Author name code: gary-allen
ADS astronomy entries on 2022-09-14
author:"Gary, G. Allen" 
------------------------------------------------------------------------  

Title: On the Estimation of the SHARP Parameter MEANALP from AIA
    Images Using Deep Neural Networks
Authors: Benson, B.; Pan, W. D.; Prasad, A.; Gary, G. A.; Hu, Q.
Bibcode: 2021SoPh..296..163B
Altcode:
  Space-weather HMI Active Region Patches (SHARPs) data from the
  Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
  Observatory (SDO) provides high cadence data from the full-disk
  photospheric magnetic field. The SHARP's MEANALP (α<SUB>m</SUB>)
  parameter, which characterizes the twist, can provide a measure of
  nonpotentiality of an active region, which can be a condition for
  the occurrence of solar flares. The SDO/Atmospheric Imaging Assembly
  (AIA) captures images at a higher cadence (12 or 24 seconds) than the
  SDO/HMI. Hence, if the α<SUB>m</SUB> can be inferred from the AIA data,
  we can estimate the magnetic field evolution of an active region at a
  higher temporal cadence. Shortly before a flare occurs, we observed
  a change in the α<SUB>m</SUB> in some active regions that produced
  stronger (M- or X-class) flares. Therefore, we study the ability of
  neural networks to estimate the α<SUB>m</SUB> parameter from SDO/AIA
  images. We propose a classification and regression scheme to train
  deep neural networks using AIA filtergrams of active regions with the
  objective to estimate the α<SUB>m</SUB> of active regions outside
  our training set. Our results show a classification accuracy greater
  than 85% within two classes to identify the range of the α<SUB>m</SUB>
  parameter. We also attempt to understand the nature of the solar images
  using variational autoencoders. Thus, this study opens a promising new
  application of neural networks which can be extended to other SHARP
  parameters in the future.

Title: Forecasting Solar Cycle 25 Using Deep Neural Networks
Authors: Benson, B.; Pan, W. D.; Prasad, A.; Gary, G. A.; Hu, Q.
Bibcode: 2020SoPh..295...65B
Altcode: 2020arXiv200512406B
  With recent advances in the field of machine learning, the use of
  deep neural networks for time series forecasting has become more
  prevalent. The quasi-periodic nature of the solar cycle makes it a good
  candidate for applying time series forecasting methods. We employ a
  combination of WaveNet and Long Short-Term Memory neural networks to
  forecast the sunspot number using the years 1749 to 2019 and total
  sunspot area using the years 1874 to 2019 time series data for the
  upcoming Solar Cycle 25. Three other models involving the use of LSTMs
  and 1D ConvNets are also compared with our best model. Our analysis
  shows that the WaveNet and LSTM model is able to better capture the
  overall trend and learn the inherent long and short term dependencies
  in time series data. Using this method we forecast 11 years of monthly
  averaged data for Solar Cycle 25. Our forecasts show that the upcoming
  Solar Cycle 25 will have a maximum sunspot number around 106 ± 19.75
  and maximum total sunspot area around 1771 ± 381.17. This indicates
  that the cycle would be slightly weaker than Solar Cycle 24.

Title: Comparison of Two Coronal Magnetic Field Models to Reconstruct
    a Sigmoidal Solar Active Region with Coronal Loops
Authors: Duan, Aiying; Jiang, Chaowei; Hu, Qiang; Zhang, Huai; Gary,
   G. Allen; Wu, S. T.; Cao, Jinbin
Bibcode: 2017ApJ...842..119D
Altcode: 2017arXiv170600595D
  Magnetic field extrapolation is an important tool to study the
  three-dimensional (3D) solar coronal magnetic field, which is difficult
  to directly measure. Various analytic models and numerical codes exist,
  but their results often drastically differ. Thus, a critical comparison
  of the modeled magnetic field lines with the observed coronal loops is
  strongly required to establish the credibility of the model. Here we
  compare two different non-potential extrapolation codes, a nonlinear
  force-free field code (CESE-MHD-NLFFF) and a non-force-free field
  (NFFF) code, in modeling a solar active region (AR) that has a
  sigmoidal configuration just before a major flare erupted from the
  region. A 2D coronal-loop tracing and fitting method is employed to
  study the 3D misalignment angles between the extrapolated magnetic
  field lines and the EUV loops as imaged by SDO/AIA. It is found that
  the CESE-MHD-NLFFF code with preprocessed magnetogram performs the best,
  outputting a field that matches the coronal loops in the AR core imaged
  in AIA 94 Å with a misalignment angle of ∼10°. This suggests that
  the CESE-MHD-NLFFF code, even without using the information of the
  coronal loops in constraining the magnetic field, performs as good
  as some coronal-loop forward-fitting models. For the loops as imaged
  by AIA 171 Å in the outskirts of the AR, all the codes including the
  potential field give comparable results of the mean misalignment angle
  (∼30°). Thus, further improvement of the codes is needed for a
  better reconstruction of the long loops enveloping the core region.

Title: Determining the 3D Structure of the Corona Using Vertical
    Height Constraints on Observed Active Region Loops
Authors: Gary, G. Allen; Hu, Qiang; Lee, Jong Kwan; Aschwanden,
   Markus J.
Bibcode: 2014SoPh..289.3703G
Altcode: 2014SoPh..tmp...87G
  The corona associated with an active region is structured by
  high-temperature, magnetically dominated closed and open loops. The
  projected 2D geometry of these loops is captured in EUV filtergrams. In
  this study using SDO/AIA 171 Å filtergrams, we expand our previous
  method to derive the 3D structure of these loops, independent of
  heliostereoscopy. We employ an automated loop recognition scheme
  (Occult-2) and fit the extracted loops with 2D cubic Bézier
  splines. Utilizing SDO/HMI magnetograms, we extrapolate the magnetic
  field to obtain simple field models within a rectangular cuboid. Using
  these models, we minimize the misalignment angle with respect to
  Bézier control points to extend the splines to 3D (Gary, Hu, and Lee
  2014). The derived Bézier control points give the 3D structure of
  the fitted loops. We demonstrate the process by deriving the position
  of 3D coronal loops in three active regions (AR 11117, AR 11158, and
  AR 11283). The numerical minimization process converges and produces
  3D curves which are consistent with the height of the loop structures
  when the active region is seen on the limb. From this we conclude that
  the method can be important in both determining estimates of the 3D
  magnetic field structure and determining the best magnetic model among
  competing advanced magnetohydrodynamics or force-free magnetic-field
  computer simulations.

Title: A Small-scale Eruption Leading to a Blowout Macrospicule Jet
    in an On-disk Coronal Hole
Authors: Adams, Mitzi; Sterling, Alphonse C.; Moore, Ronald L.; Gary,
   G. Allen
Bibcode: 2014ApJ...783...11A
Altcode:
  We examine the three-dimensional magnetic structure and dynamics
  of a solar EUV-macrospicule jet that occurred on 2011 February 27
  in an on-disk coronal hole. The observations are from the Solar
  Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) and
  the SDO Helioseismic and Magnetic Imager (HMI). The observations
  reveal that in this event, closed-field-carrying cool absorbing
  plasma, as in an erupting mini-filament, erupted and opened,
  forming a blowout jet. Contrary to some jet models, there was no
  substantial recently emerged, closed, bipolar-magnetic field in the
  base of the jet. Instead, over several hours, flux convergence and
  cancellation at the polarity inversion line inside an evolved arcade
  in the base apparently destabilized the entire arcade, including its
  cool-plasma-carrying core field, to undergo a blowout eruption in the
  manner of many standard-sized, arcade-blowout eruptions that produce
  a flare and coronal mass ejection. Internal reconnection made bright
  "flare" loops over the polarity inversion line inside the blowing-out
  arcade field, and external reconnection of the blowing-out arcade field
  with an ambient open field made longer and dimmer EUV loops on the
  outside of the blowing-out arcade. That the loops made by the external
  reconnection were much larger than the loops made by the internal
  reconnection makes this event a new variety of blowout jet, a variety
  not recognized in previous observations and models of blowout jets.

Title: Erratum: Erratum to: A Rapid, Manual Method to Map Coronal-Loop
    Structures of an Active Region Using Cubic Bézier Curves and Its
    Applications to Misalignment Angle Analysis
Authors: Gary, G. Allen; Hu, Qiang; Lee, Jong Kwan
Bibcode: 2014SoPh..289..867G
Altcode:
  No abstract at ADS

Title: A Rapid, Manual Method to Map Coronal-Loop Structures of an
    Active Region Using Cubic Bézier Curves and Its Applications to
    Misalignment Angle Analysis
Authors: Gary, G. Allen; Hu, Qiang; Lee, Jong Kwan
Bibcode: 2014SoPh..289..847G
Altcode:
  A rapid and flexible manual method is described that maps individual
  coronal loops of a 2D EUV image as Bézier curves using only four points
  per loop. Using the coronal loops as surrogates of magnetic-field
  lines, the mapping results restrict the magnetic-field models
  derived from extrapolations of magnetograms to those admissible and
  inadmissible via a fitness parameter. We outline explicitly how the
  coronal loops can be employed in constraining competing magnetic-field
  models by transforming 2D coronal-loop images into 3D field lines. The
  magnetic-field extrapolations must satisfy not only the lower boundary
  conditions of the vector field (the vector magnetogram) but also
  must have a set of field lines that satisfies the mapped coronal
  loops in the volume, analogous to an upper boundary condition. This
  method uses the minimization of the misalignment angles between the
  magnetic-field model and the best set of 3D field lines that match
  a set of closed coronal loops. The presented method is an important
  tool in determining the fitness of magnetic-field models for the solar
  atmosphere. The magnetic-field structure is crucial in determining
  the overall dynamics of the solar atmosphere.

Title: Coronal Loop Mapping to Infer the Best Magnetic Field Models
    for Active Region Prominences
Authors: Gary, G. Allen; Hu, Qiang; Lee, Jong Kwan
Bibcode: 2014IAUS..300..416G
Altcode:
  This article comments on the results of a new, rapid, and
  flexible manual method to map on-disk individual coronal loops of a
  two-dimensional EUV image into the three-dimensional coronal loops. The
  method by Gary, Hu, and Lee (2013) employs cubic Bézier splines to
  map coronal loops using only four free parameters per loop. A set of 2D
  splines for coronal loops is transformed to the best 3D pseudo-magnetic
  field lines for a particular coronal model. The results restrict the
  magnetic field models derived from extrapolations of magnetograms to
  those admissible and inadmissible via a fitness parameter. This method
  uses the minimization of the misalignment angles between the magnetic
  field model and the best set of 3D field lines that match a set of
  closed coronal loops. We comment on the implication of the fitness
  parameter in connection with the magnetic free energy and comment on
  extensions of our earlier work by considering the issues of employing
  open coronal loops or employing partial coronal loop.

Title: A Small-Scale Filament Eruption Leading to a Blowout
    Macrospicule Jet in an On-Disk Coronal Hole
Authors: Sterling, Alphonse C.; Adams, M.; Moore, R. L.; Tennant,
   A. F.; Gary, G. A.
Bibcode: 2013SPD....44...17S
Altcode:
  We observe an eruptive jet that occurred in an on-disk solar coronal
  hole, using EUV images from the Solar Dynamics Observatory (SDO)
  Atmospheric Imaging Assembly (AIA), supplemented by magnetic data from
  the SDO Helioseismic and Magnetic Imager (HMI). This jet is similar to
  features variously called macrospicules or erupting minifilaments. After
  an initial pre-eruptive phase, a concentration of absorbing, cool
  material in the AIA images moves with a substantially-horizontal motion
  toward a region of open magnetic field, and subsequently jets out along
  that vertical field. Prior to and during the jet's ~20 min lifetime,
  the magnetic flux integrated over the local region shows flux changes
  of &amp;lt 20% of the background flux levels, with a time-averaged
  emergence rate of no more than &lt;3 × 10^15 Mx/s in the neighborhood
  of the jet. Contrary to some jet models, there was no substantial
  recently-emerged bipolar field in the base of the jet. Instead, there
  was an established evolving magnetic arcade that held mini-filament-like
  cool plasma in its core field. We propose that subtle evolution of the
  magnetic flux in and around this arcade destabilized its core field,
  as in some standard-sized arcade blowout eruptions that produce a flare
  and CME following the slow rise of a standard-sized filament in the
  core of the arcade. Closed field carrying the cool plasma erupted into
  the open field and formed the blowout jet, evidently at least partly
  by interchange reconnection with the open field. Internal reconnection
  made compact bright "flare" loops inside the blowing-out arcade, while,
  on the outside, interchange reconnection made longer and dimmer EUV
  "crinkle" loops. That the loops made by the external reconnection were
  considerably larger than the loops made by the internal reconnection
  makes this event a new variety of blowout jet, a variety not recognized
  in previous observations and models of blowout jets.

Title: Beckers Effect in a Fabry-Pérot Imaging Interferometer and
    Its Effects on Magnetic Field Measurements
Authors: Robinson, Brian; Balasubramaniam, K.; Gary, G.
Bibcode: 2012AAS...22020623R
Altcode:
  The Beckers effect and its impact on the optical performance of a
  triple-etalon Fabry-Pérot imaging spectral interferometer, such
  as that intended for use in the Advanced Technology Solar Telescope
  visible tunable filter, are analyzed in terms of its impacts on line
  profiles and spatial resolution. In this multi-etalon design, the
  interferometer is mounted in a telecentric beam. The Beckers effect
  refers to the pupil apodization in this configuration caused by the
  dependence of the spectral transmittance of Fabry-Pérot etalons on the
  angle of incidence of impinging rays. We find that the effect on the
  imaging and spectral performance can be significant even for the high
  F-number intermediate images required for narrowband imaging. We go on
  to explore the impact on Stokes line profiles at 6303Å as well as the
  cross-talk caused by the degraded point spread function, and analyze
  the resultant error in the calculated magnetic fields. We gratefully
  acknowledge the National Science Foundation and the National Solar
  Observatory for their support of this work.

Title: Modeling of Magnetic Non-Potentiality of Active Region using
a 3D Data-Driven Active Region Evolution Model: Seeking Necessary
    and Sufficient Conditions for Solar Eruption
Authors: Wu, S. T.; Falconer, D.; Hu, Q.; Wang, A.; Gary, G. A.
Bibcode: 2012AAS...22020439W
Altcode:
  One of the major interesting problems for space weather forecasting is
  to have the capability of predicting solar eruptive events. To achieve
  this goal, we must investigate the evolution of an Active Region. In
  this presentation, we will present an investigation of the magnetic
  field structures for two productive Active Regions using a data-driven
  3D MHD model: AR 10720 of Jan 15, 2005, where the measured magnetic
  field from Big Bear Solar Observatory (BBSO) digital vector magnetogram
  (DGVM) was used and (ii) AR11117 of October 25, 2010 where the vector
  magnetic field are measured by SDO/HMI. The numerical results include
  the change of magnetic flux, the net electric current, the length
  of magnetic shear of the main neutral line, and the flux normalized
  measure of the field twist. From these results we found the above four
  non-potential magnetic parameters increase and decrease before and after
  solar eruption. In other words, these four parameters are necessary
  conditions for solar eruption. Then we reveal a particular feature:
  “the fragmented neutral line”. This fragmented neutral line could
  be interpreted as the variability of the shear angle (angle between the
  observed and potential horizontal field) along the neutral line. It may
  be an additional condition for eruption. This suggests that the active
  region probability of producing an eruption is not only dependent on
  active region free energy but also on the variability of the shear
  angle which appears to correspond to the fragmented neutral line.

Title: Response to ``Comment on `Resolving the 180° Ambiguity in
Solar Vector Magnetic Field Data: Evaluating the Effects of Noise,
    Spatial Resolution, and Method Assumptions' ''
Authors: Leka, K. D.; Barnes, Graham; Gary, G. Allen; Crouch, A. D.;
   Liu, Y.
Bibcode: 2012SoPh..276..441L
Altcode: 2011arXiv1110.2697L
  We address points recently discussed in Georgoulis (2011, Solar Phys.,
  doi:10.1007/s11207-011-9819-1) in reference to Leka et al. (2009b,
  Solar Phys.260, 83). Most importantly, we find that the results of
  Georgoulis (2011) support a conclusion of Leka et al. (2009b): that
  limited spatial resolution and the presence of unresolved magnetic
  structures can challenge ambiguity-resolution algorithms. Moreover,
  the findings of both Metcalf et al. (2006, Solar Phys.237, 267) and
  Leka et al. (2009b) are confirmed in Georgoulis (2011): a method's
  performance can be diminished when the observed field fails to
  conform to that method's assumptions. The implication of boundaries
  in models of solar magnetic structures is discussed; we confirm that
  the distribution of the field components in the model used in Leka
  et al. (2009b) is closer to what is observed on the Sun than what is
  proposed in Georgoulis (2011). It is also shown that method does matter
  with regards to simulating limited spatial resolution and avoiding an
  inadvertent introduction of bias. Finally, the assignment of categories
  to data-analysis algorithms is revisited; we argue that assignments
  are only useful and elucidating when used appropriately.

Title: Obituary: Einar A. Tandberg-Hanssen (1921-2011)
Authors: Gary, G.; Emslie, A.; Hathaway, David; Moore, Ronald
Bibcode: 2011BAAS...43..032G
Altcode:
  Dr. Einar Andreas Tandberg-Hanssen was born on 6 August 1921,
  in Bergen, Norway, and died on July 22, 2011, in Huntsville, AL,
  USA, due to complications from ALS (Amyotrophic lateral sclerosis,
  often referred to as Lou Gehrig's disease). <P />His parents were
  administrator Birger Tandberg-Hanssen (1883-1951) and secretary Antonie
  "Mona" Meier (1895-1967). <P />He married Erna Rönning (27 October
  1921 - 22 November 1994), a nurse, on 22 June 1951. She was the
  daughter of Captain Einar Rönning (1890-1969) and Borghild Lyshaug
  (1897-1980). <P />Einar and Erna had two daughters, Else Biesman (and
  husband Allen of Rapid City, SD, USA) and Karin Brock (and husband
  Mike of Gulf Shores, AL, USA). At the time of his death Einar had eight
  grandchildren and eight great-grandchildren. <P />Dr. Tandberg-Hanssen
  was an internationally-known member of the solar physics community,
  with over a hundred published scientific papers and several books,
  including Solar Activity (1967), Solar Prominences (1974), The
  Physics of Solar Flares (1988) and The Nature of Solar Prominences
  (1995). <P />Einar grew up in Langesund and Skien, Norway, where he
  took the qualifying exams at Skien High School in 1941. After the war
  he studied natural sciences at the University of Oslo and received his
  undergraduate degree in astronomy in 1950. <P />He worked as a research
  assistant in the Institute of Theoretical Astrophysics at the University
  of Oslo for three intervals in the 1950s, interspersed by fellowships
  at the Institut d'Astrophysique in Paris, Caltech in Pasadena, CA, the
  High Altitude Observatory in Boulder, CO, and the Cavendish Laboratory
  in the UK (at the invitation of British radio-astronomer Sir Martin
  Ryle). He earned a doctorate in astrophysics at the University in
  Oslo in 1960 with a dissertation titled "An Investigation of the
  Temperature Conditions in Prominences with a Special Study of the
  Excitation of Helium." <P />From 1959-61, Tandberg-Hanssen was a
  professor at the University in Oslo. He then traveled back to the High
  Altitude Observatory in Boulder, Colorado, where he was employed until
  1974. He was then employed at the Space Science Laboratory at NASA's
  Marshall Space Flight Center (MSFC) in Huntsville, Alabama. There,
  he was a Senior Research Scientist and later Deputy Director of the
  Laboratory. He served as Lab Director from 1987 until his retirement
  from NASA in 1993. He promptly took a part-time post within the Center
  for Space Plasma and Aeronomic Research at The University of Alabama
  in Huntsville, where he worked until his death. <P />During his tenure
  at NASA, he, along with Dr. Mona Hagyard and Dr. S. T. Wu, built up
  a substantial, internationally-based group of solar physicists at
  MSFC and UA Huntsville. He was a lead investigator on two instruments
  aboard NASA spacecraft: the S-056 X-Ray Event Analyzer on the Skylab
  Apollo Telescope Mount (which provided pioneering, high-time-cadence
  temperature and density information on solar X-ray-emitting regions)
  and the Ultraviolet Spectrometer and Polarimeter on the Solar Maximum
  Mission (which carried out sweeping new studies of EUV emission from
  solar active regions and flares). Dr. Tandberg-Hanssen's books about
  various aspects of solar activity, viz.Solar Activity (Blaisdell, 1967),
  Solar Prominences (Reidel, 1974), The Physics of Solar Flares (with
  A. G. Emslie) (Cambridge, 1988), and The Nature of Solar Prominences
  (Reidel, 1995), have become international standard works within the
  discipline of solar physics. <P />In 1982, Dr. Tandberg-Hanssen
  was elected to membership in the Norwegian Academy of Science
  and Letters. From 1979-82 and 1982-85, respectively, he served as
  vice-president and president of Commission 10 of the International
  Astronomical Union (IAU). He served as president of the Federation of
  Astronomical and Geophysical Data Analysis Services from 1990-1994. He
  has received the NASA Exceptional Service Medal. He was also a long
  time editor of the journal Solar Physics. <P />Dr. Tandberg-Hanssen's
  Solar Physics Memoir paper, entitled Solar Prominences - An Intriguing
  Phenomenon http://www.springerlink.com/content/1166j74k577kv332/
  was published shortly before his death. The article starts with an
  autobiographical account, where the author relates how his several
  study-trips abroad gradually led him to the study of solar physics
  in general, and prominences particularly. <P />Einar's residence
  as a research fellow at the Institut d'Astrophysique in Paris in
  the 1950s laid the foundation for a lifelong interest in France and
  French culture. His great interest in and knowledge of French mediaeval
  churches, as well as the Norwegian stave churches, is reflected in two
  books, Letters to My Daughters (Ivy House Pub. Group, 2004), and The Joy
  of Travel: More Letters to My Daughters (Pentland Press, 2007), which
  serve as a review, tourist guide and history book, shaped in the form of
  letters home to his two daughters, from his many travels in Norway and
  France. <P />Einar was a true gentleman and a true scholar. As evidenced
  by his papers, his books, and his dealings with others, he was always
  seeking not only to expand his own knowledge and understanding, but also
  to find new ways of communicating his remarkable insight to others. He
  is survived by his daughters, Else and Karin, and their families.

