Author name code: robbrecht
ADS astronomy entries on 2022-09-14
author:"Robbrecht, Eva" 
------------------------------------------------------------------------  

Title: Verification of space weather forecasting at the Regional
    Warning Center in Belgium
Authors: Devos, Andy; Verbeeck, Cis; Robbrecht, Eva
Bibcode: 2014JSWSC...4A..29D
Altcode:
  The Solar Influences Data analysis Center (SIDC) in Brussels at the
  Royal Observatory of Belgium (ROB) has been providing daily space
  weather forecasts for more than a decade. A verification analysis was
  applied to evaluate the performance of the SIDC forecasts of fundamental
  space weather parameters such as the F10.7 radio flux, solar flare
  activity, and local geomagnetic index. Strengths and weaknesses
  are determined compared to common numerical models. Descriptive
  model statistics, common verification measures, error analysis
  and conditional plots related to forecasts and observations are
  presented. The verification analysis methods have been designed such
  that future improvements and additions can easily be included, for
  example with new forecasting models. The SIDC forecast (together with
  the persistence model) achieves the best performance for forecasting
  F10.7 on day 1, but has potential for improvement for a larger lead
  time mainly by applying estimates from the persistence and corrected
  recurrence models. The persistence model is superior for the forecast
  of flares, though corrected recurrence models are slightly better in
  foreseeing M- and X-class flares and the SIDC forecast estimates B-
  and C-class flares very well. The SIDC forecast scores better than all
  models in forecasting the local K-index. It best reproduces observations
  in the range of K = 2-4, but underestimates larger K values. The SIDC
  forecast provides a distribution that best matches the observations of
  the K-index. The analysis presented here demonstrates the influence of
  solar activity on the confidence level of the forecasts, as well as
  the hinted influence of the forecaster on duty due to the subjective
  nature of forecasting. The output aids to identify the strong and
  weak points of the SIDC forecast as well as those of the models
  considered. Though the presented analysis needs further extension,
  it already illustrates the opportunity to regularly reevaluate space
  weather forecasts and to stimulate ideas for improvement and increase
  the reliability of space weather forecasting.

Title: Determining the North-South Displacement of the Heliospheric
    Current Sheet from Coronal Streamer Observations
Authors: Robbrecht, E.; Wang, Y. -M.
Bibcode: 2012ApJ...755..135R
Altcode:
  Inferences based on interplanetary field measurements have suggested
  a statistical tendency for the heliospheric current sheet (HCS)
  to be displaced southward of the heliographic equator during the
  past four solar cycles. Here, we use synoptic maps of white-light
  streamer structures to determine more directly the longitudinally
  averaged latitude of the HCS, after separating out the contribution of
  streamers without magnetic polarity reversals ("pseudostreamers"). We
  find a strong tendency for the HCS to be shifted southward by a few
  degrees during 2007-2011, but no significant shift during the 1996-1997
  sunspot minimum. Fluctuations in the magnitude and direction of the
  north-south shifts often occur on timescales as short as one or two
  Carrington rotations, as a result of changes in the streamer structures
  due to active region emergence. The largest shifts occurred during
  2010-2011 and were on the order of -6°. Such southward displacements
  are consistent with the overwhelming dominance of northern-hemisphere
  sunspot activity during the rising phase of the current solar cycle 24,
  resulting in a strong axisymmetric quadrupole component whose sign at
  the equator matched that of the north polar field; the symmetry-breaking
  effect of the quadrupole was further enhanced by the weakness of the
  polar fields.

Title: Forecasting Geomagnetic Storms and Solar Energetic Particle
Events: the COMESEP Project
Authors: Crosby, N.; Veronig, A.; Robbrecht, E.; Vrsnak, B.;
   Vennerstrøm, S.; Malandraki, O.; Dalla, S.; Srivastava, N.; Hesse,
   M.; Odstrcil, D.
Bibcode: 2012EGUGA..1412544C
Altcode:
  COMESEP (COronal Mass Ejections and Solar Energetic Particles),
  funded by the European Union Framework 7 programme, is a three-year
  collaborative project that has been running for one year. Tools for
  forecasting geomagnetic storms and solar energetic particle (SEP)
  radiation storms are being developed under the project. By analysis
  of historical data, complemented by the extensive data coverage of
  solar cycle 23, the key ingredients that lead to magnetic storms and
  SEP events and the factors that are responsible for false alarms are
  being identified. To enhance our understanding of the 3D kinematics
  and interplanetary propagation of coronal mass ejections (CMEs), the
  structure, propagation and evolution of CMEs are being investigated. In
  parallel, the sources and propagation of SEPs are being examined and
  modeled. Based on the insights gained, and making use of algorithms for
  the automated detection of CMEs, forecasting tools for geomagnetic and
  SEP radiation storms are being developed and optimised. Validation and
  implementation of the produced tools into an operational Space Weather
  Alert system will be performed. Geomagnetic and SEP radiation storm
  alerts will be based on the COMESEP definition of risk. COMESEP is a
  unique cross-collaboration effort and bridges the gap between the SEP
  and CME scientific communities. For more information about the project,
  see the COMESEP website http://www.comesep.eu/ . This work has received
  funding from the European Commission FP7 Project COMESEP (263252).

Title: On the Nature of the Solar Wind from Coronal Pseudostreamers
Authors: Wang, Y. -M.; Grappin, R.; Robbrecht, E.; Sheeley, N. R., Jr.
Bibcode: 2012ApJ...749..182W
Altcode:
  Coronal pseudostreamers, which separate like-polarity coronal holes, do
  not have current sheet extensions, unlike the familiar helmet streamers
  that separate opposite-polarity holes. Both types of streamers taper
  into narrow plasma sheets that are maintained by continual interchange
  reconnection with the adjacent open magnetic field lines. White-light
  observations show that pseudostreamers do not emit plasma blobs; this
  important difference from helmet streamers is due to the convergence
  of like-polarity field lines above the X-point, which prevents the
  underlying loops from expanding outward and pinching off. The main
  component of the pseudostreamer wind has the form of steady outflow
  along the open field lines rooted just inside the boundaries of the
  adjacent coronal holes. These flux tubes are characterized by very
  rapid expansion below the X-point, followed by reconvergence at greater
  heights. Analysis of an idealized pseudostreamer configuration shows
  that, as the separation between the underlying holes increases, the
  X-point rises and the expansion factor f <SUB>ss</SUB> at the source
  surface increases. In situ observations of pseudostreamer crossings
  indicate wind speeds v ranging from ~350 to ~550 km s<SUP>-1</SUP>,
  with O<SUP>7 +</SUP>/O<SUP>6 +</SUP> ratios that are enhanced compared
  with those in high-speed streams but substantially lower than in the
  slow solar wind. Hydrodynamic energy-balance models show that the
  empirical v-f <SUB>ss</SUB> relation overestimates the wind speeds
  from nonmonotonically expanding flux tubes, particularly when the
  X-point is located at low heights and f <SUB>ss</SUB> is small. We
  conclude that pseudostreamers produce a "hybrid" type of outflow that
  is intermediate between classical slow and fast solar wind.

Title: Asymmetric Sunspot Activity and the Southward Displacement
    of the Heliospheric Current Sheet
Authors: Wang, Y. -M.; Robbrecht, E.
Bibcode: 2011ApJ...736..136W
Altcode:
  Observations of the interplanetary magnetic field (IMF) have suggested
  a statistical tendency for the heliospheric current sheet (HCS)
  to be shifted a few degrees southward of the heliographic equator
  during the period 1965-2010, particularly in the years near sunspot
  minimum. Using potential-field source-surface extrapolations and
  photospheric flux-transport simulations, we demonstrate that this
  southward displacement follows from Joy's law and the observed
  hemispheric asymmetry in the sunspot numbers, with activity being
  stronger in the southern (northern) hemisphere during the declining
  (rising) phase of cycles 20-23. The hemispheric asymmetry gives rise
  to an axisymmetric quadrupole field, whose equatorial zone has the
  sign of the leading-polarity flux in the dominant hemisphere; during
  the last four cycles, the polarity of the IMF around the equator thus
  tended to match that of the north polar field both before and after
  polar field reversal. However, large fluctuations are introduced by
  the nonaxisymmetric field components, which depend on the longitudinal
  distribution of sunspot activity in either hemisphere. Consistent
  with this model, the HCS showed an average northward displacement
  during cycle 19, when the "usual" alternation was reversed and
  the northern hemisphere became far more active than the southern
  hemisphere during the declining phase of the cycle. We propose a new
  method for determining the north-south displacement of the HCS from
  coronal streamer observations.

