsp.conf..366V
  No abstract at ADS

Title: MHS model of an active region associated to a flare
Authors: López Fuentes, M.; Mandrini, C. H.; Rovira, M. G.;
   Démoulin, P.
Bibcode: 1998BAAA...42...34L
Altcode:
  Using observations obtained by different instruments, we have analyzed
  the active region (AR) NOAA 7070 associated to an X3/B3 flare. The
  intense UV emission has been an outstanding characteristic of this
  event, 17 times larges than that of the whole solar disk. This
  is similar to the emission observed in stars in which flares are
  produced. We have modelled the atmospheric magnetic field, using
  a magnetohydrostatic approach using photospheric magnetograms as
  boundary conditions. The magnetic field presents a high shear close
  to the AR inversion line. This is seen not only in the transverse
  component of the photospheric, but also in the coronal loops observed in
  X-rays. The high shear of the coronal loops disappears after the flare,
  and they show a topology closer to that of a potential field. This is
  in agreement with what is expected when the field relaxes after the
  stored energy has been released. Using the magnetic virial theorem,
  and after the computed model, we estimate that the energy variation
  is enough to account for the observed flare.

Title: 3-D magnetic configurations supporting prominences. I. The
    natural presence of lateral feet
Authors: Aulanier, G.; Demoulin, P.
Bibcode: 1998A&A...329.1125A
Altcode:
  It is now commonly accepted that prominence plasma is supported
  in magnetic dips, in particular in twisted flux-tubes. But present
  two-dimensional models are unable to explain the observed presence
  and structure of prominences feet. This requires three-dimensional
  models. We modeled the field using linear force-free field
  equations. Combining a small number of harmonics, and using
  observational constraints, we have found the area in the parameter
  space where prominences are likely to be present. Then, adding 3-D
  harmonics, we show that feet appear periodically underneath the
  prominence body. For great helicity, the parameter space is mostly
  fulfilled by configurations which have feet alternating between both
  sides of the prominence axis, as observed. The theoretical photospheric
  field has a quasi-bipolar pattern and the prominence stands above a
  magnetic corridor containing only small parasitic polarities. The
  lateral feet are formed by dips in the vicinity of these small
  polarities. These configurations show in a natural fashion a number
  of well-established as well as more recent observational aspects of
  prominences, in particular the vector magnetic field measurements
  in prominences and the chirality patterns (the dextral/sinistral,
  right/left bearing, skew of the overlying coronal arcade and fibril
  organization in prominence channels).

Title: Bright Points and Subflares in UV Lines and in X-Rays
Authors: Rovira, M.; Schmieder, B.; Demoulin, P.; Simnett, G. M.;
   Hagyard, M. J.; Reichmann, E.; Tandberg-Hanssen, E.
Bibcode: 1998msfc.rept.....R
Altcode:
  We have analysed an active region which was observed in Hα (MSDP),
  UV lines (SMM/UVSP), and in X rays (SMM/HXIS). In this active region
  there were only a few subflares and many small bright points visible in
  UV and in X rays. Using an extrapolation based on the Fourier transform
  we have computed magnetic field lines connecting different photospheric
  magnetic polarities from ground-based magnetograms. Along the magnetic
  inversion lines we find 2 different zones: 1. a high shear region
  (less than 70 degrees) where subflares occur 2. a low shear region
  along the magnetic inversion line where UV bright points are observed.

Title: 3-D Modelling of a Filament Observed in Hα and with SOHO
Authors: Aulanier, G.; Schmieder, B.; Démoulin, P.; Mein, N.; van
   Driel-Gesztelyi, L.; Mein, P.; Vial, J. C.; Deforest, C.
Bibcode: 1998ESASP.417..217A
Altcode: 1998cesh.conf..217A
  No abstract at ADS

Title: The Energetics of Flux-Rope Prominence Models in Axially
    Symmetric Systems
Authors: Lin, J.; Forbes, T. G.; Isenberg, P. A.; Demoulin, P.
Bibcode: 1998ASPC..150..350L
Altcode: 1998npsp.conf..350L; 1998IAUCo.167..350L
  No abstract at ADS

Title: 3-D Modelling of a Filament Observed in Hα and with SOHO/MDI
Authors: Aulanier, G.; Démoulin, P.; van Driel-Gesztelyi, L.; Mein,
   P.; Deforest, C.
Bibcode: 1998ASPC..155..326A
Altcode: 1998sasp.conf..326A
  No abstract at ADS

Title: Magnetic Fields in Filaments (Review)
Authors: Demoulin, P.
Bibcode: 1998ASPC..150...78D
Altcode: 1998npsp.conf...78D; 1998IAUCo.167...78D
  No abstract at ADS

Title: 3-D Twisted Flux-Tube in a Linear Force-Free Equilibrium
Authors: Aulanier, G.; Demoulin, P.
Bibcode: 1998ASPC..150...86A
Altcode: 1998npsp.conf...86A; 1998IAUCo.167...86A
  No abstract at ADS

Title: Quasi-separatrix layers in solar flares. II. Observed magnetic
    configurations.
Authors: Demoulin, P.; Bagala, L. G.; Mandrini, C. H.; Henoux, J. C.;
   Rovira, M. G.
Bibcode: 1997A&A...325..305D
Altcode:
  We show that the location of Hα or OV flare brightenings is related
  to the properties of the field-line linkage of the underlying magnetic
  region. The coronal magnetic field is extrapolated from the observed
  photospheric field assuming a linear force-free field configuration
  in order to determine the regions of rapid change in field-line
  linkage, called "quasi-separatrix layers" or QSLs. They are open
  layers that behave physically like separatrices: breakdown of ideal
  magnetohydrodynamics and release of free magnetic-energy may occur
  at these locations when their thickness is small enough. A feature
  common to all the flaring regions studied is found to be the presence
  of QSLs where Hα flare kernels are observed. The brightenings are
  along restricted regions of very thin QSLs; an upper bound of their
  thickness is 1Mm but it is several order of magnitude smaller in most
  of the cases. These places coincide in general with zones where the
  longitudinal field component is greater than 100G. These results allow
  us to constrain present models of solar flares and localise where a
  break-down of ideal MHD can occur. The studied flares are found to be
  fed in general by only one electric current loop, but they imply the
  interaction of two magnetic bipoles. The extrapolated coronal field
  lines involved in the process have their photospheric footpoints
  located at both sides of QSLs, as expected in recent 3D magnetic
  reconnection models.

Title: Magnetic reconnection driven by emergence of sheared magnetic
    field.
Authors: Schmieder, B.; Aulanier, G.; Demoulin, P.; van
   Driel-Gesztelyi, L.; Roudier, T.; Nitta, N.; Cauzzi, G.
Bibcode: 1997A&A...325.1213S
Altcode:
  Recurrent subflares (Class C) were observed in the NOAA 7608 active
  region on 27 October 1993. From multi-wavelength observations
  (white-light, magnetic field, H-alpha, X-ray), obtained during a
  coordinated campaign between Pic du Midi and Yohkoh, it appears that
  these flares were double ribbon flares caused by new flux emergence. As
  the flare begins, the X-ray emission observed with Yohkoh/SXT is
  loop-shaped with the axis almost parallel to the magnetic inversion
  line, while during the flare development, X-ray loops appear at the
  location of the emerging flux. The extrapolation of the photospheric
  magnetic field in a linear force-free field configuration allows
  identification of the magnetic configuration given by the flares. The
  Hα flare ribbons are located at the intersections of the computed
  quasi-separatrice layers (QSLs) with the chromosphere. We show that
  the initial loop-shaped X-ray emission region is in fact formed by
  several smaller loops directed in a nearly orthogonal direction with
  their feet anchored close to or in the Hα ribbons. During the flare
  development there are X-ray loops which represent only one foot of
  open or largescale magnetic loops. For the studied flares the puzzling
  soft X-rays observations could only be understood with the help of Hα
  and magnetic data combined with a modeling of the coronal magnetic
  field. Further, from the deduced magnetic field topology, the width
  of the QSLs and our present knowledge of 3-D magnetic reconnection,
  we conclude that the flare was due to magnetic reconnection driven
  by emergence of sheared magnetic field impacting in the pre-existing
  coronal field.

Title: The Importance of Photospheric Intense Flux Tubes for Coronal
    Heating
Authors: Démoulin, P.; Priest, E. R.
Bibcode: 1997SoPh..175..123D
Altcode:
  Dissipation of magnetic energy in the corona requires the creation of
  very fine scale-lengths because of the high magnetic Reynolds number
  of the plasma. The formation of current sheets is a natural possible
  solution to this problem and it is now known that a magnetic field
  that is stressed by continous photospheric motions through a series
  of equilibria can easily form such sheets. Furthermore, in a large
  class of 3D magnetic fields without null points there are locations,
  called `quasi-separatrix layers' (QSLs), where the field-line linkage
  changes drastically. They are the relevant generalisation of normal
  separatrices to configurations without nulls: along them concentrated
  electric currents are formed by smooth boundary motions and 3D magnetic
  reconnection takes place when the layers are thin enough. With a
  homogenous normal magnetic field component at the boundaries, the
  existence of thin enough QSL to dissipate magnetic energy rapidly
  requires that the field is formed by flux tubes that are twisted by a
  few turns. However, the photospheric field is not homogeneous but is
  fragmented into a large number of thin flux tubes. We show that such
  thin tubes imply the presence of a large number of very thin QSLs in
  the corona. The main parameter on which their presence depends is the
  ratio between the magnetic flux located outside the flux tubes to the
  flux inside. The thickness of the QSLs is approximately given by the
  distance between neighbouring flux tubes multiplied by the ratio of
  fluxes to a power between two and three (depending on the density
  of flux tubes). Because most of the photospheric magnetic flux is
  confined in thin flux tubes, very thin QSLs are present in the corona
  with a thickness much smaller than the flux tube size. We suggest that a
  turbulent resistivity is triggered in a QSL, which then rapidly evolves
  into a dynamic current sheet that releases energy by fast reconnection
  at a rate that we estimate to be sufficient to heat the corona. We
  conclude that the fragmentation of the photospheric magnetic field
  stimulates the dissipation of magnetic energy in the corona.

Title: Quelques données sur la comète Hale-Bopp.
Authors: Demoulin, P.
Bibcode: 1997Ciel...59..213D
Altcode:
  No abstract at ADS

Title: Evidence of Magnetic Reconnection from Hα, Soft X-Ray and
    Photospheric Magnetic Field Observations
Authors: Mandrini, C. H.; DÉmoulin, P.; BagalÁ, L. G.; Van
   Driel-Gesztelyi, L.; HÉnoux, J. C.; Schmieder, B.; Rovira, M. G.
Bibcode: 1997SoPh..174..229M
Altcode:
  A conventional view of magnetic reconnection is mainly based on
  the 2-D picture of an X-type neutral point, or on the extension of
  it to 3-D, and it is thought to be accompanied by flux transport
  across separatrices (places where the field-line mapping is
  discontinuous). This view is too restrictive when we realize the variety
  of configurations that are seen flaring. We designed an algorithm,
  called Source Method (SM), to determine the magnetic topology of
  active regions (ARs). The observed photospheric field was extrapolated
  to the corona using subphotospheric sources and the topology was
  defined by the link between these sources. Hα flare brightenings
  were found to be located at the intersection with the chromosphere
  of the separatrices so defined. These results and the knowledge we
  gained on the properties of magnetic field-line linkage, led us to
  generalize the concept of separatrices to `quasi-separatrix layers'
  (QSLs) and to design a new method (`quasi-separatrix layers method',
  QSLM) to determine the magnetic topology of ARs. QSLs are regions where
  the magnetic field-line linkage changes drastically (discontinuously
  when they behave like separatrices) and the QSLM can be applied to ARs
  where the photospheric field has been extrapolated using any kind of
  technique. In this paper we apply the QSLM to observed flaring regions
  presenting very different configurations and also to a decaying AR where
  a minor phenomenon, like an X-ray bright point (XBP), is observed. We
  find that the locations of flare and XBP brightenings are related to the
  properties of the field-line linkage of the underlying magnetic region,
  as expected from recent developments of 3-D magnetic reconnection. The
  extrapolated coronal field lines representing the structures involved
  in the analyzed events have their photospheric footpoints located
  at both sides of QSLs. Our results strongly support the hypothesis
  that magnetic reconnection is at work in various coronal phenomena,
  ranging from the less energetic ones to large-scale eruptions.

