aulanier

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Author name code: aulanier
ADS astronomy entries on 2022-09-14
author:"Aulanier, Guillaume"

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Title: Filament Leg--Leg Reconnection as a Source of Prominent
Supra-Arcade Downflows
Authors: Dudik, Jaroslav; Aulanier, Guillaume; Kasparova, Jana;
Karlicky, Marian; Zemanova, Alena; Lorincik, Juraj; Druckmuller,
Miloslav
2022arXiv220900306D Altcode:
We report on interaction of the legs of the erupting filament
of 2012 August 31 and associated prominent supra-arcade downflows
(P-SADs) as observed by the Atmospheric Imaging Assembly onboard the
Solar Dynamics Observatory. We employ a number of image processing
techniques to enhance weak interacting features. As the filament erupts,
both legs stretch outwards. The positive-polarity leg also untwists
and splits into two parts. The first part runs into the conjugate
(negative-polarity) leg, tearing it apart. The second part then
converges into the remnant of the conjugate leg, after which both
weaken and finally disappear. All these episodes of interaction of
oppositely-oriented filament legs are followed by appearance of P-SADs,
seen in the on-disk projection to be shaped as loop-tops, along with
many weaker SADs. All SADs are preceded by hot supra-arcade downflowing
loops. This observed evolution is consistent with the three-dimensional
rr-rf (leg-leg) reconnection, where the erupting flux rope reconnects
with itself. In our observations, as well as in some models, the
reconnection in this geometry is found to be long-lasting. It plays
a substantial role in the evolution of the flux rope of the erupting
filament and leads to prominent supra-arcade downflows.

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Title: The European Solar Telescope
Authors: Quintero Noda, C.; Schlichenmaier, R.; Bellot Rubio, L. R.;
Löfdahl, M. G.; Khomenko, E.; Jurcak, J.; Leenaarts, J.; Kuckein,
C.; González Manrique, S. J.; Gunar, S.; Nelson, C. J.; de la Cruz
Rodríguez, J.; Tziotziou, K.; Tsiropoula, G.; Aulanier, G.; Collados,
M.; the EST team
2022arXiv220710905Q Altcode:
The European Solar Telescope (EST) is a project aimed at studying
the magnetic connectivity of the solar atmosphere, from the deep
photosphere to the upper chromosphere. Its design combines the knowledge
and expertise gathered by the European solar physics community during
the construction and operation of state-of-the-art solar telescopes
operating in visible and near-infrared wavelengths: the Swedish 1m Solar
Telescope (SST), the German Vacuum Tower Telescope (VTT) and GREGOR,
the French Télescope Héliographique pour l'Étude du Magnétisme
et des Instabilités Solaires (THÉMIS), and the Dutch Open Telescope
(DOT). With its 4.2 m primary mirror and an open configuration, EST will
become the most powerful European ground-based facility to study the Sun
in the coming decades in the visible and near-infrared bands. EST uses
the most innovative technological advances: the first adaptive secondary
mirror ever used in a solar telescope, a complex multi-conjugate
adaptive optics with deformable mirrors that form part of the optical
design in a natural way, a polarimetrically compensated telescope design
that eliminates the complex temporal variation and wavelength dependence
of the telescope Mueller matrix, and an instrument suite containing
several (etalon-based) tunable imaging spectropolarimeters and several
integral field unit spectropolarimeters. This publication summarises
some fundamental science questions that can be addressed with the
telescope, together with a complete description of its major subsystems.