Title: Observed Aspects of Reconnection in Solar Eruptions
Authors: Moore, Ronald L.; Sterling, Alphonse C.; Gary, G. Allen;
   Cirtain, Jonathan W.; Falconer, David A.
Bibcode: 2011SSRv..160...73M
Altcode: 2011SSRv..tmp..113M; 2011SSRv..tmp..189M; 2011SSRv..tmp...30M
  The observed magnetic field configuration and signatures of reconnection
  in the large solar magnetic eruptions that make major flares and coronal
  mass ejections and in the much smaller magnetic eruptions that make
  X-ray jets are illustrated with cartoons and representative observed
  eruptions. The main reconnection signatures considered are the imaged
  bright emission from the heated plasma on reconnected field lines. In
  any of these eruptions, large or small, the magnetic field that drives
  the eruption and/or that drives the buildup to the eruption is initially
  a closed bipolar arcade. From the form and configuration of the magnetic
  field in and around the driving arcade and from the development of the
  reconnection signatures in coordination with the eruption, we infer
  that (1) at the onset of reconnection the reconnection current sheet
  is small compared to the driving arcade, and (2) the current sheet can
  grow to the size of the driving arcade only after reconnection starts
  and the unleashed erupting field dynamically forces the current sheet to
  grow much larger, building it up faster than the reconnection can tear
  it down. We conjecture that the fundamental reason the quasi-static
  pre-eruption field is prohibited from having a large current sheet is
  that the magnetic pressure is much greater than the plasma pressure
  in the chromosphere and low corona in eruptive solar magnetic fields.

Title: Modeling of Solar Active Region Using Three-Dimensional
    Time-Dependent Magnetohydrodynamic (MHD) Simulation
Authors: Hu, Qiang; Wang, A.; Gary, G. A.; Wu, S. T.
Bibcode: 2011shin.confE..19H
Altcode:
  A data-driven, self-consistent, and three-dimensional
  magnetohydrodynamic model together with time-dependent boundary
  conditions based on the method of characteristics to accommodate
  the observations on the photosphere are presented. To illustrate
  this model, Active Regions 10720 and 11117 observed by SOHO/MDI and
  SDO/HMI, respectively, are chosen for the analyses. Specific physical
  parameters are derived and shown to characterize the dynamic evolution
  of the active region magnetic field that may play a role leading to
  eruptions. Recent development in coronal loop identification that may
  help in model validation will also be reported.

Title: Optimal Pre-Initial Conditions for Data-Driven MHD Simulations
    of Solar Active Regions
Authors: Hu, Q.; Wang, A.; Wu, S.; Gary, G. A.
Bibcode: 2010AGUFMSH42A..04H
Altcode:
  With the available high-quality photospheric vector magnetic field
  measurements returned by the Solar Dynamics Observatory (SDO), both for
  an active region and also possibly on a global scale, we present our
  approach of non-force-free extrapolation of the solar coronal magnetic
  field from vector magnetograms. In particular, we combine our analysis
  with data-driven MHD simulation of solar active regions that utilizes a
  vector magnetogram as part of the bottom boundary conditions. We also
  derive an approximation for the coronal plasma pressure distribution
  based on the extrapolated non-force-free magnetic field. We provide
  our extrapolated magnetic field and the corresponding plasma pressure
  estimate as initial input to the MHD system. Then several case studies
  with different initial plasma pressure estimates are presented. We
  show that our extrapolation result is a viable and optimal choice in
  terms of agreement with observed photospheric vector magnetogram as
  pre-initial conditions for data-driven self-consistent MHD simulation
  of solar active regions. We further discuss the potential application
  of the combined approach to the dynamic simulation of solar active
  region evolution.

Title: A Combined Approach for Coronal Magnetic Field Modeling
Authors: Hu, Qiang; Wang, A.; Wu, S. T.; Gary, G. A.
Bibcode: 2010AAS...21640523H
Altcode:
  With the expectation of high-quality photospheric vector magnetic
  field measurements to be returned by the Solar Dynamics Observatory,
  both for a finite active region and also possibly on a global scale,
  we present our approach of non-force-free extrapolation of the solar
  coronal magnetic field from vector magnetograms. In particular,
  we combine our analysis with sophisticated MHD simulations of solar
  active regions by providing our extrapolation result as initial input
  to the MHD system. We derive an approximation for the coronal plasma
  pressure based on the extrapolated non-force-free magnetic field. We
  show that our extrapolation result is close to a fully evolved MHD state
  through the self-consistent dynamic simulation. We further discuss the
  potential application of the method to the full-disk vector magnetic
  field measurements to be returned by SDO. QH acknowledges NASA grants
  NNX07AO73G and NNX10AG03G for support.

Title: Non-force-free extrapolation of solar coronal magnetic field
    using vector magnetograms
Authors: Hu, Qiang; Dasgupta, B.; Derosa, M. L.; Büchner, J.; Gary,
   G. A.
Bibcode: 2010JASTP..72..219H
Altcode:
  We report our recent improvement in non-force-free extrapolation
  of coronal magnetic field, using vector magnetograms. Based on the
  principle of minimum (energy) dissipation rate (MDR), a generally
  non-force-free magnetic field solution is expressed as the superposition
  of one potential field and two (constant-[alpha]) linear force-free
  fields, with distinct [alpha] parameters. With a known potential field,
  the system is reduced to a second-order one that can be solved using
  one single-layer vector magnetogram. We devise an iteration procedure
  to determine the potential field, by achieving satisfactory agreement
  between the MDR-model computed and measured transverse magnetic
  field vectors on the bottom boundary. We illustrate this approach by
  applying it to real magnetograph measurement of solar active region
  AR 10953. We show that the results are satisfactory as judged from
  the quantitative magnetic field measurement, and the behavior of the
  derived Lorentz force.

Title: Non-force-free Extrapolation of Coronal Magnetic Field with
    Applications to Vector Magnetograms
Authors: Hu, Q.; Wang, A.; Dasgupta, B.; Gary, G. A.; Wu, S.
Bibcode: 2009AGUFMSH41B1654H
Altcode:
  Motivated by increasingly more advanced solar observations, we recently
  develop a method of non-force-free extrapolation of the solar coronal
  magnetic field from vector magnetograms, especially those for a finite
  active region. Based on a more complex variational principle, the
  principle of minimum (energy) dissipation rate (MDR), we adopt and
  solve a more complex equation governing the coronal magnetic field
  that is non-force-free in general. We describe the theoretical basis
  in the context of general solar atmosphere conditions, and derive
  the extrapolation approach utilizing vector magnetograms as bottom
  boundary conditions. We illustrate the approach using both MHD numerical
  simulation results, and real vector magnetograph measurements of solar
  active regions. We wish to establish the validity of our approach,
  especially by detailed inter-comparison with self-consistent, full MHD
  simulation results, and investigations of the dynamics associated with
  non-vanishing forces.

Title: Minimum Dissipative Processes in Laboratory and Astrophysical
    Plasmas
Authors: Janaki, M. S.; Dasgupta, B.; Hu, Q.; Shaikh, D.; Zank, G. P.;
   Gary, G. A.
Bibcode: 2009AGUFMNG43A1206J
Altcode:
  The usual theory of plasma relaxation, based on selective decay
  of magnetic energy over the (global) magnetic helicity predicts
  a force-free state for a plasma. Such force-free state is often
  unrealistic in nature, an alternative theory of relaxation has been
  proposed by many authors, which is based on a well-known theorem of
  irreversible thermodynamics, principle of minimum entropy production
  rate. This is equivalent to minimum dissipation rate of energy. To
  demonstrate this, we perform self-consistent, time-dependent numerical
  simulations of dissipative plasmas at a higher Landquist number,
  typically ~ O(106-107), using full three dimensional compressible
  MHD code with a numerical resolution of 1283. Our simulations follow
  the time variation of global helicity, magnetic energy, and the
  dissipation rate and show that the global helicity remains approximately
  constant while magnetic energy is decaying faster and dissipation
  rate is decaying even faster than the magnetic energy. Existence of a
  perpendicular component of current is also demonstrated. We describe the
  application of our model to various laboratory plasma devices, like,
  Reversed Field Pinch (RFP) Tokamak, Field Reversed Configurations
  (FRC) and Spheromak. Using a two fluid description, we also show
  that Solar arcade structures can be modeled as a minimum dissipative
  relaxed state, and different types of arcade structures are generated
  with the variation of a single parameter characterizing the relaxed
  state. Finally, we outline a novel approach to non-force free coronal
  magnetic field extrapolation from vector magnetograms.

Title: Resolving the 180° Ambiguity in Solar Vector Magnetic
Field Data: Evaluating the Effects of Noise, Spatial Resolution,
    and Method Assumptions
Authors: Leka, K. D.; Barnes, Graham; Crouch, A. D.; Metcalf, Thomas
   R.; Gary, G. Allen; Jing, Ju; Liu, Y.
Bibcode: 2009SoPh..260...83L
Altcode:
  The objective testing of algorithms for performing ambiguity
  resolution in vector magnetic field data is continued, with an
  examination of the effects of noise in the data. Through the use
  of analytic magnetic field models, two types of noise are "added"
  prior to resolving: noise to simulate Poisson photon noise in the
  observed polarization spectra, and a spatial binning to simulate the
  effects of unresolved structure. The results are compared through
  the use of quantitative metrics and performance maps. We find that
  while no algorithm severely propagates the effects of Poisson noise
  beyond very local influences, some algorithms are more robust against
  high photon-noise levels than others. In the case of limited spatial
  resolution, loss of information regarding fine-scale structure can
  easily result in erroneous solutions. Our tests imply that photon
  noise and limited spatial resolution can act so as to make assumptions
  used in some ambiguity resolution algorithms no longer consistent
  with the observed magnetogram. We confirm a finding of the earlier
  comparison study that results can be very sensitive to the details of
  the treatment of the observed boundary and the assumptions governing
  that treatment. We discuss the implications of these findings, given the
  relative sensitivities of the algorithms to the two sources of noise
  tested here. We also touch on further implications for interpreting
  observational vector magnetic field data for general solar physics
  research.

Title: The "Main Sequence" of Explosive Solar Active Regions:
    Discovery and Interpretation
Authors: Falconer, David A.; Moore, Ronald L.; Gary, G. Allen;
   Adams, Mitzi
Bibcode: 2009ApJ...700L.166F
Altcode:
  We examine the location and distribution of the production of coronal
  mass ejections (CMEs) and major flares by sunspot active regions
  in the phase space of two whole-active-region magnetic quantities
  measured from 1897 SOHO/MDI magnetograms. These magnetograms track the
  evolution of 44 active regions across the central disk of radius 0.5
  R <SUB>Sun</SUB>. The two quantities are <SUP>L</SUP>WL<SUB>SG</SUB>,
  a gauge of the total free energy in an active region's magnetic field,
  and <SUP>L</SUP>Φ, a measure of the active region's total magnetic
  flux. From these data and each active region's history of production
  of CMEs, X flares, and M flares, we find (1) that CME/flare-productive
  active regions are concentrated in a straight-line "main sequence"
  in (log <SUP>L</SUP>WL<SUB>SG</SUB>, log <SUP>L</SUP>Φ) space, (2)
  that main-sequence active regions have nearly their maximum attainable
  free magnetic energy, and (3) evidence that this arrangement plausibly
  results from equilibrium between input of free energy to an explosive
  active region's magnetic field in the chromosphere and corona by
  contortion of the field via convection in and below the photosphere
  and loss of free energy via CMEs, flares, and coronal heating, an
  equilibrium between energy gain and loss that is analogous to that of
  the main sequence of hydrogen-burning stars in (mass, luminosity) space.

Title: Evaluation of a Selected Case of the Minimum Dissipative Rate
    Method for Non-Force-Free Solar Magnetic Field Extrapolations
Authors: Gary, G. Allen
Bibcode: 2009SoPh..257..271G
Altcode:
  The minimum dissipative rate (MDR) method for deriving a coronal
  non-force-free magnetic field solution is partially evaluated. These
  magnetic field solutions employ a combination of three linear
  (constant-α) force-free-field solutions with one being a potential
  field (i.e., α=0). The particular case of the solutions where the other
  two α's are of equal magnitude but of opposite sign is examined. This
  is motivated by studying the SOLIS (Synoptic Optical Long-term
  Investigation of the Sun (SOLIS), a National Solar Observatory facility)
  vector magnetograms of AR 10987, which show a global α value consistent
  with an α=0 value as evaluated by (∇×B)<SUB>z</SUB>/B<SUB>z</SUB>
  over the region. Typical of the current state of the observing
  technology, there is no definitive twist for input into the general MDR
  method. This suggests that the special α case, of two α's with equal
  magnitudes and opposite signs, is appropriate given the data. Only
  for an extensively twisted active region does a dominant, nonzero α
  normally emerge from a distribution of local values. For a special set
  of conditions, is it found that (i) the resulting magnetic field is a
  vertically inflated magnetic field resulting from the electric currents
  being parallel to the photosphere, similar to the results of Gary and
  Alexander (Solar Phys. 186:123, 1999), and (ii) for α≈(α<SUB>max
  </SUB>/2), the Lorentz force per unit volume normalized by the square
  of the magnetic field is on the order of 1.4×10<SUP>−10</SUP>
  cm<SUP>−1</SUP>. The Lorentz force (F<SUB>L</SUB>) is a factor of
  ten higher than that of the magnetic force d(B<SUP>2</SUP>/8π)/dz,
  a component of F<SUB>L</SUB>. The calculated photospheric electric
  current densities are an order of magnitude smaller than the maximum
  observed in all active regions. Hence both the Lorentz force density and
  the generated electric current density seem to be physically consistent
  with possible solar dynamics. The results imply that the field could
  be inflated with an overpressure along the neutral line. However,
  the implementation of this or any other extrapolation method using
  the electric current density as a lower boundary condition must be
  done cautiously, with the current magnetography.

Title: Analyses of magnetic field structures for active region 10720
    using a data-driven 3D MHD model
Authors: Wu, S. T.; Wang, A. H.; Gary, G. Allen; Kucera, Ales; Rybak,
   Jan; Liu, Yang; Vrśnak, Bojan; Yurchyshyn, Vasyl
Bibcode: 2009AdSpR..44...46W
Altcode:
  In order to understand solar eruptive events (flares and CMEs) we
  need to investigate the changes at the solar surface. Thus, we use
  a data-driven, three-dimensional magnetohydrodynamic (MHD) model to
  analyze a flare and coronal mass ejection productive active region,
  AR 10720 on January 15, 2005. The measured magnetic field from Big
  Bear Solar Observatory (BBSO) digital vector magnetograph (DGVM) was
  used to model the non-potential coronal magnetic field changes and the
  evolution of electric current before and after the event occurred. The
  numerical results include the change of magnetic flux ( Φ), the net
  electric current ( I<SUB>N</SUB>), the length of magnetic shear of the
  main neutral line ( L<SUB>ss</SUB>), the flux normalized measure of
  the field twist (α={μI<SUB>N</SUB>}/{Φ}) with μ being the magnetic
  permeability. The current helicity ( H<SUB>c</SUB>) injected into the
  corona and the photospheric surface velocity are also computed. The
  characteristic parameters of the buildup process before the event and
  the decay process after the event are investigated and the amount of
  magnetic energy converted to drive the event is estimated.

Title: The "Main Sequence” of Explosive Solar Active Regions:
    Discovery and Interpretation
Authors: Falconer, David; Moore, R. L.; Gary, G. A.; Adams, M.
Bibcode: 2009SPD....40.1925F
Altcode:
  We examine the location and distribution of the production of coronal
  mass ejections (CMEs) and major flares by sunspot active regions in
  the phase space of two whole-active-region magnetic quantities measured
  from 1865 SOHO/MDI magnetograms. These magnetograms track the evolution
  of 44 full-grown active regions across the central disk of radius 0.5
  R<SUB>Sun</SUB>. The two quantities are <SUP>L</SUP>WL<SUB>SG</SUB>,
  a gauge of the total free energy in an active region's magnetic
  field above the photosphere, and <SUP>L</SUP>Φ, a measure of the
  active region's total magnetic flux. We compiled each active region's
  production of CMEs, X flares, and M flares during its rotation across
  the disk. In addition, at the time of each magnetogram, we evaluated
  from the NOAA Catalog of Active Region Flares a flare-power measure, the
  active region's 48-hour average power output in 1-8 Å radiation from
  X and M flares. From these data, we find that (1) CME/flare-productive
  active regions are concentrated in a straight-line "main sequence” in
  (Log <SUP>L</SUP>WL<SUB>SG</SUB>, Log <SUP>L</SUP>Φ) space, (2) this
  line is close behind a front of maximum attainable magnetic twist, and
  (3) the average flare-power measure increases sharply across this line
  as the leading front is approached. These results suggest that the main
  sequence of explosive active regions is the consequence of equilibrium
  between input of free energy by contortion of the field via convection
  in and below the photosphere and loss of free energy via CMEs, flares,
  and coronal heating, an equilibrium between energy gain and loss
  that is analogous to that of the main sequence of hydrogen-burning
  stars in Mass-Luminosity space. <P />This work was funded by NASA's
  LWS TR&amp;T Program, NSF's SHINE Program, AFOSR's MURI Program,
  and NASA's Technical Excellence Initiative Program.

Title: Future possibilities for doppler and magnetic field
measurements in the extended solar atmosphere: Dissecting the
    transition region
Authors: Gary, G. Allen; Davis, John M.; West, Edward A.
Bibcode: 2009AdSpR..43...96G
Altcode:
  For the first time, a vacuum ultraviolet (VUV) telescope can be built
  to rapidly observe the magnetic fields, plasma flows, and heating
  events in the Sun’s atmosphere. These observations can provide key
  data for space weather models. The vacuum ultraviolet region allows
  remote sensing of the upper levels of the solar atmosphere where the
  magnetic field dominates the physics. A VUV Fabry-Pérot interferometer
  (FPI) will allow us to observe the magnetic field, flows, and heating
  events in the mid-transition region (between the chromosphere and
  corona). Observations of this region are needed to directly probe the
  magnetic structure and activity at the base of the corona where the
  magnetic field is approximately force-free, i.e., where gas pressures
  are very small. This is a key element in developing accurate models of
  the Sun’s dynamics for space weather. The specific region of interest
  is the 100 km thick transition region, between the chromosphere and
  the much hotter corona, which strongly emits at 155 nm from triply
  ionized carbon (C<SUP>3+</SUP>) at 100,000 K. This is best observed
  by an imaging interferometer that combines the best attributes of
  a spectrograph and an imager. We present the latest results from the
  NASA Marshall Space Flight Center (MSFC) FPI. The major elements of the
  tunable CIV VUV FPI are the 35 mm MgF<SUB>2</SUB> etalon plates with a
  plate finesse of F&gt;25 at 155 nm, the π-dielectric coatings, a Hansen
  mechanical mount in a pressurize canister, and the piezoelectric control
  system. The control system for the etalon is a capacitance-stabilized
  Hovemere Ltd. standard system. The special Cascade Optical Corporation
  reflectance coatings are 25 pi-multilayers of high low refractive layers
  paired in phase. This CIV interferometer, when flown above Earth’s
  atmosphere, will obtain narrow-passband images, magnetograms, and
  Dopplergrams of the transition region in the CIV 155 nm line at a rapid
  cadence. We recently measured the MSFC VUV FPI using the University
  of Toronto’s fluoride excimer laser as a proxy for CIV 155 nm. The
  test demonstrated the first tunable interferometer with the passband
  required for a VUV filter magnetograph. The measured values have a
  full-width half-maximum (FWHM) passband of 10 pm, a free-spectral range
  (FSR) of 61 pm, and a transmittance of 58% at 157 nm. The resulting VUV
  interferometer finesse is 5.9. With this success, we are developing an
  instrument suitable for a flight on an orbiting solar observatory. A
  description of the interferometer for this mission is described.

Title: Magnetogram Measures of Total Nonpotentiality for Prediction
    of Solar Coronal Mass Ejections from Active Regions of Any Degree
    of Magnetic Complexity
Authors: Falconer, D. A.; Moore, R. L.; Gary, G. A.
Bibcode: 2008ApJ...689.1433F
Altcode:
  For investigating the magnetic causes of coronal mass ejections
  (CMEs) and for forecasting the CME productivity of active regions,
  in previous work we have gauged the total nonpotentiality of a
  whole active region by either of two measures, L<SUB>SSM</SUB>
  and L<SUB>SGM</SUB>, two measures of the magnetic field along the
  main neutral line in a vector magnetogram of the active region. This
  previous work was therefore restricted to nominally bipolar active
  regions, active regions that have a clearly identifiable main neutral
  line. In the present paper, we show that our work can be extended
  to include multipolar active regions of any degree of magnetic
  complexity by replacing L<SUB>SSM</SUB> and L<SUB>SGM</SUB> with their
  generalized counterparts, WL<SUB>SS</SUB> and WL<SUB>SG</SUB>, which
  are corresponding integral measures covering all neutral lines in an
  active region instead of only the main neutral line. In addition, we
  show that for active regions within 30 heliocentric degrees of disk
  center, WL<SUB>SG</SUB> can be adequately measured from line-of-sight
  magnetograms instead of vector magnetograms. This approximate measure
  of active-region total nonpotentiality,<SUP>L</SUP>WL<SUB>SG</SUB>,
  with the extensive set of 96 minute cadence full-disk line-of-sight
  magnetograms from SOHO MDI, can be used to study the evolution of
  active-region total nonpotentiality leading to the production of CMEs.

Title: Analyses of Hinode Magnetic Field Observations Using a 3D
    MHD Model
Authors: Gary, G. A.; Wu, S. T.; Wang, A. H.
Bibcode: 2008ASPC..397..167G
Altcode:
  A data-driven 3D MHD model (Wu et al. 2006) is used to investigate
  the sources of solar eruptive events. As an example, the Hinode data
  on 12 December 2006 (AR 10930) have been used to deduce the physical
  parameters before and after the observed flare. These parameters
  including the main length of strong magnetic shear and strong transverse
  field L_{ss} and current helicity. The 3D magnetic field lines are
  drawn and show the field topology before the flare. These are very
  preliminary results, and further study is needed for correlation
  between an active region configuration and an eruptive phenomenon.