Title: Can we Extrapolate a Magnetic Field when its Topology is
    Complex?
Authors: DÉmoulin, P.; HÉnoux, J. C.; Mandrini, C. H.; Priest, E. R.
Bibcode: 1997SoPh..174...73D
Altcode:
  In order to understand various solar phenomena controlled by the
  magnetic field, such as X-ray bright points, flares and prominence
  eruptions, the structure of the coronal magnetic field must be
  known. This requires a precise extrapolation of the photospheric
  magnetic field. Presently, only potential or linear force-free
  field approximations can be used easily. A more realistic modelling
  of the field is still an active research area because of well-known
  difficulties related to the nonlinear mixed elliptic-hyperbolic nature
  of the equations. An additional difficulty arises due to the complexity
  of the magnetic field structure which is caused by a discrete partition
  of the photospheric magnetic field. This complexity is not limited
  to magnetic regions having magnetic nulls (and so separatrices)
  but also occurs in those containing thin elongated volumes (called
  Quasi-Separatrix Layers) where the photospheric field-line linkage
  changes rapidly. There is a wide range for the thickness of such layers,
  which is determined by the character (bipolar or quadrupolar) of the
  magnetic region, by the sizes of the photospheric field concentrations
  and by the intensity of the electric currents. The aim of this paper
  is to analyse the recent nonlinear force-free field extrapolation
  techniques for complex coronal magnetic fields.

Title: 3-D reconnection related to new emerging flux
Authors: Schmeider, B.; Démoulin, P.; Aulanier, G.; Malherbe, J. M.;
   van Driel-Gesztelyi, L.; Mandrini, C. H.; Roudier, T.; Nitta, N.;
   Harra-Murnion, L. K.
Bibcode: 1997AdSpR..19.1871S
Altcode:
  We present evidences that emergence of new flux in the lower
  atmosphere leads to magnetic reconnection of field lines. In a
  first phase the phenomenon is observed in the chromosphere by the
  formation of dark filaments (arch filament system) which are overlaid
  by bright loops visible in soft X-rays. Different types of event appear
  according to the magnetic field configuration and the amount of energy
  involved. 3-D modelling of the photospheric magnetic field provides a
  new tool for understanding reconnection in real configurations. The
  observed chromospheric and coronal loops are good diagnostics for
  the modelling. We document our statement by examples obtained during
  coordinated campaigns with the Hα Multichannel Subtractive Double
  Pass spectrographs-MSDP (Pic du Midi and Tenerife) and the Yohkoh
  instruments.

Title: Magnetic reconnection driven by an emerging flux.
Authors: Aulanier, G.; Démoulin, P.; Schmieder, B.; Malherbe, J. M.;
   van Driel-Gesztelyi, L.; Roudier, T.
Bibcode: 1997joso.proc...51A
Altcode:
  No abstract at ADS

Title: Fulguraciones Solares en Regiones Activas Interactuantes
Authors: Bagalá, L. G.; Rovira, M. G.; Mandrini, C. H.; Démoulin, P.
Bibcode: 1997BAAA...41...57B
Altcode:
  We present a topological approach for the 30th January 1992 solar
  flares of AR 7031. We study Hα and soft X-ray emission for the most
  important flares, and compare these brightenings with the properties of
  the field-line linkage of the underlying magnetic region. The coronal
  magnetic field is computed from the observed photospheric field using
  a linear force-free extrapolation and the regions of drastic change in
  field-line linkage (called ``quasi-separatrix layers'' or QSLs) are
  determined by a computer algorithm. We find that a feature common to
  the two flares studied is the presence of QSLs where Hα flare kernels
  are observed. The extrapolated coronal field lines representing these
  structures have their photospheric footpoints located at both sides
  of QSLs, as expected if 3D magnetic reconnection were occurring at
  QSLs. These results allow us to constrain present models of solar
  flares.

Title: Retrieval of ozone vertical column amounts from ground-based
    high resolution infrared solar spectra.
Authors: Hamdouni, A.; Barbe, A.; Demoulin, P.; Zander, R.
Bibcode: 1997JQSRT..57...11H
Altcode:
  Good infrared spectral regions to retrieve accurately the vertical
  column amount of ozone from ground observations are proposed. Their
  selection was based on studies of the influence of spectroscopic
  (frequencies, halfwidths, intensities) as well as geophysical parameters
  (volume mixing ratios, temperature profiles) with a particular attention
  for temperature. The results, obtained in three different spectral
  regions, with a realistic T profile are very consistent.

Title: Fulguraciones en una configuración tipo δ
Authors: Luoni, M. L.; Mandrini, C. H.; Rovira, M. G.; Démoulin,
   P.; Gaizauskas, V.
Bibcode: 1997BAAA...41...62L
Altcode:
  Through the determination of the magnetic field topology, we focus
  this study on the flaring activity occurring in a nest of five
  bipoles. These bipoles belonged to a ``great complex of activity"
  (Mc Math 15314). We are interested in the largest and best observed
  flare on May 28, 1978, a class 1B/X1, occurring in a δ spot. The
  usual spreading action during the growth of the bipoles lead to the
  formation of a δ-configuration: the preceding and following spots of
  the two inner regions overlapped into a single penumbra. In this case,
  the spots approached continuously during five days. We first compute
  the coronal magnetic field using subphotospheric sources to model the
  longitudinal magnetograms and derive the location of separatrices,
  for May 27 and 28. Quasi-separatrix layers are a generalization of
  separatrices for any magnetic field configuration, these are thin
  volumes where the connectivity of field lines changes drastically. We
  calculate them using a model of the field obtained by extrapolation
  of the observations based on the fast Fourier transform method. With
  both approaches, we show that the plage brightenings, on the 27,
  and the flare kernels, on the 28, are located at the intersection of
  separatrices with the photosphere. This confirms the importance of
  the magnetic field topology for solar flares. Taking into account Hα
  observations and the magnetic field modelling, we conclude that energy
  is released in the solar corona, between the preceding and following
  spots, in the region of the separator. Bright and dark post-flare loops
  follow the location of separatrices and quasi-separatrix layers. This is
  consistent with magnetic reconnection models. Our results confirm the
  importance of the field topology for the comprehension of the active
  phenomena and allow us to characterize the energy release mechanism
  that is at their origin.

Title: Reorganization of the solar corona following a C4.7 flare
Authors: van Driel-Gesztelyi, L.; Manoharan, P. K.; Pick, M.;
   Démoulin, P. P.
Bibcode: 1997AdSpR..19.1883V
Altcode:
  Yohkoh X-ray images, multifrequency two-dimensional observations of
  the Nancay Radioheliograph, Kitt Peak and Mees magnetograms provide
  a unique set of data with which to study a C4.7 long-duration flare
  that was observed close to the equator (S07, W11) on 25 Oct. 1994
  at 09:49 UT. Linear force-free field extrapolations indicate a
  very high degree of non-potentiality in the active region. The
  X-ray flare started with the expansion of spectacular twisted
  loops. Fifteen minutes after the flare onset sporadic radio (type
  III) bursts were observed spreading over an area of almost &lt;FR
  SHAPE="SOL"&gt;1&lt;DE&gt;3&lt;/DE&gt;&lt;/FR&gt; of the solar disc
  and two remote X-ray brightenings appeared over quiet regions of
  opposite magnetic polarity located in on opposite hemispheres of the
  Sun. In the close vicinity of these remote brightenings two coronal
  holes formed. The timing and location of these events combined with
  the overall magnetic configuration provide evidence for a large-scale
  magnetic reconnection occurring between the expanding twisted loops
  and the overlying huge loops which inter-connect quiet solar regions.

Title: Quasi-Separatrix Layers and Their Relationship with Solar
    Flares
Authors: Bagala, L. G.; Mandrini, C. H.; Rovira, M. G.; Demoulin,
   P.; Henoux, J. C.
Bibcode: 1996RMxAC...4Q..90B
Altcode:
  No abstract at ADS

Title: Quasi-Separatrix Layers in Simple Magnetic Configurations
Authors: Mandrini, C. H.; Demoulin, P.; Henoux, J. C.; Priest, E.
Bibcode: 1996RMxAC...4Q.104M
Altcode:
  No abstract at ADS

Title: Evidence for Large-Scale Solar Magnetic Reconnection from
    Radio and X-Ray Measurements
Authors: Manoharan, P. K.; van Driel-Gesztelyi, L.; Pick, M.;
   Demoulin, P.
Bibcode: 1996ApJ...468L..73M
Altcode:
  Utilizing Yohkoh Soft X-ray Telescope and Nancay radioheliograph data,
  we present, for the first time, observations of expanding twisted
  X-ray loops and a series of nonthermal radio bursts that follow the
  loop expansion in time and space up to ~12' distance. The loops were
  produced during a long-duration C4.7 flare close to disk center on 1994
  October 25 at 1049 UT. The series of radio bursts were observed on the
  southern hemisphere above a weak positive-polarity region. The Kitt
  Peak magnetogram shows the existence of a weak negative-polarity region
  on the northern hemisphere at the same heliolongitude. Simultaneously
  with the nonthermal radio bursts, we observed the appearance of two
  remote X-ray brightenings and subsequent formation of two coronal
  holes above these weak (quiet) magnetic regions of opposite polarity,
  which strongly suggest the involvement of these remote regions in the
  event. During the 6 hr--long gradual phase of the flare, new X-ray
  loop connections developed among the active region and the remote
  quiet regions. A nonthermal radio continuum emission originating
  from the active region was also observed. We propose that the series
  of radio bursts, two remote X-ray brightenings, and new coronal loop
  connections were all signatures of a large-scale reconnection process
  between the expanding twisted flare loops and overlying transequatorial
  loops connecting quiet-Sun regions. The reconnection was only partial;
  the external part of the overlying large-scale fields were pushed out in
  the solar wind by the expanding twisted loops, leading to the formation
  of the coronal holes. The interaction between the active region and
  the large-scale fields seemed to be active during the entire gradual
  phase of the flare. This scenario may also explain the measurement of
  high-energy electrons in the interplanetary medium from 74 deg south
  heliolatitude as observed by Ulysses.

Title: 3D Magnetic Reconnection at an X-Ray Bright Point
Authors: Mandrini, C. H.; Démoulin, P.; Van Driel-Gesztelyi, L.;
   Schmieder, B.; Cauzzi, G.; Hofmann, A.
Bibcode: 1996SoPh..168..115M
Altcode:
  On May 1, 1993, a flaring X-ray bright point (XBP) was observed for
  about 16 hours in the old, disintegrating, bipolar active region (AR)
  NOAA 7493. During this period, a minor magnetic bipole (10<SUP>20</SUP>
  Mx) emerged in the region. We have found observational evidence showing
  that the XBP brightenings were due to magnetic reconnection between
  the new bipole and pre-existing plage fields. The aim of the present
  work is to substantiate with magnetic modelling what has been shown
  by the observations. For this purpose we extrapolate the observed
  photospheric magnetic fields in the linear force-free approximation
  and follow its evolution during the lifetime of the XBP. From the
  computed coronal field lines we determine the location of regions of
  drastic change in field-line linkage, called `quasi-separatrix layers'
  or QSLs. QSLs are open layers that behave physically like separatrices:
  the break down of ideal magnetohydrodynamics and the release of free
  magnetic energy may occur at these locations when their thickness
  is small enough. The extrapolated field lines, with photospheric
  footpoints on both sides of QSLs, match the observed chromospheric and
  coronal structures (arch filament system, XBP and faint X-ray loops
  (FXL)). We study also the evolution of the width of the QSL located
  over the new negative polarity pore: the calculated QSL is very thin
  (typically less than 100 m) during the lifetime of the XBP, but becomes
  much thicker (≥ 10<SUP>4</SUP> m) after the XBP has faded. Furthermore
  we show that peaks in X-ray brightness propagate along the FXL with a
  velocity of ≈ 670 km s<SUP>-1</SUP>, starting from the XBP location,
  implying that the energy is released where the emerging bipole impacts
  against pre-existing coronal loops. We discuss the possible mechanism
  of energy transport and conclude that the energy is conducted to the
  remote footpoints of the FXL by a thermal front. These results strongly
  support the supposition that the XBP brightness and flaring are due
  to the interaction of different flux systems, through 3D magnetic
  reconnection, at QSLs.

Title: Differential Magnetic Field Shear in an Active Region
Authors: Schmieder, B.; Demoulin, P.; Aulanier, G.; Golub, L.
Bibcode: 1996ApJ...467..881S
Altcode:
  The three-dimensional extrapolation of magnetic field lines from a
  magneto gram obtained at Kitt Peak allows us to understand the global
  structure of the NOAA active region 6718, as observed in X-rays with the
  Normal Incidence X-ray Telescope (NIXT) and in Hα with the Multichannel
  Subtractive Double Pass spectrograph (MSDP) in Meudon on 1991 July
  11. This active region was in a quiet stage. Bright X-ray loops connect
  plages having field strengths of ∼300 G, while Hα fibriles connect
  penumbrae having strong spot fields to the surrounding network. Small,
  intense X-ray features in the moat region around a large spot, which
  could be called X-ray-bright points, are due mainly to the emergence of
  magnetic flux and merging of these fields with surrounding ones. A set
  of large-scale, sheared X-ray loops is observed in the central part
  of the active region. Based on the fit between the observed coronal
  structure and the field configurations (and assuming a linear force-free
  field), we propose a differential magnetic field shear model for this
  active region. The decreasing shear in outer portions of the active
  region may indicate a continual relaxation of the magnetic field to
  a lower energy state in the progressively older portions of the AR.