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Title: Mini solar flare and jet due to small scale surface motions
Authors: Joshi, Reetika; Vilmer, Nicole; Chandra, Ramesh; Heinzel,
Petr; Bommier, Veronique; Schmieder, Brigitte; Aulanier, Guillaume;
Tomin, James
2022cosp...44.2535J Altcode:
Here we present the study of the fine structure and dynamics of the
plasma at a jet base forming a mini-flare between two emerging magnetic
fluxes (EMFs) observed with Interface Region Imaging Spectrograph
(IRIS) and the Solar Dynamics Observatory instruments. This active
region is an outcome of the collapse of two EMFs overlaid by arch
filament systems. We observed that, before the jet an extension of
the flux rope was present and a part of it was detached and formed
a small bipole with a bald patch region, which dynamically became
an X-current sheet over the dome of one EMF where the reconnection
took place. At the time in the site of reconnection, the IRIS C II,
Si IV, and Mg II line profiles present bi directional flows in a tiny
region. These types of spectra are typically associated with twist,
rotation, or the presence of plasma in helical structures. The tilt
observed in our spectra can be explained by the presence of a helical
structure at the jet base during the reconnection process due to a
transfer of the twist from a flux rope in the vicinity of the jet. We
also combined the observations of the Balmer continuum obtained with
the IRIS (spectra and SJIs 2832 Å). The calibrated Balmer continuum
was compared to non-local thermodynamic equilibrium radiative transfer
flare models and the radiated energy was estimated. Assuming thick
target HXR emission, we calculated the energy of the non thermal
electrons detected by the Fermi/GBM and compared it to the radiated
energy. The electron-beam flux estimated from Fermi/GBM between 10$
^{9}$ and 10$ ^{10}$ erg s$ ^{-1}$ cm$ ^{-2}$ is consistent with the
beam flux required in non-LTE radiative transfer models to obtain the
excess of Balmer continuum emission observed in this IRIS spectra. We
conclude that the bombardment of electrons could be in a region smaller
than the IRIS spatial resolution.

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Title: Empirical atmosphere model in a mini flare during magnetic
reconnection
Authors: Schmieder, Brigitte; Joshi, Reetika; Chandra, Ramesh;
Aulanier, Guillaume; Tei, Akiko; Heinzel, Petr; Tomin, James; Vilmer,
Nicole; Bommier, Veronique
2021arXiv211206790S Altcode:
A spatio-temporal analysis of IRIS spectra of MgII, CII, and SiIV ions
allows us to study the dynamics and the stratification of the flare
atmosphere along the line of sight during the magnetic reconnection
phase at the jet base. Strong asymmetric MgII and CII line profiles with
extended blue wings observed at the reconnection site are interpreted
by the presence of two chromospheric temperature clouds: one explosive
cloud with blueshifts at 290 km/s and one cloud with smaller Doppler
shift (around 36 km/s). Simultaneously at the same location a mini
flare was observed with strong emission in multi temperatures (AIA),
in several spectral IRIS lines (e.g. Oiv and Siiv, Mgii), absorption
of identified chromospheric lines in Siiv line profile, enhancement
of the Balmer continuum and X-ray emission by FERMI/GBM. With the
standard thick-target flare model we calculate the energy of non thermal
electrons observed by FERMI and compare it to the energy radiated by
the Balmer continuum emission. We show that the low energy input by
non thermal electrons above 20 keV was still sufficient to produce
the excess of Balmer continuum.

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Title: The return of the jet
Authors: Aulanier, Guillaume
2021NatAs...5.1096A Altcode: 2021NatAs.tmp..129A
Turmoil has engulfed the solar community for decades about which
physical mechanisms are sufficient to trigger and drive solar
eruptions. New high-resolution numerical magnetohydrodynamic simulations
bring an old idea back into the light: the reconnection jet from the
tether-cutting model.

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Title: Saddle-shaped Solar Flare Arcades
Authors: Lörinčík, Juraj; Dudík, Jaroslav; Aulanier, Guillaume
2021ApJ...909L...4L Altcode: 2021arXiv210210858L
Arcades of flare loops form as a consequence of magnetic reconnection
powering solar flares and eruptions. We analyze the morphology and
evolution of flare arcades that formed during five well-known eruptive
flares. We show that the arcades have a common saddle-like shape. The
saddles occur despite the fact that the flares were of different classes
(C to X), occurred in different magnetic environments, and were observed
in various projections. The saddles are related to the presence of
longer, relatively higher, and inclined flare loops, consistently
observed at the ends of the arcades, which we term "cantles." Our
observations indicate that cantles typically join straight portions
of flare ribbons with hooked extensions of the conjugate ribbons. The
origin of the cantles is investigated in stereoscopic observations of
the 2011 May 9 eruptive flare carried out by the Atmospheric Imaging
Assembly and Extreme Ultraviolet Imager. The mutual separation of
the instruments led to ideal observational conditions allowing for
simultaneous analysis of the evolving cantle and the underlying ribbon
hook. Based on our analysis we suggest that the formation of one of the
cantles can be explained by magnetic reconnection between the erupting
structure and its overlying arcades. We propose that the morphology of
flare arcades can provide information about the reconnection geometries
in which the individual flare loops originate.