Title: The Evolution of Dark Canopies Around Active Regions
Authors: Wang, Y. -M.; Robbrecht, E.; Muglach, K.
Bibcode: 2011ApJ...733...20W
Altcode: 2011arXiv1103.4373W
  As observed in spectral lines originating from the chromosphere,
  transition region, and low corona, active regions are surrounded by an
  extensive "circumfacular" area which is darker than the quiet Sun. We
  examine the properties of these dark moat- or canopy-like areas using Fe
  IX 17.1 nm images and line-of-sight magnetograms from the Solar Dynamics
  Observatory. The 17.1 nm canopies consist of fibrils (horizontal fields
  containing extreme-ultraviolet-absorbing chromospheric material)
  clumped into featherlike structures. The dark fibrils initially
  form a quasiradial or vortical pattern as the low-lying field lines
  fanning out from the emerging active region connect to surrounding
  network and intranetwork elements of opposite polarity. The area
  occupied by the 17.1 nm fibrils expands as supergranular convection
  causes the active-region flux to spread into the background medium;
  the outer boundary of the dark canopy stabilizes where the diffusing
  flux encounters a unipolar region of opposite sign. The dark fibrils
  tend to accumulate in regions of weak longitudinal field and to become
  rooted in mixed-polarity flux. To explain the latter observation,
  we note that the low-lying fibrils are more likely to interact with
  small loops associated with weak, opposite-polarity flux elements
  in close proximity, than with high loops anchored inside strong
  unipolar network flux. As a result, the 17.1 nm fibrils gradually
  become concentrated around the large-scale polarity inversion lines
  (PILs), where most of the mixed-polarity flux is located. Systematic
  flux cancellation, assisted by rotational shearing, removes the field
  component transverse to the PIL and causes the fibrils to coalesce
  into long PIL-aligned filaments.

Title: Validation of CME Detection Software (CACTus) by Means of
    Simulated Data, and Analysis of Projection Effects on CME Velocity
    Measurements
Authors: Bonte, K.; Jacobs, C.; Robbrecht, E.; De Groof, A.; Berghmans,
   D.; Poedts, S.
Bibcode: 2011SoPh..270..253B
Altcode: 2011SoPh..tmp...52B; 2011SoPh..tmp...72B
  In the context of space weather forecasting, an automated detection
  of coronal mass ejections (CMEs) becomes more and more important
  for efficiently handling a large data flow which is expected from
  recently-launched and future solar missions. In this paper we validate
  the detection software package "CACTus" by applying the program to
  synthetic data from our 3D time-dependent CME simulations instead of
  observational data. The main strength of this study is that we know
  in advance what should be detected. We describe the sensitivities
  and strengths of automated detection, more specific for the CACTus
  program, resulting in a better understanding of CME detection on one
  hand and the calibration of the CACTus software on the other hand,
  suggesting possible improvements of the package. In addition, the
  simulation is an ideal tool to investigate projection effects on CME
  velocity measurements.

Title: The Evolution of Dark Canopies Around Active Regions
Authors: Muglach, Karin; Wang, Y. M.; Robbrecht, E.
Bibcode: 2011SPD....42.1718M
Altcode: 2011BAAS..43S.1718M
  As observed in spectral lines originating from the chromosphere,
  transition region, and low corona, active regions are surrounded
  by an extensive 'circumfacular' area which is darker than the quiet
  Sun. We examine the properties of these dark moat- or canopy-like areas
  using Fe IX 17.1 nm images and line-of-sight magnetograms from the
  Solar Dynamics Observatory. The 17.1 nm canopies consist of fibrils
  (horizontal fields containing EUV-absorbing chromospheric material)
  clumped into featherlike structures. The dark fibrils initially
  form a quasiradial or vortical pattern as the low-lying field lines
  fanning out from the emerging active region connect to surrounding
  network and intranetwork elements of the opposite polarity. The area
  occupied by the 17.1 nm fibrils expands as supergranular convection
  causes the active region flux to spread into the background medium;
  the outer boundary of the dark canopy stabilizes where the diffusing
  flux encounters a unipolar region of the opposite sign. The dark fibrils
  tend to accumulate in regions of weak longitudinal field and to become
  rooted in mixed-polarity flux. To explain the latter observation,
  we note that the low-lying fibrils are more likely to interact with
  small loops associated with weak, opposite-polarity flux elements
  in close proximity, than with high loops anchored inside strong
  unipolar network flux. As a result, the 17.1 nm fibrils gradually
  become concentrated around the large-scale polarity inversion lines
  (PILs), where most of the mixed-polarity flux is located. Systematic
  flux cancellation, assisted by rotational shearing, removes the field
  component transverse to the PIL and causes the fibrils to coalesce
  into long PIL-aligned filaments.

Title: The Temperature-dependent Nature of Coronal Dimmings
Authors: Robbrecht, Eva; Wang, Yi-Ming
Bibcode: 2010ApJ...720L..88R
Altcode: 2010arXiv1007.5191R
  The opening-up of the magnetic field during solar eruptive events
  is often accompanied by a dimming of the local coronal emission. From
  observations of filament eruptions recorded with the Extreme-Ultraviolet
  Imager on STEREO during 2008-2009, it is evident that these dimmings
  are much more pronounced in 19.5 nm than in the lower-temperature line
  17.1 nm, as viewed either on the disk or above the limb. We conclude
  that most of the cooler coronal plasma is not ejected but remains
  gravitationally bound when the loops open up. This result is consistent
  with Doppler measurements by Imada and coworkers, who found that
  the upflow speeds in a transient coronal hole increased dramatically
  above a temperature of 1 MK it is also consistent with the quasistatic
  behavior of polar plumes, as compared with the hotter interplume regions
  that are the main source of the fast solar wind. When the open flux
  reconnects and closes down again, the trapped plasma is initially heated
  to such high temperatures that it is no longer visible at Fe IX 17.1
  nm. Correspondingly, 17.1 nm images show a dark ribbon or "heat wave"
  propagating away from the polarity inversion line and coinciding with
  the brightened Fe XV 28.4 nm and Fe XII 19.5 nm post-eruptive loops and
  their footpoint areas. Such dark ribbons provide a clear example of
  dimmings that are not caused by a density depletion. The propagation
  of the "heat wave" is driven by the closing-down, not the opening-up,
  of the flux and can be observed both off-limb and on-disk.

Title: Sun to 1 AU propagation and evolution of a slow
    streamer-blowout coronal mass ejection
Authors: Lynch, B. J.; Li, Y.; Thernisien, A. F. R.; Robbrecht, E.;
   Fisher, G. H.; Luhmann, J. G.; Vourlidas, A.
Bibcode: 2010JGRA..115.7106L
Altcode: 2010JGRA..11507106L
  We present a comprehensive analysis of the evolution of the classic,
  slow streamer-blowout CME of 1 June 2008 observed by the STEREO twin
  spacecraft to infer relevant properties of the pre-eruption source
  region which includes a substantial portion of the coronal helmet
  streamer belt. The CME was directed ∼40° East of the Sun-Earth
  line and the Heliospheric Imager observations are consistent with
  the CME propagating essentially radially to 1 AU. The elongation-time
  J-map constructed from the STEREO-A HI images tracks the arrival of two
  density peaks that bound the magnetic flux rope ICME seen at STEREO-B on
  6 June 2008. From the STEREO-A elongation-time plots we measure the ICME
  flux rope radial size R<SUB>c</SUB>(t) and find it well approximated by
  the constant expansion value V<SUB>exp</SUB> = 24.5 km/s obtained from
  the STEREO-B declining velocity profile within the magnetic cloud. The
  flux rope spatial orientation, determined by forward modeling fits to
  the STEREO COR2 and HI1 data, approaches the observed 1 AU flux rope
  orientation and suggests large-scale rotation during propagation, as
  predicted by recent numerical simulations. We compare the ICME flux
  content to the PFSS model coronal field for Carrington Rotation 2070
  and find sufficient streamer belt flux to account for the observed
  ICME poloidal/twist flux if reconnection during CME initiation process
  is responsible for the conversion of overlying field into the flux
  rope twist component in the standard fashion. However, the PFSS model
  field cannot account for the ICME toroidal/axial flux component. We
  estimate the field strength of the pre-eruption sheared/axial component
  in the low corona and the timescales required to accumulate this
  energized pre-eruption configuration via differential rotation and
  flux cancelation by supergranular diffusion at the polarity inversion
  line. We show that both mechanisms are capable of generating the
  desired shear component over time periods of roughly 1-2 months. We
  discuss the implications for slow streamer-blowout CMEs arising as
  a natural consequence of the corona's re-adjustment to the long term
  evolutionary driving of the photospheric fields.