Title: (Erratum) Stationary subalfvenic and low-β MHD flows in
    solar coronal loops and arcades.
Authors: Surlantzis, G.; Demoulin, P.; Heyvaerts, J.; Sauty, C.
Bibcode: 1996A&A...310..351S
Altcode:
  Erratum to Astron. Astrophys. 284, 985-999 (1994)

Title: Three-dimensional magnetic reconnection without null points
    2. Application to twisted flux tubes
Authors: Démoulin, P.; Priest, E. R.; Lonie, D. P.
Bibcode: 1996JGR...101.7631D
Altcode:
  Magnetic reconnection has traditionally been associated
  exclusively with the presence of magnetic null points or field
  lines tangential to a boundary. However, in many cases introducing a
  three-dimensional perturbation in a two-and-half-dimensional magnetic
  configuration implies the disappearance of separatrices. Faced
  with this structural instability of separatrices when going from
  two-and-half to three-dimensional configurations, several approaches
  have been investigated to replace the topological ideas familiar
  in two-dimensional, but no unanimity has yet emerged on the way
  reconnection should be defined. While it is true that the field line
  linkage is continuous in three-dimensional, we show here that extremely
  thin layers (called quasi-separatrix layers (QSLs)) are present. In
  these layers the gradient of the mapping of field lines from one part
  of a boundary to another is very much larger than normal (by many
  orders of magnitude). Even for highly conductive media these extremely
  thin layers behave physically like separatrices. Thus reconnection
  without null points can occur in QSLs with a breakdown of ideal MHD
  and a change in connectivity of plasma elements. We have analyzed
  several twisted flux tube configurations, going progressively from
  two-and-half to three-dimensional, showing that QSLs are structurally
  stable features (in contrast to separatrices). The relative thickness w
  of QSLs depends mainly on the maximum twist; typically, with two turns,
  w~10<SUP>-6</SUP>, while with four turns, w~10<SUP>-12</SUP>. In these
  twisted configurations the shape of the QSLs, at the intersection with
  the lower planar boundary, is typical of the two ribbons observed in
  two-ribbon solar flares, confirming that the accompanying prominence
  eruption involves the reconnection of twisted magnetic structures. We
  conclude that reconnection occurs in three-dimensional in thin layers
  or QSLs, which generalise the traditional separatrices (related only
  to magnetic null points or field lines tangential to the boundary).

Title: Quasi-Separatrix layers in solar flares. I. Method.
Authors: Demoulin, P.; Henoux, J. C.; Priest, E. R.; Mandrini, C. H.
Bibcode: 1996A&A...308..643D
Altcode:
  Magnetic reconnection is usually thought to be linked to the presence
  of magnetic null points and to be accompanied by the transport of
  magnetic field lines across separatrices, the set of field lines where
  the mapping of field lines is discontinuous. In view of the variety
  of observed flaring configurations, we show that this view is too
  restrictive. Instead, Priest and Demoulin (1995) have explored a way
  of generalising the concept of separatrices to magnetic configurations
  without field-line linkage discontinuities. They propose that magnetic
  reconnection may also occur in 3D in the absence of null points at
  "quasi-separatrix layers" (QSLs), which are regions where there is
  drastic change in field-line linkage. In previous studies we have shown
  that solar flare kernels are linked to the topology of the active-region
  magnetic field. The observed photospheric field was extrapolated to
  the corona using subphotospheric magnetic sources and the topology was
  defined by the magnetic linkage between these sources, the method being
  called SM (for Source Method). In this paper we define a new method,
  called QSLM (for Quasi-Separatrix Layers Method), which finds the
  location of QSLs above the photosphere. It is designed to be applied to
  any kind of magnetic field representation, while, in the present paper,
  we apply it only to simple theoretical magnetic configurations in order
  to compare it with the SM. It generalises the concept of separatrices to
  magnetic configurations without field-line linkage discontinuities. The
  QSLM determines elongated regions that are in general located along
  small portions of the separatrices defined by the SM, and in the limit
  of very concentrated photospheric fields both methods give the same
  result. In bipolar magnetic configurations two QSLs are found at both
  sides of the inversion line, while in quadrupolar configurations four
  appear. We find that there is a wide range for the thickness of the
  QSLs, which is determined by the character (bipolar or quadrupolar)
  of the magnetic region and by the sizes of the photospheric field
  concentrations. We then show that smooth photospheric motions induce
  concentrated currents at the locations defined by the QSLM. We prove
  this only for initially potential configurations but, due to the form
  of the equations, we conjecture that it is also valid for any kind
  of initial magnetic equilibrium. We conclude that, even in bipolar
  configurations, there are localized places where current build-up can
  be induced by photospheric motions, leading to ideal MHD breakdown
  with strong flows and magnetic energy release.

Title: Las fulguraciones como manifestación de reconexión en el
    campo magnético solar
Authors: Bagalá, L. G.; Mandrini, M. C.; Rovira, M. G.; Démoulin, P.
Bibcode: 1996BAAA...40R...2B
Altcode:
  Las fulguraciones solares son fenómenos transitorios de liberación
  de energía que se desarrollan en las estructuras magnéticas
  de las regiones activas del Sol. Las fulguraciones pueden llegar
  a liberar hasta 10<SUP>32</SUP> erg en 100 seg. en todo el rango
  electromagnético, y acelerar partículas. En este trabajo mostramos que
  la ubicación de los abrillantamientos en Hα de diversas fulguraciones
  está relacionado con las propiedades de las conexiones de las
  líneas del campo magnético de la región, como se espera por las
  teorías de reconexión en 3D recientemente desarrolladas (Démoulin
  et al, 1996a). El campo magnético coronal se extrapola del campo
  fotosférico observado suponiendo una configuración libre de fuerzas
  lineal. Por medio de un algoritmo se determinan las regiones donde
  existe un cambio drástico en la conectividad de las líneas de campo
  (límites ``cuasi-discontinuos'', o cuasi-separatrices CS). Las CS
  son bandas abiertas que identifican zonas donde el campo magnético se
  reconectará con más probabilidad y, siempre que las mismas sean lo
  suficientemente finas, se producirá allíla liberación de energía
  proveniente del campo magnético. Hemos encontrado que en todas las
  regiones fulgurantes estudiadas (Démoulin et al, 1996b) existen CS
  en los mismos lugares donde se observaron los abrillantamientos en
  Hα. Allídonde coinciden los abrillantamientos con las CS, éstas
  tienen un espesor menor que 1 Mm. Las líneas de campo coronales
  extrapoladas de nuestro modelo tienen sus orígenes fotosféricos a
  ambos lados de las CS, como se espera dados los recientes estudios
  de reconexión magnética en 3D. Estos resultados ponen a prueba los
  modelos presentes sobre fulguraciones solares.

Title: Flare Associated Large-Scale Magnetic Reconnection
Authors: Manoharan, P. K.; van Driel-Gesztelyi, L.; Pick, M.;
   Demoulin, P.
Bibcode: 1996ASPC..111..398M
Altcode: 1997ASPC..111..398M
  Reports a unique set of observations, for a low heliolatitude flare,
  obtained with the Yohkoh satellite and the Nançay radioheliograph. This
  flare starts with the expansion of spectacularly twisted loops,
  followed by sporadic radio bursts (some of them are detected at high
  heliolatitude, ≡65°S), appearance of two remote X-ray brightenings
  and formation of two coronal holes on opposite hemispheres of the
  Sun. The timing and location of these events provide evidence for
  a large-scale magnetic reconnection between the expanding twisted
  flare loops and overlying huge loops inter-connecting quiet regions
  on the Sun.

Title: Reconexión magnética en una región activa en decaimiento
Authors: Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.;
   Schmieder, B.; Bagalá, L. G.; Rovira, M. G.
Bibcode: 1996BAAA...40....5M
Altcode:
  Se han obtenido observaciones desde Tierra (Hα y magnetogramas)
  coordinadas con el Soft X-ray Telescope (SXT), a bordo del satélite
  japonés Yohkoh, de una región activa bipolar en decaimiento. Estos
  datos constituyen la base para el estudio de un punto brillante en rayos
  X (PBX) y de la actividad relacionada con el mismo en distintas capas
  de la atmósfera solar. Las observaciones muestran que el PBX está
  relacionado con la aparición de un bipolo menor (~ 10<SUP>20</SUP> Mx)
  y que su abrillantamiento continuo, así como sus aumentos de brillo
  esporádicos (``fulguraciones"), son el resultado de la reconexión
  entre el pequeño arco emergente (visto en Hα como un sistema de
  filamentos arqueados, SFA) y arcos mayores asociados al campo facular
  preexistente. Se ha extrapolado el campo magnético observado en la
  aproximación libre de fuerzas lineal y se ha seguido su evolución
  a lo largo de la vida del PBX. Se ha calculado la posición de las
  cuasiseparatrices (CSs) a partir del campo modelado. Las líneas de
  campo extrapoladas, cuyas bases fotosféricas se encuentran a ambos
  lados de las CSs, están de acuerdo con las estructuras cromosféricas
  y coronales observadas. Se ha calculado el espesor de la CD ubicada
  a lo largo de la polaridad negativa emergente, encontrándose que su
  variación está de acuerdo con la evolución de la intensidad del PBX;
  la CS es muy delgada durante la vida del PBX (~ 100 m), mientras que
  su espesor aumenta considerablemente (&gt;= 10^4 m) cuando el PBX
  desaparece de las imágenes del SXT. Estos resultados señalan que
  el abrillantamiento y las ``fulguraciones" de este PBX se deben al
  proceso de reconexión en 3D que tiene lugar en las CSs.

Title: Dynamics of solar magnetic arches in the photosphere and
    the chromosphere.
Authors: Mein, P.; Demoulin, P.; Mein, N.; Engvold, O.; Molowny-Horas,
   R.; Heinzel, P.; Gontikakis, C.
Bibcode: 1996A&A...305..343M
Altcode:
  Mass motions in chromospheric arch filaments have been observed
  with imaging spectroscopy (MSDP) at the VTT telescope of the Teide
  Observatory. Coordinated observations of time sequences of continuum
  images were carried out at the SVST telescope of the Observatorio
  del Roque de los Muchachos, which provided transverse velocities of
  photospheric tracers, by "local correlation tracking." Hα profiles
  along 3 arch filaments are analysed in terms of "differential
  cloud MODel", to discuss the Doppler velocities of chromospheric
  material. Models of ascending arches with downflows in both legs
  are investigated. The gas pressure is neglected, but the free-fall
  equations are integrated versus time (non-stationary case). We first
  assume circular lines of force with constant radius. We can account
  for chromospheric velocities, but we cannot fit the slow motion of
  footpoints derived from photospheric tracers. A better agreement is
  obtained by assuming lines of force with fixed footpoints and variable
  radius. Typical values are: half distance between footpoints of 10 to
  15Mm, upward velocity at the top of loops of 4km/s after an integration
  time of 800s. The obtained values are consistent with the sizes and
  the lifetime of arch filaments.

Title: Modelisation of magnetic field.
Authors: Démoulin, P.
Bibcode: 1996joso.proc..117D
Altcode:
  Magnetic reconnection is usually thought to be linked to the presence
  of magnetic null points and to be accompanied by the transport of
  magnetic field lines across separatrices, the set of field lines where
  the mapping of field lines is discontinuous. In view of the variety
  of observed flaring configurations, the author shows that this view
  is too restrictive. He generalises the concept of separatrices to
  Quasi-Separatrix Layers and applies this method to X-bright points
  and eruption of twisted structures and reports the results.

Title: 3D Magnetic Reconnection: Example of an X-Ray Bright Point
Authors: Demoulin, P.; Mandrini, C. H.; van Driel-Gesztelyi, L.;
   Priest, E. R.; Henoux, J. C.; Schmieder, B.
Bibcode: 1996ASPC..111...49D
Altcode: 1997ASPC..111...49D
  In the classical view magnetic reconnection occurs at neutral points
  and implies transport of magnetic field-lines across separatrices. The
  authors show that reconnection may also occur in the absence of neutral
  points at so-called "quasi-separatrix layers" (QSLs), where there is a
  steep gradient in field-line linkage at the boundaries. Reconnection
  occurs in QSLs where the field-line velocity becomes larger than the
  allowed maximal plasma velocity or where the electric-current density
  becomes too great. The authors describe both a theoretical and an
  observed configuration. In the case of a simple sheared X-field they
  show that even a smooth continuous shear flow, imposed at the boundary,
  gives strong plasma jetting inside and parallel to the QSLs. Applying
  the QSL method to an X-ray bright point observed by Yohkoh, they find
  field lines in the extrapolated field which are on both sides of QSLs
  and which are in good agreement with loops observed in Hα and X-rays
  related to emerging flux. The evolution of the QSL width may explain
  the brightness evolution of the XBP.