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Title: Multi-thermal atmosphere of a mini-solar flare during magnetic
reconnection observed with IRIS
Authors: Joshi, Reetika; Schmieder, Brigitte; Tei, Akiko; Aulanier,
Guillaume; Lörinčík, Juraj; Chandra, Ramesh; Heinzel, Petr
2021A&A...645A..80J Altcode: 2020arXiv201015401J
Context. The Interface Region Imaging Spectrograph (IRIS) with its
high spatial and temporal resolution facilitates exceptional plasma
diagnostics of solar chromospheric and coronal activity during magnetic
reconnection. Aims: The aim of this work is to study the fine
structure and dynamics of the plasma at a jet base forming a mini-flare
between two emerging magnetic fluxes (EMFs) observed with IRIS and the
Solar Dynamics Observatory instruments. Methods: We proceed to
a spatio-temporal analysis of IRIS spectra observed in the spectral
ranges of Mg II, C II, and Si IV ions. Doppler velocities from Mg II
lines were computed using a cloud model technique. Results:
Strong asymmetric Mg II and C II line profiles with extended blue
wings observed at the reconnection site (jet base) are interpreted by
the presence of two chromospheric temperature clouds: one explosive
cloud with blueshifts at 290 km s-1 and one cloud with
smaller Doppler shift (around 36 km s-1). Simultaneously at
the same location (jet base), strong emission of several transition
region lines (e.g. O IV and Si IV), emission of the Mg II triplet
lines, and absorption of identified chromospheric lines in Si IV
broad profiles have been observed and analysed. Conclusions:
Such observations of IRIS line and continuum emissions allow us
to propose a stratification model for the white light, mini-flare
atmosphere with multiple layers of different temperatures along the
line of sight in a reconnection current sheet. It is the first time
that we could quantify the fast speed (possibly Alfvénic flows)
of cool clouds ejected perpendicularly to the jet direction via the
cloud model technique. We conjecture that the ejected clouds come from
plasma which was trapped between the two EMFs before reconnection or
be caused by chromospheric-temperature (cool) upflow material similar
to a surge during reconnection. Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202039229/olm">https://www.aanda.org</A>

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Title: Magnetic support of the solar filaments
Authors: Schmieder, Brigitte; Aulanier, Guillaume; Gunár, Stanislav;
Dudik, Jaroslav; Heinzel, Petr
2021cosp...43E1766S Altcode:
The scale height in prominence is 500 km at maximum. However, non
activated prominences can reach an altitude of 50000 km or more. Hanging
filaments observed over the limb give the impression of quasi vertical
structures. It was already the view in the past but reactivated by the
movies of Hinode in Ca II line showing fuzzing vertical structures. In
the corona it is not possible to measure the magnetic field supporting
prominences. Only extrapolations of the photospheric magnetic field
explain how cool plasma embedded in the dips of the magnetic field
lines can be supported in the hot corona. I will review a few papers
showing the distribution of the cool plasma dips and the observations
of filaments on the disk visible in H$\alpha$ and in UV. A recent
paper shows how a 3D extrapolation model and a radiative-transfer
based H$\alpha$ visualization method leads to H$\alpha$ prominence
fine structures. Finally, I will discuss the perspective effects on
the perceived morphology of observed and modeled prominences.