Title: On the "Extended" Solar Cycle in Coronal Emission
Authors: Robbrecht, E.; Wang, Y. -M.; Sheeley, N. R., Jr.; Rich, N. B.
Bibcode: 2010ApJ...716..693R
Altcode:
  Butterfly diagrams (latitude-time plots) of coronal emission show a
  zone of enhanced brightness that appears near the poles just after
  solar maximum and migrates toward lower latitudes; a bifurcation seems
  to occur at sunspot minimum, with one branch continuing to migrate
  equatorward with the sunspots of the new cycle and the other branch
  heading back to the poles. The resulting patterns have been likened to
  those seen in torsional oscillations and have been taken as evidence
  for an extended solar cycle lasting over ~17 yr. In order to clarify
  the nature of the overlapping bands of coronal emission, we construct
  butterfly diagrams from green-line simulations covering the period
  1967-2009 and from 19.5 nm and 30.4 nm observations taken with the
  Extreme-Ultraviolet Imaging Telescope during 1996-2009. As anticipated
  from earlier studies, we find that the high-latitude enhancements mark
  the footpoint areas of closed loops with one end rooted outside the
  evolving boundaries of the polar coronal holes. The strong underlying
  fields were built up over the declining phase of the cycle through
  the poleward transport of active-region flux by the surface meridional
  flow. Rather than being a precursor of the new-cycle sunspot activity
  zone, the high-latitude emission forms a physically distinct, U-shaped
  band that curves upward again as active-region fields emerge at
  midlatitudes and reconnect with the receding polar-hole boundaries. We
  conclude that the so-called extended cycle in coronal emission is a
  manifestation not of early new-cycle activity, but of the poleward
  concentration of old-cycle trailing-polarity flux by meridional flow.

Title: Formation and Evolution of Coronal Holes Following the
    Emergence of Active Regions
Authors: Wang, Y. -M.; Robbrecht, E.; Rouillard, A. P.; Sheeley,
   N. R., Jr.; Thernisien, A. F. R.
Bibcode: 2010ApJ...715...39W
Altcode:
  The low level of solar activity over the past four years has provided
  unusually favorable conditions for tracking the formation and evolution
  of individual coronal holes and their wind streams. Employing
  extreme-ultraviolet images recorded with the Solar Terrestrial
  Relations Observatory during 2007-2009, we analyze three cases
  in which small coronal holes first appear at the edges of newly
  emerged active regions and then expand via flux transport processes,
  eventually becoming attached to the polar holes. The holes form
  gradually over timescales comparable to or greater than that for
  the active regions to emerge, without any obvious association with
  coronal mass ejections. The evolving hole areas coincide approximately
  with the footpoints of open field lines derived from potential-field
  source-surface extrapolations of the photospheric field. One of these
  coronal-hole systems, centered at the equator and maintained by a
  succession of old-cycle active regions emerging in the same longitude
  range, persists in one form or another for up to two years. The other
  two holes, located at midlatitudes and originating from new-cycle
  active regions, become strongly sheared and decay away after a few
  rotations. The hole boundaries and the small active-region holes, both
  of which are sources of slow wind, are observed to undergo continual
  short-term (lsim1 day) fluctuations on spatial scales comparable to
  that of the supergranulation. From in situ measurements, we identify
  a number of plasma sheets associated with pseudostreamers separating
  holes of the same polarity.

Title: Heatwaves on the Sun
Authors: Robbrecht, Eva; Wang, Yi-Ming; Vourlidas, Angelos;
   Patsourakos, Spiros
Bibcode: 2010cosp...38.1791R
Altcode: 2010cosp.meet.1791R
  Dimmings have been observed for several years now, but their
  interpretation is still problematic. A dimming is an observational
  effect of diminished brightness with respect to pre-event images, which
  is usually interpreted as a density depletion. But not all dimmings are
  what they appear to be. In this paper we report on an unusual "dimming
  wave" which is not a density depletion but rather a heat wave. Thanks
  to the stereoscopic view from the SECCHI/EUVI imagers we are able not
  only to uncover the nature of the wave, but also to understand its
  three dimensional evolution and its relationship to a quiet sun CME.

Title: Sun to 1 AU Propagation of a Slow Streamer-Blowout Coronal
    Mass Ejection
Authors: Lynch, B. J.; Li, Y.; Thernisien, A. F.; Robbrecht, E.;
   Luhmann, J. G.; Vourlidas, A.
Bibcode: 2009AGUFMSH41A1635L
Altcode:
  We present the time history and evolution of the 3-dimensional size,
  shape, and orientation of the slow, classic streamer blowout CME of
  2008 Jun 01 by combining STEREO-A remote imaging of its interplanetary
  propagation with in situ STEREO-B plasma and field measurements at
  1~AU. The STEREO-A HI coverage allows unambigious identification of
  the CME white light front-cavity structure and the resulting ICME flux
  rope boundaries in running difference images. The elongation-time tracks
  predict the arrival of the ICME at STEREO-B on 2008 June 06 remarkably
  well. Starting from the simplest in situ flux rope model for the
  coherent magnetic cloud field structure, we utilize the unprecedented
  coverage of the coronal and heliospheric imaging observations to obtain
  important corrections for the ICME flux rope geometry. MHD modeling
  results obtained from the NASA Community Coordinated Modeling Center
  for the ambient heliopsheric solar wind stream structure and a simple
  CME-like density-pulse propagation are used to verify the overall
  propagation direction and characterize some of the observed evolutionary
  properties. The ICME radial expansion, i.e. the time evolution of
  the flux rope radius Rc(t) from the STEREO-A elongation-time plots,
  is well approximated by the standard treatment of constant radial
  expansion Vexp = 24.5 km/s measured from the in situ bulk velocity
  profile. The 3-dimensional spatial orientation of the ICME flux rope
  determined by forward modeling in the inner heliosphere shows excellent
  agreement with the observed 1~AU flux rope orientation and evidence
  for large scale rotation of the ICME flux rope during its propagation,
  as predicted by recent numerical simulations. In addition, measurements
  of the CME's latitudinal angular width allows us to improve the estimate
  the actual flux rope cross-sectional area and measurements of the CME's
  longitudinal extent allows us to estimate a more realistic CME ``loop
  length". These geometric quantities are used to improve the estimates of
  the ICME in situ toroidal and poloidal magnetic fluxes, ΦT and ΦP. The
  in situ flux values are then compared to the magnetic fluxes inferred
  from this event's source region, which includes a substantial portion of
  the large scale coronal helmet streamer belt. We conlude by discussing
  our results in the context of both CME initiation and the physical
  mechanism(s) that energize the pre-eruption configuration. Support
  for this work was provided by NASA HGI NNX08AJ04G.