Title: Emerging Flux, Reconnection, and XBP
Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Demoulin, P.;
   Mandrini, C.; Cauzzi, G.; Hofmann, A.; Nitta, N.; Kurokawa, H.; Mein,
   N.; Mein, P.
Bibcode: 1996mpsa.conf..459V
Altcode: 1996IAUCo.153..459V
  No abstract at ADS

Title: Emerging flux seen by Yohkoh.
Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Mandrini, C.;
   Démoulin, P.; Cauzzi, G.; Hofmann, A.; Nitta, N.; Kurokawa, H.;
   Mein, N.; Mein, P.
Bibcode: 1996joso.proc..124V
Altcode:
  No abstract at ADS

Title: Three-dimensional magnetic reconnection without null
    points. 1. Basic theory of magnetic flipping
Authors: Priest, E. R.; Démoulin, P.
Bibcode: 1995JGR...10023443P
Altcode:
  In two or three dimensions, magnetic reconnection may occur at
  neutral points and is accompanied by the transport of magnetic field
  lines across separatrices, the field lines (or flux surfaces in three
  dimensions) at which the mapping of field lines is discontinuous. Here
  we show that reconnection may also occur in three dimensions in the
  absence of neutral points at so-called ``quasi-separatrix layers,''
  where there is a steep gradient in field line linkage. Reconnection is
  a global property, and so, in order to determine where it can occur,
  the first step is to enclose the volume being considered by a boundary
  (such as a spherical surface). Then the mapping of field lines from
  one part of the boundary to another is determined, and quasi-separatrix
  layers may be identified as regions where the gradient of the mapping
  or its inverse is very much larger than normal. The most effective
  measure of the presence of such layers is the norm of the displacement
  gradient tensor; their qualitative location is robust and insensitive
  to the particular surface that is chosen. Reconnection itself occurs
  when there is a breakdown of ideal MHD and a change of connectivity
  of plasma elements, where the field line velocity becomes larger
  than the plasma velocity, so that the field lines slip through the
  plasma. <P />This breakdown can occur in the quasi-separatrix layers
  with an electric field component parallel to the magnetic field. In
  three dimensions the electric field E (and therefore the field line
  velocity v<SUB>⊥</SUB>) depends partly on the imposed values of E
  (or v<SUB>⊥</SUB>) at the boundary and partly on the gradients of the
  inverse mapping function. We show that the inverse mapping determines
  the location of the narrow layers where the breakdown of ideal MHD
  can occur, while the imposed boundary values of v<SUB>⊥</SUB>
  determine mainly the detailed flow pattern inside the layers. Thus,
  in general, E (and therefore v<SUB>⊥</SUB>) becomes much larger than
  its boundary values at locations where the gradients of the inverse
  mapping function are large. An example is given of a sheared X field,
  where a slow smooth continuous shear flow imposed on the boundary
  across one quasi-separatrix produces a flipping of magnetic field lines
  as they slip rapidly through the plasma in the other quasi-separatrix
  layer. It results in a strong plasma jetting localized in, and parallel
  to, the separatrix layers.

Title: Constraints on flare models set by the active region magnetic
    topology Magnetic topology of AR 6233.
Authors: Mandrini, C. H.; Demoulin, P.; Rovira, M. G.; de La
   Beaujardiere, J. -F.; Henoux, J. C.
Bibcode: 1995A&A...303..927M
Altcode:
  We present a detailed analysis of the magnetic topology of AR 6233
  on two consecutive days (August 28 and 29, 1990) and compare the
  location of the magnetic separatrices and separators with off-band
  Hα observations and other flare manifestations, such as intense
  nonthermal electron precipitation and high coronal pressure sites,
  for two flares that occured on these days. Since for one of the days
  of our analysis we have two magnetograms covering fields of view with
  different scale lengths, we analyzed the dependence of the topology
  of the region of interest on the presence of external magnetic field
  concentrations. We have found that considering these concentrations
  does not modify the location of separatrices in the region. Because
  transverse magnetograms indicate that strong magnetic shear is present
  along the longitudinal inversion line where flare brightenings are
  located, the observed photospheric magnetic field is modeled in an
  approach in which a combination of sources with current-free and non
  current-free magnetic field is used. This model allows us to obtain a
  better fit between the observed and modeled transverse field, then we
  find a closer relationship between separatrices and flare features. The
  results of a current-free and of a linear force-free approach are also
  shown for comparison. As in other flaring regions studied previously,
  chromospheric flare brightenings are found on separatrices. The
  topological structure obtained for these flares is rather complex. We
  find that the connectivity of field lines may change drastically
  from one edge of a ribbon to the other. Electron precipitation and
  high coronal pressure sites, and some photospheric intense currents
  are also found in the immediate vicinity of separatrices. The early
  kernels of August 28 flare are found closer to the separatrices of
  the nonpotential field, while the later are closer to those of the
  potential field. All these results agree with the hypothesis that
  magnetic energy is stored in field-aligned currents and released due
  to magnetic field reconnection, with a noticeable relaxation of the
  field, either at the separator region or on separatrices.

Title: A Topological Approach to Understand a Multiple-Loop Solar
    Flare
Authors: Bagalá, L. G.; Mandrini, C. H.; Rovira, M. G.; Démoulin,
   P.; Hénoux, J. C.
Bibcode: 1995SoPh..161..103B
Altcode:
  We analyze the UV and X-ray data obtained by the SMM satellite for
  the flare starting at 02:36 UT on November 12, 1980 in AR 2779. From
  a detailed revision of the OV emission, we find that the observations
  are compatible with energy being released in a zone above the magnetic
  inversion line of the AR intermediate bipole. This energy is then
  transported mainly by conduction towards the two distant kernels located
  in the AR main bipole. One of these kernels is first identified in
  this paper. Accelerated particles contribute to the energy transport
  only during the impulsive phase.

Title: Reduction, Analysis, and Properties of Electric Current
    Systems in Solar Active Regions
Authors: Gary, G. Allen; Demoulin, Pascal
Bibcode: 1995ApJ...445..982G
Altcode:
  The specific attraction and, in large part, the significance of solar
  magnetograms lie in the fact that they give the most important data on
  the electric currents and the nonpotentiality of active regions. Using
  the vector magnetograms from the Marshall Space Flight Center (MSFC),
  we employ a unique technique in the area of data analysis for resolving
  the 180 deg ambiguity in order to calculate the spatial structure of the
  vertical electric current density. The 180 deg ambiguity is resolved
  by applying concepts from the nonlinear multivariable optimization
  theory. The technique is shown to be of particular importance in very
  nonpotential active regions. The characterization of the vertical
  electric current density for a set of vector magnetograms using this
  method then gives the spatial scale, locations, and magnitude of these
  current systems. The method, which employs an intermediate parametric
  function which covers the magnetogram and which defines the local
  `preferred' direction, minimizes a specific functional of the observed
  transverse magnetic field. The specific functional that is successful is
  the integral of the square of the vertical current density. We find that
  the vertical electric current densities have common characteristics for
  the extended bipolar (beta) (gamma) (delta)-regions studied. The largest
  current systems have j<SUB>z</SUB>'s which maximizes around 30 mA/sq
  m and have a linear decreasing distribution to a diameter of 30 Mn.

Title: Magnetic Field Topology at the Location of an X1/1B Solar Flare
Authors: Gaizauskas, V.; Démoulin, P.; Mandrini, C. H.; Rovira,
   M. G.; Harvey, K. L.
Bibcode: 1995SPD....26.1319G
Altcode: 1995BAAS...27R.991G
  No abstract at ADS

Title: Evolution of Active Regions Leading to Flares
Authors: Schmieder, B.; Demoulin, P.; Henoux, J. -C.; Driel-Gesztelyi,
   L. V.; Mandrini, C.; Rovira, M.
Bibcode: 1994kofu.symp..297S
Altcode:
  We model observed longitudinal magnetic fields obtained in Potsdam,
  Meudon, MSFC Hunstville by a series of magnetic sources located
  below the photosphere. H_alpha flare kernels are found situated on
  intersecting separatrices (surfaces delimiting regions of different
  magnetic connectivities). We deduce that energy release occurs
  mainly at the separator by magnetic reconnection. Evidence for both
  neutralized and un-neutralized currents are observed in different
  flaring regions. Moreover we have found two photospheric currents of
  opposite sign, linked in the corona by field lines, at the border of
  flare kernels.

Title: Are magnetic null points important in solar flares ?
Authors: Demoulin, P.; Henoux, J. C.; Mandrini, C. H.
Bibcode: 1994A&A...285.1023D
Altcode:
  When they are present, null points (points where the 3 components of
  the magnetic field vanish) determine the topology of the magnetic
  field configuration. It has been suggested that the presence of
  nulls is related to flares, and that they settle the region where
  the energy is released by magnetic reconnection. Since solar flares
  are initially coronal events, nulls should be located above the
  photosphere. Therefore, we investigate the location of nulls in
  configurations formed by a parasitic and a main bipole (4 magnetic
  sources). For both potential and linear-force free field approaches,
  we have found that a null was present in the corona only when the two
  bipoles were nearly antiparallel. The flaring regions analysed here
  are those where the magnetic topology has been related to flare kernels
  in previous papers. These observations show that flares occur for any
  horizontal orientation of the parasitic bipole to the main one, having
  only in particular cases a null in the extrapolated field. When a null
  is present, it can be at any place along the separator and it is not
  necessarily related to the region where the energy is released. These
  results are found both in the subflares and the intense X-ray flares
  studied. Examples of observed configurations that can be analysed
  with 2D or 3D models are presented. We conclude that nulls above the
  photosphere are not needed for flaring but that the spatial properties
  of the coronal field still determines the location where reconnection
  takes place. Results are discuss in the context of present understanding
  of 3D reconnection.

Title: Observational support of reconnection in solar flares
Authors: Démoulin, P.; Hénoux, J. C.; Schmieder, B.; Mandrini,
   C. H.; Rovira, M. G.; Somov, B.
Bibcode: 1994SSRv...68..129D
Altcode:
  We present a detailed analysis of the magnetic topology of flaring
  active region. TheH <SUB>α</SUB> kernels are found to be located at the
  intersection of the separatrices with the chromosphere when the shear,
  deduced from the fibrils or/and transverse magnetic field direction,
  is taken into account. We show that the kernels are magnetically
  connected by field lines passing close to the separator. We confirm,
  for other flares, previous studies which show that photospheric current
  concentrations are located at the borders of flare ribbons. Moreover
  we found two photospheric current concentrations of opposite sign,
  linked in the corona by field lines which follow separatrices. These
  give evidence that magnetic energy is released by reconnection processes
  in solar flares.

Title: Stationary subalfvenic and low-β MHD flows in solar coronal
    loops and arcades.
Authors: Surlantzis, G.; Demoulin, P.; Heyvaerts, J.; Sauty, C.
Bibcode: 1994A&A...284..985S
Altcode:
  We present general two-dimensional solutions for low-β and subalfvenic
  stationary MHD flow. Our method of solution applies to any type of
  boundary conditions. It solves for the pertubation of the magnetic
  configuration brought about by flows and by the development of
  shock waves in it. Solutions in cartesian and cylindrical geometries
  are presented to model flows in coronal loops and counter-Evershed
  flows above spots. In symmetrical magnetic configurations, when the
  distribution of pressure at the foot points is symmetrical, the flow is
  necessarily subsonic. Otherwise it can become supersonic at the summit
  of the magnetic field line and then passes through a shock. Such shocks
  can be very inclined to the magnetic field and the shocked material may
  form a dense hot sheet around a cooler core, a situation which seems to
  be observed in cool loops. For asymmetrical magnetic configurations,
  the flow accelerates towards the low gas pressure foot point and
  could be subsonic or trans-sonic depending on the pressure difference
  between the foot points. Loops can have a significant density contrast
  against their environment only if their energy flux differs markedly
  from the background one. In asymmetrical loops one leg can be much
  less dense than the other and poorly visible. Near spots, the sign
  of the difference of pressure between the two foot points is such as
  to drive a reverse Evershed flow towards the spot. Additional effects
  would be needed to drive a direct Evershed flow.

Title: Interpretation of multiwavelength observations of November 5,
    1980 solar flares by the magnetic topology of AR 2766
Authors: Demoulin, P.; Mandrini, C. H.; Rovira, M. G.; Henoux, J. C.;
   Machado, M. E.
Bibcode: 1994SoPh..150..221D
Altcode:
  We present a detailed analysis of the magnetic topology of AR 2776
  together with Hα UV, X-rays, and radio observations of the November
  5, 1980 flares in order to understand the role of the active region
  large-scale topology on the flare process. As at present the coronal
  magnetic field is modeled by an ensemble of sub-photospheric sources
  whose positions and intensities are deduced from a least-square fit
  between the computed and observed longitudinal magnetic fields. Charges
  and dipole representations are shown to lead to similar modeling of
  the magnetic topology provided that the number of sources is great
  enough. However, for AR 2776, departure from a potential field has to
  be taken into account, therefore a linear force-free field extrapolation
  is used.