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Title: Twist transfer to a solar jet from a big flux rope detected
in the HMI magnetogram
Authors: Joshi, Reetika; Schmieder, Brigitte; Aulanier, Guillaume;
Chandra, Ramesh; Bommier, Veronique
2021cosp...43E1752J Altcode:
Solar jets often have a helical structure containing both hot and
cool ejected plasma. Different mechanisms are proposed to trigger
jets by magnetic reconnection between the emergence of magnetic flux
and environment, or induced by twisted photospheric motions bringing
the system to instability. Multi-wavelength observations of a twisted
jet observed with the AIA and IRIS is presented to understand how the
twist was injected in the jet from a flux rope, fortunately, IRIS
spectrographic slit was just crossing the reconnection site. This
active region is a result of the collapse of two emerging magnetic
fluxes (EMFs) overlaid by arch filament systems. In the magnetic field
maps, we evidenced the pattern of a long sigmoidal flux rope along
the polarity inversion line between the two EMFs which is the site of
the reconnection. Before the jet, there was an extension of the flux
rope, and a part of it was detached and formed a small bipole with a
bald patch region which dynamically became an X-current sheet over the
dome of one EMF where the reconnection took place. At the time of the
reconnection, the Mg II spectra exhibited a strong extension of the
blue wing which is decreasing over a distance of 10 Mm (from -300 km/s
to a few km/s). This is the signature of the transfer of the twist to
the jet. Comparison with numerical magnetohydrodynamics simulations
confirmed the existence of the long flux rope in the neighborhood
of the jet. We conjecture that there is a transfer of twist to the
jet during the extension of the flux rope to the reconnection site
without the flux rope eruption. The reconnection would start in the
low atmosphere in the bald patch reconnection region and extend at an
X-point along the current sheet formed above.

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Title: Signature of the expansion of eruptive flux ropes measured
by electric currents
Authors: Schmieder, Brigitte; Aulanier, Guillaume; Janvier, Miho;
Masson, Sophie; Barczynski, Krzysztof
2021cosp...43E1758S Altcode:
MHD models demonstrate that hooks of flare ribbons are the footprints
of eruptive flux ropes and that a decrease of the electric currents
could be the signature of the evolution of the coronal magnetic
field, e.g. the expansion of a line-tied flux rope with constant
end-to-end external twist during the eruption. However in circuit
models the surface electric current has a subsurface fixed source
and therefore the currents should be constant . We analyze 19 X-class
flares observed by Solar Dynamics Observatory (SDO) from 2011 to 2016,
where flare ribbons with hooks are identifiable. For the first time
fine measurements of time-evolution of electric currents inside the
hooks in the observations as well as in the OHM 3D MHD simulation are
performed. Our analysis shows a decrease of the electric current in the
area surrounded by the ribbon hooks during and after the eruption. In
the simulation the rate of current deceasing is similar to that of the
field line elongation. So we interpret the decrease of the electric
currents as due to the expansion of the flux rope in the corona during
the eruption. Our analysis brings a new stone to the standard flare
model in 3D.

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Title: Imaging Evidence for Solar Wind Outflows Originating from a
Coronal Mass Ejection Footpoint
Authors: Lörinčík, Juraj; Dudík, Jaroslav; Aulanier, Guillaume;
Schmieder, Brigitte; Golub, Leon
2021ApJ...906...62L Altcode: 2020arXiv201004250L
We report on Atmospheric Imaging Assembly observations of plasma
outflows originating in a coronal dimming during a 2015 April 28
filament eruption. After the filament started to erupt, two flare
ribbons formed, one of which had a well-visible hook enclosing a core
(twin) dimming region. Along multiple funnels located in this dimming,
a motion of plasma directed outward started to be visible in the
171 and 193 Å filter channels of the instrument. In time-distance
diagrams, this motion generated a strip-like pattern, which lasted
for more than 5 hr and whose characteristics did not change along
the funnel. We therefore suggest the motion is a signature of
outflows corresponding to velocities ranging between ≍70 and 140
km s-1. Interestingly, the pattern of the outflows and
their velocities were found to be similar to those we observed in a
neighboring ordinary coronal hole. Therefore, the outflows were most
likely a signature of a coronal mass ejection-induced solar wind flowing
along the open-field structures rooted in the dimming region. Further,
the evolution of the hook encircling the dimming region was examined
in the context of the latest predictions imposed for 3D magnetic
reconnection. The observations indicate that the filament's footpoints
were, during their transformation to the dimming region, reconnecting
with surrounding canopies. To our knowledge, our observations present
the first imaging evidence for outflows of plasma from a dimming region.