Title: Anatomy of the Solar Ultraviolet Magnetograph Investigation
    Sounding Rocket
Authors: Abunaemeh, M. A.; Cirtain, J.; Kobayashi, K.; Winebarger,
   A. R.; West, E. A.; Davis, J. M.; Gary, G. A.
Bibcode: 2008AGUSMSP51B..01A
Altcode:
  A major focus of solar physics is to understand how the solar magnetic
  field stores and releases the energy that drives the dynamic phenomena
  of the outer atmosphere, namely flares and coronal mass ejections
  (CMEs). A crucial element in our current knowledge is how the field
  evolves as it changes from being pressure-dominated in the photosphere
  to being force-free in the corona. There have been ways to study
  the evolution indirectly by extrapolation or through morphology,
  but direct and quantitative measurements of magnetic field strength
  in the force-free corona is difficult and few attempts have ever been
  made. The Solar Ultraviolet Magnetograph Investigation (SUMI) sounding
  rocket has been developed by NASA Marshall Space and Flight Center
  (MSFC)and National Space and Science Center (NSSTC) to measure the
  linear and circular polarization of magnetically sensitive 280nm Mg
  II line and also to measure the circular polarization of the 155nm C
  IV emission lines originating in this force-free region. SUMI uses a
  Ritchey-Chretien telescope design with dielectric coating applied to the
  front surfaces of both telescope mirrors for the purpose of decreasing
  the thermal load. The out-of-band radiation is transmitted and then
  reflected out of the telescope. The polarimeter consists of a MgF2
  rotatable waveplate and a double Wollaston polarizing beamsplitter. The
  waveplate is designed to measure the circular polarization at C IV
  (270° retardance at 155nm) and a full Stokes vector at Mg II (131°
  retardance at 280nm). SUMI measures both orthogonal polarizations in
  both C IV and Mg II simultaneously. Two toroidal varied-line-spacing
  (TVLS) grating are used, one for each polarization. There are two
  Mg II cameras, one for each polarization, and one C IV camera that
  captures both polarizations. All cameras use back- illuminated CCDs
  with measured quantum efficiency of more than 60%. SUMI is in the last
  stage of alignment and system testing and is expected to be launched
  in summer 2008. This SUMI result will be an essential complement to
  visible-light magnetographs for understanding how magnetic energy
  stored in a sheared field region is released in flares and CMEs. We
  will be describing the anatomy of the SUMI sounding rocket and the
  detector test and calibration program and the NASA/MFSC and NSSTC
  facilities where the instrument is being developed.

Title: The "Main Sequence" of Explosive Solar Active Regions:
    Discovery and Interpretation
Authors: Falconer, D.; Moore, R.; Gary, G. A.
Bibcode: 2008AGUSMSP24A..07F
Altcode:
  From ~ 2000 MDI magnetograms of 44 evolving active regions within
  30 heliocentric degrees of disk center, we measured active-region
  magnetic size and total nonpotentiality. Besides displaying the upper
  limit on active- region size above which the sun rarely produces
  active regions and the lower limit on active-region size below which
  a magnetic flux concentration is not an active region, we discovered
  that active-region total nonpotentiality has an upper bound that
  increases with active-region magnetic size. For a given size, an active
  region can have only so much total nonpotentiality. We show that this
  limit amounts to an upper bound on a particular measure of an active
  region's nonpotentiality per unit flux, that is, an upper bound on a
  flux-normalized measure of an active region's nonpotentiality. This
  limit plausibly represents an upper bound on the overall degree of
  twist in an active region's magnetic field. If so, an active region's
  magnetic twist can increase to this limit but go no further. After being
  near the limit for a while the active region can loose nonpotentiality
  and retreat from the limit. Albeit entirely different physics, this
  evolution is analogous to how stars evolve to the main sequence,
  stay there a while and then evolve away from it. Unlike the stellar
  evolution path, an active region can evolve to its limit multiple
  times. We present evidence that what is enforcing this upper limit on
  flux-normalized nonpotentiality is that as an active region's magnetic
  field becomes more twisted, it more rapidly releases energy in the form
  of flares and CMEs. When an active region's energy-burn-down rate by
  flares and CMEs equals the rate of buildup of its nonpotential energy,
  it can get no more nonpotential. The upper limit on flux- normalized
  nonpotentiality is determined by the burn-down rate dependence on the
  flux-normalized nonpotentiality and an upper limit on how rapidly an
  active region's nonpotentiality can buildup. This work is funded by
  the NASA LWS TR&amp;T Program, by the NSF SHINE Program, by the AFOSR
  MURI Program, and by the NASA Technical Excellence Initiative.

Title: Comparison of Five Numerical Codes for Automated Tracing of
    Coronal Loops
Authors: Aschwanden, Markus J.; Lee, Jong Kwan; Gary, G. Allen; Smith,
   Michael; Inhester, Bernd
Bibcode: 2008SoPh..248..359A
Altcode:
  The three-dimensional (3D) modeling of coronal loops and filaments
  requires algorithms that automatically trace curvilinear features in
  solar EUV or soft X-ray images. We compare five existing algorithms
  that have been developed and customized to trace curvilinear features
  in solar images: i) the oriented-connectivity method (OCM), which is
  an extension of the Strous pixel-labeling algorithm (developed by Lee,
  Newman, and Gary); ii) the dynamic aperture-based loop-segmentation
  method (developed by Lee, Newman, and Gary); iii) unbiased detection of
  curvilinear structures (developed by Steger, Raghupathy, and Smith); iv)
  the oriented-direction method (developed by Aschwanden); and v) ridge
  detection by automated scaling (developed by Inhester). We test the
  five existing numerical codes with a TRACE image that shows a bipolar
  active region and contains over 100 discernable loops. We evaluate the
  performance of the five codes by comparing the cumulative distribution
  of loop lengths, the median and maximum loop length, the completeness
  or detection efficiency, the accuracy, and flux sensitivity. These
  algorithms are useful for the reconstruction of the 3D geometry of
  coronal loops from stereoscopic observations with the STEREO spacecraft,
  or for quantitative comparisons of observed EUV loop geometries with
  (nonlinear force-free) magnetic field extrapolation models.

Title: Future Possibilities for Doppler and Magnetic Field
    Measurements in the Extended Solar Atmosphere
Authors: Gary, Gilmer Allen; Davis, John M.; West, Edward A.; Gary,
   Gilmer Allen
Bibcode: 2008cosp...37..978G
Altcode: 2008cosp.meet..978G
  For the first time, a vacuum ultraviolet telescope can be built to
  observe magnetic fields, plasma flows, and heating events in the Sun's
  atmosphere. These observations can provide key data for space weather
  models. The vacuum ultraviolet (VUV) region allows remote sensing of
  the upper levels of the solar atmosphere where the magnetic field
  dominates the physics. A VUV Fabry- Perot interferometer (FPI)
  will allow us to observe the magnetic field, flows, and heating
  events in the mid-transition region (between the chromosphere and
  corona). Observations of this region are needed to directly probe the
  magnetic structure and activity at the base of the corona where the
  magnetic field is approximately force-free, i.e., where gas pressures
  are very small. This is a key element in developing accurate models of
  the Sun's dynamics for space weather. The specific region of interest
  is the 100km-thick transition region, between the chromosphere and
  the much hotter corona. This region radiates strongly at 155 nm from
  the triply ionized carbon (CIV) lines formed at 100,000 K. The region
  is best studied using an imaging interferometer that combines the
  best attributes of a spectrograph and an imager. The major elements
  of the NASA Marshall Space Flight Center (MSFC) tunable CIV VUV FP
  interferometer are the 35mm magnesium fluoride etalon plates with
  a plate finesse of F greater than 25 at 155 nm, the pi-dielectric
  coatings, a Hansen mechanical mount in a pressurize canister, and the
  piezoelectric control system. The control system for the etalon is
  a capacitance-stabilized Hovemere Ltd. standard system. The special
  Cascade Optical Corporation reflectance coatings are 25 pimultilayers
  of high-low refractive layers paired in phase. We recently measured
  the MSFC VUV FPI using the University of Toronto's fluoride excimer
  laser as a proxy for the CIV 155nm line. The test demonstrated that
  the tunable interferometer possessed the passband required for a VUV
  filter magnetograph. The measured values have a full-width half-maximum
  (FWHM) passband of 10pm, a free-spectral range (FSR) of 61 pm, and a
  transmittance of 58 percent at 157 nm. The resulting VUV interferometer
  finesse is 5.9. With this successful demonstration, we have proposed a
  Small Explorer mission that will obtain rapid cadence, narrow-passband
  images, magnetograms, and Dopplergrams of the transition region in the
  CIV 155 nm line. The observations will be used to conduct studies of the
  evolution of the solar magnetic field from non-force free conditions
  in the photosphere to nearly force free conditions in the transition
  region and its role in coronal heating and solar flares.

Title: Evolution strategies optimization of the multiple Fabry-Perót
    imaging interferometer for the advanced technology solar telescope
Authors: Robinson, Brian; Gary, G. Allen; Balasubramaniam, K. S.
Bibcode: 2008OptEn..47j3002R
Altcode:
  No abstract at ADS

Title: Solar confocal interferometers for sub-picometer-resolution
    spectral filters
Authors: Gary, G. A.; Pietraszewski, C.; West, E. A.; Dines, T. C.
Bibcode: 2007A&A...467..375G
Altcode:
  Aims:The confocal Fabry-Pérot interferometer allows sub-picometer
  spectral resolution of Fraunhofer line profiles. Such high spectral
  resolution is needed to keep pace with the higher spatial resolution
  of the new set of large-aperture solar telescopes. The line-of-sight
  spatial resolution derived for line profile inversions would then track
  the improvements of the transverse spatial scale provided by the larger
  apertures. In particular, profile inversion allows improved velocity
  and magnetic field gradients to be determined independent of multiple
  line analysis using different energy levels and ions. The confocal
  interferometer's unique properties allow a simultaneous increase
  in both étendue and spectral power. The higher throughput for the
  interferometer provides significant decrease in the aperture, which
  is important in spaceflight considerations. <BR />Methods: We have
  constructed and tested two confocal interferometers. A slow-response
  thermal-controlled interferometer provides a stable system for
  laboratory investigation, while a piezoelectric interferometer provides
  a rapid response for solar observations. <BR />Results: In this paper
  we provide design parameters, show construction details, and report
  on the laboratory test for these interferometers. The field of view
  versus aperture for confocal interferometers is compared with other
  types of spectral imaging filters. We propose a multiple etalon system
  for observing with these units using existing planar interferometers
  as pre-filters. The radiometry for these tests established that high
  spectral resolution profiles can be obtained with imaging confocal
  interferometers. These sub-picometer spectral data of the photosphere
  in both the visible and near-infrared can provide important height
  variation information. However, at the diffraction-limited spatial
  resolution of the telescope, the spectral data is photon starved due
  to the decreased spectral passband.

Title: Forecasting coronal mass ejections from line-of-sight
    magnetograms
Authors: Falconer, D. A.; Moore, R. L.; Gary, G. A.
Bibcode: 2007JASTP..69...86F
Altcode: 2007JATP...69...86F
  We show that the length of strong-gradient, strong-field main neutral
  line, L<SUB>SGM</SUB>, which can be measured from line-of-sight
  magnetograms such as from SOHO/MDI, is both a measure of active-region
  nonpotentiality and a useful predictor of an active region's future
  Coronal mass ejections (CME) productivity. To demonstrate that
  L<SUB>SGM</SUB> is a nonpotentiality measure, we show that it is
  strongly correlated with a direct measure of nonpotentiality. For an
  appropriate choice of a threshold value, an active region's measured
  L<SUB>SGM</SUB> can be used as a predictor of whether the active
  region will produce a CME within a few days after the magnetogram. For
  our set of 36 Marshall Space Flight CentreMSFC vector magnetograms of
  bipolar active regions, L<SUB>SGM</SUB> is found to have a success rate
  of 80% for prediction of CME productivity in the 0 2 day window. The
  development of L<SUB>SGM</SUB> as a method of measuring nonpotentiality
  for forecasting large, fast CMEs from present space-based assets is
  of value to NASA's space exploration initiative (manned missions to
  the Moon and Mars).

Title: Solar CIV vacuum-ultraviolet Fabry-Perot interferometers
Authors: Gary, G. A.; West, E. A.; Rees, D.; McKay, J. A.; Zukic,
   M.; Herman, P.
Bibcode: 2007A&A...461..707G
Altcode:
  Aims:A tunable, high spectral resolution, high effective finesse,
  vacuum ultraviolet (VUV) Fabry-Perot interferometer (FPI) is designed
  for obtaining narrow-passband images, magnetograms, and Dopplergrams
  of the transition region emission line of CIV (155 nm). <BR />Methods:
  The integral part of the CIV narrow passband filter package (with a 2-10
  pm FWHM) consists of a multiple etalon system composed of a tunable
  interferometer that provides high-spectral resolution and a static
  low-spectral resolution interferometer that allows a large effective
  free spectral range. The prefilter for the interferometers is provided
  by a set of four mirrors with dielectric high-reflective coatings. A
  tunable VUV piezoelectric-control interferometer has undergone testing
  using the surrogate F{2} eximer laser line at 157 nm for the CIV
  line. We present the results of these tests with a description of the
  overall concept for a complete narrow-band CIV spectral filter. The
  static interferometer of the filter will be built using a set of fixed
  MgF{2} plates. The four-mirror prefilter is designed to have dielectric
  multilayer Π-stacks employing the concept used in the Ultraviolet
  Imager of NASA's Polar Spacecraft. A 10-pm dual etalon system allows
  the effective free spectral range to be commensurate with the prefilter
  profile. With an additional etalon, a triple etalon system would allow
  a spectrographic resolution of 2 pm. The basic strategy has been to
  combine the expertise of spaceflight etalon manufacturing with VUV
  coating technology to build a VUV FPI which combines the best attributes
  of imagers and spectrographs into a single compact instrument. <BR
  />Results: High spectral-resolution spectro-polarimetry observations
  of the transition region CIV emission can be performed to increase
  our understanding of the magnetic forces, mass motion, evolution, and
  energy release within the solar atmosphere at the base of the corona
  where most of the magnetic field is approximately force-free. The 2D
  imaging of the full vector magnetic field at the height of maximum
  magnetic influence (minimum plasma beta) can be accomplished, albeit
  difficult, by measuring the Zeeman splitting of the CIV resonance
  pair. Designs of multiple VUV FPIs can be developed for integration
  into future orbiting solar observatories to obtain rapid cadence,
  spectral imaging of the transition region.

Title: C IV Vacuum Ultraviolet Fabry-Perot Interferometers for
    Transition-Region Magnetography
Authors: Gary, G. A.; West, E. A.; Rees, D. E.; Zukic, M.; Herman,
   P.; Li, J.
Bibcode: 2006ASPC..358..181G
Altcode:
  The vacuum ultraviolet region allows remote sensing of the upper
  levels of the solar atmosphere where the magnetic field dominates
  the physics. Obtaining an imaging interferometer that observes the
  transition region is the goal of this program. This paper gives
  a summary of our instrument development program (1998-2005) for a
  high-spectral-resolution, piezoelectric tunable Vacuum Ultraviolet
  Fabry-Perot Interferometer (VUV FPI) for obtaining narrow-passband
  images, magnetograms, and Dopplergrams of the transition region emission
  line of C IV (155 nm). A VUV interferometer will allow us to observe
  the magnetic field, flows, and heating events in the mid-transition
  region. The MSFC VUV FPI has measured values of <P />FWHM ∼ 9 pm,
  FSR ∼ 62 pm, finesse ∼5.3, and transmittance ∼ 50% at 157
  nm. For the measurements, the University of Toronto's F<SUB>2</SUB>
  eximer laser was used as an appropriate proxy for C IV 155 nm. This
  has provided the first tunable interferometer with a FWHM compatible
  to VUV filter magnetograph.

Title: Large Field-of-View KD*P Modulator for Solar Polarization
    Measurements
Authors: West, E. A.; Gary, G. A.
Bibcode: 2006ASPC..358..209W
Altcode:
  This paper describes the evolution of the Marshall Space Flight
  Center's (MSFC) electro-optical polarimeter with emphasis on the
  field-of-view characteristics of the KD*P modulator. Understanding those
  characteristics was essential to the success of the MSFC solar vector
  magnetograph. We show how the field-of-view (FOV) errors of KD*P look
  similar to the linear polarization patterns seen in simple sunspots,
  and why the placement of the KD*P in a collimated beam was essential in
  separating the instrumental polarization from the solar signal. Finally,
  we describe a modulator design which minimizes those FOV errors.

Title: 3-D Structure of Sunspots Using Imaging Spectroscopy
Authors: Balasubramaniam, K. S.; Gary, G. A.; Reardon, K.
Bibcode: 2006ASPC..354..237B
Altcode:
  We use the Interferometric BIdimensional Spectrometer (IBIS) of the
  INAF/Arcetri Astrophysical Observatory and installed at the National
  Solar Observatory (NSO) Dunn Solar Telescope, to understand the
  structure of sunspots. Using the spectral lines Fe I 6301.5 Å, Fe II
  7224.4 Å, and Ca II 8542.6 Å, we examine the spectroscopic variation
  of sunspot penumbral and umbral structures at the heights of formation
  of these lines. These high resolution observations were acquired on
  2004 July 30 -- 31, of active region NOAA 10654, using the high order
  NSO adaptive optics system. We map the spatio-temporal variation of
  Doppler signatures in these spectral lines, from the photosphere to
  the chromosphere. From a 70-minute temporal average of individual
  32-second cadence Doppler observations we find that the averaged
  velocities decrease with height. They are about 3.5 times larger in the
  deeper photosphere (Fe II 7224.4 Å; height-of-formation ≈ 50 km)
  than in the upper photosphere Fe I 6301.5 Å; height-of-formation
  ≈ 350 km), There is a remarkable coherence of Doppler signals
  over the height difference of 300 km. From a high-speed animation
  of the Doppler sequence we find evidence for what appears to be
  ejection of high speed gas concentrations from edges of penumbral
  filaments into the surrounding granular photosphere. The Evershed
  flow persists a few arcseconds beyond the traditionally demarcated
  penumbra-granulation boundary. We present these and other results and
  discuss the implications of these measurements for sunspot models.

Title: The Solar Ultraviolet Magnetograph Investigation: Polarization
    Properties
Authors: West, E. A.; Kobayashi, K.; Gary, G. A.; Davis, J. M.
Bibcode: 2006ASPC..358..161W
Altcode:
  This paper describes the objectives of the Marshall Space Flight
  Center (MSFC) Solar Ultraviolet Magnetograph Investigation (SUMI)
  and the optical components that have been developed to meet those
  objectives. A sounding rocket payload is being developed to test the
  feasibility of magnetic-field measurements in the Sun's transition
  region. The optics have been optimized for simultaneous measurements
  of two magnetic lines formed in the transition region (C IV 1550 Å
  and Mg II 2800 Å). Finally, we illustrate the polarization properties
  of the SUMI polarimeter and toroidal variable-line-space gratings.

Title: An Overview of Existing Algorithms for Resolving the
180<SUP>°</SUP> Ambiguity in Vector Magnetic Fields: Quantitative
    Tests with Synthetic Data
Authors: Metcalf, Thomas R.; Leka, K. D.; Barnes, Graham; Lites,
   Bruce W.; Georgoulis, Manolis K.; Pevtsov, A. A.; Balasubramaniam,
   K. S.; Gary, G. Allen; Jing, Ju; Li, Jing; Liu, Y.; Wang, H. N.;
   Abramenko, Valentyna; Yurchyshyn, Vasyl; Moon, Y. -J.
Bibcode: 2006SoPh..237..267M
Altcode: 2006SoPh..tmp...14M
  We report here on the present state-of-the-art in algorithms used
  for resolving the 180° ambiguity in solar vector magnetic field
  measurements. With present observations and techniques, some assumption
  must be made about the solar magnetic field in order to resolve
  this ambiguity. Our focus is the application of numerous existing
  algorithms to test data for which the correct answer is known. In
  this context, we compare the algorithms quantitatively and seek to
  understand where each succeeds, where it fails, and why. We have
  considered five basic approaches: comparing the observed field to a
  reference field or direction, minimizing the vertical gradient of the
  magnetic pressure, minimizing the vertical current density, minimizing
  some approximation to the total current density, and minimizing some
  approximation to the field's divergence. Of the automated methods
  requiring no human intervention, those which minimize the square of
  the vertical current density in conjunction with an approximation for
  the vanishing divergence of the magnetic field show the most promise.

Title: Magnetic Causes of Solar Coronal Mass Ejections: Dominance
    of the Free Magnetic Energy over the Magnetic Twist Alone
Authors: Falconer, D. A.; Moore, R. L.; Gary, G. A.
Bibcode: 2006ApJ...644.1258F
Altcode:
  We examine the magnetic causes of coronal mass ejections (CMEs)
  by examining, along with the correlations of active-region magnetic
  measures with each other, the correlations of these measures with
  active-region CME productivity observed in time windows of a few days,
  either centered on or extending forward from the day of the magnetic
  measurement. The measures are from 36 vector magnetograms of bipolar
  active regions observed within ~30° of disk center by the Marshal
  Space Flight Center (MSFC) vector magnetograph. From each magnetogram,
  we extract six whole-active-region measures twice, once from the
  original plane-of-the-sky magnetogram and again after deprojection of
  the magnetogram to disk center. Three of the measures are alternative
  measures of the total nonpotentiality of the active region, two are
  alternative measures of the overall twist in the active-region's
  magnetic field, and one is a measure of the magnetic size of the
  active region (the active region's magnetic flux content). From the
  deprojected magnetograms, we find evidence that (1) magnetic twist and
  magnetic size are separate but comparably strong causes of active-region
  CME productivity, and (2) the total free magnetic energy in an active
  region's magnetic field is a stronger determinant of the active region's
  CME productivity than is the field's overall twist (or helicity)
  alone. From comparison of results from the non-deprojected magnetograms
  with corresponding results from the deprojected magnetograms, we find
  evidence that (for prediction of active-region CME productivity and for
  further studies of active-region magnetic size as a cause of CMEs),
  for active regions within ~30° of disk center, active-region total
  nonpotentiality and flux content can be adequately measured from
  line-of-sight magnetograms, such as from SOHO MDI.