Title: On the Weakening of the Polar Magnetic Fields during Solar
    Cycle 23
Authors: Wang, Y. -M.; Robbrecht, E.; Sheeley, N. R., Jr.
Bibcode: 2009ApJ...707.1372W
Altcode:
  The Sun's polar fields are currently ~40% weaker than they were during
  the previous three sunspot minima. This weakening has been accompanied
  by a corresponding decrease in the interplanetary magnetic field (IMF)
  strength, by a ~20% shrinkage in the polar coronal-hole areas, and by
  a reduction in the solar-wind mass flux over the poles. It has also
  been reflected in coronal streamer structure and the heliospheric
  current sheet, which only showed the expected flattening into the
  equatorial plane after sunspot numbers fell to unusually low values
  in mid-2008. From latitude-time plots of the photospheric field,
  it has long been apparent that the polar fields are formed through
  the transport of trailing-polarity flux from the sunspot latitudes
  to the poles. To address the question of why the polar fields are
  now so weak, we simulate the evolution of the photospheric field and
  radial IMF strength from 1965 to the present, employing a surface
  transport model that includes the effects of active region emergence,
  differential rotation, supergranular convection, and a poleward bulk
  flow. We find that the observed evolution can be reproduced if the
  amplitude of the surface meridional flow is varied by as little as 15%
  (between 14.5 and 17 m s<SUP>-1</SUP>), with the higher average speeds
  being required during the long cycles 20 and 23.

Title: No Trace Left Behind: STEREO Observation of a Coronal Mass
    Ejection Without Low Coronal Signatures
Authors: Robbrecht, Eva; Patsourakos, Spiros; Vourlidas, Angelos
Bibcode: 2009ApJ...701..283R
Altcode: 2009arXiv0905.2583R
  The availability of high-quality synoptic observations of the
  extreme-ultraviolet (EUV) and visible corona during the SOHO mission
  has advanced our understanding of the low corona manifestations of
  coronal mass ejections (CMEs). The EUV imager/white light coronagraph
  connection has been proven so powerful, it is routinely assumed that if
  no EUV signatures are present when a CME is observed by a coronagraph,
  then the event must originate behind the visible limb. This assumption
  carries strong implications for space weather forecasting but has not
  been put to the test. This paper presents the first detailed analysis
  of a frontside, large-scale CME that has no obvious counterparts in
  the low corona as observed in EUV and Hα wavelengths. The event was
  observed by the SECCHI instruments onboard the STEREO mission. The
  COR2A coronagraph observed a slow flux-rope-type CME, while an
  extremely faint partial halo was observed in COR2B. The event evolved
  very slowly and is typical of the streamer-blowout CME class. EUVI A
  171 Å images show a concave feature above the east limb, relatively
  stable for about two days before the eruption, when it rises into
  the coronagraphic fields and develops into the core of the CME. None
  of the typical low corona signatures of a CME (flaring, EUV dimming,
  filament eruption, waves) were observed in the EUVI B images, which we
  attribute to the unusually large height from which the flux rope lifted
  off. This interpretation is supported by the CME mass measurements
  and estimates of the expected EUV dimming intensity. Only thanks to
  the availability of the two viewpoints we were able to identify the
  likely source region. The event originated along a neutral line over
  the quiet-Sun. No active regions were present anywhere on the visible
  (from STEREO B) face of the disk. Leaving no trace behind on the solar
  disk, this observation shows unambiguously that a CME eruption does
  not need to have clear on-disk signatures. Also it sheds light on the
  question of "mystery" geomagnetic storms, storms without clear solar
  origin (formerly called problem storms). We discuss the implications
  for space weather monitoring. Preliminary inspection of STEREO data
  indicates that events like this are not uncommon, particularly during
  the ongoing period of deep solar minimum.

Title: No trace left behind: STEREO Observation of a Coronal Mass
    Ejection Lacking Low Coronal Signatures
Authors: Vourlidas, Angelos; Robbrecht, E.; Patsourakos, S.
Bibcode: 2009SPD....40.2104V
Altcode:
  The availability of high quality synoptic observations of the EUV and
  visible corona during the SOHO mission has advanced our understanding
  of the low corona manifestations of CMEs. The EUV imager/White light
  coronagraph connection has been proven so powerful, it is routinely
  assumed that if no EUV signatures are present when a CME is observed
  by a coronagraph, then the event must originate behind the visible
  limb. This assumption carries strong implications for space weather
  forecasting but has not been put to the test. This paper presents the
  first detailed analysis of a frontside, large-scale CME that has no
  obvious counterparts in the low corona. The event was observed by the
  SECCHI instruments on the STEREO mission. The COR2A coronagraph observed
  the event as a typical flux-rope type CME, while an extremely faint
  partial halo was observed in COR2B. The event evolved very slowly and
  is typical of the streamer-blowout CME class. EUVI-A 171A images show
  a concave feature above the east limb, relatively stable for about
  two days before the eruption, when it rises into the coronagraphic
  fields and develops into the core of the CME. None of the typical low
  corona signatures of a CME (flaring, EUV dimming, filament eruption,
  waves) were observed. Thanks to the two STEREO viewpoints we were able
  to identify the likely source region. The event originated along a
  quiet sun neutral line. No active regions were present anywhere on the
  visible face of the disk. Leaving no trace behind, this observation
  shows unambiguously that a CME eruption does not need to have clear
  on-disk signatures. Also it sheds light on the question of `mystery'
  geomagnetic storms; storms without clear solar origin. Preliminary
  inspection of STEREO data indicates that events like this are not
  uncommon, particularly during the ongoing period of deep solar minimum.

Title: Automated LASCO CME Catalog for Solar Cycle 23: Are CMEs
    Scale Invariant?
Authors: Robbrecht, E.; Berghmans, D.; Van der Linden, R. A. M.
Bibcode: 2009ApJ...691.1222R
Altcode: 2008arXiv0810.1252R
  In this paper, we present the first automatically constructed LASCO
  coronal mass ejection (CME) catalog, a result of the application of
  the Computer Aided CME Tracking software (CACTus) on the LASCO archive
  during the interval 1997 September-2007 January. We have studied the CME
  characteristics and have compared them with similar results obtained
  by manual detection (CDAW CME catalog). On average, CACTus detects
  less than two events per day during solar minimum, up to eight events
  during maximum, nearly half of them being narrow (&lt;20°). Assuming
  a correction factor, we find that the CACTus CME rate is surprisingly
  consistent with CME rates found during the past 30 years. The CACTus
  statistics show that small-scale outflow is ubiquitously observed in the
  outer corona. The majority of CACTus-only events are narrow transients
  related to previous CME activity or to intensity variations in the slow
  solar wind, reflecting its turbulent nature. A significant fraction
  (about 15%) of CACTus-only events were identified as independent
  events, thus not related to other CME activity. The CACTus CME width
  distribution is essentially scale invariant in angular span over a
  range of scales from 20° to 120° while previous catalogs present a
  broad maximum around 30°. The possibility that the size of coronal
  mass outflows follow a power-law distribution could indicate that
  no typical CME size exists, i.e., that the narrow transients are not
  different from the larger well defined CMEs.

Title: First STEREO observation of a quiet sun CME
Authors: Robbrecht, E.; Patsourakos, S.; Vourlidas, A.
Bibcode: 2008AGUFMSH13B1560R
Altcode:
  Streamer-blowouts form a particular class of CMEs characterized by a
  slow rise and swelling of the streamer that can last for days. While
  they are more massive than the average CME, their slow development
  complicates their association with features/activity in the low
  corona and hampers studies on their initiation mechanism(s). This
  paper reports on the first observation from 2 viewpoints of a streamer
  blowout CME. The event was observed by the SECCHI/COR2 A instrument
  as a typical flux-rope type CME, while a very faint partial halo was
  observed in COR2-B. The CME erupted from the east limb in the COR2 A
  field of view. EUVI-171 A images show a bright feature above the limb,
  traveling from the southern hemisphere towards the equator after which
  it slowly rises into the coronagraphic fields of view developing into
  the flux-rope structure CME. At the time of eruption the separation
  between the two STEREO spacecraft is sufficiently large (54 deg) to
  observe the source region face-on in STEREO-B. However, inspection of
  EUVI B data didn't reveal any particular source region, other than the
  quiet sun. No flaring activity could be related to the eruption. This
  observation shows unambiguously that a CME eruption does not necessarily
  have clear on-disk signature. Also it sheds light on the long-standing
  question of the necessity of having a flare for producing a CME. This
  result supplies strong constraints for CME initiation models. This type
  of observation could not have been achieved without the multi-viewpoint
  observations by STEREO.