Title: Relationship between magnetic field evolution and flaring
    sites in AR 6659 in June 1991
Authors: Schmieder, B.; Hagyard, M. J.; Guoxiang, Ai; Hongqi, Zhang;
   Kalman, B.; Gyori, L.; Rompolt, B.; Demoulin, P.; Machado, M. E.
Bibcode: 1994SoPh..150..199S
Altcode:
  During the international campaign of June 1991, the active region AR
  6659 produced six very large, long-duration flares (X10/12) during its
  passage across the solar disk. We present the characteristics of four
  of them (June 4, 6, 9, 15). Precise measurements of the spot motions
  from Debrecen and Tokyo white-light pictures are used to understand the
  fragmentation of the main sunspot group with time. This fragmentation
  leads to a continuous restructuring of the magnetic field pattern
  while rapid changes are evidenced due to fast new flux emergence
  (magnetograms of MFSC, Huairou). The first process leads to a shearing
  of the field lines along which there is energy storage; the second one
  is the trigger which causes the release of energy by creating a complex
  topology. We conjecture that these two processes with different time
  scales are relevant to the production of flares.

Title: Relationship between electric currents, photospheric motions,
    chromospheric activity, and magnetic field topology
Authors: van Driel-Gesztelyi, L.; Hofmann, A.; Demoulin, P.; Schmieder,
   B.; Csepura, G.
Bibcode: 1994SoPh..149..309V
Altcode:
  Through coordinated observations made during the Max'91 campaign in June
  1989 in Potsdam (magnetograms), Debrecen (white light and Hα), and
  Meudon (MSDP), we follow the evolution of the sunspot group in active
  region NOAA 5555 for 6 days. The topology of the coronal magnetic field
  is investigated by using a method based on the concept of separatrices -
  applied previously (Mandriniet al., 1991) to a magnetic region slightly
  distorted by field-aligned currents. The present active region differs
  by having significant magnetic shear. We find that the Hα flare
  kernels and the main photospheric electric current cells are located
  close to the intersection of the separatrices with the chromosphere,
  in a linear force-free field configuration adapted to the observed
  shear. Sunspot motions, strong currents, isolated polarities, or
  intersecting separatrices are not in themselves sufficient to produce a
  flare. A combination of them all is required. This supports the idea
  that flares are due to magnetic reconnection, when flux tubes with
  field-aligned currents move towards the separatrix locations.

Title: Zones with quasi-discontinuous magnetic connections in the
    photosphere and solar flares
Authors: Bagalá, L. G.; Mandrini, C. H.; Démoulin, P.
Bibcode: 1994BAAA...39...46B
Altcode:
  The topological structure of active regions is related with flare
  brightening. (Mandrini et a!, 1991, 1993; Démoulin et ai, 1992, 1993,
  1994). In these works, we modeled the observed longitudinal magnetic
  field by means of a discrete number of sub-photospheric magnetic poles,
  and derived the magnetic topology taking into account the connections
  between these poles (source method, MF). We present here a new method
  (quasi-discontinuity method, MQD). It finds the regions above the
  photosphere where the connectivity of field lines changes drastically.

Title: Electric Current Systems in Solar Active Regions
Authors: Gary, G. Allen; Demoulin, Pascal
Bibcode: 1994ASPC...68..171G
Altcode: 1994sare.conf..171G
  No abstract at ADS

Title: CFHT eclipse observation of the very fine-scale solar corona
Authors: Koutchmy, S.; Belmahdi, M.; Coulter, R. L.; Demoulin, P.;
   Gaizauskas, V.; MacQueen, R. M.; Monnet, G.; Mouette, J.; Noens,
   J. C.; November, L. J.
Bibcode: 1994A&A...281..249K
Altcode:
  At the July 11, 1991 solar total eclipse, a modern large optical
  telescope, Canada-France-Hawaii telescope (CFHT), was used to
  probe the solar corona. The best possible pictures were obtained
  with the CFHT, using fast imaging techniques and post-facto image
  selection and processing. Several cameras were run during totality
  to acquire sub-arcsec spatial resolution white-light images, with
  both narrow-band and broad-band filters. The setup and the observing
  procedure are described. Preliminary results, together with an
  evaluation of the merits of the experiment, are given, as well as a
  sample of images. Fine-scale coronal features were observed for the
  first time in a time series, confirming the importance of plasmoid-like
  activity in the inner corona. The observation of the smallest coronal
  feature ever reported is analyzed, giving a typical cross-section of
  0.4 +/- 0.1 arcsec. On a larger scale, dark loops around a foreground
  prominence are resolved for the first time, suggesting that sheet-like
  voids exist above a filament channel.

Title: Magnetic topology of a complex active region
Authors: Mandrini, C. H.; Rovira, M. G.; Démoulin, P.; de La
   Beaujarière, J. -F.; Hénoux, J. C.
Bibcode: 1994BAAA...39...52M
Altcode:
  We present a detailed analysis of the magnetic topology of AR 6233
  on two consecutive days (August 28 and 29, 1990). We compare the
  location of the magnetic separatrices and separators with off-band Hα
  observations and other flare manifestations, such as intense non-thermal
  electron precipitation and high coronal pressure sites, for two flares
  that occurred on these days. Because transverse magnetograms indicate
  that strong magnetic shear is present along the longitudinal inversion
  line, where flare brightening are located, the observed photospheric
  magnetic field is modeled in an approach in which a combination
  of sources with current-free and non current-free magnetic held is
  used. This model allows us to obtain a better ht between the observed
  and modeled transverse held. Then, we find a closer relationship between
  separatrices and hare features. The results of a current-free and of
  a linear force-free approach are also discussed. As in other haring
  regions studied previously, chromospheric flare brightening are found
  on separatrices. The topological structure obtained for these flares is
  rather complex and cannot be explained by classical flare models. We
  find that the connectivity of field lines may change drastically from
  one edge of an Ha; ribbon to the other. Electron precipitation and
  high coronal pressure sites, and some photospheric intense currents
  are also found in the immediate vicinity of separatrices. The early
  kernels of August 28 flare are found closer to the separatrices of the
  non-potential held, while the later are closer to those of the potential
  held. All these results agree with the hypothesis that magnetic energy
  is stored in field-aligned currents and released due to magnetic held
  reconnection, with a noticeable relaxation of the held, either at the
  separator region or on separatrices.

Title: Dynamics of solar magnetic arches in photosphere and
    chromosphere
Authors: Mein, P.; Mein, N.; Démoulin, P.; Gontikakis, C.; Engvold,
   O.; Molowby, R.
Bibcode: 1994smf..conf..366M
Altcode:
  No abstract at ADS

Title: Understanding Solar Active Phenomena: A Phenomenological
    Approach
Authors: Machado, M. E.; Demoulin, P.; Gary, G. A.; Henoux, J. C.;
   Mandrini, C. H.; Rovira, M. G.
Bibcode: 1994step.conf..125M
Altcode:
  No abstract at ADS

Title: The control of the corona by the convective zone magnetic
    fields
Authors: Démoulin, P.
Bibcode: 1994LNP...432..121D
Altcode: 1994LNPM...11..121D
  A review is presented on the physics of the convective zone and the
  implications at the coronal level. Solar magnetic fields are created in
  the convective layer from the kinetic energy of the dense plasma. At
  the coronal level, the magnetic field controls the plasma and is
  forced to evolve according to the time-dependent boundary conditions
  given at the photospheric level by the convective zone. The coronal
  field cannot find a smooth equilibrium when its topology is complex
  and current sheets are formed. These are the preferred regions where
  reconnection can occur. Present development of 3D reconnection is
  reviewed, and we show how observed flare kernels are related to the
  magnetic field topology. Then we describe how our present theoretical
  understanding of flares can help us to understand both large and small
  scale coronal events.

Title: Twisted Flux Tubes and Sunspot Motions in AR 5555
Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Schmieder, B.;
   Hofmann, A.; Csepura, G.
Bibcode: 1994emsp.conf..115V
Altcode:
  No abstract at ADS

Title: Magnetic reconnection as a mechanism for solar flares
Authors: Bagala, L. G.; Rovira, M. G.; Mandrini, C. H.; Demoulin,
   P.; Henoux, J. C.
Bibcode: 1994iaf..conf.....B
Altcode:
  In this paper we summarize the results of our quantitative analysis of
  the 3D magnetic topology of several active regions (ARs). We show that
  the flare brightenings in different wavelengths (H-alpha, UV, X-rays)
  are located at the intersection of separatrices with the chromospheric
  plane. Flare kernels are magnetically connected by field lines passing
  close to the separator in different types of configurations. We also
  find that photospheric current concentrations are associated with flare
  brightenings and can be linked in the corona by field lines following
  separatrices, supporting the hypothesis that magnetic energy is stored
  in field-aligned currents. Since magnetic reconnection is expected to
  take place at the separator region or on separatrices, these results
  strongly suggest that this is the process driving energy release in
  solar flares.

Title: Catastrophic Evolution of a Force-free Flux Rope: A Model
    for Eruptive Flares
Authors: Isenberg, P. A.; Forbes, T. G.; Demoulin, P.
Bibcode: 1993ApJ...417..368I
Altcode:
  We present a self-consistent, two-dimensional, magnetohydrodynamic
  model of an eruptive flare based on an ideal-MHD coronal magnetic
  field configuration which is line-tied at the photosphere and contains
  a forcefree flux rope. If the flux rope is not too large, the gradual
  disappearance of the photospheric field causes the flux rope to lose
  equilibrium catastrophically and jump to a higher altitude, releasing
  magnetic energy in the process. During the jump, an extended current
  sheet forms below the flux rope, and subsequent reconnection of this
  current sheet allows the flux rope to escape into the outer corona. A
  critical flux-rope radius, which depends on the form of the photospheric
  field, divides configurations which undergo a catastrophic loss of
  equilibrium from those which do not. For a photospheric field equivalent
  to that produced by a submerged, two-dimensional magnetic quadrupole,
  the critical radius is 0.23 times the length scale of the photospheric
  field. This result shows that catastrophic eruptions can occur for
  flux ropes having plausible solar values. We identify the catastrophic
  loss of equilibrium with the impulsive phase of eruptive flares and
  the subsequent reconnection of the current sheet with the gradual phase.

Title: Multiwavelength Observations and Magnetic Field Modelling of
    a Solar Flare
Authors: Bagala, L. G.; Rovira, M. G.; Mandrini, C. H.; Demoulin,
   P.; Henoux, J. C.
Bibcode: 1993RMxAA..26..135B
Altcode:
  No abstract at ADS

Title: Filament formation
Authors: Démoulin, P.
Bibcode: 1993AdSpR..13i..95D
Altcode: 1993AdSpR..13...95D
  Prominences are thin structures consisting of cold plasma embedded in
  the hot corona. Because the plasma beta is low, the magnetic field plays
  a key role in all the processes involved. During their quiescent stage,
  magnetic measurements can be made inside them. These give local but also
  direct information on the neighbouring coronal field. Our understanding
  of the formation of prominences simultaneously improves our knowledge
  about the coronal magnetic field. Based on our present observational
  and theoretical understanding of prominences, this review will attempt
  to answer the following questions: What are the magnetic configurations
  favourable for the formation of prominences? What can we learn about
  the coronal magnetic field from the study of prominences? How can
  prominence plasma be formed?

Title: Sites of flares and filaments in solar active regions
Authors: Schmieder, B.; van-Driel, L.; Hofmann, A.; Démoulin, P.;
   Hénoux, J. C.; Hagyard, M.
Bibcode: 1993AdSpR..13i.119S
Altcode: 1993AdSpR..13..119S
  We applied a method developed to derive from magnetic field data the
  location of energy release in solar active regions. This method has
  been applied to two sets of data (June 13-15 1980 and June 23-25 1989)
  using magnetograms (Meudon, MSFC, Potsdam) and Hα data (Debrecen,
  MSDP Meudon). The Hα flares are located at intersections of the
  separatrices with the chromosphere in places where high density currents
  are observed. This supports the idea that the energy released in flares
  is due to magnetic reconnection at the location of a separator and
  subsequently transported to the chromosphere along field lines. It is
  found that strong magnetic shear is a necessary condition for filament
  formation. Magnetic shear merely determines the importance of the
  flare and is certainly not a necessary condition for flare activity.

Title: Relationship between magnetic field evolution and flaring
    sites in AR 6659 on June 1991
Authors: Schmieder, B.; Démoulin, P.; Hagyard, M.; Machado, M. E.;
   Guo, Xiang Ai; Zhang, Hongqi; Fu, Qijun; Zhi, Kai Li; Luan, Ti;
   Kalman, B.; Györi, L.
Bibcode: 1993AdSpR..13i.123S
Altcode: 1993AdSpR..13..123S
  During the international campaign of June 1991, the active region AR
  6659 produced 6 very large long duration flares at the same location
  during its passage across the solar disk. Vector magnetograms were
  obtained at Marshall (Huntsville) and Huairou Station (Beijing) with
  a time difference of 10 to 12 hours, thus giving a good survey of
  the magnetic field evolution with time. The flare of June 6/01:08 UT
  (X12 plus/4B) was observed in Shahe Station (Beijing) in white light,
  in Hα and in radio centimetric wavelengths. The evolution of the flare
  of June 9/01:43 UT (X10/3B) has been followed in Hα at the Yunnan
  Observatory (Kunming). An other one was well observed on June 15 at
  08:20 UT in Wroclaw and in Debrecen. Some subflares were observed at
  Sac Peak on June 4, 5, 7 at Meudon on June 10, 14 and Debrecen on
  June 12 and 13. <P />In this short communication we concentrate on
  the relationship between magnetic field shear and flare sites.