Title: Imaging Spectroscopy Of Sunspots Using IBIS
Authors: Balasubramaniam, K. S.; Gary, G. A.; Reardon, K.
Bibcode: 2006SPD....37.0712B
Altcode: 2006BAAS...38..229B
  We use the Interferometric BIdimensional Spectrometer (IBIS) of
  the INAF/Arcetri Astrophysical Observatory and installed at the
  National Solar Observatory (NSO) Dunn Solar Telescope, to understand
  the structure of sunspots. These high resolution observations were
  acquired on 2004 July 30-31, of active region NOAA 10654, using the
  high order NSO adaptive optics system. We map the spatio-temporal
  variation of the penumbral Doppler signatures in three spectral
  lines, FeI 6301.5 Å, FeII 7224.4 Å, and CaII 8542.6 Å, from the
  photosphere to the chromosphere. From a 70-minute temporal average
  of individual 32-second cadence Doppler observations we find that
  the averaged velocities decrease with height, about 3.5 times larger
  in the deeper photosphere (FeII 7224.4 Å height-of-formation ≈50
  km) than in the upper photosphere FeI 6301.5 Å height-of-formation
  ≈350 km), There is a remarkable coherence of Doppler signals over
  the height difference of 300 km. From a high-speed animation of the
  Doppler sequence we find evidence for what appears to be ejection of
  high speed gas concentrations from edges of penumbral filaments into
  the surrounding granular photosphere. The Evershed flow persists a few
  arcseconds beyond the traditionally demarcated penumbra-granulation
  boundary. We present these and other results and discuss implications
  of these measurements for sunspot models.

Title: Oriented connectivity-based method for segmenting solar loops
Authors: Lee, Jong Kwan; Newman, Timothy S.; Gary, G. Allen
Bibcode: 2006PatRe..39..246L
Altcode:
  A method based on oriented connectivity that can automatically segment
  arc-like structures (solar loops) from intensity images of the Sun's
  corona is introduced. The method is a constructive approach that
  uses model-guided processing to enable extraction of credible loop
  structures. Since the solar loops are vestiges of the solar magnetic
  field, the model-guided processing exploits external estimates of this
  field's local orientations that are derived from a physical magnetic
  field model. Empirical studies of the method's effectiveness are
  also presented. The oriented connectivity-based method is the first
  automatic method for the segmentation of solar loops.

Title: Advanced technology solar telescope multiple Fabry-Pérot
    interferometer telecentric optical design
Authors: Robinson, Brian M.; Balasubramaniam, K. S.; Gary, Gilmer A.
Bibcode: 2006OptEn..45b3001R
Altcode:
  We present four preliminary designs for a telecentric optical
  train supporting the Advanced Technology Solar Telescope (ATST)
  multiple Fabry-Pérot interferometer (MFPI), which is to be used as
  an imaging spectrometer and imaging spectropolarimeter. The point
  of departure for all three designs is the F/40 telecentric image
  at the Coudé focus of the ATST. The first design, representing the
  high-spectral-resolution mode of operation, produces an intermediate
  F/300 telecentric image within the triple étalon system and a 34-arcsec
  field of view (FOV). The second design, intermediate between high- and
  low-spectral-resolution modes of operation, produces an intermediate
  F/150 telecentric image at the étalons and a 1.1-arcmin FOV. The
  third and fourth designs each represent a low-resolution mode of
  operation, producing an F/82 telecentric image at the étalons and
  a 2-arcmin FOV. Each design results in good telecentricity and image
  quality. Departures from telecentricity at the intermediate image plane
  cause field-dependent shifts of the bandpass peak, which are negligible
  compared to the bandpass FWHM. The root mean square (rms) geometric spot
  sizes at the final image plane fit well within the area of a camera
  pixel, which is itself in accordance with the Nyquist criterion, half
  the width of the 28-µm-wide resolution element (as determined from
  the diffraction limit of the ATST). For each configuration, we also
  examine the impact that the Beckers effect (the pupil apodization
  caused by the angle-dependent amplitude transmittance of the MFPI)
  has on the image quality of the MFPI instrument.

Title: MTRAP: the magnetic transition region probe
Authors: Davis, J. M.; West, E. A.; Moore, R. L.; Gary, G. A.;
   Kobayashi, K.; Oberright, J. E.; Evans, D. C.; Wood, H. J.; Saba,
   J. L. R.; Alexander, D.
Bibcode: 2005SPIE.5901..273D
Altcode:
  The Magnetic Transition Region Probe is a space telescope designed to
  measure the magnetic field at several heights and temperatures in the
  solar atmosphere, providing observations spanning the chromospheric
  region where the field is expected to become force free. The primary
  goal is to provide an early warning system (hours to days) for solar
  energetic particle events that pose a serious hazard to astronauts in
  deep space and to understand the source regions of these particles. The
  required magnetic field data consist of simultaneous circular and linear
  polarization measurements in several spectral lines over the wavelength
  range from 150 to 855 nm. Because the observations are photon limited
  an optical telescope with a large (&gt;18m<SUP>2</SUP>) collecting area
  is required. To keep the heat dissipation problem manageable we have
  chosen to implement MTRAP with six separate Gregorian telescopes, each
  with ~ 3 m<SUP>2</SUP> collecting area, that are brought to a common
  focus. The necessary large field of view (5 × 5 arcmin<SUP>2</SUP>)
  and high angular resolution (0.025 arcsec pixels) require large
  detector arrays and, because of the requirements on signal to noise
  (10<SUP>3</SUP>), pixels with large full well depths to reduce the
  readout time and improve the temporal resolution. The optical and
  engineering considerations that have gone into the development of a
  concept that meets MTRAP's requirements are described.

Title: The solar ultraviolet magnetograph investigation: polarization
    properties
Authors: West, E. A.; Porter, J. G.; Davis, J. M.; Gary, G. A.;
   Kobayashi, K.; Noble, M.
Bibcode: 2005SPIE.5901..226W
Altcode:
  This paper will describe the objectives of the Marshall Space
  Flight Center (MSFC) Solar Ultraviolet Magnetograph Investigation
  (SUMI) and the optical components that have been developed to meet
  those objectives. A sounding rocket payload is being developed to
  test the feasibility of magnetic field measurements in the Sun's
  transition region. The optics have been optimized for simultaneous
  measurements of two magnetic lines formed in the transition region (CIV
  at 1550Å and MgII at 2800Å). Finally, this paper will concentrate
  on the polarization properties of the SUMI polarimeter and toroidal
  variable-line-space gratings.

Title: Shape and Reconnection of the Exploding Magnetic Field in
    the Onset of CMEs
Authors: Moore, R. L.; Sterling, A. C.; Falconer, D. A.; Gary, G. A.
Bibcode: 2005AGUSMSH54B..01M
Altcode:
  From chromospheric and coronal images and line-of-sight and vector
  magnetograms of magnetic regions that produce CMEs, and from
  chromospheric and coronal movies of the onsets of CME eruptions,
  it appears that the magnetic field that explodes to drive the CME
  is initially the strongly sheared core of a magnetic arcade encasing
  a polarity dividing line in the magnetic flux. Before or during the
  onset of the explosion, the sheared core field becomes a flux rope,
  often carrying chromospheric material within it. For the erupting flux
  rope to drive the explosion, that is, for its magnetic energy content
  to decrease in the explosion, the flux rope's cross-sectional area
  must increase faster than its length. For instance, for isotropic
  expansion, the area increases as the square of the length, and the
  magnetic energy content of the flux rope decreases as the inverse of
  the length. The instability that initiates the eruption of the flux
  rope might be an ideal MHD kink instability, or might involve runaway
  tether-cutting reconnection. The reconnection begins below the flux
  rope (internal to the arcade) when the overall field configuration
  of the region is effectively that of a single bipole. When the flux
  rope resides in a multi-bipolar configuration having a magnetic null
  above the flux rope, the runaway tether-cutting reconnection might
  begin either below the flux rope or at the null above (external to)
  the arcade. We present examples of observed CME onsets that illustrate
  the above alternatives. In each example, reconnection below the flux
  rope begins early in the eruption. This indicates that internal
  tether cutting reconnection (classic tether-cutting reconnection)
  is important in unleashing the CME explosion in all cases, including
  those in which the explosion may be triggered by MHD kinking or by
  external reconnection (classic breakout reconnection).

Title: Triple Fabry-Pérot Imaging Interferometer for High Resolution
    Solar Spectroscopy using the ATST
Authors: Robinson, B. M.; Gary, G. A.; Balasubramaniam, K. S.
Bibcode: 2005AGUSMSP34A..05R
Altcode:
  We present a telecenrically mounted triple Fabry-Pérot imaging
  interferometer for the NSOs Advanced Technology Solar Telescope
  (ATST). It consists of three Fabry-Pérot etalons and the feed and
  imaging optics. This system provides high throughput, flexibility
  and breadth of operation when compared to other spectroscopic
  imaging systems. It can operate in four distinct modes: as a
  spectro-polarimeter, a filter-vector magnetograph, an intermediate-band
  imager, and broadband high-resolution imager. In the proposed
  telecentric mount configuration, the transmittance of the etalon system
  is not a function of position in the field, so that instantaneous
  spectroscopic measurements can be performed across the entire field
  of view; however, the transmission peak of the interferometer is
  broadened. Mitigation of this broadening requires a low F# image at
  the etalons. Together with the requirement that the field of view be
  large enough to observe large-scale processes in the solar atmosphere,
  this limitation dictates that the diameter of the etalons have a large
  aperture. Specifically, for a spectrographic passband full-width at
  half-maximum (FWHM) of around 2 pm, and entrance pupil diameter of 4 m,
  and a field of view of 35", the required etalon diameter is around 200
  mm. This is beyond the size of current Fabry-Pérot etalons and near
  the current projected limit of manufacturability. The development
  of this instrument will bring these large etalons to realization
  and take Fabry-Pérot imaging interferometry to the next level of
  operational capability within telescopes of large aperture. This
  instrument will provide spectral, spatial, and temporal resolution
  which is not currently available to large aperture solar astronomy,
  but which is necessary, in conjunction with the new class telescopes,
  to the continuing discovery of laws that govern the dynamics of the sun
  and the earth-sun connection. The resolution afforded by higher aperture
  telescopes and instrumentation will give scientists new insight into
  the magnetohydrodynamic processes occurring on the Sun via simultaneous
  spectral and spatial measurements across the entire field of view. We
  will describe the optical train supporting the filter system and the
  expected imaging performance. We will analyze the effects of spectral
  resolution of the instrument due etalon spacing parameters, optical
  configuration, and the plate defect finesse. We present calculations of
  the pupil apodization for three modes of operation and the consequences
  for the imaging and spectroscopic performance of the system; and a
  treatment of noise contributions from the parasitic off-band spectral
  orders and ghost images arising from multiple reflections within the
  etalon system.

Title: Photospheric and Chromospheric structure of Sunspots using
    IBIS.
Authors: Balasubramaniam, K. S.; Gary, G. A.; Reardon, K.
Bibcode: 2005AGUSMSP11A..04B
Altcode:
  We use the Interferometric BIdimensional Spectrometer (IBIS) of the
  INAF/Arcetri Astrophysical Observatory and installed at the National
  Solar Observatory's (NSO) Dunn Solar Telescope, to understand the
  structure of sunspots. Using the spectral lines FeI 6301.5Å, FeII
  7224.4Å and CaII 8542.6Å, we examine the spectroscopic variation of
  sunspot penumbral and umbral structures about the heights of formation
  of these lines. Simultaneous white-light imaging data helps us to
  register and track the images. We map the spatio-temporal variation
  of Doppler signatures in these spectral lines, from the photosphere
  to the chromosphere, and discuss the implication of these variations
  for sunspot models. These high resolution observations were acquired
  on 2004 July 30-31, on a sunspot NOAA 10654, using the higher order
  NSO adaptive optics system.

Title: The Marshall Space Flight Center solar ultraviolet magnetograph
Authors: West, Edward A.; Porter, Jason G.; Davis, John M.; Gary,
   G. A.; Noble, Matthew W.; Lewis, Matthew; Thomas, Roger J.
Bibcode: 2004SPIE.5488..801W
Altcode:
  This paper will describe the objectives of the Marshall Space
  Flight Center (MSFC) Solar Ultraviolet Magnetograph Investigation
  (SUMI) and the optical components that have been developed to meet
  those objectives. In order to test the scientific feasibility of
  measuring magnetic fields in the UV, a sounding rocket payload
  is being developed. This paper will discuss: (1) the scientific
  measurements that will be made by the SUMI sounding rocket program,
  (2) how the optics have been optimized for simultaneous measurements of
  two magnetic lines CIV (1550Å) and MgII (2800Å), and (3) the optical,
  reflectance, transmission and polarization measurements that have been
  made on the SUMI telescope mirrors and polarimeter.

Title: Optical design for a Fabry-Perot image interferometer for
    solar observations
Authors: Moretto, Gilberto; Gary, G. Allen; Balasubramaniam, K. S.;
   Rimmele, Thomas R.
Bibcode: 2004SPIE.5492.1773M
Altcode:
  We outline here a preliminary optical design study for a telecentric
  tunable Fabry-Perot etalon system. The first result of the optical
  optimization into a design, which delivers performance image quality
  and telecentricity, is presented here. Bearing in mind the possible
  use of such a study design - as a possible instrument for the Advanced
  Technology Solar Telescope (ATST) - we also show that a hybrid design
  strategy delivers a compact design that will fit inside the ATST's
  Coude optical tables.

Title: Instrumentation for the Advanced Technology Solar Telescope
Authors: Rimmele, Thomas R.; Hubbard, Robert P.; Balasubramaniam,
   K. S.; Berger, Tom; Elmore, David; Gary, G. Allen; Jennings, Don;
   Keller, Christoph; Kuhn, Jeff; Lin, Haosheng; Mickey, Don; Moretto,
   Gilberto; Socas-Navarro, Hector; Stenflo, Jan O.; Wang, Haimin
Bibcode: 2004SPIE.5492..944R
Altcode:
  The 4-m aperture Advanced Technology Solar Telescope (ATST) is the
  next generation ground based solar telescope. In this paper we provide
  an overview of the ATST post-focus instrumentation. The majority of
  ATST instrumentation is located in an instrument Coude lab facility,
  where a rotating platform provides image de-rotation. A high order
  adaptive optics system delivers a corrected beam to the Coude lab
  facility. Alternatively, instruments can be mounted at Nasmyth or
  a small Gregorian area. For example, instruments for observing the
  faint corona preferably will be mounted at Nasmyth focus where maximum
  throughput is achieved. In addition, the Nasmyth focus has minimum
  telescope polarization and minimum stray light. We describe the set of
  first generation instruments, which include a Visible-Light Broadband
  Imager (VLBI), Visible and Near-Infrared (NIR) Spectropolarimeters,
  Visible and NIR Tunable Filters, a Thermal-Infrared Polarimeter &amp;
  Spectrometer and a UV-Polarimeter. We also discuss unique and efficient
  approaches to the ATST instrumentation, which builds on the use of
  common components such as detector systems, polarimetry packages and
  various opto-mechanical components.

Title: Eruption of a Multiple-Turn Helical Magnetic Flux Tube in a
Large Flare: Evidence for External and Internal Reconnection That
    Fits the Breakout Model of Solar Magnetic Eruptions
Authors: Gary, G. Allen; Moore, R. L.
Bibcode: 2004ApJ...611..545G
Altcode:
  We present observations and an interpretation of a unique multiple-turn
  spiral flux tube eruption from active region 10030 on 2002 July 15. The
  TRACE C IV observations clearly show a flux tube that is helical and
  erupting from within a sheared magnetic field. These observations are
  interpreted in the context of the breakout model for magnetic field
  explosions. The initiation of the helix eruption, as determined by a
  linear backward extrapolation, starts 25 s after the peak of the flare's
  strongest impulsive spike of microwave gyrosynchrotron radiation early
  in the flare's explosive phase, implying that the sheared core field
  is not the site of the initial reconnection. Within the quadrupolar
  configuration of the active region, the external and internal
  reconnection sites are identified in each of two consecutive eruptive
  flares that produce a double coronal mass ejection (CME). The first
  external breakout reconnection apparently releases an underlying sheared
  core field and allows it to erupt, leading to internal reconnection in
  the wake of the erupting helix. This internal reconnection releases the
  helix and heats the two-ribbon flare. These events lead to the first
  CME and are followed by a second breakout that initiates a second and
  larger halo CME. The strong magnetic shear in the region is compatible
  with the observed rapid proper motion and evolution of the active
  region. The multiple-turn helix originates from above a sheared-field
  magnetic inversion line within a filament channel, and starts to erupt
  only after fast breakout reconnection has started. These observations
  are counter to the standard flare model and support the breakout model
  for eruptive flare initiation.

Title: Forecasting Coronal Mass Ejections from Magnetograms
Authors: Falconer, D. A.; Moore, R. L.; Gary, G. A.; Balasubramanian,
   S.
Bibcode: 2004AAS...204.2705F
Altcode: 2004BAAS...36..693F
  We report further results from our ongoing assessment of
  magnetogram-based measures of active-region nonpotentiality (magnetic
  shear and twist), magnetic complexity and size as predictors of
  coronal mass ejections (CMEs). From a set of 36 vector magnetograms
  of predominantly bipolar active regions (Falconer, Moore, &amp;
  Gary 2004, ApJ, submitted), we have found: (1) Each of five different
  measures of active-region nonpotentiality has a 75-80 (with correlation
  confidence level &gt; 95%) in predicting whether an active region will
  produce a CME within 2 days after the magnetogram. (2) One of these
  measures can be obtained from a line-of-sight magnetogram without use
  of a vector magnetogram. Hence this measure appears to be the best
  practical measure of active-region nonpotentiality for operational
  CME forecasting. (3) Our measure of active-region size has a 65%
  success rate in predicting CMEs in this window, but the correlation
  is not statistically significant (confidence level ∼ 80%) for our
  sample size. We have applied a measure of active-region complexity (the
  fraction of magnetic flux not in the active region's primary bipole)
  to our set of 36 magnetograms and found a correlation with the CME
  productivity of the active regions. We are also applying measures of
  nonpotentiality, size, and complexity to multi-bipolar active regions to
  assess their CME-prediction ability for these more complicated active
  regions. <P />This work was funded by NASA through its LWS TR&amp;T
  Program and its Solar and Heliospheric Physics SR&amp;T Program,
  and by NSF through its Solar Terrestrial Research and SHINE Programs.

Title: A measure from line-of-sight magnetograms for prediction of
    coronal mass ejections
Authors: Falconer, D. A.; Moore, R. L.; Gary, G. A.
Bibcode: 2003JGRA..108.1380F
Altcode:
  From a sample of 17 vector magnetograms of 12 bipolar active regions we
  have recently found (1) that a measure of the overall nonpotentiality
  (the overall twist and shear in the magnetic field) of an active region
  is given by the strong shear length L<SUB>SS</SUB>, the length of
  the portion of the main neutral line on which the observed transverse
  fields is strong (&gt;150 Guass (G)) and strongly sheared (shear angle
  &gt;45°), and (2) that L<SUB>SS</SUB> is well correlated with the
  coronal mass ejection (CME) productivity of the active regions during
  the ±2-day time window centered on the day of the magnetogram. In the
  present paper, from the same sample of 17 vector magnetograms, we show
  that there is a viable proxy for L<SUB>SS</SUB> that can be measured
  from a line-of-sight magnetogram. This proxy is the strong gradient
  length L<SUB>SG</SUB>, the length of the portion of the main neutral
  line on which the potential transverse field is strong (&gt;150 G), and
  the gradient of the line-of-sight field is sufficiently steep (greater
  than ∼50 G/Mm). In our sample of active regions, L<SUB>SG</SUB> is
  statistically significantly correlated with L<SUB>SS</SUB> (correlation
  confidence level &gt;95%), and L<SUB>SG</SUB> is as strongly
  correlated with active region CME productivity as is L<SUB>SS</SUB>
  (correlation confidence level ∼99.7%). Because L<SUB>SG</SUB> can
  be measured from line-of-sight magnetograms obtained from conventional
  magnetographs, such as the magnetograph mode of the Michelson Doppler
  Imager (MDI) on board the Solar and Heliospheric Observatory, it is
  a dependable substitute for L<SUB>SS</SUB> for use in operational
  CME forecasting. In addition, via measurement of L<SUB>SG</SUB>, the
  years-long, nearly continuous sequence of 1.5-hour cadence full disk
  line-of-sight magnetograms from MDI can be used to track the growth
  and decay of the large-scale nonpotentiality in active regions and to
  examine the role of this evolution in active region CME productivity.

Title: Automated Coronal Loop Identification using Digital Image
    Processing Techniques
Authors: Lee, J. K.; Gary, G. A.; Newman, T. S.
Bibcode: 2003SPD....34.0305L
Altcode: 2003BAAS...35..809L
  The results of a Master's thesis study of computer algorithms
  for automatic extraction and identification (i.e., collectively,
  "detection") of optically-thin, 3-dimensional, (solar) coronal-loop
  center "lines" from extreme ultraviolet and X-ray 2-dimensional images
  will be presented. The center lines, which can be considered to be
  splines, are proxies of magnetic field lines. Detecting the loops
  is challenging because there are no unique shapes, the loop edges
  are often indistinct, and because photon and detector noise heavily
  influence the images. Three techniques for detecting the projected
  magnetic field lines have been considered and will be described in
  the presentation. The three techniques used are (i) linear feature
  recognition of local patterns (related to the inertia-tensor concept),
  (ii) parametric space inferences via the Hough transform, and (iii)
  topological adaptive contours (snakes) that constrain curvature and
  continuity. Since coronal loop topology is dominated by the magnetic
  field structure, a first-order magnetic field approximation using
  multiple dipoles provides a priori information that has also been
  incorporated into the detection process. Synthesized images have been
  generated to benchmark the suitability of the three techniques, and the
  performance of the three techniques on both synthesized and solar images
  will be presented and numerically evaluated in the presentation. The
  process of automatic detection of coronal loops is important in the
  reconstruction of the coronal magnetic field where the derived magnetic
  field lines provide a boundary condition for magnetic models ( cf. ,
  Gary (2001, Solar Phys., 203, 71) and Wiegelmann &amp; Neukirch (2002,
  Solar Phys., 208, 233)). . This work was supported by NASA's Office
  of Space Science - Solar and Heliospheric Physics Supporting Research
  and Technology Program.