Title: Preface: SOHO 20 - Transient events on the Sun and in the
    heliosphere
Authors: Robbrecht, E.; Hochedez, J. -F.; Fleck, B.; Gurman, J.;
   Forsyth, R.
Bibcode: 2008AnGeo..26.2953R
Altcode:
  No abstract at ADS

Title: New techniques for the characterisation of dynamical phenomena
    in solar coronal images
Authors: Robbrecht, E.
Bibcode: 2007PhDT........11R
Altcode:
  During a total solar eclipse, a narrow strip of the Earth's surface
  is shielded completely by the Moon from the disk of the Sun. In this
  strip, the corona appears crown-like around the shade of the Moon. It
  was uncertain until the middle of the 20th century whether the corona
  was a solar phenomenon or if it was related to the Moon or whether
  it represented an artifact produced by the Earth's atmosphere. The
  answer to this question was provided by Grotrian (1939) and Edlèn
  (1942). Based on studies of iron emission lines, they suggested
  that the surface of the Sun is surrounded by a hot tenuous gas
  having a temperature of million degrees Kelvin and thus in a state
  of high ionization. This discovery was a result from spectroscopy,
  a field of research which started in 1666 with Sir Isaac Newton's
  observations of sunlight, dispersed by a prism. <P />It is now clear
  that the hot solar corona is made of a low density plasma, highly
  structured by the magnetic field on length scales ranging from the
  Sun's diameter to the limit of angular resolution (e.g. Démoulin and
  Klein 2000). The need to resolve and study the corona down to such
  scales has determined a vigorous scientific and technological impulse
  toward the development of solar Ultraviolet (UV) and X-ray telescopes
  with high spatial and temporal resolution. With the advent of the
  satellite SOHO (Solar and Heliospheric Observatory, see chapter 1),
  the picture of a quiet corona was definitely sent to the past. EUV
  (Extreme UV) image sequences of the lower solar corona revealed a finely
  structured medium constantly agitated by a wide variety of transients
  (e.g. Harrison 1998). Active regions consisting of large magnetic
  loops with enhanced temperature and density are observed, as well as
  "quiet" areas, coronal holes and numerous structures of different
  scales such as plumes, jets, spicules, X-ray bright points, blinkers,
  all structured by magnetic fields. Launched in 1998, the Transition
  Region And Coronal Explorer (TRACE) was an important step on the
  way to subarcsecond telescopes. It allows a spatial resolution of 1"
  in the EUV and UV bands and, simultaneously, a temporal resolution of
  the order of a few seconds. <P />Coronal physics studies are dominated
  by two major and interlinked problems: coronal heating and solar wind
  acceleration. Above the chromosphere there is a thin transition layer
  in which the temperature suddenly increases and density drops. How
  can the temperature of the solar corona be three orders of magnitude
  higher than the temperature of the photosphere? In order for this
  huge temperature gradient to be stationary, non-thermal energy must
  be transported from below the photosphere towards the chromosphere
  and corona and converted into heat to balance the radiative and
  conductive losses. This puzzle of origin, transport and conversion
  of energy is referred to as the "coronal heating problem". Due to its
  fundamental role in the structuring of the corona, the magnetic field
  is supposed to play an important role in the heating. <P />In this
  dissertation we describe two aspects of solar coronal dynamics: waves
  in coronal loops (Part I) and coronal mass ejections (Part II). We
  investigate the influence of (semi-) automated techniques on solar
  coronal research. This is a timely discussion since the observation
  of solar phenomena is transitioning from manual detection to "Solar
  Image Processing". Our results are mainly based on images from the
  Extreme UV Imaging Telescope (EIT) and the Large Angle and Spectrometric
  Coronagraph (LASCO), two instruments onboard the satellite SOHO (Solar
  and Heliospheric Observatory) of which we recently celebrated its 11th
  anniversary. The high quality of the images together with the long
  timespan created a valuable database for solar physics research. <P
  />Part I reports on the first detection of slow magnetoacoustic waves in
  transequatorial coronal loops observed in high cadence image sequences
  simultaneously produced by EIT and TRACE (Transition Region And Coronal
  Explorer). Ten years of EUV observations made it clear that these
  disturbances are a widespread phenomenon in active region loops. The
  existence of these waves in the corona had been predicted by the theory
  of magnetohydrodynamics (MHD), which we revise briefly. Just like in
  helioseismology, coronal seismology uses observations of oscillations
  to derive physical parameters which are not directly measurable, such
  as the Alfvén speed or the magnetic field strength. The comparison
  with helioseismology does not fully hold in the sense that the dense
  photosphere does not allow any seeing inside. Instead, for the corona
  we do have direct observations, but because of its optical thinness
  these observations leave space for many interpretations. <P />At the
  end of the forties, it was suggested that the corona could be heated
  by the dissipation of acoustic waves (sound waves) driven by the p-mode
  oscillations, generated by turbulence in the convection zone. While they
  travel upwards, these waves form shocks and heat the plasma by viscous
  dissipation. Nowadays, they are believed to be only important for lower
  chromospheric heating. By the time the upper chromosphere is reached,
  the acoustic waves are heavily damped and what rests is reflected by
  the steep temperature and density gradients in the transition zone. As
  such, they cannot deposit enough energy in the corona to sufficiently
  heat it to the observed temperatures. Dissipation of magnetic energy
  by Alfvén waves or directly by the reconnection process in current
  sheets are considered to be more likely to heat the corona. <P />Part
  II addresses the question of detecting coronal mass ejections (CMEs)
  in coronagraphic white light data. The study of CMEs is a rather young
  (≲ 30 years) field of research. Coronal mass ejections are sudden
  expulsions of mass and magnetic field from the solar corona into the
  interplanetary medium. A classical CME carries away some 10^15 g of
  coronal mass and can liberate energies of 10^23-10^25 J. They are often
  observed n association with low coronal activity, such as flares and
  filament eruptions. During the first years of CME observation, it was
  believed that a flare was a necessary condition for CME occurrence. The
  widely accepted picture today is that flares and CMEs are both
  different manifestations of magnetic field restructuring through
  reconnection (flare) and the expulsion of mass (CME). Up till now,
  the SOHO mission has been the best mission for CME studies because of
  the increased resolution, cadence, sensitivity and dynamic range of the
  LASCO instruments, but also because of the large array of ground-based
  instruments (Howard 2006). The complexity of the CME-picture grew
  likewise. The next mission with a coronagraph is the NASA STEREO mission
  (Solar Terrestrial Relations Observatory), launched on 26 Oct. 2006. <P
  />In chapter 4 we test the possibility of automatically detecting
  CMEs in LASCO data. We describe the algorithm CACTus (Computer Aided
  CME Tracking) and test its validity on a short period of 6 days. In
  chapter 5 we present our newly constructed CME catalog based on our
  automated detection scheme. It is the first automatically generated
  catalog which runs over a complete solar cycle (cycle 23). It required
  no human interaction, which implies it is totally objective. It includes
  all transients obeying the observational definition of CME as a "new,
  discrete, bright, white-light feature in the coronagraph field-of-view
  moving radially outward" (Hundhausen et al. 1984). As a result, our
  catalog contains much more events, mostly narrow, than are included
  in the classical CDAW CME catalog (Yashiro et al. 2004) which is
  assembled manually. We discuss the CME rate over the solar cycle and
  present important new statistics on the CACTus CME parameters (size,
  latitude, speed). <P />CME research has gained an increased interest
  due to their strong space weather impact. Space weather is defined
  by the European Space Agency (ESA) 1 as the "conditions on the Sun
  and in the solar wind, magnetosphere, ionosphere and thermosphere
  that can influence the performance and reliability of space-borne
  and ground-based technological systems and can endanger human life
  or health." The significance of space weather lies in its potential
  impact on man-made technologies on Earth and in space, for example, on
  satellites and spacecraft, electricity power grids, pipelines, radio
  and telephone communications and on geophysical exploration. Space
  weather also has implications for manned space flight, both in Earth
  orbit and further out into space. Solar activity is the main source
  of space weather. It is now well established that CMEs are the primary
  cause of geomagnetic storms and that their associated shocks accelerate
  high energetic particles. These particles can directly and indirectly
  influence the operation of spacecraft and affect communication and
  navigation. In order to protect systems and people that might be at
  risk from space weather effects, we need to understand the causes
  of space weather and try to predict its impact on the heliosphere
  as soon as possible. A growing field in this respect is Solar mage
  Processing (SIP). It allows continuous monitoring and interpretation
  of new incoming data. This is not only interesting for space weather
  forecasting, but it is also needed to be able to handle efficiently
  the large data flow which is expected from recently launched and future
  missions. In chapter 6 we revise the current capabilities for automated
  detection of CMEs and related phenomena.