Title: Conditions for the appearance of "bald patches" at the
    solar surface
Authors: Titov, V. S.; Priest, E. R.; Demoulin, P.
Bibcode: 1993A&A...276..564T
Altcode:
  A general criterion for the existence of sections of the photospheric
  polarity inversion line where the overlying magnetic field lines
  are parallel to the photosphere is presented. It is shown that
  such sections, called "bald patches", exist for a wide range of
  parameters in potential and constant-α force-free fields created by
  four concentrated sources of magnetic flux. Bald patches appear when
  the polarity inversion line is bent too much in an S-like manner. The
  appearance of bald patches may be important for the formation of
  prominences and possibly for solar flares.

Title: Common Evolution of Adjacent Sunspot Groups
Authors: van Driel-Gesztelyi, L.; Csepura, G.; Nagy, I.; Gerlei, O.;
   Schmieder, B.; Rayrole, J.; Demoulin, P.
Bibcode: 1993SoPh..145...77V
Altcode:
  The evolution of two adjacent bipolar sunspot groups is studied using
  Debrecen full-disc, white-light photoheliograms and Hα filtergrams
  as well as Meudon magnetograms. The proper motions of the principal
  preceding spots of both groups show quite similar patterns; the
  spots move along almost parallel tracks and change the direction
  of their motion on the same day at almost the same heliographic
  longitude. Also, three simultaneous emergences of magnetic flux were
  observed in both groups. These observations support the idea that
  these adjacent sunspot groups were magnetically linked below the
  photosphere. Matching the extrapolated magnetic field lines with the
  chromospheric fibril structure appears to be different in the two groups
  since they indicate quite different model solutions for each group,
  i.e., a near-potential magnetic field configuration in the older group
  (1) and a twisted force-free field configuration in the younger group
  (2). The latter configuration could be created by a considerable twist
  of the main bunch of flux tubes in Group 2, which is reflected in the
  relative sunspot motions. It is also showed how this twist contributed
  to the formation of a filament between the two groups.

Title: Evidence for magnetic reconnection in large-scale magnetic
    structures in solar flares
Authors: Mandrini, C. H.; Rovira, M. G.; Demoulin, P.; Henoux, J. C.;
   Machado, M. E.; Wilkinson, L. K.
Bibcode: 1993A&A...272..609M
Altcode:
  Modelling the observed vertical magnetic field of an active region (NOAA
  2372) for two consecutive days, April 7 and 8, 1980, by the potential
  field of an ensemble of magnetic dipoles, we derived the location of
  the separatrices, surfaces that separate cells of different field line
  connectivities, and of the separator which is the intersection of the
  separatrices. The overall temporal evolution of the magnetic fields
  and the location of the off-band Hα kernels of flares, that occurred
  before the obtention of the magnetograms, support the hypothesis that
  the flares were due to magnetic reconnection taking place in the main
  separator of the active region. The triggering of reconnection in
  a second separator appearing on April 8 by reconnection in the main
  separator is strongly suggested by the observed magnetic connectivities
  and the kernels locations. The location of the emerging currents on
  the separatrices support the idea that flares are fed by the release
  of magnetic free energy.

Title: A Model for an Inverse Polarity Prominence Supported in a
    Dip of a Quadrupolar Region
Authors: Demoulin, P.; Priest, E. R.
Bibcode: 1993SoPh..144..283D
Altcode:
  We investigate the formation and support of solar prominences in a
  quadrupolar magnetic configuration. The prominence is modeled as a
  current sheet with mass in equilibrium in a two-dimensional field. The
  model possesses an important property which is now thought to be
  necessary, namely that the prominence forms within the dip, rather
  than the dip being created by the prominence.

Title: Evidence for magnetic reconnection in solar flares
Authors: Demoulin, P.; van Driel-Gesztelyi, L.; Schmieder, B.; Hemoux,
   J. C.; Csepura, G.; Hagyard, M. J.
Bibcode: 1993A&A...271..292D
Altcode:
  From a study of the magnetic field topology in an active region,
  evidence is derived that solar flares are produced by magnetic
  reconnection. We study a complex group with two active regions (AR
  25 t 1 and AR 2512) for three consecutive days, June 13-15 1980. The
  observed longitudinal magnetic field is used to model the coronal
  magnetic field by the potential field created by a series of magnetic
  charges. This computed field matches satisfactorily the Ho fibrils
  and the observed transverse field direction. A set of flares occurs
  principally in the northern group (AR 2511). During these three days,
  two different magnetic configurations in succession are responsible
  for the occurrence of these flares: first the intrusion of a new
  opposite flux in the following polarity, secondly the emergence of new
  flux between the main polarities. In this last case flares occurred,
  although the emerging bipole is almost parallel to the main bipole. We
  show that even in this bipolar configuration a separator is present
  and that observed H flare ribbons are located near the intersection of
  the computed separatrices with the photosphere. This provides strong
  support to a model where reconnection releases the stored magnetic
  energy. The induced evolution of the magnetic field forces reconnection
  along others separators. They are connected by magnetic field lines
  to fainter kernels.

Title: The solar corona's magnetism.
Authors: Amari, T.; Démoulin, P.
Bibcode: 1993Rech...24..258A
Altcode:
  No abstract at ADS

Title: Observational Evidence for Magnetic Reconnection in Solar
    Flares (Invited)
Authors: Henoux, J. C.; Demoulin, P.; Mandrini, C. H.; Rovira, M. G.
Bibcode: 1993ASPC...46..333H
Altcode: 1993IAUCo.141..333H; 1993mvfs.conf..333H
  No abstract at ADS

Title: Interpretación de las observaciones de fulguraciones solares
    en función de la topología de la región activa
Authors: Rovira, M. G.; Mandrini, C. H.; Demoulin, P.; Henoux, J. C.;
   Machado, M. E.
Bibcode: 1993BAAA...38..114R
Altcode:
  Con el objeto de comprender el rol que juega la topología a gran escala
  durante las fulguraciones solares, realizamos un estudio detallado de la
  estructura topológica de la región activa (AR) 2776 y la comparamos
  con observaciones en Hα , UV, rayos X y radio de dos fulguraciones
  que tuvieron lugar el 5 de Noviembre de 1980. Como en casos anteriores
  el campo magnético coronal se modeló usando un conjunto de fuentes
  subfotosféricas, cuyas posiciones e intensidades se dedujeron a partir
  de un ajuste por cuadrados mínimos al campo longitudinal observado. En
  este caso, dado que el campo de AR 2776 no es potencial, se uso en
  el modelo una extrapolación libre de fuerzas lineal. La relación
  entre la posición de los cuatro abrillantamientos en Hα de distintas
  fulguraciones y la topología de regiones activas cuadrupolares ha
  sido estudiada anteriormente. En este caso la región es bipolar y
  las fulguraciones muestran una estructura de dos bandas. Estas se
  ubican sobre las separatrices cuando se tiene en cuenta el shear del
  campo, deducido de la dirección de las fibrillas observadas a nivel
  cromosférico. Este estudio esta de acuerdo con la hipótesis de que
  la energía magnética está almacenada en corrientes alineadas con
  el campo y que se libera por reconección del mismo, en la región
  del separador, antes de ser transportada a la cromosfera. También es
  posible que parte de la energía magnética se almacene y se libere
  sobre las separatrices. La ubicación de las corrientes fotosféricas,
  deducidas de los magnetogramas vectoriales, en la intersección de
  las separatrices con la fotosfera concuerda con este último punto.

Title: Estabilidad de la estructura topológica de una región activa
    en presencia de fuentes de campo externas
Authors: Mandrini, C. H.; Rovira, M. G.; Demoulin, P.; Henoux, J. C.;
   de La Beaujardiere, J.
Bibcode: 1993BAAA...38..115M
Altcode:
  A partir de las observaciones del campo magnético longitudinal
  de la región activa (AR) 6233, obtenidas en el Observatorio Mees
  (Universidad de Hawaii), derivamos su estructura topológica y
  estudiamos la evolución de la misma a lo largo de dos días. En
  el bipolo principal de esta región se desarrollaron numerosas
  fulguraciones y microfulguraciones en el período de estudio. Dado que
  en este caso contamos con magnetogramas que cubren distintas escalas
  espaciales, analizamos la influencia que las fuentes de campo externas
  a dicho bipolo tienen sobre la estructura topológica de la zona en
  donde se produjeron las fulguraciones. Esta se obtiene a partir de
  un modelo del campo de AR 6233 tanto en la aproximación potencial,
  como en la libre de fuerzas lineal. Nuestros resultados muestran
  que la estructura topológica básica de la región de interés
  permanece invariante en ambos casos. Esto justificaría el uso, debido
  a limitaciones instrumentales, de magnetogramas que cubren una porción
  limitada de la región activa al modelar el campo como se ha hecho en
  estudios anteriores.

Title: MHD Equilibria in Uniform Gravity
Authors: Surlantzis, G.; Démoulin, P.; Heyvaerts, J.; Sauty, C.
Bibcode: 1993ASSL..183..629S
Altcode: 1993pssc.symp..629S
  No abstract at ADS

Title: Helical Structures around Quiescent Solar Prominences Computed
    from Observable Magnetic Fields
Authors: Demoulin, P.; Raadu, M. A.
Bibcode: 1992SoPh..142..291D
Altcode:
  We analyse the magnetic support of solar prominences in two-dimensional
  linear force-free fields. A line current is added to model a helical
  configuration, well suited to trap dense plasma in its bottom part. The
  prominence is modeled as a vertical mass-loaded current sheet in
  equilibrium between gravity and magnetic forces.

Title: Structural Characteristics of Eruptive Prominences
Authors: Demoulin, P.; Vial, J. C.
Bibcode: 1992SoPh..141..289D
Altcode:
  Nowadays the primordial importance of the magnetic field for coronal
  plasma physics is well known. However, its determination is only made in
  cool regions, mainly the photosphere and prominences. The extrapolation
  to the corona gives some indications of the magnetic structure but is
  not presently sufficiently reliable. So it is important to consider
  all the other observable physical effects of the magnetic field.

Title: Determination of force-free magnetic fields above the
    photosphere using three-component boundary conditions. II - Analysis
    and minimization of scale-related growing modes and of computational
    induced singularities
Authors: Demoulin, P.; Cuperman, S.; Semel, M.
Bibcode: 1992A&A...263..351D
Altcode:
  The problem of the extrapolation of the observed three-component
  photospheric magnetic fields within is studied within the framework
  of the nonlinear force-free field model. The possible vertically
  growing modes and their relationship to the horizontal and vertical
  chosen scales is discussed, and the mathematical singularities arising
  along neutral field lines and leading to nondefinite alpha values are
  examined. A search is made for simple procedures aimed at minimizing
  these algorithm-dependent computational errors.

Title: Book-Review - Dynamics of Quiescent Prominences
Authors: Ruzdjak, V.; Tandberg-Hanssen, E.; Demoulin, P.
Bibcode: 1992SSRv...61..427R
Altcode:
  No abstract at ADS

Title: Development of a Topological Model for Solar Flares
Authors: Demoulin, P.; Henoux, J. C.; Mandrini, C. H.
Bibcode: 1992SoPh..139..105D
Altcode:
  The main theoretical studies of the process involved in solar flares
  have been made in the two-dimensional approximation. However, the
  preliminary studies made with three field components suggest that
  reconnection could take place in the separatrices, the separator
  (intersection of separatrices) being a privileged location for this
  process. As a consequence the sites of flare kernels must be located on
  the intersections of the separatrices with the photosphere. Therefore,
  in order to understand the role of interacting large-scale structures
  in solar flares, we have analysed the topology of three-dimensional
  potential and linear force-free fields. The magnetic field has been
  modelled by a distribution of charges or dipoles located below the
  photosphere. This modelling permits us to define the field connectivity
  by the charges or the dipoles at both ends of every field line.

Title: The properties of sources and sinks of a linear force-free
    field
Authors: Demoulin, P.; Priest, E. R.
Bibcode: 1992A&A...258..535D
Altcode:
  In a highly conducting plasma, the magnetic field topology
  determines where, for example, current sheets can form, which is
  of great importance as a potential coronal heating source. With the
  classical extrapolation of a continuous weak photospheric field, the
  determination of topology is in general a difficult challenge. Because
  of the concentration of the photospheric field at intense flux tubes in
  supergranulation boundaries a more realistic field representation may
  be a description in terms of magnetic singularities located just below
  the photosphere. In this paper we analyze in detail the generalization
  to linear force-free fields of the standard multipole expansion
  for singular potential fields. Solutions are presented in spherical
  coordinates with the constraint that all singularities are located
  in the half-space z is less than 0 below the solar photospheric plane
  (z = 0). A great variety of solutions is shown to exist depending on
  two continuous and one discrete parameter. The properties of monopole
  and dipole solutions in particular are discussed and it is shown that
  isolated magnetic charges exist only in the potential limit and not
  in a linear force-free field.