Title: Parametric Transformation Analysis of Observed Coronal
    Magnetic Structures
Authors: Gary, G. A.
Bibcode: 2003SPD....34.1609G
Altcode: 2003BAAS...35..834G
  Twisted coronal features are important signatures for predicting
  solar eruptive events, and yet not clearly understood. We present
  new results for determining the complex, non-potential magnetic
  field configurations of active regions. This research uses free-form
  deformation mathematics to generate the 3-dimensional coronal magnetic
  field. We use a parametric representation of the magnetic field lines
  such that the field lines can be manipulated to match the observed EUV
  and SXR coronal loops. The objective is to derive sigmoidal magnetic
  field solutions which allow beta &gt; 1 regions to be included,
  aligned and non-aligned electric currents to be calculated, and the
  Lorentz force to be determined. The advantage of our technique is that
  the solution is independent of the unknown upper and side boundary
  conditions, allows non-vanishing magnetic forces, and provides a global
  magnetic field solution, which contains high- and low-beta regimes and
  is consistent with the observed coronal structure of the region. We
  show that the mathematical description is unique and physical. This
  work was supported by NASA's Office of Space Science - Solar and
  Heliospheric Physics Supporting Research and Technology program.

Title: CME Prediction from Line-of-Sight Magnetograms
Authors: Falconer, D. A.; Moore, R. L.; Gary, G. A.
Bibcode: 2003SPD....34.0503F
Altcode: 2003BAAS...35R.814F
  We have previously shown for bipolar active regions that measures of
  active-region nonpotentiality from vector magnetograms are correlated
  with active-region CME productivity (Falconer, Moore, &amp; Gary
  2002, ApJ, 569, 1016). Guided by those measures and results, we have
  now obtained a measure from line-of-sight magnetograms that is well
  correlated both with our measures of active-region nonpotentiality from
  vector magnetograms and with active-region CME productivity. The measure
  is the length of strong-gradient main neutral line (L<SUB>G</SUB>). This
  is the length of a bipolar region's main neutral line on which the
  potential transverse field is greater than 150G, and the gradient in
  the line-of-sight field is greater than 50G/Mm. <P />From the sample
  of 17 MSFC magnetograms of 12 basically bipolar active regions used in
  our previous paper, we find that L<SUB>G</SUB> is strongly correlated
  (99.7%) with one of our vector-magnetogram measures of nonpotentiality,
  the length of strong-gradient main neutral line L<SUB>SS</SUB>. We
  also find that L<SUB>G</SUB> is as strongly correlated (99.7%)
  with CME productivity as is L<SUB>SS</SUB>. Being obtainable from
  line-of-sight magnetograms, L<SUB>G</SUB> makes the much larger data
  set of line-of-sight magnetograms (i.e. from SOHO/MDI and Kitt Peak)
  available for CME prediction study. This is especially important for
  evolutionary studies, with SOHO/MDI having no day/night, cloudy weather,
  or atmospheric seeing problems. <P />This work was supported by funding
  from NSF's Division of Atmospheric Sciences (Space Weather and Shine
  Programs) and by NASA's Office of Space Science (Living with a Star
  Program and Solar and Heliospheric Physics Supporting Research and
  Technology Program).

Title: SUMI - The Solar Ultraviolet Magnetograph Investigation
Authors: Porter, J. G.; West, E. A.; Davis, J. M.; Gary, G. A.; Noble,
   M. W.; Thomas, R. J.; Rabin, D. M.; Uitenbroek, H.
Bibcode: 2003SPD....34.2015P
Altcode: 2003BAAS...35..847P
  Solar physics has been successful in characterizing the full vector
  magnetic field in the photosphere, where the ratio of gas pressure to
  magnetic pressure (β ) is greater than 1. However, at higher levels
  in the atmosphere, where β is much less than 1 and flares and CMEs
  are believed to be triggered, observations are difficult, severely
  limiting the understanding of these processes. In response to this
  situation, we are developing SUMI (the Solar Ultraviolet Magnetograph
  Investigation) a unique instrument designed to measure the circular
  and linear polarization of upper chromospheric Mg II lines (280 nm) and
  circular polarization of transition region C IV lines (155 nm). To date
  the telescope mirrors have been built, tested and coated with dielectric
  stacks designed to reflect only the wavelengths of interest. We have
  also developed a unique UV polarimeter and completed the design of a
  high-resolution spectrograph that uses dual toroidal varied-line-space
  (TVLS) gratings. Incorporating measurements of those components
  developed so far, the revised estimate of the system throughput exceeds
  our original estimate by more than an order of magnitude. A sounding
  rocket flight is anticipated in 2006. Our objectives and progress
  are detailed in this presentation. <P />This work is supported by
  NASA SR&amp;T.

Title: Multiple Etalon Systems for the Advanced Technology Solar
    Telescope
Authors: Gary, G. A.; Balasubramaniam, K. S.; Sigwarth, Michael
Bibcode: 2003SPIE.4853..252G
Altcode:
  Multiple etalon systems are discussed that meet the science requirements
  for a narrow-passband imaging system for the 4-meter National Solar
  Observatory (NSO)/Advance Technology Solar Telescope (ATST). A
  multiple etalon system can provide an imaging interferometer that
  works in four distinct modes: as a spectro-polarimeter, a filter-vector
  magnetograph, an intermediate-band imager, and broadband high-resolution
  imager. Specific dual and triple etalon configurations are described
  that provide a spectrographic passband of 2.0-3.5 pm and reduce
  parasitic light levels to 10<SUP>-4 </SUP>as required for precise
  polarization measurement, e.g., Zeeman measurements of magnetic
  sensitive lines. A TESOS-like (Telecentric Etalon SOlar Spectrometer)
  triple etalon system provides a spectral purity of 10<SUP>-5</SUP>. The
  triple designs have the advantage of reducing the finesse requirement
  on each etalon; allow the use of more stable blocking filters, and have
  very high spectral purity. A dual-etalon double-pass (Cavallini-like)
  system can provide a competing configuration. Such a dual-etalon design
  can provide high contrast. The selection of the final focal plane
  instrument will depend on a trade-off between an ideal instrument and
  practical reality. The trade study will include the number of etalons,
  their aperture sizes, complexities of the optical train, number of
  blocking filters, configuration of the electronic control system,
  computer interfaces, temperature controllers, etalon controllers,
  and their associated feedback electronics. The heritage of single and
  multiple etalon systems comes from their use in several observatories,
  including the Marshall Space Flight Center (MSFC) Solar Observatory,
  Sacramento Peak Observatory (NSO), and Kiepenheuer-Institut für
  Sonnenphysik (KIS, Germany), Mees Solar Observatory (University of
  Hawaii), and Arcetri Astrophysical Observatory (Italy). The design
  of the ATST multiple etalon system will benefit from the experience
  gained at these observatories.

Title: High Resolution Imaging Spectroscopy of Sunspots
Authors: Balasubramaniam, K. S.; Titus, T.; Gary, G. Allen
Bibcode: 2003ASPC..286..259B
Altcode: 2003ctmf.conf..259B
  No abstract at ADS

Title: Forecasting Coronal Mass Ejections from Vector Magnetograms
Authors: Falconer, D. A.; Moore, R. L.; Gary, G. A.
Bibcode: 2002AAS...200.2005F
Altcode: 2002BAAS...34..673F
  In a 17 vector magnetogram study of 12 bipolar active regions
  (Falconer, Moore, &amp; Gary 2002, ApJ in press), we evaluated from
  each vector magnetogram four global measures of the magnetic field of
  the observed active region, and examined the correlation of each of
  these quantities with the CME productivity of the active regions. The
  four global magnetic quantities were 1) the total magnetic flux (Φ ),
  which is a measure of the size of an active region, and three measures
  of the global nonpotentiality of an active region: 2) the length of
  strong-field, strong-shear main neutral line (L<SUB>SS</SUB>), the
  net current (I<SUB>N</SUB>), and the magnetic twist parameter ( α =μ
  I<SUB>N</SUB>/Φ ). The CME productivity of each active region for each
  day of its disk passage was determined from Yohkoh/SXT coronal X-ray
  images together with GOES X-ray flux observations and, when available,
  SOHO/LASCO observations. For a centered time window of 5 days (day of
  the magnetogram +/- 2 days) for CME production, for each of the three
  measures of global nonpotentiality, whether the measure was above its
  median value was well correlated with whether the active region produced
  any CMEs. For each, the confidence level of the correlation was &gt;=
  99%. The sample size was too small to show a statistically significant
  correlation (confidence level &gt;= 95%) of the global nonpotentiality
  measures with future CME production, that is, from the date of the
  magnetogram forward. We are doubling our sample, and will report on
  our statistical evaluation of global nonpotentiality as a predictor of
  future CME productivity. The vector magnetograms of the added active
  regions are from the first year of operation (September 2000 - October
  2001) of the upgraded MSFC vector magnetograph. This work is funded by
  NSF through its Space Weather Program, and by NASA through its Living
  With a Star Targeted Research and Technology Program and its Solar and
  Heliospheric Physics Supporting Research and Technology Program. The
  upgrade of the MSFC vector magnetograph was funded by the HESSI mission.

Title: Correlation of the Coronal Mass Ejection Productivity of
    Solar Active Regions with Measures of Their Global Nonpotentiality
from Vector Magnetograms: Baseline Results
Authors: Falconer, D. A.; Moore, R. L.; Gary, G. A.
Bibcode: 2002ApJ...569.1016F
Altcode:
  From conventional magnetograms and chromospheric and coronal images,
  it is known qualitatively that the fastest coronal mass ejections
  (CMEs) are magnetic explosions from sunspot active regions in which
  the magnetic field is globally strongly sheared and twisted from its
  minimum-energy potential configuration. In this paper, we present
  measurements from active region vector magnetograms that begin to
  quantify the dependence of the CME productivity of an active region
  on the global nonpotentiality of its magnetic field. From each of 17
  magnetograms of 12 bipolar active regions, we obtain a measure of the
  size of the active region (the magnetic flux content, Φ) and three
  different measures of the global nonpotentiality (L<SUB>SS</SUB>, the
  length of strong-shear, strong-field main neutral line; I<SUB>N</SUB>,
  the net electric current arching from one polarity to the other;
  and α=μI<SUB>N</SUB>/Φ, a flux-normalized measure of the field
  twist). From these measurements and the observed CME productivity of
  the active regions, we find that: (1) All three measures of global
  nonpotentiality are statistically significantly correlated with
  each other and with the active region flux content. (2) All three
  measures of global nonpotentiality are significantly correlated with
  CME productivity. The flux content has some correlation with CME
  productivity, but at a less than statistically significant confidence
  level (less than 95%). (3) The net current is less strongly correlated
  with CME productivity than is α, and the correlation of flux
  content with CME productivity is weaker still. If these differences
  in correlation strength, and a significant correlation of α with
  flux content, persist to larger samples of active regions, this would
  suggest that active region size does not affect CME productivity except
  through global nonpotentiality. (4) For each of the four global magnetic
  quantities, the correlation with CME productivity is stronger for a +/-2
  day time window for the CME production than for windows half as wide or
  twice as wide. This plausibly results from most CME-productive active
  regions producing less than one CME per day, and from active region
  evolution often significantly changing the global nonpotentiality over
  the course of several days. These results establish that measures of
  active region global nonpotentiality from vector magnetograms (such as
  L<SUB>SS</SUB>, I<SUB>N</SUB>, and α) should be useful for prediction
  of active region CMEs.

Title: Development of a new vector magnetograph at Marshall Space
    Flight Center
Authors: West, Edward A.; Hagyard, Mona J.; Gary, G. Allen; Smith,
   James; Adams, Mitzi; Cloyd, Richard A.
Bibcode: 2002SPIE.4481..270W
Altcode:
  This paper will describe a new vector magnetograph that has been
  developed at Marshall Space Flight Center. This magnetograph was a test
  ed for space flight concepts. One of those concepts that is currently
  being tested is the increased sensitivity to linear polarization by
  replacing electro-optical and rotating waveplates with a rotating linear
  analyzer. Our paper will describe the motivation for developing this
  magnetograph, compare this instrument with traditional magnetograph
  designs.

Title: Development of a polarimeter for magnetic field measurements
    in the ultraviolet
Authors: West, Edward A.; Porter, Jason G.; Davis, John M.; Gary,
   G. Allen; Adams, Mitzi
Bibcode: 2002SPIE.4481..109W
Altcode:
  The polarizing optics that are being developed for the Solar UV
  Magnetograph Investigation (SUMI) are described. This polarimeter
  is being designed for a sounding rocket payload which will make
  simultaneous measurements of two magnetically sensitive lines CIV and
  MgII. With a limited observing program, the polarizing optics will be
  optimized for circular and linear polarization measurements in active
  regions. The Q polarization will represent exploratory measurements of
  the transverse field in strong sunspots. This paper will give a brief
  overview of the SUMI instrument and its scientific goals, will describe
  the polarimeter that will be used in the sounding rocket program,
  and will present some of the measurements that have been made on the
  SUMI polarization optics.

Title: Use of Yohkoh SXT in Measuring the Net Current and CME
    Productivity of Active Regions
Authors: Falconer, D. A.; Moore, R. L.; Gary, G. A.
Bibcode: 2002mwoc.conf..303F
Altcode:
  In our investigation of the correlation of global nonpotentiality of
  active regions to their CME productivity (Falconer, D. A. 2001, JGR,
  in press, and Falconer, Moore, &amp; Gary, 2000, EOS 82, 20 S323),
  we use Yohkoh SXT images for two purposes. The first use is to help
  resolve the 180<SUP>o</SUP> ambiguity in the direction of the observed
  transverse magnetic field. Resolution of the 180<SUP>o</SUP> ambiguity
  is important, since the net current, one of our measures of global
  nonpotentiality, is derived from integrating the dot product of the
  transverse field around a contour (I<SUB>N</SUB> = int B<SUB>T</SUB>cdot
  dl). The ambiguity results from the observed transverse field being
  determined from the linear polarization, which gives the plane of the
  direction, but leaves a 180<SUP>o</SUP> ambiguity. Automated methods
  to resolve the ambiguity ranging from the simple acute angle rule
  (Falconer, D. A. 2001) to the more sophisticated annealing method
  (Metcalf T. R. 1994). For many active regions, especially ones that are
  nearly potential these methods work well. But for very nonpotential
  active regions where the shear angle (the angle between the observed
  and potential transverse field) is near 90<SUP>o</SUP> throughout
  large swaths along the main neutral line, both methods can resolve
  the ambiguity incorrectly for long segments of the neutral line. By
  determining from coronal images, such as those from Yohkoh/SXT, the
  sense of shear along the main neutral line in the active region, these
  cases can be identified and corrected by a modification of the acute
  angle rule described here. The second use of Yohkoh/SXT in this study
  is to check for the cusped coronal arcades of long-duration eruptive
  flares. This signature is an excellent proxy for CMEs, and was used
  by Canfield, Hudson, and McKenzie (1999 GRL V26, 6, 627-630). This
  work is funded by NSF through the Space Weather Program and by NASA
  through the Solar Physics Supporting Research and Technology Program.

Title: Optical characteristics of the Marshall Space Flight Center
    solar ultraviolet magnetograph
Authors: West, Edward A.; Porter, Jason G.; Davis, John M.; Gary,
   G. Allen; Adams, Mitzi; Smith, W. Scott; Hraba, John F.
Bibcode: 2001SPIE.4498..101W
Altcode:
  This paper will describe the scientific objectives of the Marshall
  Space Flight Center (MSFC) Solar Ultraviolet Magnetograph Investigation
  (SUMI) and the optical components that have been developed to meet
  those objectives. In order to test the scientific feasibility of
  measuring magnetic fields in the UV, a sounding rocket payload is being
  developed. This paper will discuss: (1) the scientific measurements that
  will be made by the SUMI sounding rocket program, (2) how the optics
  have been optimized for simultaneous measurements of two magnetic lines
  CIV (1550 Angstroms) and MgII (2800 Angstroms), and (3) the optical,
  reflectance, transmission and polarization measurements that have been
  made on the SUMI telescope mirrors and polarimeter.

Title: Plasma Beta above a Solar Active Region: Rethinking the
    Paradigm
Authors: Gary, G. Allen
Bibcode: 2001SoPh..203...71G
Altcode:
  In this paper, we present a model of the plasma beta above an active
  region and discuss its consequences in terms of coronal magnetic field
  modeling. The β-plasma model is representative and derived from a
  collection of sources. The resulting β variation with height in the
  solar atmosphere is used to emphasize that the assumption that the
  magnetic pressure dominates over the plasma pressure must be carefully
  employed when extrapolating the magnetic field. This paper points out
  (1) that the paradigm that the coronal magnetic field can be constructed
  from a force-free magnetic field must be used in the correct context,
  since the force-free region is sandwiched between two regions which have
  β&gt;1, (2) that the chromospheric Mg ii-C iv magnetic measurements
  occur near the β-minimum, and (3) that, moving from the photosphere
  upwards, β can return to ∼1 at relatively low coronal heights,
  e.g., R∼1.2 R<SUB>s</SUB>.

Title: Deriving Coronal Magnetic Fields Using Parametric
    Transformation Analysis
Authors: Gary, G. A.
Bibcode: 2001AGUSM..SP51A01G
Altcode:
  When plasma β &gt;1 then the gas pressure dominates over the magnetic
  pressure. This ratio as a function along the coronal magnetic field
  lines varies from β &gt; 1 in the photosphere at the base of the field
  lines, to β &lt;&lt; 1 in the mid-corona, to β &gt; 1 in the upper
  corona. Almost all magnetic field extrapolations do not or cannot
  take into account the full range of β . They essentially assume β
  &lt;&lt; 1 , since the full boundary conditions do not exist in the
  β &gt; 1 regions. We use a basic parametric representation of the
  magnetic field lines such that the field lines can be manipulated
  to match linear features in the EUV and SXR coronal images in a
  least squares sense. This research employs free-form deformation
  mathematics to generate the associated coronal magnetic field. In our
  research program, the complex magnetic field topology uses Parametric
  Transformation Analysis (PTA) which is a new and innovative method to
  describe the coronal fields that we are developing. In this technique
  the field lines can be viewed as being embedded in a plastic medium,
  the frozen-in-field-line concept. As the medium is deformed the field
  lines are similarly deformed. However the advantage of the PTA method
  is that the field line movement represents a transformation of one
  magnetic field solution into another magnetic field solution. When
  fully implemented, this method will allow the resulting magnetic field
  solution to fully match the magnetic field lines with EUV/SXR coronal
  loops by minimizing the differences in direction and dispersion of a
  collection of PTA magnetic field lines and observed field lines. The
  derived magnetic field will then allow β &gt; 1 regions to be included,
  the electric currents to be calculated, and the Lorentz force to be
  determined. The advantage of this technique is that the solution is
  (i) independent of the upper and side boundary conditions, (ii) allows
  non-vanishing magnetic forces, and (iii) provides a global magnetic
  field solution, which contains high- and low- β regimes and maximizes
  the similarity between the field lines structure and all the coronal
  images of the region. The coronal image analysis is crucial to the
  investigation and for the first time these images can be exploited
  to derive the coronal magnetic field in a well-posed mathematical
  formulation. This program is an outgrowth of an investigation in
  which an extrapolated potential field was required to be "inflated" in
  order to have the field lines match the Yohkoh/SXT images (Gary &amp;
  Alexander 1999, Solar Physics, 186, 123). The field lines were radially
  stretched resulting in a better match to the coronal loops of an active
  region. The PTA method of radial and non-radial deformations of field
  lines to provide a match to the EUV/SXR images will be presented.

Title: Prediction of Coronal Mass Ejections from Vector Magnetograms:
    Quantitative Measures as Predictors
Authors: Falconer, D. A.; Moore, R. L.; Gary, G. A.
Bibcode: 2001AGUSM..SH41C04F
Altcode:
  In a pilot study of 4 active regions (Falconer, D.A. 2001, JGR, in
  press), we derived two quantitative measures of an active region's
  global nonpotentiality from the region's vector magnetogram, 1) the
  net current (I<SUB>N</SUB>), and 2) the length of the strong-shear,
  strong-field main neutral line (L<SUB>SS</SUB>), and used these two
  measures of the CME productivity of the active regions. We compared the
  global nonpotentiality measures to the active regions' CME productivity
  determined from GOES and Yohkoh/SXT observations. We found that two
  of the active regions were highly globally nonpotential and were
  CME productive, while the other two active regions had little global
  nonpotentiality and produced no CMEs. At the Fall 2000 AGU (Falconer,
  Moore, &amp; Gary, 2000, EOS 81, 48 F998), we reported on an expanded
  study (12 active regions and 17 magnetograms) in which we evaluated
  four quantitative global measures of an active region's magnetic field
  and compared these measures with the CME productivity. The four global
  measures (all derived from MSFC vector magnetograms) included our two
  previous measures (I<SUB>N</SUB> and L<SUB>SS</SUB>) as well as two new
  ones, the total magnetic flux (Φ ) (a measure of an active region's
  size), and the normalized twist (α =μ I<SUB>N</SUB>/Φ ). We found
  that the three measures of global nonpotentiality (I<SUB>N</SUB>,
  L<SUB>SS</SUB>, α ) were all well correlated (&gt;99% confidence
  level) with an active region's CME productivity within (2 days of
  the day of the magnetogram. We will now report on our findings of how
  good our quantitative measures are as predictors of active-region CME
  productivity, using only CMEs that occurred after the magnetogram. We
  report the preliminary skill test of these quantitative measures as
  predictors. We compare the CME prediction success of our quantitative
  measures to the CME prediction success based on an active region's past
  CME productivity. We examine the cases of the handful of false positive
  and false negatives to look for improvements to our predictors. This
  work is funded by NSF through the Space Weather Program and by NASA
  through the Solar Physics Supporting Research and Technology Program.