Title: Current and future space weather services and products from
    the SIDC- Brussels
Authors: Lawrence, G.; Kretzschmar, M.; Berghmans, D.; Clete,
   F.; Hochedez, J.; van der Linden, R.; Delouille, V.; Gissot, S.;
   Marque, C.; Nicula, B.; Patoul, J.; Podladchikova, E.; Robbrecht,
   E.; Vanlommel, P.; Dehant, V.
Bibcode: 2006AGUFMSA51A..04L
Altcode:
  The SIDC-Brussels, as WDC for the sunspot index and European RWC of the
  ISES, is the European hub for solar data and forecasts. Its services
  and products, while long established and widely recognised and used,
  are continuously being enhanced and supplemented. We present in
  detail the current status and outline the imminent improvements and
  additions. The Solar Weather Browser (SWB) is a free, downloadable,
  multi-platform visualisation package for real-time browsing of processed
  solar images from a variety of space and ground based sources, combined
  with context information (events, regions IDs, etc.) via a wide choice
  of overlay combinations. The Estimated International Sunspot Number
  (EISN) has been produced and distributed daily since January 2006 by the
  SIDC. Intended to support operational model predictions of ionospheric
  radio propagation, we present some early statistical results. CACTus,
  the operational Computer-Aided CME Tracking algorithm, now freely
  available to the community via the SSW software framework, is being
  tested for its real-time application to the STEREO/SECCHI COR-2 "space
  weather beacon" coronagraph telemetry stream. Also NEMO, a software
  package for the automated detection and morphological analysis of EIT
  waves presently being tested, details the relation between coronal EUV
  wave fronts and dimmings and characterizes their evolution; we present
  sample results of both developments. The Velociraptor software processes
  and interprets movies of the EUV solar corona, an algorithm identifying
  outstanding motions such as loop openings that are associated to
  space weather events. Sample results using EIT and TRACE data will be
  shown. A new flare catalog called B2X is presented, compliled via a
  method to detect automatically, and characterise according to time,
  localization, size, EUV flares belonging to classes B to X anywhere
  on the solar disc and at the limb. In addition we present a summary
  of the full range of products available from SIDC which can be chosen
  in any combination tailored to the individual, or group's needs. All
  products are available via the revamped SIDC website, http://www.sidc.be

Title: A Broad Perspective on Automated CME Tracking: Towards Higher
    Level Space Weather Forecasting
Authors: Robbrecht, Eva; Berghmans, David
Bibcode: 2006GMS...165...33R
Altcode:
  We discuss our current capabilities to deliver the CME parameters
  required for the space weather forecasting process. The ever
  growing importance of space weather has lead to new requirements
  on the timeliness and objectiveness of CME detection. It has become
  indispensable to report the occurrence of Earth-directed CMEs and to
  predict their possible impact on the geospace environment. Early 2005,
  we are on the eve of a new era in space weather forecasting. We point
  out the restricted accuracy on the current forecasts and discuss a
  chance for amelioration. This invokes data-driven models (empirical
  and numerical), triggered by a real-time CME disturbance, simulating
  the propagation and interaction of the ejection with the ambient solar
  wind. We discuss the link between the direct observable parameters
  (like the CME projected speed and angle around the occulter) and the
  required input parameters (like radial speed, direction, …). The only
  way to guarantee the real-time value of the simulations is by employing
  software which autonomously detect CME parameters in a variety of
  data. This paper focusses on the automated CME detection algorithms
  that are currently available. Automated CME tracking is yet in its
  infancy, therefore this `review' will be an outlook on the potential
  of this field rather than looking back on already achieved milestones.

Title: A broad Perspective on Automated CME Tracking: towards higher
    level space weather forecasting
Authors: Robbrecht, E.; Berghmans, D.
Bibcode: 2006GMS...165.....R
Altcode:
  We discuss our current capabilities to deliver the CME parameters
  required for the space weather forecasting process. The ever
  growing importance of space weather has lead to new requirements
  on the timeliness and objectiveness of CME detection. It has become
  indispensable to report the occurrence of Earth-directed CMEs and to
  predict their possible impact on the geospace environment. Early 2005,
  we are on the eve of a new era in space weather forecasting. We point
  out the restricted accuracy on the current forecasts and discuss a
  chance for amelioration. This invokes data-driven models (empirical
  and numerical), triggered by a real-time CME disturbance, simulating
  the propagation and interaction of the ejection with the ambient solar
  wind. We discuss the link between the direct observable parameters
  (like the CME projected speed and angle around the occulter) and the
  required input parameters (like radial speed, direction, ...). The only
  way to guarantee the real-time value of the simulations is by employing
  software which autonomously detect CME parameters in a variety of
  data. This paper focusses on the automated CME detection algorithms
  that are currently available. Automated CME tracking is yet in its
  infancy, therefore this `review' will be an outlook on the potential
  of this field rather than looking back on already achieved milestones.

Title: History of the Sunspot Index: 25 years SIDC
Authors: Berghmans, D.; van der Linden, R. A. M.; Vanlommel, P.;
   Clette, F.; Robbrecht, E.
Bibcode: 2006BGGKP...7..288B
Altcode:
  The sunspot number is the oldest solar activity index. For a long time,
  it was the only index representative of the solar cycle, and many
  studies on the cyclical behavior of the Sun were performed using the
  sunspot number. The Sunspot Index Data Center (SIDC) was founded in
  January 1981 to continue the work of the Swiss Federal Observatory ,
  when this institution decided to stop computing and publishing the
  sunspot number. The SIDC now also provides daily activity reports and
  forecasts of the status of the space environment. This 'space weather'
  activity is part of the International Space Environment Services (ISES,
  a permanent service of the FAGS) that co-ordinates 10 regional warning
  centers (RWC). In this paper we will give an overview of the history
  of the sunspot number, as well as a short overview of the 25-year
  history of the SIDC.

Title: Objective CME detection over the solar cycle: A first attempt
Authors: Robbrecht, E.; Berghmans, D.; van der Linden, R. A. M.
Bibcode: 2006AdSpR..38..475R
Altcode:
  We recently developed a software package to autonomously detect
  coronal mass ejections (CMEs) in image sequences from large angle
  spectrometric coronagraph (LASCO). The detection is not done in the
  original images, instead we detect bright ridges in (time, height) plots
  using a modified version of the Hough transform. Experimental results
  on real-time data have shown that the developed technique can achieve
  excellent results in measuring starting time and principal angle and
  good results for the angular width and velocity measurement compared to
  the CMEs listed in the manually assembled catalog. The real-time output
  of the software can be found online at www.sidc.oma.be/cactus. With
  the present paper, we report on the first large scale application of
  the software to the LASCO archive. In an ongoing work, we have applied
  the software on a first sample of 29 months selected from archive data
  in the period July 1997 to December 2002. The results in this paper
  show that relevant characteristics of CMEs over the solar cycle are
  successfully recovered with the automated procedure. This proves that
  a completely automatically produced CME catalog is within reach.