Title: Linear force-free magnetic field around quiescent solar
    prominences computed from observable boundary conditions
Authors: Demoulin, P.; Raadu, M. A.; Malherbe, J. M.
Bibcode: 1992A&A...257..278D
Altcode:
  The magnetic support of solar prominences in two-dimensional linear
  force-free fields is analyzed. The prominence was modeled as a
  vertical current sheet with mass in equilibrium between gravity and
  magnetic forces. A finite difference numerical technique was used
  which incorporates both vertical photospheric and horizontal prominence
  magnetic field observations as boundary conditions. The mixed-boundary
  value problem is described and the current singularity generally present
  is eliminated by a modification of the initial boundary condition. Using
  the linear force-free hypothesis the bipolar and quadripolar regions
  were found to be associated with normal and inverse prominence polarity
  respectively. An increase of magnetic shear decreases the mass supported
  for a given vertical dependence of the field component orthogonal to
  the prominence.

Title: Weighted Current Sheets Supported in Normal and Inverse
Configurations: A Model for Prominence Observations
Authors: Demoulin, P.; Forbes, T. G.
Bibcode: 1992ApJ...387..394D
Altcode:
  A technique which incorporates both photospheric and prominence
  magnetic field observations is used to analyze the magnetic support
  of solar prominences in two dimensions. The prominence is modeled
  by a mass-loaded current sheet which is supported against gravity
  by magnetic fields from a bipolar source in the photosphere and a
  massless line current in the corona. It is found that prominence
  support can be achieved in three different kinds of configurations:
  an arcade topology with a normal polarity; a helical topology with a
  normal polarity; and a helical topology with an inverse polarity. In
  all cases the important parameter is the variation of the horizontal
  component of the prominence field with height. Adding a line current
  external to the prominence eliminates the nonsupport problem which
  plagues virtually all previous prominence models with inverse polarity.

Title: Reconección magnética entre estructuras a gran escala
    durante fulguraciones solares
Authors: Mandrini, C. H.; Rovira, M. G.; Demoulin, P.; Henoux, J. C.;
   Machado, M. E.
Bibcode: 1992BAAA...37..112M
Altcode:
  A partir del modelado del campo magnético de la región activa
  NOAA 2372 se determina la ubicación de sus distintas estructuras
  topológicas: separatrices y separador. Este análisis se hace
  en base a observaciones del campo magnético a lo largo de tres
  días. La evolución temporal del campo global y la ubicación de los
  abrillantamientos en H a de varias fulguraciones, en relación con
  la topología determinada, están de acuerdo con el hecho de que las
  fulguraciones son el resultado del proceso de reconección que tiene
  lugar en el separador principal de la región activa.

Title: Fulguraciones solares y su relación con la topología del
    campo magnético
Authors: Balgala, L. G.; Rovira, M. G.; Mandrini, C. H.; Demoulin, P.
Bibcode: 1992BAAA...37..112B
Altcode:
  En base a una distribución de dipolos magnéticos modelamos el campo
  de una región activa visible sobre el disco solar en noviembre
  de 1980. Comparamos la estructura topológica calculada a partir
  de este modelo, en su aproximación potencial, con la emisión en
  líneas cromosféricas y de la región de transición debidas a una
  figuración solar. Extendimos este análisis a las imágenes obtenidas
  por el Hard X-ray Imaging Spectrometer en el continuo de rayos X,
  entre 3,5 y 30 keV.

Title: Interaction of Largescale Magnetic Structures in Solar Flares
Authors: Mandrini, C. H.; Demoulin, P.; Henoux, J. C.
Bibcode: 1992LNP...399...54M
Altcode: 1992IAUCo.133...54M; 1992esf..coll...54M
  Modelling the observed vertical magnetic field of active region (AR)
  NOAA 2372 by the potential field of an ensemble of magnetic dipoles,
  we have derived the likely location of the separatrices, surfaces
  that separate cells of different field line connectivities, and of
  the separator which is the intersection of the separatrices. The
  connectivity of every magnetic field line, which is defined by the
  dipoles located at its ends, is computed by a code that, starting
  from any pixel in the photospheric plane, integrates numerically the
  differential equation defining a line of force towards both ends of
  this line until one dipole is reached. This code allows us to obtain the
  topology of the field in three dimensions. We have compared our results
  with observations of a 1B/M1 flare that developed in AR 2372 on April
  6, 1980 at 20:53 UT (Lin and Gaizauskas, 1987), twenty minutes before
  obtaining the magnetogram. We found that four of the five off-band Ha
  kernels were located near or at the separatrices. These Ha kernels
  are connected by field lines that pass close to the separator. This
  indicates that the flare may have resulted from the interaction of
  large scale magnetic structures in the separator region. Moreover, Lin
  and Gaizauskas (1987) showed that the Ha flare kernels coincided with
  the peak values of the longitudinal electric current density. This
  finding and the fact that no strong current and no Ha kernel are
  observed at the intersection of the separator with the photosphere,
  lead to the conclusion that the magnetic energy released during the
  flare is mostly stored in an ensemble of currents flowing along lines of
  force. Some instability, presumably due to reconnection taking place
  in the separator, is likely to be the origin of the energy release
  and of the observed flare.

Title: Evidence for the interaction of large scale magnetic structures
    in solar flares.
Authors: Mandrini, C. H.; Demoulin, P.; Henoux, J. C.; Machado, M. E.
Bibcode: 1991A&A...250..541M
Altcode:
  By modeling the observed vertical magnetic field of an active region
  AR 2372 by the potential field of an ensemble of magnetic dipoles, the
  likely location of the separatrices, surfaces that separates cells of
  different field line connectivities, and of the separator which is the
  intersection of the separatrices, is derived. Four of the five off-band
  H-alpha kernels of a flare that occurred less than 20 minutes before
  obtaining the magnetogram are shown to have taken place near or at
  the separatrices. These H-alpha kernels are connected by field lines
  that pass near the separator. This indicates that the flare may have
  resulted from the interaction in the separator region of large scale
  magnetic structures.

Title: Determination of absolute strengths of N2 quadrupole lines
    from high-resolution ground-based IR solar observations
Authors: Demoulin, P.; Zander, R.; Farmer, C. B.; Rinsland, C. P.
Bibcode: 1991JGR....9613003D
Altcode:
  The strength of S-branch lines of the N2 (1-0) electric quadrupole
  vibration-rotation band are determined by an analysis of solar
  absorption spectra. The solar data were recorded with a Fourier
  transform spectrometer and are characterized by high resolution,
  and a high signal-to-noise ratio. By extrapolating equivalent width
  measurements of the lines from varying air masses to zero air mass, the
  line strengths are found for the transitions from S7 to S10. The results
  presented do not include half widths and are found to be accurate to
  within 5 percent, and following a redetermination the N2 transitions
  are accurate to within 0.0002/cm. Line-of-sight atmospheric air masses
  associated with remotely sensed IR spectroscopic observations can be
  determined directly by utilizing the highly accurate data.

Title: Removal of singularities in the Cauchy problem for the
    extrapolation of solar force-free magnetic fields
Authors: Cuperman, S.; Demoulin, P.; Semel, M.
Bibcode: 1991A&A...245..285C
Altcode:
  The singularities occurring in the Cauchy problem for the
  extrapolation of solar nonlinear force-free magnetic fields at
  positions of vanishing normal component, B(z), are removed. This is
  based on the observation that the constancy of the quantity alpha(r),
  characterizing the force-free magnetic fields, along a given magnetic
  field line, implies that the singularity in Maxwell's equation is of
  mathematical rather than of physical origin. Thus, requiring also the
  vanishing of the numerator at P(0) leads to an undetermined form for
  alpha. By using Taylor's expansions in two variables (x and y) about
  P(0) for both numerator and denominator, the actual value for alpha,
  namely alpha (P(0), is obtained. The procedure is tested on the case
  of the analytical model proposed by Low (1982).

Title: Instability of a prominence supported in a linear force-free
    field. II - Effect of twist or flux conservation
Authors: Demoulin, P.; Ferreira, J.; Priest, E. R.
Bibcode: 1991A&A...245..289D
Altcode:
  Ideal MHD equations are used to study the vertical stability of
  a prominence in a linear force-free field in two dimensions. The
  prominence is modeled by a line current in equilibrium at a height
  between the background magnetic force, the repulsion of image currents
  and gravity. Attention is given to boundary conditions, current
  evolution, parameters, stability results with boundary conditions,
  and the effects of lateral boundaries.

Title: Ground-Based Infrared Measurements of HNO<SUB>3</SUB> Total
Column Abundances: Long-Term Trend and Variability
Authors: Rinsland, C. P.; Zander, R.; Demoulin, P.
Bibcode: 1991JGR....96.9379R
Altcode:
  The long-term trend and variability of the total column amount of
  atmospheric nitric acid (HNO<SUB>3</SUB>) have been investigated
  based on time series of infrared solar absorption spectra recorded
  at two remote high-altitude sites, the International Scientific
  Station of the Jungfraujoch (ISSJ) in the Swiss Alps (altitude
  3.6 km, latitude 46.5°N, longitude 8.0°E) and the National Solar
  Observatory McMath solar telescope facility on Kitt Peak (altitude
  2.1 km, latitude 31.9°N, longitude 111.6°W), southwest of Tucson,
  Arizona. The HNO<SUB>3</SUB> ν5 band Q branch at 879.1 cm<SUP>-1</SUP>
  and three P branch manifolds near 869 cm<SUP>-1</SUP> were analyzed
  using a nonlinear least squares spectral fitting technique and a
  consistent set of spectroscopic line parameters. The ISSJ measurements
  evaluated in the present work consist of two solar spectra recorded
  with a grating spectrometer in June 1951 and a set of observations
  obtained with a high-resolution Fourier transform spectrometer between
  June 1986 and June 1990. The modern ISSJ measurements show a ∼20%
  peak-to-peak amplitude seasonal cycle with a winter maximum superimposed
  on significant variability and a summer minimum; the June results
  from 1986 to 1990 are both higher and lower than the two retrieved
  June 1951 HNO<SUB>3</SUB> total column amounts. The fitted trend,
  (-0.16±0.50)% yr<SUP>-1</SUP>, 2σ, indicates that there has been no
  detectable change in the HNO<SUB>3</SUB> total column over the last 4
  decades. The Kitt Peak measurements, recorded with a high-resolution
  Fourier transform spectrometer between December 1980 and June 1990,
  also show marked variability in the HNO<SUB>3</SUB> total column,
  but in contrast to the ISSJ measurements, no obvious seasonal cycle
  is observed. The deduced trend in the total column above Kitt Peak,
  (-0.8±1.6)% yr<SUP>-1</SUP>, 2σ, is consistent with the ISSJ time
  series of measurements, in that no significant HNO<SUB>3</SUB> long-term
  trend has been found. The sets of measurements from the two sites
  are compared with each other and with previously published results,
  with emphasis on the reported variability of HNO<SUB>3</SUB> and the
  changes in the HNO<SUB>3</SUB> total column with season and latitude.

Title: Solar prominences.
Authors: Démoulin, P.
Bibcode: 1991gamp.conf..281D
Altcode:
  A rapid overview of observations is given, and then it is tried to
  understand thermal and magnetic processes that lead to prominence
  formation. One section is devoted to what we can learn about the Sun,
  from prominences. The support and eruption of prominences are totally
  omitted.

Title: Solar Prominences
Authors: Demoulin, P.
Bibcode: 1991assm.conf..281D
Altcode:
  No abstract at ADS

Title: The creation of the magnetic environment for prominence
    formation in a coronal arcade
Authors: Amari, T.; Démoulin, P.; Browning, P.; Hood, A.; Priest, E.
Bibcode: 1991A&A...241..604A
Altcode:
  The possibility of prominence formation in sheared coronal arcades is
  investigated. The creation of a dip at the summit of field lines is
  a likely requirement before a prominence can form; then dense plasma
  can be supported against gravity by the Lorentz force. It is proved
  that, in fact, no shear profile can create a dip in a two-dimensional
  force-free arcade if the photospheric field is bipolar. However,
  numerical investigations show that shearing an arcade can induce very
  flat field lines. It is investigated, in order of magnitude, how this
  flattening of the field can increase the free fall time of a dense
  plasma. Also, the interaction between shear and twist is analyzed; the
  critical twist needed to have a dip is a decreasing function of shear.

Title: How to Form a Dip in a Magnetic Field Before the Formation
    of a Solar Prominence
Authors: Démoulin, P.; Priest, E. R.
Bibcode: 1990LNP...363..269D
Altcode: 1990doqp.coll..269D; 1990IAUCo.117..269D
  Magnetic fields with downward curvature are not favourable for
  prominence formation since the presence of a small quantity of dense
  material at the summit of a low-beta arcade cannot deform sufficiently
  the magnetic field lines to remain there in a stable manner. Thus a
  dip at the field line summit is needed before a prominence can form. We
  investigate different ways of forming such an upward curvature. Results
  with a twisted flux tube or a sheared arcade are reviewed, and a third
  possibility, namely a quadrupolar region is proposed.