Title: Overview of the Solar Ultraviolet Magnetograph Investigation
Authors: West, Edward A.; Porter, Jason G.; Davis, John M.; Gary,
   G. Allen; Rabin, Douglas M.; Thomas, Roger J.; Davila, Joseph M.
Bibcode: 2000SPIE.4139..350W
Altcode:
  Traditional magnetographs measure the solar magnetic field at the
  visible 'surface' of the Sun, the photosphere. The Solar Ultraviolet
  Magnetograph Investigation (SUMI) is a hardware development study
  for an instrument to measure the solar magnetic field higher in the
  atmosphere, in the upper chromosphere and in the transition region at
  the base of the corona. The magnetic pressure at these levels is much
  stronger than the gas pressure (in contrast to the situation at the
  photosphere), so the field controls the structure and dynamics of the
  atmosphere. Rapid changes in the magnetic structure of the atmosphere
  become possible at this height, with the release of energy. Measurements
  of the vector magnetic field in this region will significantly improve
  our understanding of the physical processes heating the Sun's upper
  atmosphere and driving transient phenomena such as flares and coronal
  mass ejections. The instrument will incorporate new technologies to
  achieve the polarization efficiencies required to measure the magnetic
  splitting of lines in the VUV an UV (C<SUB>IV</SUB> at 1550 angstrom and
  Mg<SUB>II</SUB> at 2800 angstrom). We describe the scientific goals,
  the optical components that are being developed for a sounding rocket
  program, and the SUMI baseline design.

Title: Erratum: An Assessment of Magnetic Conditions for Strong
    Coronal Heating in Solar Active Regions by Comparing Observed Loops
    with Computed Potential Field Lines
Authors: Falconer, D. A.; Gary, G. A.; Moore, R. L.; Porter, J. G.
Bibcode: 2000ApJ...538..467F
Altcode:
  In the paper ``An Assessment of Magnetic Conditions for Strong
  Coronal Heating in Solar Active Regions by Comparing Observed Loops
  with Computed Potential Field Lines'' by D. A. Falconer, G. A. Gary,
  R. L. Moore, and J. G. Porter (ApJ, 528, 1004 [2000]), Figure 4 was
  rotated 180° and so did not match the figure caption. The correct
  orientation and figure caption is given here.

Title: SUMI: The Solar Ultraviolet Magnetograph
Authors: Davis, J. M.; Porter, J. G.; Gary, G. A.; West, E. A.; Rabin,
   D. M.; Thomas, R. J.; Davila, J. M.
Bibcode: 2000SPD....31.0299D
Altcode: 2000BAAS...32..828D
  A major focus of solar physics is the measurement of the temporal
  and spatial variability of solar magnetic fields from the photosphere
  into the lower corona, together with the study of how their behavior
  produces the dynamic phenomena in this region such as flares and
  CMEs. Considerable success has been achieved in the characterization of
  the full vector field in the photosphere, where β , the ratio of the
  gas pressure to the magnetic pressure, is gtrsim1. At higher levels
  in the atmosphere where β &lt;&lt;1, the magnetic field (through
  the Lorentz force) controls the structure and dynamics of the solar
  atmosphere, and rapid changes in structure with release of energy
  become possible. However, observations of the field at these higher
  levels have proven to be difficult, placing a serious limitation on our
  understanding of the physical processes occurring there. This poster
  will discuss the Solar Ultraviolet Magnetograph Investigation (SUMI),
  a hardware development study for an instrument capable of measuring
  the polarization in ultraviolet lines of C IV and Mg II formed in the
  transition region and upper chromosphere. We are currently developing
  optical technologies necessary to build an instrument that will
  achieve a major advance in performance over that of earlier attempts
  (e.g., SMM/UVSP). Initially configured as a sounding rocket payload,
  such a UV magnetograph would allow us to make exploratory measurements
  extending the observation of solar magnetic fields into new and dynamic
  regimes. This work is supported by NASA through the SEC Program in
  Solar Physics and the program for Technology Development for Explorer
  Missions and Sofia.

Title: Three-dimensional Stereoscopic Analysis of Solar Active Region
    Loops. II. SOHO/EIT Observations at Temperatures of 1.5-2.5 MK
Authors: Aschwanden, Markus J.; Alexander, David; Hurlburt, Neal;
   Newmark, Jeffrey S.; Neupert, Werner M.; Klimchuk, J. A.; Gary,
   G. Allen
Bibcode: 2000ApJ...531.1129A
Altcode:
  In this paper we study the three-dimensional structure of hot
  (T<SUB>e</SUB>~1.5-2.5 MK) loops in solar active region NOAA
  7986, observed on 1996 August 30 with the Extreme-ultraviolet
  Imaging Telescope (EIT) on board the Solar and Heliospheric
  Observatory (SOHO). This complements a first study (Paper I) on
  cooler (T<SUB>e</SUB>~1.0-1.5 MK) loops of the same active region,
  using the same method of Dynamic Stereoscopy to reconstruct the
  three-dimensional geometry. We reconstruct the three-dimensional
  coordinates x(s), y(s), z(s), the density n<SUB>e</SUB>(s), and
  temperature profile T<SUB>e</SUB>(s) of 35 individual loop segments
  (as a function of the loop coordinate s) using EIT 195 and 284 Å
  images. The major findings are as follows. (1) All loops are found
  to be in hydrostatic equilibrium, in the entire temperature regime
  of T<SUB>e</SUB>=1.0-2.5 MK. (2) The analyzed loops have a height of
  2-3 scale heights, and thus only segments extending over about one
  vertical scale height have sufficient emission measure contrast for
  detection. (3) The temperature gradient over the lowest scale height
  is of order dT/ds~1-10 K km<SUP>-1</SUP>. (4) The radiative loss
  rate is found to exceed the conductive loss rate by about two orders
  or magnitude in the coronal loop segments, implying that the loops
  cannot be in quasi-static equilibrium, since standard steady-state loop
  models show that radiative and conductive losses are comparable. (5) A
  steady state could only be maintained if the heating rate E<SUB>H</SUB>
  matches exactly the radiative loss rate in hydrostatic equilibrium,
  requiring a heat deposition length λ<SUB>H</SUB> of the half density
  scale height λ. (6) We find a correlation of p~L<SUP>-1</SUP> between
  loop base pressure and loop length, which is not consistent with the
  scaling law predicted from steady-state models of large-scale loops. All
  observational findings indicate consistently that the energy balance
  of the observed EUV loops cannot be described by steady-state models.

Title: An Assessment of Magnetic Conditions for Strong Coronal
    Heating in Solar Active Regions by Comparing Observed Loops with
    Computed Potential Field Lines
Authors: Falconer, D. A.; Gary, G. A.; Moore, R. L.; Porter, J. G.
Bibcode: 2000ApJ...528.1004F
Altcode:
  We report further results on the magnetic origins of coronal heating
  found from registering coronal images with photospheric vector
  magnetograms. For two complementary active regions, we use computed
  potential field lines to examine the global nonpotentiality of bright
  extended coronal loops and the three-dimensional structure of the
  magnetic field at their feet, and assess the role of these magnetic
  conditions in the strong coronal heating in these loops. The two
  active regions are complementary, in that one is globally potential
  and the other is globally nonpotential, while each is predominantly
  bipolar, and each has an island of included polarity in its trailing
  polarity domain. We find the following: (1) The brightest main-arch
  loops of the globally potential active region are brighter than the
  brightest main-arch loops of the globally strongly nonpotential active
  region. (2) In each active region, only a few of the mainarch magnetic
  loops are strongly heated, and these are all rooted near the island. (3)
  The end of each main-arch bright loop apparently bifurcates above the
  island, so that it embraces the island and the magnetic null above the
  island. (4) At any one time, there are other main-arch magnetic loops
  that embrace the island in the same manner as do the bright loops but
  that are not selected for strong coronal heating. (5) There is continual
  microflaring in sheared core fields around the island, but the main-arch
  bright loops show little response to these microflares. <P />From these
  observational and modeling results we draw the following conclusions:
  (1) The heating of the main-arch bright loops arises mainly from
  conditions at the island end of these loops and not from their global
  nonpotentiality. (2) There is, at most, only a loose coupling between
  the coronal heating in the bright loops of the main arch and the coronal
  heating in the sheared core fields at their feet, although in both the
  heating is driven by conditions/events in and around the island. (3)
  The main-arch bright loops are likely to be heated via reconnection
  driven at the magnetic null over the island. The details of how and
  where (along the null line) the reconnection is driven determine
  which of the split-end loops are selected for strong heating. (4)
  The null does not appear to be directly involved in the heating of
  the sheared core fields or in the heating of an extended loop rooted
  in the island. Rather, these all appear to be heated by microflares
  in the sheared core field.

Title: Magnetic field configuration of active region NOAA 6555 at
    the time of a long-duration flare on 23 March 1991 - An Exception
    to Standard Flare Reconnection Model
Authors: Choudhary, Debi Prasad; Gary, G. Allen
Bibcode: 1999SoPh..188..345C
Altcode:
  The high-resolution Hα images observed during the decay phase
  of a long-duration flare on 23 March 1991 are used to study the
  three-dimensional magnetic field configuration of the active region NOAA
  6555. Whereas all the large flares in NOAA 6555 occurred at the location
  of high magnetic shear and flux emergence, this long-duration flare was
  observed in the region of low magnetic shear at the photosphere. The Hα
  loops activity started soon after the maximum phase of the flare. There
  were a few long loop at the initial phase of the activity. Some of
  these were sheared in the chromosphere at an angle of about 45° to
  the east-west axis. Gradually, an increasing number of shorter loops,
  oriented along the east-west axis, started appearing. The chromospheric
  Dopplergrams show blue shifts at the end points of the loops. By using
  different magnetic field models, we have extrapolated the photospheric
  magnetograms to chromospheric heights. The magnetic field lines computed
  by using the potential field model correspond to most of the observed
  Hα loops. The height of the Hα loops were derived by comparing them
  with the computed field lines. From the temporal evolution of the Hα
  loop activity, we derive the negative rate of appearance of Hα features
  as a function of height. It is found that the field lines oriented along
  one of the neutral lines were sheared and low lying. The higher field
  lines were mostly potential. The paper also outlines a possible scenario
  for describing the post-flare stage of the observed long-duration flare.

Title: β in streamers
Authors: Suess, S. T.; Gary, G. A.; Nerney, S. F.
Bibcode: 1999AIPC..471..247S
Altcode: 1999sowi.conf..247S
  The ratio of thermal pressure to magnetic pressure (β) is greater
  than unity above ~1.2R<SUB>S</SUB> in streamers.

Title: Constructing the Coronal Magnetic Field By Correlating
    Parameterized Magnetic Field Lines With Observed Coronal Plasma
    Structures
Authors: Gary, G. Allen; Alexander, David
Bibcode: 1999SoPh..186..123G
Altcode:
  A method is presented for constructing the coronal magnetic field
  from photospheric magnetograms and observed coronal loops. A set of
  magnetic field lines generated from magnetogram data is parameterized
  and then deformed by varying the parameterized values. The coronal flux
  tubes associated with this field are adjusted until the correlation
  between the field lines and the observed coronal loops is maximized. A
  mathematical formulation is described which ensures that (i) the
  normal component of the photospheric field remains unchanged, (ii)
  the field is given in the entire corona over an active region, (iii)
  the field remains divergence-free, and (iv) electric currents are
  introduced into the field. It is demonstrated that a parameterization
  of a potential field, comprising a radial stretching of the field,
  can provide a match for a simple bipolar active region, AR 7999,
  which crossed the central meridian on 1996 November 26. The result is a
  non-force-free magnetic field with the Lorentz force being of the order
  of 10<SUP>−5.5</SUP> g cm s<SUP>−2</SUP> resulting from an electric
  current density of 0.079 μA m<SUP>−2</SUP>. Calculations show that
  the plasma beta becomes larger than unity at a relatively low height of
  ∼0.25 r<SUB>⊙</SUB> supporting the non-force-free conclusion. The
  presence of such strong non-radial currents requires large transverse
  pressure gradients to maintain a magnetostatic atmosphere, required
  by the relatively persistent nature of the coronal structures observed
  in AR 7999. This scheme is an important tool in generating a magnetic
  field solution consistent with the coronal flux tube observations and
  the observed photospheric magnetic field.

Title: Rendering Three-Dimensional Solar Coronal Structures of Active
    Region 8227
Authors: Gary, G. A.; Alexander, D.; Fletcher, L.
Bibcode: 1999AAS...194.7807G
Altcode: 1999BAAS...31..962G
  Coronal X-ray and EUV synthesized images of Active Region 8227
  (May-June 1996) are constructed and compared with TRACE, Yohkoh/SXT, and
  SOHO/EIT observations. Using the rendering technique of Gary (1997) and
  Alexander, Gary, and Thompson (1998), specific geometric and physical
  models are used to integrate the plasma emission along the line of sight
  to obtain a rendered image. The instrumental profiles are convolved
  in the integration process as well as unique heating functions. We
  analyze coronal X-ray and EUV structures via the constructing of
  synthesized images and investigate how different heating rates within
  the active region loop system affect the emission characteristics. The
  intercomparison of the emission seen in different telescopes with
  that predicted by the assumed model provides a diagnostic tool for
  determining the properties of the heating and a physical explanation for
  the observed distributions. Of particular note is the presence of bright
  EUV emission at the base of hot X-ray loops, reminiscent of the "moss"
  observed by Berger &amp; et al. (1999), and Fletcher &amp; De Pontieu
  (1999). Gary, G. A.: 1997, Solar Physics, 174, 241. Alexander, D.,
  Gary, G. A., and Thompson, B.J.: 1998, Proc. 2nd ASPE, PASP Conference
  Series. Berger, T. E., De Pontieu, B., Schrijver, C. J., Title, A. M.,
  1999. ApJ Letts. (submitted) Fletcher, L., De Pontieu, B. 1999, ApJ
  Letts. (submitted)

Title: Three-dimensional Stereoscopic Analysis of Solar Active
    Region Loops. I. SOHO/EIT Observations at Temperatures of (1.0-1.5)
    × 10<SUP>6</SUP> K
Authors: Aschwanden, Markus J.; Newmark, Jeffrey S.; Delaboudinière,
   Jean-Pierre; Neupert, Werner M.; Klimchuk, J. A.; Gary, G. Allen;
   Portier-Fozzani, Fabrice; Zucker, Arik
Bibcode: 1999ApJ...515..842A
Altcode:
  The three-dimensional structure of solar active region NOAA 7986
  observed on 1996 August 30 with the Extreme-Ultraviolet Imaging
  Telescope (EIT) on board the Solar and Heliospheric Observatory
  (SOHO) is analyzed. We develop a new method of dynamic stereoscopy to
  reconstruct the three-dimensional geometry of dynamically changing
  loops, which allows us to determine the orientation of the mean
  loop plane with respect to the line of sight, a prerequisite to
  correct properly for projection effects in three-dimensional loop
  models. With this method and the filter-ratio technique applied
  to EIT 171 and 195 Å images we determine the three-dimensional
  coordinates [x(s), y(s), z(s)], the loop width w(s), the electron
  density n<SUB>e</SUB>(s), and the electron temperature T<SUB>e</SUB>(s)
  as a function of the loop length s for 30 loop segments. Fitting the
  loop densities with an exponential density model n<SUB>e</SUB>(h)
  we find that the mean of inferred scale height temperatures,
  T<SUP>λ</SUP><SUB>e</SUB>=1.22+/-0.23 MK, matches closely that of EIT
  filter-ratio temperatures, T<SUP>EIT</SUP><SUB>e</SUB>=1.21+/-0.06
  MK. We conclude that these cool and rather large-scale loops (with
  heights of h~30-225 Mm) are in hydrostatic equilibrium. Most of the
  loops show no significant thickness variation w(s), but we measure
  for most of them a positive temperature gradient (dT/ds&gt;0) across
  the first scale height above the footpoint. Based on these temperature
  gradients we find that the conductive loss rate is about 2 orders of
  magnitude smaller than the radiative loss rate, which is in strong
  contrast to hot active region loops seen in soft X-rays. We infer a
  mean radiative loss time of τ<SUB>rad</SUB>~40 minutes at the loop
  base. Because thermal conduction is negligible in these cool EUV
  loops, they are not in steady state, and radiative loss has entirely
  to be balanced by the heating function. A statistical heating model
  with recurrent heating events distributed along the entire loop can
  explain the observed temperature gradients if the mean recurrence time
  is &lt;~10 minutes. We computed also a potential field model (from
  SOHO/MDI magnetograms) and found a reasonable match with the traced
  EIT loops. With the magnetic field model we determined also the height
  dependence of the magnetic field B(h), the plasma parameter β(h),
  and the Alfvén velocity v<SUB>A</SUB>(h). No correlation was found
  between the heating rate requirement E<SUB>H0</SUB> and the magnetic
  field B<SUB>foot</SUB> at the loop footpoints.

Title: Complex H α Loop Activity in a Long Duration Flare
Authors: Prasad, D.; Gary, G.; Ambastha, A.
Bibcode: 1999ASPC..183..523P
Altcode: 1999hrsp.conf..523P
  No abstract at ADS

Title: Beta in Streamers
Authors: Suess, Steven T.; Gary, G. A.; Nerney, S. F.
Bibcode: 1999AIPC..471.....S
Altcode:
  Streamers are often described as regions of the corona in which the
  density is higher than in coronal holes because the plasma is trapped by
  closed loops of magnetic flux. In contrast, Magnetohydrodynamics (MHD)
  models of the global corona show that the plasma beta identically equal
  to 8(pi)p/B<SUP>2</SUP> &gt; 1 in streamers above approximately 1.2Rs
  heliocentric height (p=pressure, B=magnetic field strength). There are
  three recent contributions to this topic. The first is that heating
  near the cusp further drives Beta up and can result in release of new
  slow solar wind from the top of the streamer. The second is SOHO/UVCS
  observations, in combination with a potential field/source surface
  model of the magnetic field, show beta &gt; 1 above 1.2Rs in a streamer
  observed near solar sunspot minimum. The third is a magnetic field
  reconstruction technique (using field deforming algorithms) which was
  applied both to an isolated active region (AR 7999) and to the Pneuman
  &amp; Kopp global MHD model. In the active region, beta becomes larger
  than unity at approximately 1.2Rs. In the Pneuman &amp; Kopp model,
  beta = 1.0 at the base of the streamer and rises with increasing
  height, becoming 15-20 at 1.6Rs and 35-55 at 1.7RS. The collective
  implication of these three results is that beta &gt; 1 everywhere in
  streamers above approximately 1.2 Rs. Global simulations go on to show
  that the reason streamers do not simply explode under such high beta
  conditions is that they are held down by pressure from the sides due
  to the magnetic fields (and low beta) in adjacent coronal holes. The
  main role of the closed magnetic loops near the cusp is to keep the
  streamer from continuously leaking plasma, as otherwise happens in a
  magnetic pinch which is similar but has no closed loops. The purpose
  of this note is to summarize the results implying that beta &gt;
  1 is a general property of streamers above 1.2 Rs.

Title: On Analysis of Dual Spacecraft Stereoscopic Observations to
    Determine the Three-Dimensional Morphology and Plasma Properties of
    Solar Coronal Flux Tubes
Authors: Gary, G. Allen; Davis, John M.; Moore, Ronald
Bibcode: 1998SoPh..183...45G
Altcode:
  By using two spacecraft equipped with multi-bandpass X-ray telescopes,
  it is possible to obtain direct 3-dimensional morphology of coronal
  structures which is essential for understanding the energetics and
  dynamics of the solar atmosphere. X-ray observations taken only in
  orbit about the Earth are inadequate to fully resolve the 3-dimensional
  nature of the solar corona. These Earth-orbit observations produce
  2-dimensional images and an appropriate model must be included
  to derive the 3-dimensional structures from the line-of-sight
  information. Stereoscopic observations from space will remove this
  limitation and are needed if we are to improve our knowledge of the
  3-dimensional morphology of the corona.

Title: Report on new mission concept study: Stereo X-Ray Corona
    Imager mission
Authors: Liewer, Paulett C.; Davis, John M.; de Jong, E. M.; Gary,
   G. A.; Klimchuk, James A.; Reinert, Richard P.
Bibcode: 1998SPIE.3442...53L
Altcode:
  Studies of the 3D structure and dynamics of the solar corona
  have been severely limited by the constraint of single viewpoint
  observations. The Stereo X-Ray Coronal Imager (SXCI) mission will send
  a single instrument, an X-ray telescope, into deep space expressly to
  record stereoscopic images of the solar corona. The SXCI spacecraft
  will be inserted into an approximately 1 ZAU heliocentric orbit leading
  Earth by approximately 25 degrees at the end of nine months. The SXCI
  x-ray telescope forms one element of a stereo pair, the second element
  being an identical x-ray telescope in Earth orbit placed there as part
  of the NOAA GOES program. X-ray emission is a powerful diagnostic of
  the corona and its magnetic fields, and 3D information on the coronal
  magnetic structure would be obtained by combining the data from the
  two x-ray telescopes. This information can be used to address the major
  solar physics questions of (1) what causes explosive coronal events such
  as coronal mass ejections, eruptive flares and prominence eruptions and
  (2) what causes the transient heating of coronal loops. Stereoscopic
  views of the optically thin corona will resolve some ambiguities
  inherent in single line-of-sight observations. Triangulation gives 3D
  solar coordinates of features which can be seen in the simultaneous
  images form both telescopes. As part of this study, tools were
  developed for determining the 3D geometry of coronal features using
  triangulation. Advanced technologies for visualization and analysis of
  stereo images were tested. Results of mission and spacecraft studies
  are also reported.