Title: A Complete LASCO CME-Catalog based on Automated Detection
Authors: Robbrecht, E.; Berghmans, D.; van der Linden, R. A. M.
Bibcode: 2006cosp...36.3564R
Altcode: 2006cosp.meet.3564R
  We present our new CME catalog a result of the large scale application
  of our software CACTus on the LASCO archive We recently improved the
  algorithm and upgraded the test-version of the catalog available online
  at www sidc be cactus The automatic detection of a CME is done in two
  steps and is applied simultaneously on c2 and c3 running difference
  images 1 detection of bright features moving radially outward 2
  clustering detections into CMEs The recent improvements are undertaken
  in the second step of this process Unique for our detection method
  is that we use the condition moving radially outward as part of the
  detection criterion The detection itself is done using the stroboscopic
  method i e in height time slices where height means radial distance
  from the sun An outwardly moving feature appears then as a bright ridge
  extracted by a modified version of the Hough transform Per month the
  output consists of a table containing the CME characteristics and an
  overview map in a angle time -coordinate system that clearly shows all
  detected CMEs As a result of our method we also have for each CME a
  linear speed profile along the angular width of the CME We studied the
  characteristics of the CMEs detected with CACTus over the solar cycle
  and compared them with results obtained from other catalogs This paper
  shows that relevant characteristics of CMEs over the solar cycle are
  successfully recovered with the automated procedure Recent tests prove
  that in general automated procedures detect far more small features
  than human

Title: Solar weather monitoring
Authors: Hochedez, J. -F.; Zhukov, A.; Robbrecht, E.; van der Linden,
   R.; Berghmans, D.; Vanlommel, P.; Theissen, A.; Clette, F.
Bibcode: 2005AnGeo..23.3149H
Altcode:
  Space Weather nowcasting and forecasting require solar observations
  because geoeffective disturbances can arise from three types of solar
  phenomena: coronal mass ejections (CMEs), flares and coronal holes. For
  each, we discuss their definition and review their precursors in terms
  of remote sensing and in-situ observations. The objectives of Space
  Weather require some specific instrumental features, which we list
  using the experience gained from the daily operations of the Solar
  Influences Data analysis Centre (SIDC) at the Royal Observatory of
  Belgium. Nowcasting requires real-time monitoring to assess quickly and
  reliably the severity of any potentially geoeffective solar event. Both
  research and forecasting could incorporate more observations in order
  to feed case studies and data assimilation respectively. Numerical
  models will result in better predictions of geomagnetic storms
  and solar energetic particle (SEP) events. We review the data types
  available to monitor solar activity and interplanetary conditions. They
  come from space missions and ground observatories and range from
  sequences of dopplergrams, magnetograms, white-light, chromospheric,
  coronal, coronagraphic and radio images, to irradiance and in-situ
  time-series. Their role is summarized together with indications about
  current and future solar monitoring instruments.

Title: Solar activity: nowcasting and forecasting at the SIDC
Authors: Berghmans, D.; van der Linden, R. A. M.; Vanlommel, P.;
   Warnant, R.; Zhukov, A.; Robbrecht, E.; Clette, F.; Podladchikova,
   O.; Nicula, B.; Hochedez, J. -F.; Wauters, L.; Willems, S.
Bibcode: 2005AnGeo..23.3115B
Altcode:
  The Solar Influences Data analysis Center (SIDC) is the World Data
  Center for the production and the distribution of the International
  Sunspot Index, coordinating a network of about 80 stations
  worldwide. From this core activity, the SIDC has grown in recent years
  to a European center for nowcasting and forecasting of solar activity
  on all timescales. This paper reviews the services (data, forecasts,
  alerts, software) that the SIDC currently offers to the scientific
  community. The SIDC operates instruments both on the ground and in
  space. The USET telescope in Brussels produces daily white light and
  Hα images. Several members of the SIDC are co-investigators of the
  EIT instrument onboard SOHO and are involved in the development of the
  next generation of Europe's solar weather monitoring capabilities. While
  the SIDC is staffed only during day-time (7 days/week), the monitoring
  service is a 24 h activity thanks to the implementation of autonomous
  software for data handling and analysis and the sending of automated
  alerts. We will give an overview of recently developed techniques for
  visualization and automated analysis of solar images and detection of
  events significant for space weather (e.g. CMEs or EIT waves). As part
  of the involvement of the SIDC in the ESA Pilot Project for Space
  Weather Applications we have developed services dedicated to the
  users of the Global Positioning System (GPS). As a Regional Warning
  Center (RWC) of the International Space Environment Service (ISES),
  the SIDC produces daily forecasts of flaring probability, geomagnetic
  activity and 10.7 cm radio flux. The accuracy of these forecasts will
  be investigated through an in-depth quality analysis.

Title: Entering The Era Of Automated Cme Recognition: A Review Of
    Existing Tools
Authors: Robbrecht, E.; Berghmans, D.
Bibcode: 2005SoPh..228..239R
Altcode:
  We consider the problem of the observational identification of CMEs. The
  ever growing importance of space weather has led to new requirements on
  the timeliness and objectiveness of CME detection. It is not sufficient
  any more to simply detect CMEs, a complete set of characteristics
  (speed, direction, mass, chirality) must be reported as soon as
  possible to estimate its geoeffectiveness. Recent developments in
  (solar) feature recognition greatly improved the ability to address
  these new needs. Progress was achieved in automating the detection of
  CMEs in coronagraphic data. This has led to near-real-time messages
  alerting the space weather community day and night. In attempting to
  generate ever-prompter alerts, we can employ a far broader set of solar
  observations than coronagraphic data alone. At present an extensive
  set of automatic recognition tools exists for a number of CME-related
  phenomena occurring in the lower corona. This paper deals with detection
  techniques for disappearing filaments in Hα images, dimmings, EIT waves
  and erupting prominences in radio data. We believe that incorporating
  all automatically generated alerts into one report per CME can provide
  valuable CME information, especially when no coronagraphic images are
  available. This paper is thus a quest to reach a maximal success rate
  with the help of an integrated system of tools acting on a variety of
  data. Future grid-technology systems will greatly facilitate this.

Title: Automated recognition of coronal mass ejections (CMEs) in
    near-real-time data
Authors: Robbrecht, E.; Berghmans, D.
Bibcode: 2004A&A...425.1097R
Altcode:
  This paper presents a new method and first applications of software that
  we have developed to autonomously detect CMEs in image sequences from
  LASCO (Large Angle Spectrometric Coronagraph). The crux of the software
  is the detection of CMEs as bright ridges in (time, height) maps using
  the Hough transform. The next step employs clustering and morphological
  closing operations to mark out different CMEs. The output is a list of
  events, similar to the classic catalogs, with starting time, principle
  angle, angular width and velocity estimation for each CME. In addition
  we present a new type of CME overview map that clearly shows all
  detected CMEs in a (principal angle, time of occurrence) coordinate
  system. In contrast to catalogs assembled by human operators, these CME
  detections can be done without any human interference on real-time data
  24 h per day (see http://sidc.oma.be/cactus for the real-time output
  with data covering the last 4 days). Therefore the detection is not
  only more immediate, but, more importantly, also more objective. In
  this paper we describe the software and validate its performance by
  comparing its output with the SOHO LASCO CME catalog. Experimental
  results on real-time data show that the developed technique can achieve
  excellent results in measuring starting time and principal angle and
  good results for the angular width and velocity measurement compared to
  the CMEs listed in the catalog. Its overall success rate is presently
  about 94%. The software also reveals CMEs or other features that have
  not been listed in the catalog. Such unreported cases might influence
  CME statistics and they demonstrate that also the present catalogs do
  not have a 100% success rate. This inevitably leads to a discussion
  on the definition of a CME. Prospects for improvement and exploitation
  are discussed.

Title: The expanding space weather services of the SIDC at the Royal
    Observatory of Belgium
Authors: van der Linden, R. A. M.; Berghmans, D.; Vanlommel, P.;
   Robbrecht, E.; Cugnon, P.; Clette, F.; Wauters, L.; Zhukov, A.
Bibcode: 2004cosp...35.2781V
Altcode: 2004cosp.meet.2781V
  Originally founded in 1981 as the World Data Centre for the Sunspot
  Index, the SIDC (Solar Influences Data analysis Centre) shifted to
  a higher gear in 2000, when it became a Regional Warning Centre of
  the ISES (taking over this activity from Meudon). The obvious link
  between space weather and solar activity - a prime research topic of
  the solar physics department of the Royal Observatory of Belgium -
  and the equally obvious relevance of continuous long-term monitoring
  of solar activity have made the SIDC well-placed to embark on this new
  future. Thanks to becoming one of the Service Development Activities in
  the Space Weather Applications Pilot Project recently set up by ESA, the
  SIDC has been able to further improve and expand these activities. In
  this paper we discuss some of the new tools, models and data that have
  been or will be developed to this purpose. It will also be detailed how
  the scientific and operational involvement of the Royal Observatory of
  Belgium in many future space missions oriented towards solar physics
  and solar monitoring will help the SIDC become an independent European
  space weather monitoring and forecasting centre.