Title: Relationship between a spot and a filament observed during
    spacelab 2 mission
Authors: Schmieder, B.; Dere, K. P.; Raadu, M. A.; Démoulin, P.;
   Alissandrakis, C. E.
Bibcode: 1990AdSpR..10i.195S
Altcode: 1990AdSpR..10..195S
  During the Spacelab 2 Mission, an active region including a sunspot,
  plages, fibrils and a filament which disappears during the observation
  period, was observed in Hα and in the C IV lines. The analysis of the
  observations leads to several conclusions. Shear in the active region
  filament is observed before its disappearance. Hα and C IV upflows
  in the filament are well correlated spatially, but the transition
  zone (C IV) velocities are an order of magnitude larger than the Hα
  chromospheric ones. Over the sunspot, the reverse-Evershed effect is
  observed in Hα and in C IV Dopplershift images while strong downflows
  are also detected in the C IV profiles. <P />Magnetograph data for
  the whole region are used to calculate the linear force-free magnetic
  field. A single value of the force-free parameter α is found to give a
  good fit to both the sheared filament structure and the sunspot spiral
  structures, indicating a causal relationship. <P />We propose a model
  based on the inductive coupling between current systems associated with
  the filament and the sunspot. Relaxation phenomena due to resistive
  effects in the filament could lead to irreversible conversion of
  magnetic energy into kinetic energy and heating.

Title: Formation of a Filament around a Magnetic Region
Authors: Schmieder, B.; Démoulin, P.; Ferreira, J.; Alissandrakis,
   C. E.
Bibcode: 1990LNP...363..232S
Altcode: 1990doqp.coll..232S; 1990IAUCo.117..232S
  The evolution of the active region AR4682 observed in 1985 during six
  rotations was dominated by three different phenomena: . the large
  scale pattern activity: relationship between two active regions,
  formation of a quiescent filament during the decay phase of the
  active region, . the presence of two pivot points along the filament
  surrounding the sunspot-with the long term one is associated the
  existence of the filament, with the short term one the activity with
  partial disappearance, . the magnetic shear during one rotation. The
  magnetic field lines have been extrapolated from photospheric data
  using Alissandrakis code (1981). The magnetic configuration with the
  existence of a dip favors the formation of a filament. We note that
  the shearing of the sunspot region and of the filament are both well
  described by force-free magnetic fields with the same constant α. This
  suggests that they are both a consequent of the same shear process.

Title: A three-dimensional model for solar prominences
Authors: Démoulin, P.; Priest, E. R.; Anzer, U.
Bibcode: 1990LNP...363..268D
Altcode: 1990doqp.coll..268P; 1990LNP...363..268P; 1990IAUCo.117..268P
  We suggest here a model for the 3D structure of quiescent prominences by
  a superposition of two fields. A 3D force-free field with constant is
  assumed to exist in the corona prior to the prominence formation. The
  prominence itself is represented by a line current which interacts
  with the coronal field. The three-dimensional field is represented by
  analytical functions and concentration of the magnetic field at the
  photospheric level by convection cells is taken into account. When the
  field created by the photospheric pattern supports the prominence,
  the prominence feet are found to be located at supergranule centres
  otherwise; they are located at cell boundaries.

Title: A three-dimensional model for solar prominences
Authors: Demoulin, P.; Priest, E. R.; Anzer, U.
Bibcode: 1989A&A...221..326D
Altcode:
  In an attempt to model the external force field of a prominence,
  a three-dimensional linear force-free field configuration was
  studied. The model consists of a fundamental together with a harmonic
  that is periodic along the prominence. The variation of the prominence
  height along the prominence is calculated and it is suggested that
  feet occur where the prominence sags down to low heights.

Title: A twisted flux model for solar prominences. II - Formation of a
    dip in a magnetic structure before the formation of a solar prominence
Authors: Demoulin, P.; Priest, E. R.
Bibcode: 1989A&A...214..360D
Altcode:
  The possibility of dip formation in a linear force-free field before the
  formation of a filament is investigated. The creation of a dip prior
  to prominence formation requires a greatly sheared magnetic field and
  a particular magnetic base flux. In the present work, attention is
  given to a bipolar region devoid of parasite polarity.

Title: Dynamics of a filament at the boundary of a SPOT region with
    magnetic shear
Authors: Schmiedler, B.; Demoulin, P.; Raadu, M. A.; Dere, K. P.
Bibcode: 1989A&A...213..402S
Altcode:
  H-alpha (MSDP), magnetograph (Meudon), and C IV (HRTS) observations are
  used to investigate the relationship between the dynamics of a solar
  filament and a spot region with vortex structure. Comparisons are made
  between the structures in H-alpha and C IV intensity and Doppler-shift
  images. These show filament shearing and a good correlation between
  H-alpha and C IV upflow, the C IV filament being very dynamic (+ or -
  50 km/s). Magnetograph data for the whole region including the sunspot
  are used to calculate linear force-free fields. The magnetic structure
  at the filament is found to be favorable for support.

Title: The magnetic field around quiescent solar prominences computed
    from observational boundary conditions
Authors: Demoulin, P.; Malherbe, J. M.; Priest, E. R.
Bibcode: 1989A&A...211..428D
Altcode:
  A generalization of Anzer's model (1972) for quiescent prominence
  support is presented. The coronal field is assumed to be current-free
  except inside the prominence where currents support dense material
  against gravity. The prominence is taken to be an infinitely thin
  current sheet of finite extent along the vertical axis. The hypothesis
  of two-dimensional fields allows the use of complex functions to
  solve the mixed boundary problem which is defined by the observed
  vertical field in the photosphere and the horizontal magnetic field
  in the prominence. These boundary conditions are not sufficient to
  determine a unique solution for the magnetic field. The indeterminacy
  is decreased by physical considerations, and some models for Normal
  (N) and Inverse (I) configurations are presented. In both cases it
  is possible to find field configurations which can support the fintie
  prominence against gravity.

Title: Structure et stabilité thermique et magnétique des
protubérances solaires Title: Structure et stabilité thermique et
magnétique des protubérances solaires Title: Thermal and magnetic
    structure and stability of solar prominences;
Authors: Démoulin, Pascal
Bibcode: 1989PhDT.......141D
Altcode:
  No abstract at ADS

Title: How to Form a Dip in a Magnetic Field Before the Formation
    of a Solar Prominence
Authors: Demoulin, P.; Priest, E. R.
Bibcode: 1989HvaOB..13..261D
Altcode:
  No abstract at ADS

Title: A Three-Dimensional Model for Solar Prominences
Authors: Demoulin, P.; Priest, E. R.; Anzer, U.
Bibcode: 1989HvaOB..13..253D
Altcode:
  No abstract at ADS

Title: Formation of a Filament around a Magnetic Region
Authors: Schmieder, B.; Demoulin, P.; Ferreira, J.; Alissandrakis,
   C. E.
Bibcode: 1989HvaOB..13....1S
Altcode:
  No abstract at ADS

Title: Instability of a prominence supported in a linear force-free
    field
Authors: Demoulin, P.; Priest, E. R.
Bibcode: 1988A&A...206..336D
Altcode:
  The authors analyse the equilibrium of a prominence by modelling it as
  a line of current under the action of gravity and of a two-dimensional
  constant force-free field. They show that a region of non-equilibrium
  may occur, if the field strength is great enough, for some distribution
  of the base flux. This occurs for both Kippenhahn-Schlüter and
  Kuperus-Raadu topologies and the region of non-equilibrium increases
  with the shear.

Title: Some dynamical aspects of a quiescent filament
Authors: Schmieder, B.; Demoulin, P.; Poland, A.; Thompson, B.
Bibcode: 1988A&A...197..281S
Altcode:
  A typical quiescent filament was observed on the disk in the Hα
  and C IV lines during a period of approximately one hour. Vertical
  velocities (&lt;2.5 km s<SUP>-1</SUP>) with a time scale of 5 min and
  a spatial scale of a few tens of seconds of arc were detected in Hα,
  and associated with microturbulence in both lines. The C IV observations
  correlated well with those in Hα, and showed no indication of material
  heating from Hα to C IV temperatures. Two mechanisms to explain these
  observations are proposed: mass motion along twisted magnetic field
  or instabilities triggering waves along the filament.

Title: Can a thermal instability form a prominence?
Authors: Démoulin, P.; Einaudi, G.
Bibcode: 1988dssp.conf...93D
Altcode:
  The aim of this work is to clarify definitely the conditions under
  which the transition region is stabilized and to show that there exist
  instabilities which can lead to the formation of a prominence.

Title: Non equilibrium of a prominence current in a linear force
    free field.
Authors: Demoulin, P.; Priest, E.
Bibcode: 1988dssp.conf...45D
Altcode:
  The authors analyse the equilibrium of a prominence by modelling
  it as a line of current under the action of gravity and of a two
  dimensional constant force free field. They show that a region of non
  equilibrium may occur, if the field strength is great enough, for some
  distribution of the base flux. This occurs for both Kippenhahn-Schluter
  and Kuperus-Raadu topologies and the region of non equilibrium increases
  with the shear.

Title: Fine structures in solar filaments. I - Observations and
    thermal stability
Authors: Demoulin, P.; Malherbe, J. M.; Schmieder, B.; Raadu, M. A.
Bibcode: 1987A&A...183..142D
Altcode:
  Limb observations of quiescent prominences show very fine structures of
  less than one arcsecond. Here H-alpha observations on the disk, made
  with the Multichannel Subtractive Double Pass spectrograph operating
  at the Observatoire du Pic du Midi are presented. They show long
  fine structures in the body of the filament, both in intensity and
  velocity maps. Many prominence models ignore such fine structures and
  suppose that the quiescent filament is a uniform body such as is seen
  in unresolved images. It has been suggested that in a current-sheet
  model of a prominence, fine structures may be produced as a consequence
  of the tearing mode coupled to thermal instability. Here the role of
  parallel and orthogonal conduction on the stability of a periodic fine
  structure is investigated. Equilibrium conditions are found and growth
  rates determined for linear perturbations.

Title: Nonequilibrium of a Prominence Current in a Linear Force-Free
    Field
Authors: Demoulin, P.; Priest, E. R.
Bibcode: 1987dssp.work...45D
Altcode: 1987ASSL..150...45D
  No abstract at ADS

Title: Can a Thermal Instability Form a Prominence
Authors: Demoulin, P.; Einaudi, G.
Bibcode: 1987dssp.work...93D
Altcode: 1987ASSL..150...93D
  No abstract at ADS

Title: Thermal stability analysis of the fine structure of solar
    prominences.
Authors: Demoulin, Pascal; Malherbe, Jean-Marie; Schmieder, Brigitte;
   Raadu, Mickael A.
Bibcode: 1986NASCP2442..143D
Altcode:
  The authors analyse the linear thermal stability of a 2D periodic
  structure (alternatively hot and cold) in a uniform magnetic
  field. The energy equation includes wave heating (assumed proportional
  to density), radiative cooling and both conduction parallel and
  orthogonal to magnetic lines. The equilibrium is perturbed at constant
  gas pressure. The results compared with observations show that the
  computations suggest that the size of the unresolved threads could be
  of the order of 10 km only.

Title: Constraints on filament models deduced from dynamical analysis.
Authors: Simon, G.; Schmieder, B.; Demoulin, P.; Malherbe, J. M.;
   Poland, A. I.
Bibcode: 1986NASCP2442..177S
Altcode: 1986copp.nasa..177S
  The conclusions deduced from simultaneous observations with the
  Ultra-Violet Spectrometer and Polarimeter (UVSP) on the Solar Maximum
  Mission satellite, and the Multichannel Subtractive Double Pass (MSPD)
  spectrographs at Meudon and Pic du Midi observatories are presented. The
  observations were obtained in 1980 and 1984. All instruments have
  almost the same field of view and provide intensity and velocity maps
  at two temperatures. The resolution is approx. 0.5 to 1.5" for H alpha
  line and 3" for C IV. The high resolution and simultaneity of the two
  types of observations allows a more accurate description of the flows
  in prominences as functions of temperature and position. The results
  put some contraints on the models and show that dynamical aspects must
  be taken into account.

Title: Dynamics of solar filaments. VI - Center-to-limb study of
    H-alpha and C IV velocities in a quiescent filament
Authors: Simon, G.; Schmieder, B.; Demoulin, P.; Poland, A. I.
Bibcode: 1986A&A...166..319S
Altcode:
  The rotation of a stable quiescent filament from near disk center to
  the limb has been observed. Observations of intensity and velocity
  were made in H-alpha and C IV, and compared with magnetic field
  measurements. From the H-alpha observations, it is concluded that the
  filament is made up of many small scale magnetic features that are
  not coherently aligned along the neutral line. They are especially
  convoluted at the apparent 'footpoints'. The measured velocities are
  of the order of a few kilometers per second in both lines. However,
  the comparison of the standard deviations of the C IV velocities in
  and out of the filament as it rotates toward the limb shows that the
  vertical velocities in the filament are greater than the horizontal
  velocities. Measurements of velocity do not make it possible to
  distinguish between the Raadu-Kuperus (1973) or Kippenhahn-Schluter
  (1957) models for prominences because neither theory is adequately
  developed for this comparison. However, the observation of the many
  fine loops brings into question the correctness of either model.