Title: 3D-Stereoscopic Analysis of Solar Active Region Loops Observed
    with SOHO/EIT
Authors: Aschwanden, M. J.; Newmark, J. S.; Delaboudiniere, J. -P.;
   Neupert, W. M.; Klimchuk, J. A.; Gary, G. Allen; Portier-Fozzani,
   F.; Zucker, A.
Bibcode: 1998cee..workE..19A
Altcode:
  The three-dimensional (3D) structure of solar active region NOAA
  7986 observed on 1996 August 30 with the Extrem-ultraviolet Imaging
  Telescope (EIT) onboard the Solar and Heliospheric Observatory
  (SoHO) is analyzed. We develop a new method of Dynamic Stereoscopy to
  reconstruct the 3D geometry of dynamically changing loops, which allows
  us to determine the orientation of the loop plane with respect to
  the line-of-sight, a prerequisite to correct properly for projection
  effects in 3D loop models. With this method and the filter-ratio
  technique applied to EIT 171 angle and 195 angle images we determine
  the 3D coordinates [x(s),y(s),z(s)], the loop width w(s), the electron
  density n_e(s), and the electron temperature T_e(s) as function of
  the loop length s for 30 loop segments. Fitting the loop densities
  with an exponential density model n_e(h) we find that the mean of
  inferred scale height temperatures, T_e<SUP>lambda</SUP> = 1.22 plus or
  minus 0.23 MK, matches closely that of EIT filter-ratio temperatures,
  T_e<SUP>EIT</SUP> = 1.21 plus or minus 0.06 MK. We conclude that these
  cool and rather large-scale loops (with heights of h ~30-225 Mm), which
  dominate the EIT 171 angle images, are in hydrostatic equilibrium. Most
  of the loops show no significant thickness variation w(s), but we can
  measure for most of them a positive temperature gradient (dT/ds &gt;
  0) across the first scale height above the footpoint. Based on these
  temperature gradients we find that the conductive loss rate is about
  two orders of magnitude smaller than the radiative loss rate, which is
  in strong contrast to hot active region loops seen in SXR. We infer a
  mean radiative loss time of τ<SUB>rad</SUB> ~40 minutes. For steady
  state models, the heating rate has to balance the radiative loss,
  i.e. the heating rate has to scale with the squared density (E_H
  propto n_e^2). From potential-field extrapolations we determine also
  the magnetic field strength B(s), the plasma beta-parameter beta(s),
  and the Alfven velocity v_A(s) along the loops, and discuss the findings
  in the context of coronal heating models.

Title: Analysis of Active Regions via 3D Rendering Techniques
Authors: Alexander, D.; Gary, G. Allen; Thompson, B. J.
Bibcode: 1998ASPC..155..100A
Altcode: 1998sasp.conf..100A
  No abstract at ADS

Title: Measurements and analyses of the 3-D solar magnetic
    fields. Proceedings. Workshop, Huntsville, AL (USA), 9 - 11 Apr 1996.
Authors: Wu, S. -T.; Gary, G. A.
Bibcode: 1997SoPh..174....1W
Altcode:
  Dedicated to Yoshinari Nakagawa.

Title: Rendering Three-Dimensional Solar Coronal Structures
Authors: Gary, G. Allen
Bibcode: 1997SoPh..174..241G
Altcode:
  An X-ray or EUV image of the corona or chromosphere is a 2D
  representation of an extended 3D complex for which a general inversion
  process is impossible. A specific model must be incorporated in order to
  understand the full 3D structure. We approach this problem by modeling
  a set of optically-thin 3D plasma flux tubes which we render these as
  synthetic images. The resulting images allow the interpretation of the
  X-ray/EUV observations to obtain information on (1) the 3D structure of
  X-ray images, i.e., the geometric structure of the flux tubes, and on
  (2) the internal structure using specific plasma characteristics, i.e.,
  the physical structure of the flux tubes. The data-analysis technique
  uses magnetograms to characterize photospheric magnetic fields and
  extrapolation techniques to form the field lines. Using a new set of
  software tools, we have generated 3D flux tube structures around these
  field lines and integrated the plasma emission along the line of sight
  to obtain a rendered image. A set of individual flux-tube images is
  selected by a non-negative least-squares technique to provide a match
  with an observed X-ray image. The scheme minimizes the squares of
  the differences between the synthesized image and the observed image
  with a non-negative constraint on the coefficients of the brightness
  of the individual flux-tube loops. The derived images are used to
  determine the specific photospheric foot points and physical data,
  i.e., scaling laws for densities and loop lengths. The development
  has led to computer efficient integration and display software that
  is compatible for comparison with observations (e.g., Yohkoh SXT data,
  NIXT, or EIT). This analysis is important in determining directly the
  magnetic field configuration, which provides the structure of coronal
  loops, and indirectly the electric currents or waves, which provide
  the energy for the heating of the plasma. We have used very simple
  assumptions (i.e., potential magnetic fields and isothermal corona)
  to provide an initial test of the techniques before complex models are
  introduced. We have separated the physical and geometric contributions
  of the emission for a set of flux tubes and concentrated, in this
  initial study, on the geometric contributions by making approximations
  to the physical contributions. The initial results are consistent with
  the scaling laws derived from the Yohkoh SXT data.

Title: Neutral-Line Magnetic Shear and Enhanced Coronal Heating in
    Solar Active Regions
Authors: Falconer, D. A.; Moore, R. L.; Porter, J. G.; Gary, G. A.;
   Shimizu, T.
Bibcode: 1997ApJ...482..519F
Altcode:
  By examining the magnetic structure at sites in the bright coronal
  interiors of active regions that are not flaring but exhibit persistent
  strong coronal heating, we establish some new characteristics of
  the magnetic origins of this heating. We have examined the magnetic
  structure of these sites in five active regions, each of which was well
  observed by both the Yohkoh SXT and the Marshall Space Flight Center
  Vector Magnetograph and showed strong shear in its magnetic field along
  part of at least one neutral line (polarity inversion). Thus, we can
  assess whether this form of nonpotential field structure in active
  regions is a characteristic of the enhanced coronal heating and vice
  versa. From 27 orbits' worth of Yohkoh SXT images of the five active
  regions, we have obtained a sample of 94 persistently bright coronal
  features (bright in all images from a given orbit), 40 long (&gt;~20,000
  km) neutral-line segments having strong magnetic shear throughout
  (shear angle greater than 45°), and 39 long neutral-line segments
  having weak magnetic shear throughout (shear angle less than 45°). From
  this sample, we find that (1) all of our persistently bright coronal
  features are rooted in magnetic fields that are stronger than 150 G,
  (2) nearly all (95%) of these enhanced coronal features are rooted near
  neutral lines (closer than 10,000 km), (3) a great majority (80%) of the
  bright features are rooted near strong-shear portions of neutral lines,
  (4) a great majority (85%) of long strong-shear segments of neutral
  lines have persistently bright coronal features rooted near them, (5)
  a large minority (40%) of long weak-shear segments of neutral lines
  have persistently bright coronal features rooted near them, and (6)
  the brightness of a persistently bright coronal feature often changes
  greatly over a few hours. From these results, we conclude that most
  persistent enhanced heating of coronal loops in active regions (1)
  requires the presence of a polarity inversion in the magnetic field
  near at least one of the loop footpoints, (2) is greatly aided by the
  presence of strong shear in the core magnetic field along that neutral
  line, and (3) is controlled by some variable process that acts in this
  magnetic environment. We infer that this variable process is low-lying
  reconnection accompanying flux cancellation.

Title: Evidence that Strong Coronal Heating Results from Photospheric
    Magnetic Flux Cancellation
Authors: Moore, R. L.; Falconer, D. A.; Porter, J. G.; Gary, G. A.;
   Shimizu, T.
Bibcode: 1996AAS...188.8604M
Altcode: 1996BAAS...28..963M
  Soft X-ray images of the Sun's corona, such as those from the Yohkoh
  SXT, show that the sites of strongest persistent (non-flare) coronal
  heating are located within the strong (&gt;100 gauss) magnetic fields
  in sunspot regions and are limited to only certain places within these
  stong-field domains, covering only a fraction of the total area. We have
  examined the structure of the magnetic field at these sites in 5 active
  regions by superposing Yohkoh SXT coronal X-ray images on MSFC vector
  magnetograms. We find: (1) nearly all of the enhanced (outstandingly
  bright) coronal features that persist for tens of minutes are rooted
  near polarity neutral lines in the photospheric magnetic flux; (2) in
  most cases the core magnetic field closely straddling the neutral line
  at the root of the strong heating is strongly sheared; (3) the enhanced
  coronal X-ray brightness in the low-lying core fields shows spatial
  substructure that fluctuates on time scales of minutes, in the manner
  of microflaring; and (4) large parts of extensive enhanced coronal
  features often last for no more than a few hours. From these results,
  it appears that most enhanced coronal heating in active regions is a
  consequence of some process that (1) acts only in the presence of a
  photospheric polarity neutral line, (2) is episodic on times of about
  an hour, (3) usually gives stronger coronal heating in the presence of
  stronger magnetic shear, but is not required to act by the presence of
  magnetic shear, and (4) is often accompanied by microflaring in the
  core field. We point out that magnetic flux cancellation (driven by
  photospheric flows at the neutral line) is a process that plausibly
  meets all these requirements. The flux cancellation might directly
  drive microflaring, or trigger microflaring in the sheared core field,
  or both. The microflaring might directly produce the enhanced coronal
  heating in the core fields as well as generate MHD waves that propagate
  up into the enhanced extended coronal loops to provide the strong
  coronal heating in these.

Title: Potential Field Extrapolation Using Three Components of a
    Solar Vector Magnetogram with a Finite Field of View
Authors: Gary, G. Allen
Bibcode: 1996SoPh..163...43G
Altcode:
  The potential magnetic field from a finite planar boundary is
  extrapolated into the upper hemisphere using information from all
  three magnetic field components. The method determines, first,
  the transverse field associated with the observed normal magnetic
  intensity. Then by subtraction, the method determines the associated
  transverse magnetic field observed in the interior (i.e., in the field
  of view) of the magnetogram which is due to the normal flux exterior
  to the field of view of the magnetogram. Inverting this information
  gives an approximation to the exterior normal flux. The combination of
  the observed normal flux of the interior and the approximation of the
  exterior normal flux is employed to calculate the potential field. The
  formulation of the problem results in an ill-posed integral inversion
  problem in which a regularized solution is obtained using the singular
  value decomposition (SVD) technique in conjunction with an appropriate
  Tikhonov-Phillips filter. The technique can be applied to correcting
  potential field calculations which are influenced by out-of-view
  fluxes, e.g., for a high spatial resolution vector magnetogram with a
  small field of view in which there is no supporting exterior data. The
  problem studied is also important in providing a regularized solution
  of the Cauchy potential problem. The method provides a much larger
  range of convergence than the method of Gary and Musielak (1992), and,
  in fact, is stable in the total upper hemisphere.

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: Line-of-sight magnetic flux imbalances caused by electric
    currents
Authors: Gary, G. Allen; Rabin, Douglas
Bibcode: 1995SoPh..157..185G
Altcode: 1995SoPh..157..185A
  Several physical and observational effects may contribute to the
  significant imbalances of magnetic flux that are often observed in
  active regions. We consider an effect not previously treated: the
  influence of electric currents in the photosphere. Electric currents can
  cause a line-of-sight flux imbalance because of the directionality of
  the magnetic field they produce. Currents associated with magnetic flux
  tubes produce larger imbalances than do smoothly-varying distributions
  of flux and current. We estimate the magnitude of this effect for
  current densities, total currents, and magnetic geometry consistent
  with observations. The expected imbalances lie approximately in
  the range 0-15%, depending on the character of the current-carrying
  fields and the angle from which they are viewed. Observationally,
  current-induced flux imbalances could be indicated by a statistical
  dependence of the imbalance on angular distance from disk center. A
  general study of magnetic flux balance in active regions is needed to
  determine the relative importance of other - probably larger -effects
  such as dilute flux (too weak to measure or rendered invisible by
  radiative transfer effects), merging with weak background fields,
  and long-range connections between active regions.

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: 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: Interpretation of Magnetic Field Structures from Observations
    of Active Region AR 6659 in 1991 June 8-11
Authors: Wu, S. T.; Weng, F. S.; Hagyard, M. J.; Gary, G. A.
Bibcode: 1993BAAS...25.1218W
Altcode:
  No abstract at ADS

Title: Interactive Flare Sites Within an Active Region Complex
Authors: Poletto, G.; Gary, G. A.; Machado, M. E.
Bibcode: 1993SoPh..144..113P
Altcode:
  The problem of physical relationships between different active
  regions has been dealt with only rarely and mainly in connection
  with flares. How sympathetic activity can be triggered between
  distant regions is therefore, so far, largely unknown. Soft X-ray
  images of large-scale coronal structures connecting different active
  regions were obtained by Skylab nearly 20 years ago, while SMM,
  more recently, did not provide any clear evidence for this kind of
  loop. As a consequence, we do not know how common these features are
  nor how they form nor whether they represent the only means by which
  distant active regions may be linked. In the latter case, however,
  interconnecting loops should be detected by analyzing the interaction
  between different active regions. We examine here a set of images of
  an active region complex, acquired on June 24-25, 1980, by the Hard
  X-ray Imaging Spectrometer on SMM, with the purpose of establishing
  whether there was any interplay between the frequent activity observed
  at different sites in the activity center and, in such a case, how the
  interaction was established. By analyzing both quiet and active orbits
  we show that, as a rule, activity originating in one region triggers the
  other region's activity. However, we find little unambiguous evidence
  for the presence of large-scale interconnecting loops. A comparison
  of X-ray images with magnetic field observations suggested that we
  interpret the active region behavior in terms of the interaction
  between different loop systems, in a scenario quite analogous to the
  interacting bipole representation of individual flares. We conclude
  that active region interplay provides an easily observable case to
  study the time-dependent topology and the mechanisms for the spreading
  of activity in transient events over all energy scales.

Title: A Regularization Method for Extrapolation of Solar Potential
    Magnetic Fields
Authors: Gary, G. A.; Musielak, Z. E.
Bibcode: 1992ApJ...392..722G
Altcode:
  The mathematical basis of a Tikhonov regularization method for
  extrapolating the chromospheric-coronal magnetic field using
  photospheric vector magnetograms is discussed. The basic techniques
  show that the Cauchy initial value problem can be formulated for
  potential magnetic fields. The potential field analysis considers a
  set of linear, elliptic partial differential equations. It is found
  that, by introducing an appropriate smoothing of the initial data
  of the Cauchy potential problem, an approximate Fourier integral
  solution is found, and an upper bound to the error in the solution is
  derived. This specific regularization technique, which is a function
  of magnetograph measurement sensitivities, provides a method to
  extrapolate the potential magnetic field above an active region into
  the chromosphere and low corona.

Title: On Neutralized Currents in the Solar Corona
Authors: Wilkinson, Ladye K.; Emslie, A. G.; Gary, G. A.
Bibcode: 1992ApJ...392L..39W
Altcode:
  Using Ampere's integral law applied to vector magnetograph transverse
  field data, the current pattern in an active region associated with
  flaring activity is analyzed. The greater sensitivity of this integral
  formalism of Ampere's law may allow one to identify regions of weak
  return current around the actual positive current region. The effects
  of Faraday rotation on the inferred magnetic field measurements, and
  hence on the deduced current pattern, are discussed. It is concluded
  that the current patterns in the region consist either of a neutralized
  current system, well modeled by a coaxial cable, or of a potential
  field, with the apparent currents in the core an artifact induced by
  magneto-optical effects. In either case, the data do not convincingly
  show an unneutralized current system.

Title: Interacting Confined-Eruptive Flare Sites Within a Magnetic
    Active Region Complex
Authors: Gary, G. A.; Poletto, G.; Mechado, M. E.
Bibcode: 1992AAS...180.4106G
Altcode: 1992BAAS...24Q.795G
  No abstract at ADS

Title: The MSFC Solar GRO Guest Investigation
Authors: Hagyard, M. J.; Gary, G. A.; Moore, R. L.
Bibcode: 1991BAAS...23.1073H
Altcode:
  No abstract at ADS

Title: Magnetic Field Changes Associated with a Subflare and Surge
Authors: Hagyard, M. J.; West, E. A.; Gary, G. A.; Smith, J. E.
Bibcode: 1991BAAS...23.1030H
Altcode:
  No abstract at ADS

Title: A Regularization Method for the Extrapolation of Solar
    Magnetic Fields
Authors: Gary, G. A.; Musielak, Z.
Bibcode: 1991BAAS...23.1031G
Altcode:
  No abstract at ADS

Title: Solar vector magnetic field measurements.
Authors: Gary, G. A.; Hagyard, M. J.; West, E. A.
Bibcode: 1991sopo.work...65G
Altcode:
  This paper contains a discussion of recent results with the Marshall
  Space Flight Center's (MSFC) filter vector magnetograph and the
  co-aligned Hα telescope. This report emphasizes total vector magnetic
  measurements and the co-spatial, co-temporal Hα observations. The
  observations reported include magnetic shear data along the neutral
  inversion line, vector field measurements below prominences,
  and vector magnetic field measurements associated with flares and
  surge activity. The importance of a large field of view and high
  polarimetric sensitivity in solar vector magnetic field measurements
  is also discussed.

Title: On the Numerical Computation of Nonlinear Force-free Magnetic
    Fields
Authors: Wu, S. T.; Sun, M. T.; Chang, H. M.; Hagyard, M. J.; Gary,
   G. A.
Bibcode: 1990ApJ...362..698W
Altcode:
  An algorithm has been developed to extrapolate nonlinear force-free
  magnetic fields from the photosphere, given the proper boundary
  conditions. This paper presents the results of this work, describing
  the mathematical formalism that was developed, the numerical techniques
  employed, and comments on the stability criteria and accuracy developed
  for these numerical schemes. An analytical solution is used for a
  benchmark test; the results show that the computational accuracy for
  the case of a nonlinear force-free magnetic field was on the order of
  a few percent (less than 5 percent). This newly developed scheme was
  applied to analyze a solar vector magnetogram, and the results were
  compared with the results deduced from the classical potential field
  method. The comparison shows that additional physical features of the
  vector magnetogram were revealed in the nonlinear force-free case.

Title: Coaligned observations of solar magnetic fields at different
heights: MSFC Center director's discretionary fund final report
    (Project No. 88-10)
Authors: Hagyard, M. J.; West, E. A.; Gary, G. A.; Smith, J. E.
Bibcode: 1990STIN...9110832H
Altcode:
  The objective was to develop the capability for and coaligned
  observations of the structure and evolution of the Sun's magnetic field
  at two different heights in the solar atmosphere: the photosphere,
  which is the lowest region observable with optical telescopes;
  and the chromosphere, which lies just above the photosphere and
  is the region where the magnetic field dominates the gas motion so
  that a well-ordered structure governed by the field is observed. By
  obtaining this three-dimensional picture of the solar magnetic field,
  a better understanding can be developed of the magnetic forces that
  produce and control the dynamic, high-energy phenomena occurring in
  the solar atmosphere that can affect the entire heliosphere, including
  the terrestrial environment.

Title: A lunar based solar observatory rationale and concepts
Authors: Davis, John M.; Balasubramaniam, K. S.; Gary, G. A.; Moore,
   Ronald L.
Bibcode: 1990AIPC..207..567D
Altcode: 1990am...proc..567D
  The rationale for a lunar solar observatory is described and the
  requirements for various candidate instruments are developed. The unique
  characteristics of the lunar surface, its stability, low seismicity,
  and long unobstructed paths make it an ideal site for a large, high
  performance optical telescope. The capabilities of such an instrument is
  used, as an example (1) for the science that might be achieved from the
  lunar surface, (2) to identify the magnitude of the instrumentation,
  and (3) to indicate the technologies that must be developed if such
  an observatory is to become a reality.

Title: Transformation of vector magnetograms and the problems
    associated with the effects of perspective and the azimuthal ambiguity
Authors: Gary, G. Allen; Hagyard, M. J.
Bibcode: 1990SoPh..126...21G
Altcode:
  Off-center vector magnetograms which use all three components of
  the measured field provide the maximum information content from the
  photospheric field and can provide the most consistent potential field
  independent of the viewing angle by defining the normal component of
  the field. The required transformations of the magnetic field vector
  and the geometric mapping of the observed field in the image plane into
  the heliographic plane have been described. Here we discuss the total
  transformation of specific vector magnetograms to detail the problems
  and procedures that one should be aware of in analyzing observational
  magnetograms. The effect of the 180-deg ambiguity of the observed
  transverse field is considered as well as the effect of curvature of
  the photosphere. Specific results for active regions AR 2684 (September
  23, 1980) and AR 4474 (April 26, 1984) from the Marshall Space Flight
  Center Vector magnetograph are described which point to the need for
  the heliographic projection in determining the field structure of an
  active region.

Title: Concerning the extrapolation of solar nonlinear force-free
    magnetic fields
Authors: Gary, G. Allen
Bibcode: 1990MmSAI..61..457G
Altcode:
  This paper contains a review and discussion of the mathematical basis
  of the extrapolation techniques involved in using photospheric vector
  magnetograms to obtain the coronal field above the surface. The two
  basic techniques employing the Cauchy initial value problem and the
  variational techniques are reviewed in terms of the mathematical and
  practical applications. A short review is presented of the current
  research on numerical modeling techniques in the area of extrapolating
  vector magnetograms; specifically, algorithms to extrapolate nonlinear
  force-free magnetic fields from the photosphere are considered.

Title: Off Disk Center Potential Field Calculations Using Vector
    Magnetograms
Authors: Venkatakrishnan, P.; Gary, G. Allen
Bibcode: 1989SoPh..120..235V
Altcode:
  We investigate a potential field calculation for off disk-center
  vector magnetograms that uses all the three components of the measured
  field. There is neither any need for interpolation of grid points
  between the image plane and the heliographic plane nor for an extension
  or a truncation to a heliographic rectangle. Hence, the method provides
  the maximum information content from the photospheric field as well
  as the most consistent potential field independent of the viewing
  angle. The introduction of polarimetric noise produces a less tolerant
  extrapolation procedure than using the line-of-sight extrapolation,
  but the resultant standard deviation is still small enough for the
  practical utility of this method.