Title: Objective CME detection over the solar cycle
Authors: Robbrecht, E.; Berghmans, D.
Bibcode: 2004cosp...35.2702R
Altcode: 2004cosp.meet.2702R
  We have developed a software package for 'Computer Aided CME Tracking'
  (CACTus), that autonomously detects CMEs in image sequences from
  LASCO. The crux of the CACTus software is the detection of CMEs as
  bright ridges in [height, time] maps using the Hough transform. The
  output is a list of events, similar to the classic catalogs,
  with principle angle, angular width and velocity estimation for
  each CME. In contrast to catalogs assembled by human operators,
  these CME detections by software can be faster and possibly also
  more objective, as the detection criterion is written explicitly
  in a program. Especially on the timescale of a solar cycle, it is
  questionnable whether human, visual CME detection is stable, as the
  operator gains experience or personnel is replaced. In this paper we
  overview the latest improvements of CACTUS and validate its performance
  by comparing the CACTus output with the classical, visually assembled
  CME catalogs. Discrepancies between the classical catalogs and the
  CACTUS catalogs are discussed. Such discrepancies highlight not
  only the performance of CACTUS but also the caveats of the classical
  catalogs. Indeed, CACTUS sometimes finds CMEs that are not listed in
  the catalogs or interpreted differently (eg halo CME or not). It is
  important to know these caveats when using the CME catalogs as input for
  statistical CME studies over the solar cycle. The near realtime output
  of the software is available on the web(http://sidc.oma.be/cactus)
  and is updated daily.

Title: Spectroscopic Monitoring of 10 Northern SPB Candidates
Authors: Mathias, P.; Le Contel, J. -M.; Aerts, C.; De Cat, P.;
   van Winckel, H.; Robbrecht, E.; Briquet, M.; Cuypers, J.
Bibcode: 2002ASPC..259..232M
Altcode: 2002rnpp.conf..232M; 2002IAUCo.185..232M
  No abstract at ADS

Title: Slow magnetoacoustic waves in coronal loops: EIT and TRACE
Authors: Robbrecht, E.; Verwichte, E.; Berghmans, D.; Hochedez, J. F.;
   Poedts, S.; Nakariakov, V. M.
Bibcode: 2001A&A...370..591R
Altcode:
  On May 13, 1998 the EIT (Extreme ultraviolet Imaging Telescope) on board
  of SoHO (Solar and Heliospheric Observatory) and TRACE (Transition
  Region And Coronal Explorer) instruments produced simultaneous high
  cadence image sequences of the same active region (AR 8218). TRACE
  achieved a 25 s cadence in the Fe Ix (171 Å) bandpass while EIT
  achieved a 15 s cadence (operating in ``shutterless mode'', SoHO JOP
  80) in the Fe Xii (195 Å) bandpass. These high cadence observations
  in two complementary wavelengths have revealed the existence of weak
  transient disturbances in an extended coronal loop system. These
  propagating disturbances (PDs) seem to be a common phenomenon in
  this part of the active region. The disturbances originate from small
  scale brightenings at the footpoints of the loops and propagate along
  the loops. The projected propagation speeds roughly vary between 65
  and 150 km s<SUP>-1</SUP> for both instruments which is close to and
  below the expected sound speed in the coronal loops. The measured slow
  magnetoacoustic propagation speeds seem to suggest that the transients
  are sound (or slow) wave disturbances. This work differs from previous
  studies in the sense that it is based on a multi-wavelength observation
  of an entire loop bundle at high cadence by two EUV imagers. The
  observation of sound waves along the same path shows that they propagate
  along the same loop, suggesting that loops contain sharp temperature
  gradients and consist of either concentric shells or thin loop threads,
  at different temperatures.

Title: Slow magnetoacoustic waves in coronal loops
Authors: Nakariakov, V. M.; Verwichte, E.; Berghmans, D.; Robbrecht, E.
Bibcode: 2000A&A...362.1151N
Altcode:
  A theoretical model interpreting propagating disturbances of EUV
  emission intensity, recently observed in coronal loops, is constructed
  in terms of slow magnetoacoustic waves. The model is one-dimensional
  and incorporates effects of nonlinearity, dissipation due to finite
  viscosity and thermal conduction, and gravitational stratification of
  plasma in the loop. It has been found that, for the observationally
  detected parameters of the waves, the main factors influencing the
  wave evolution are dissipation and stratification. The upwardly
  propagating waves of observed periods (5-20 min) are found to decay
  significantly in the vicinity of the loop apex, explaining the rarity
  of observational detection of downwardly propagating waves. The model
  provides a theoretical basis for development of MHD seismology of the
  coronal loops.

Title: Slow magnetoacoustic waves in coronal loops: EIT vs TRACE
Authors: Robbrecht, E.; Verwichte, E.; Berghmans, D.; Hochedez, J. F.;
   Poedts, S.
Bibcode: 2000AIPC..537..271R
Altcode: 2000wdss.conf..271R
  On May 13, 1998 the EIT (Extreme-Ultraviolet Imaging Telescope) and
  TRACE (Transition Region And Coronal Explorer) instruments produced
  simultaneous high cadence image sequences of the same active region
  (AR 8218). TRACE achieved a 25 sec cadence in the Fe IX/X (171 Å)
  bandpass while EIT achieved a 15 sec cadence (operating in `shutterless
  mode,' SOHO JOP 80) in the Fe XII (195 Å) bandpass. These high
  cadence observations in two complementary wavelengths have revealed
  the existence of weak transient disturbances in an extended coronal
  loop system. These propagating disturbances (PDs) seem to be a
  common phenomenon in this part of the active region. The disturbances
  originate from small scale brightenings at the footpoints of the loops
  and propagate along the loops. The apparent propagation speeds roughly
  vary between 65 and 150 km s<SUP>-1</SUP> which is close to the expected
  sound speed of the coronal loops. The measured propagation speeds seem
  to suggest that the transients are sound (or slow) wave disturbances. .

Title: Multi-Imager Study of Transients and Propagating Disturbances
    in Active Region Loops (SOHO JOP80 Campaign)
Authors: Berghmans, D.; Clette, F.; Robbrecht, E.; McKenzie, D.
Bibcode: 1999ESASP.448..575B
Altcode: 1999ESPM....9..575B; 1999mfsp.conf..575B
  No abstract at ADS

Title: Slow Magnetoacoustic Waves in Coronal Loops?
Authors: Robbrecht, E.; Berghmans, D.; Nakariakov, V.; Poedts, S.
Bibcode: 1999ESASP.446..575R
Altcode: 1999soho....8..575R
  On May 13, 1998 the EIT and TRACE instruments produced simultaneous
  high cadence image sequences of the same active region (AR 8218). TRACE
  achieved a 25 sec cadence in the 171 deg passband while EIT achieved
  a 15 sec cadence (operating in 'shutterless mode', SOHO JOP 80) in the
  195 deg passband. These high cadence observations in two complementary
  wavelengths have revealed the existence of weak disturbances in an
  extended coronal loop system. The disturbances originate from small
  scale brightenings at the footpoints of the loops and propagate along
  the loops at an apparant speed of the order of 150 km/s which is close
  to the expected sound speed. To conclude whether these propagating
  disturbances should be interpreted as slow magnetoacoustic waves or as
  mass motions ('microflows'), we compare our observational findings with
  theoretical models. Our results suggest that the recent discovery of
  DeForest and Gurman (1998) of slow MHD waves in polar plumes, are in
  fact not typical of polar plumes but occur also in extended coronal
  structures elsewhere.