Title: The Effects of Viewing Angle on the Inference of Magnetic
    Shear in Preflare Active Regions
Authors: Wilkinson, Ladye Kathryn; Emslie, Gordon A.; Gary, G. Allen
Bibcode: 1989SoPh..119...77W
Altcode:
  The magnetic shear at a point within an active region field
  configuration can be defined (Hagyard et al., 1984b) as the difference
  in angle between the observed photospheric transverse field and that of
  a reference potential field calculated using the observed line-of-sight
  field as a boundary condition. Using analytic models for non-potential
  (but force-free) fields representative of preflaring active regions,
  we calculate the degree of magnetic shear along the magnetic neutral
  line that such fields would exhibit, as a function of the location
  and orientation of the active region on the solar disk. We find that,
  except for regions close to disk center, the position of the inferred
  neutral line (zero line-of-sight field) is significantly different
  from the actual neutral line (zero radial field), and that the
  calculated reference potential field also varies significantly with
  the position of the region. Thus the inferred degree of shear can
  vary significantly with the position and orientation of the region,
  due to (a) straightforward geometric projection effects, (b) the shift
  of the inferred neutral line relative to its true position, and (c)
  variations in the reference potential field. The significance of these
  results for flare prediction is considered.

Title: Problems in the Analysis of Off-Disk Center Vector Magnetograms
Authors: Gary, G. A.; Hagyard, M. J.
Bibcode: 1989BAAS...21Q.838G
Altcode:
  No abstract at ADS

Title: Design of the polarimeter for the Solar Activity Measurements
    Experiments (SAMEX) vector magnetograph.
Authors: West, E. A.; Reichmann, E. J.; Hagyard, M. J.; Gary, G. A.
Bibcode: 1989OptEn..28..131W
Altcode:
  In a study by the Marshall Space Flight Center (MSFC) for the Air
  Force Geophysics Laboratory (AFGL), a design concept was developed
  for a polarimeter on the vector magnetograph of the SAMEX satellite
  (Solar Activity Measurements Experiments) that would be very sensitive
  to solar vector magnetic fields. Analysis of the polarimeter designs to
  minimize crosstalk between incident circularly polarized light and the
  linear polarization measurement is stressed. After a polarimeter design
  is selected, the calibration techniques to determine the systematic
  errors in the "perfect" polarimeter are discussed.

Title: Linear Force-free Magnetic Fields for Solar Extrapolation
    and Interpretation
Authors: Gary, G. Allen
Bibcode: 1989ApJS...69..323G
Altcode:
  This paper discusses the interconnection of the various linear
  force-free magnetic field formulations, the specific phenomenological
  and topological parameters of these formulations, and their
  usefulness. Particularly, the limitations and usefulness of linear
  force-free fields are discussed. Specific field configurations are
  related to magnetographic interpretation. The relationship of the
  integral and Fourier procedures is shown explicitly. The physical
  interpretation of linear force-free fields is shown by analytic models
  and from the Marshall Space Flight Center solar vector magnetograms.

Title: Preflare activity.
Authors: Priest, E. R.; Gaizauskas, V.; Hagyard, M. J.; Schmahl, E. J.;
   Webb, D. F.; Cargill, P.; Forbes, T. G.; Hood, A. W.; Steinolfson,
   R. S.; Chapman, G. A.; Deloach, A. C.; Gary, G. A.; Jones, H. P.;
   Karpen, J. T.; Martres, M. -J.; Porter, J. G.; Schmieder, B.; Smith,
   J. B., Jr.; Toomre, J.; Woodgate, B.; Waggett, P.; Bentley, R.;
   Hurford, G.; Schadee, A.; Schrijver, J.; Harrison, R.; Martens, P.
Bibcode: 1989epos.conf....1P
Altcode:
  Contents: 1. Introduction. 2. Magnetohydrodynamic
  instability. 3. Preflare magnetic and velocity fields. 4. Coronal
  manifestations of preflare activity.

Title: Development of the SAMEX vector magnetograph at the Marshall
    Space Flight Center
Authors: West, E. A.; Hagyard, M. J.; Gary, G. A.; Arnett, G. M.
Bibcode: 1988fnsm.work...86W
Altcode:
  A breadboard design to prove the operational feasibility of SAMEX
  Vector Magnetograph is being developed. Although the breadboard
  design will not include all of the elements of the original design
  concept, critical elements such as the large detector array and the
  high resolution polarimeter will be important parts of the breadboard
  design to study the data analysis and compression techniques that will
  be needed in a SAMEX instrument, to study the calibration techniques for
  systemmatic errors in the polarimeter, and to obtain high resolution
  vector magnetograms during the next solar maximum. Although the SAMEX
  polarimeter is not optimum for a ground-based patrol instrument,
  the design concept can be confirmed with ground-based measurements
  and direct comparisons with the existing vector magnetograph. The
  extension of the scientific objectives for this breadboard design is
  possible if a tunable filter can be acquired.

Title: Active Region Coronal Loops: Structure and Variability
Authors: Haisch, Bernhard M.; Strong, Keith T.; Harrison, Richard A.;
   Gary, G. A.
Bibcode: 1988ApJS...68..371H
Altcode:
  X-ray images of a pair of active region loops are studied which show
  significant, short time-scale variability in the line fluxes of O VIII,
  Ne IX, and Mg XI and in the 3.5-11.5 keV soft X-ray bands. Vector
  magnetograms and high-resolution UV images were used to model the
  three-dimensional characteristics of the loops. X-ray light curves were
  generated spanning four consecutive orbits for both loops individually,
  and light curves of the loop tops and brightest points were also
  generated. The largest variations involve flux changes of up to several
  hundred percent on time scales of 10 minutes. No significant H-alpha
  flare activity is reported, and loop temperatures remain in the four
  to six million K range. The decay phases of the light curves indicate
  radiative cooling, inhibition of conduction, and some type of 'continued
  heating' due to ongoing, underlying activity at the microflare level.

Title: The SAMEX vector magnetograph. A design study for a space-based
    solarvector magnetograph.
Authors: Hagyard, M. J.; Gary, G. A.; West, E. A.
Bibcode: 1988NASTM4048.....H
Altcode: 1988STIN...8825424H
  This report presents the results of a study performed to develop
  a design concept for a space-based solar vector magnetograph and
  hydrogen-alpha telescope. These instruments are two of the core
  instruments for a proposed Air Force mission, the Solar Activity
  Measurements Experiments (SAMEX). This mission is designed to study
  the processes which give rise to solar activity in the solar atmosphere
  and to develop techniques for predicting solar activity and its effect
  on the terrestrial environment.

Title: Chromospheric Emission Bifurcation of Sunspots
Authors: Gary, G. A.; Moore, R. L.
Bibcode: 1988BAAS...20..704G
Altcode:
  No abstract at ADS

Title: Development of an Image Processing System to Study Changes
    in Coaligned Vector Magnetograms and H-alpha Images
Authors: West, E. A.; Hagyard, M. J.; Gary, G. A.
Bibcode: 1988BAAS...20..711W
Altcode:
  No abstract at ADS

Title: Development of the SAMEX Vector Magnetograph at the Marshall
    Space Flight Center
Authors: West, E. A.; Hagyard, M. J.; Gary, G. A.; Arnett, G. M.
Bibcode: 1988BAAS...20Q.745W
Altcode:
  No abstract at ADS

Title: Nonpotential Features Observed in the Magnetic Field of an
    Active Region
Authors: Gary, G. A.; Moore, R. L.; Hagyard, M. J.; Haisch, Bernhard M.
Bibcode: 1987ApJ...314..782G
Altcode:
  A unique coordinated data set consisting of vector magnetograms,
  H-alpha photographs, and high-resolution ultraviolet images of a
  solar active region is used, together with mathematical models, to
  calculate potential and force-free magnetic field lines and to examine
  the nonpotential nature of the active region structure. It is found
  that the overall bipolar magnetic field of the active region had a net
  twist corresponding to net current of order 3 x 10 to the 12th A and
  average density of order 4 x 10 to the -4th A/sq m flowing antiparallel
  to the field. There were three regions of enhanced nonpotentiality
  in the interior of the active region; in one the field had a marked
  nonpotential twist or shear with height above the photosphere. The
  measured total nonpotential magnetic energy stored in the entire
  active region was of order 10 to the 32nd ergs, about 3 sigma above
  the noise level.

Title: Preflare magnetic and velocity fields
Authors: Hagyard, M. J.; Gaizauskas, V.; Chapman, G. A.; Deloach,
   A. C.; Gary, G. A.; Jones, H. P.; Karpen, J. T.; Martres, M. -J.;
   Porter, J. G.; Schmeider, B.
Bibcode: 1986epos.conf.1.16H
Altcode: 1986epos.confA..16H
  A characterization is given of the preflare magnetic field, using
  theoretical models of force free fields together with observed field
  structure to determine the general morphology. Direct observational
  evidence for sheared magnetic fields is presented. The role of this
  magnetic shear in the flare process is considered within the context
  of a MHD model that describes the buildup of magnetic energy, and the
  concept of a critical value of shear is explored. The related subject
  of electric currents in the preflare state is discussed next, with
  emphasis on new insights provided by direct calculations of the vertical
  electric current density from vector magnetograph data and on the role
  of these currents in producing preflare brightenings. Results from
  investigations concerning velocity fields in flaring active regions,
  describing observations and analyses of preflare ejecta, sheared
  velocities, and vortical motions near flaring sites are given. This
  is followed by a critical review of prevalent concepts concerning the
  association of flux emergence with flares

Title: Accuracy Requirements for Vector Magnetic Field Measurements
    for Solar Flare Prediction
Authors: Moore, R. L.; Gary, G. A.; Hagyard, M. J.; Davis, J. M.
Bibcode: 1986BAAS...18.1043M
Altcode:
  No abstract at ADS

Title: A digital imaging photometry system for cometary data
    acquisition
Authors: Clifton, K. S.; Benson, C. M.; Gary, G. A.
Bibcode: 1986nasa.reptV....C
Altcode:
  This report describes a digital imaging photometry system developed in
  the Space Science Laboratory at the Marshall Space Flight center. The
  photometric system used for cometary data acquisition is based on an
  intensified secondary electron conduction (ISEC) vidicon coupled to a
  versatile data acquisition system which allows real-time interactive
  operation. Field tests on the Orion and Rosette nebulas indicate
  a limiting magnitude of approximately m<SUB>v</SUB> = 14 over
  the 40 arcmin field-of-view. Observations were conducted of Comet
  Giacobini-Zinner in August 1985. The resulting data are discussed
  in relation to the capabilities of the digital analysis system. The
  development program concluded on August 31, 1985.

Title: Non-Potential Features Observed in the Magnetic Field of an
    Active Region
Authors: Gary, G. A.; Moore, R. L.; Hagyard, M. J.; Haisch, B. M.
Bibcode: 1986BAAS...18..709G
Altcode:
  No abstract at ADS

Title: Preflare activity.
Authors: Priest, E. R.; Gaizauskas, V.; Hagyard, M. J.; Schmahl, E. J.;
   Webb, D. F.; Cargill, P.; Forbes, T. G.; Hood, A. W.; Steinolfson,
   R. S.; Chapman, G. A.; Deloach, A. C.; Gary, G. A.; Jones, H. P.;
   Karpen, J. T.; Martres, M. -J.; Porter, J. G.; Schmieder, B.; Smith,
   J. B., Jr.; Toomre, J.; Woodgate, B.; Waggett, P.; Bentley, R.;
   Hurford, G.; Schadee, A.; Schrijver, J.; Harrison, R.; Martens, P.
Bibcode: 1986NASCP2439....1P
Altcode:
  Contents: 1. Introduction: the preflare state - a review of previous
  results. 2. Magnetohydrodynamic instability: magnetic reconnection,
  nonlinear tearing, nonlinear reconnection experiments, emerging flux and
  moving satellite sunspots, main phase reconnection in two-ribbon flares,
  magnetic instability responsible for filament eruption in two-ribbon
  flares. 3. Preflare magnetic and velocity fields: general morphology of
  the preflare magnetic field, magnetic field shear, electric currents in
  the preflare active region, characterization of the preflare velocity
  field, emerging flux. 4. Coronal manifestations of preflare activity:
  defining the preflare regime, specific illustrative events, comparison
  of preflare X-rays and ultraviolet, preflare microwave intensity and
  polarization changes, non-thermal precursors, precursors of coronal
  mass ejections, short-lived and long-lived HXIS sources as possible
  precursors.

Title: Characteristics, location and origin of flare activity in a
    complex active region
Authors: Mechado, M. E.; Gary, G. A.; Hagyard, M. J.; Hernandez,
   A. M.; Rovira, M. G.; Schmieder, B.; Smith, J. B.
Bibcode: 1986AdSpR...6f..33M
Altcode: 1986AdSpR...6...33M
  We summarize the observational characteristics of series of multiple
  loop flares from a complex active region. The location of the
  highest observed photospheric magnetic shear is found to be the
  commonly observed site of flare onset, but not, in many cases, the
  magnetic region where the largest time-integrated energy release is
  observed. The observations thus reveal a consistent pattern of energy
  release processes as related to the magnetic field topology.

Title: A Variational Approach to the Non-Linear Force-Free Magnetic
    Fields
Authors: Gary, G. Allen
Bibcode: 1985BAAS...17..641G
Altcode:
  No abstract at ADS

Title: Computation of Solar Magnetic Fields from Photospheric
    Observations
Authors: Hannakam, L.; Gary, G. A.; Teuber, D. L.
Bibcode: 1984SoPh...94..219H
Altcode:
  The observational difficulties of obtaining the magnetic field
  distribution in the chromosphere and corona of the Sun has led to
  methods of extending photospheric magnetic measurements into the solar
  atmosphere by mathematical procedures. A new approach to this problem
  presented here is that a constant alpha force-free field can be uniquely
  determined from the tangential components of the measured photospheric
  flux alone. The vector magnetographs now provide measurements of
  both the solar photospheric tangential and the longitudinal magnetic
  field. This paper presents derivations for the computation of the
  solar magnetic field from these type of measurements. The fields
  considered are assumed to be a constant alpha force-free fields or
  equivalent, producing vanishing Lorentz forces. Consequently, magnetic
  field lines and currents are related by a constant and hence show an
  identical distribution. The magnetic field above simple solar regions
  are described from the solution of the field equations.

Title: Characteristics of the MSFC PDS Microdensitometer
Authors: Fountain, W. F.; Gary, G. A.; Oda, H.
Bibcode: 1984amd..conf...71F
Altcode:
  No abstract at ADS

Title: Characteristics of the MSFC, PDS microdensitometer.
Authors: Fountain, W. F.; Gary, G. A.; Oda, H.
Bibcode: 1984NASCP2317...71F
Altcode:
  This report summarizes the results of several parametric studies carried
  out on the Marshall Space Flight Center (MSFC) PDS-10 microdensitometer
  for the purposes of documenting and understanding the operation and
  limitations of the system for inhouse research and to provide a bench
  mark for comparison with other microdensitometers.

Title: An H alpha velocity study of S 252.
Authors: Fountain, W. F.; Gary, G. A.; Odell, C. R.
Bibcode: 1983ApJ...273..639F
Altcode:
  The H II region S252 (NGC 2175) was studied by means of H-alpha
  radial velocities and line widths. The velocity structure appears
  to be dominated by the western ionization front, abutting a dense
  neutral cloud which is a CO source, and by symmetry abut the ionizing
  star. This data, together with other studies of CO, H167-alpha, and
  the H II radio continuum, allow construction of a model of S252. The
  H II model is basically a double blister formed by a luminous hot star
  being located between two orthogonal, elongated neutral clouds.

Title: A study of Hα velocities in NGC 1499, NGC 7000, and IC
    1318B/C.
Authors: Fountain, W. F.; Gary, G. A.; Odell, C. R.
Bibcode: 1983ApJ...269..164F
Altcode:
  Multiple slit echelle spectrograph observations of the H-alpha emission
  line are used to map the radial velocities of the California Nebula (NGC
  1499), the North American Nebula complex (NGC 7000 and IC 5070), and
  IC 1318B/C. The California Nebula is singularly constant in velocity,
  considering its geometry. The North American Nebula complex reflects
  a very simple, classical dynamical picture. The expansion discovered
  earlier in IC 1318B/C is confirmed, detailed, and the model refined. The
  new data, along with that in earlier papers of this series, show that
  stellar wind acceleration and champagne flow mechanisms both play
  important roles in determining the evolution of H II regions.

Title: An investigation of the neutral and ionized gas in M16
Authors: Mufson, S. L.; Fountain, W. F.; Gary, G. A.; Howard, W. E.,
   III; O'Dell, C. R.; Wolff, M. T.
Bibcode: 1981ApJ...248..992M
Altcode:
  An attempt is made to understand the physical and kinematic conditions
  in the M16 active star formation site, by means of mapping observations
  of neutral and ionized hydrogen and observations of (C-12)O from
  selected positions within the H II regions. The 21-cm maps suggest
  that at least two neutral clouds are present in the M16 complex, one of
  which is likely to be the remains of the cloud in which star formation
  initially occurred, and the other is probably the cold gas remaining
  from a disrupted cloud edge where the ionization front has crossed the
  cloud-intercloud boundary. Multislit echelle spectra of the H-alpha line
  are obtained to determine the physical conditions within the ionized
  gas, and H-alpha maps show that the ionized gas is systematically
  blueshifted in the east and splits into two streams in the southwest.

Title: Erratum - an Internal Velocity Study of the Rosette Nebula
Authors: Fountain, W. F.; Gary, G. A.; O'dell, C. R.
Bibcode: 1980ApJ...236.1056F
Altcode:
  No abstract at ADS

Title: An internal velocity study of the Rosette Nebula.
Authors: Fountain, W. F.; Gary, G. A.; Odell, C. R.
Bibcode: 1979ApJ...229..971F
Altcode:
  Emission-line profiles of H-alpha were studied at about 700 points in
  the Rosette Nebula by using a multislit echelle spectrograph. Numerical
  analysis of the profiles indicates that variations in the line-of-sight
  velocity occur within the nebula, reaching about + or - 20 km/s in the
  inner regions. Evidence is presented that these highest velocities
  are more probably inward, favoring a model where the central cavity
  is due to a depletion resulting from rapid star formation

Title: An Echelle Spectrograph Study of the Rosette Nebula
Authors: Fountain, W. F.; Gary, G. A.; O'dell, C. R.
Bibcode: 1978BAAS...10R.397F
Altcode:
  No abstract at ADS

Title: Spectrographic observations of Comet West (1975n).
Authors: Gary, G. A.; Fountain, W. F.; Odell, C. R.
Bibcode: 1977PASP...89...97G
Altcode:
  The spectrum of comet West (1975 n) was recorded on March 7 and 11,
  1976, in the wavelength interval from 5700 to 8200 A at an intermediate
  resolution. One hundred twenty-two emission lines are reported, with
  78 lines having identifications with spectral features of NH2, H2O(+),
  C2, O I forbidden emission, and Na I.

Title: The contribution of interstellar particles to the
    interplanetary dust complex
Authors: Gary, G. A.
Bibcode: 1977STIN...7724038G
Altcode:
  The Poynting-Robertson effect acting on interstellar particles passing
  by the sun was shown to have the potential to capture and possibly
  to contribute some of these particles to the interplanetary dust
  complex. When the probability of encounter of the sun with interstellar
  clouds is considered, the quasi-equilibrium mass rate of accretion by
  this mechanism is comparable to the mass loss rate of the interplanetary
  complex. The mechanism then produces a quasi-equilibrium condition to
  maintain the interplanetary particle complex. This requires that the
  interstellar particles have a repulsive force due to radiation pressure
  less than the attractive gravitational force. If this assumption
  is correct for a significant fraction of the particles, then at
  intervals an interstellar cloud may pass sufficiently close to the sun
  to allow the Poynting-Robertson effect to replenish the interplanetary
  complex. The previously proposed mechanisms of gravitational encounters
  and the solar gravitational lens as a method of capture of interstellar
  particles are shown to be insufficient. Corrections to the formulations
  of these two methods are given, and a closed form formula of the
  Poynting-Robertson effect on hyperbolic orbits about a star is derived.

Title: Interpretation of the anti-tail of comet Kohoutek as a particle
    flow phenomenon.
Authors: Gary, G. A.; O'Dell, C. R.
Bibcode: 1975NASSP.355...27G
Altcode: 1975coko.conf...27G
  No abstract at ADS

Title: Interpretation of the anti-tail of comet Kohoutek as a particle
    flow phenomenon
Authors: Gary, G. A.; Odell, C. R.
Bibcode: 1974Icar...23..519G
Altcode:
  The appearance of a "sunward" spike, opposite in apparent orientation
  to the normal Type-II tail in Comet Kohoutek is interpreted as evidence
  for large particles ejected near perihelion. It is shown that the shape
  and orientation can be satisfactorily explained in this manner, after
  consideration of the increased mass flow at decreasing heliocentric
  distance. The apparent length of the spike can be a measure of the
  particle size ( d) and density ( ϱ<SUB>d</SUB>) and a value of
  ϱ<SUB>d</SUB>≅0.004 g/cm <SUP>2</SUP> fits the Skylab observations.

Title: SKYLAB observations of Comet Kohoutek
Authors: Snoddy, W. C.; Gary, G. A.
Bibcode: 1974aiaa.conf.....S
Altcode:
  This paper summarizes the special operational procedures developed
  to observe the Comet Kohoutek from Skylab and the scientific
  results from these observations. Emphasis is placed on results
  from Skylab experiments S052, White Light Coronagraph; S201, Far UV
  Electronographic Camera; S233, Kohoutek Photometric Photography; S019,
  UV Stellar Astronomy; S183, Ultraviolet Panorama Telescope; and S082B,
  Ultraviolet Spectrography. Visual observations by the astronaut crew
  and the significance of these observations are discussed.

Title: Interpretation of the Anti-Tail of Comet Kohoutek as a Particle
    Flow Phenomenon.
Authors: Gary, G. A.; O'dell, C. R.
Bibcode: 1974BAAS....6..463G
Altcode:
  No abstract at ADS