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Title: Links between prominence/filament magnetic field and plasma:
What can 3D WPFS models teach us?
Authors: Gunár, Stanislav; Schmieder, Brigitte; Aulanier, Guillaume;
Heinzel, Petr; Mackay, Duncan; Dudik, Jaroslav
2021cosp...43E1769G Altcode:
The magnetic field constitutes the skeleton and the driving force of
prominences/filaments. It supports the dense prominence plasma against
gravity and insulates it from the hot, coronal environment. The
magnetic field is also responsible for the prominence stability,
evolution and eruptions which affect the heliosphere and ultimately
the Earth. However, a strong imbalance exists between the numerous
efforts in detailed modelling of prominence magnetic field and its
understanding from observations. That is due to the complex nature of
the direct (and indirect) observations of solar magnetic fields which
are challenging at the best of times and even more so in prominences
or filaments. The direct observations of the prominence magnetic
field require high-precision spectro-polarimetric measurements and
realistic assumptions about the plasma structure which allow us to
infer the field configuration from its effect on the polarized light
emergent from the observed structures. The indirect observations rely
on the perceived location, shape and dynamics of the prominence or
filament plasma, often using moving small-scale plasma structures
as tracers guided by the field lines. Both methods thus rely on the
presence of observable plasma in the magnetic field configuration,
and on the radiation which carries the information about the in-situ
conditions to the observer. No prominence/filament magnetic field
measurements are made without these two additional components,
which are sometimes an afterthought in the magnetic field models. We
have developed 3D Whole-Prominence Fine Structure (WPFS) models to
illuminate the links between the prominence magnetic field, its plasma
distributed among numerous fine structures and the radiation which
carries the information about the prominence physical conditions to
the observer. What can we learn from these 3D models? For example,
we can see that a small change of the magnetic field configuration
can have a large effect on the perceived structure of prominences and
filaments visible in the H-alpha line. Consequently, this means that
significant changes observed in prominences or filaments do not need
to suggest that equally large changes in the underlying magnetic field
configuration had to occur. In another example, we see that seemingly
incomparable differences in the morphological look of prominences (long
horizontal fine structures versus small blobs of plasma arranged into
more-less vertical features) may not need to imply the existence of
radically different magnetic field configurations. Rather, they might
simply be manifestations of projection effects that can differ greatly
depending on the viewing angle under which we observe the naturally
three-dimensional prominences/filaments.

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Title: Decoding the Pre-Eruptive Magnetic Field Configurations of
Coronal Mass Ejections
Authors: Patsourakos, S.; Vourlidas, A.; Török, T.; Kliem, B.;
Antiochos, S. K.; Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou,
G.; Georgoulis, M. K.; Green, L. M.; Leake, J. E.; Moore, R.; Nindos,
A.; Syntelis, P.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J.
2020SSRv..216..131P Altcode: 2020arXiv201010186P
A clear understanding of the nature of the pre-eruptive magnetic
field configurations of Coronal Mass Ejections (CMEs) is required
for understanding and eventually predicting solar eruptions. Only
two, but seemingly disparate, magnetic configurations are considered
viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes
(MFR). They can form via three physical mechanisms (flux emergence,
flux cancellation, helicity condensation). Whether the CME culprit
is an SMA or an MFR, however, has been strongly debated for thirty
years. We formed an International Space Science Institute (ISSI) team to
address and resolve this issue and report the outcome here. We review
the status of the field across modeling and observations, identify
the open and closed issues, compile lists of SMA and MFR observables
to be tested against observations and outline research activities
to close the gaps in our current understanding. We propose that the
combination of multi-viewpoint multi-thermal coronal observations
and multi-height vector magnetic field measurements is the optimal
approach for resolving the issue conclusively. We demonstrate the
approach using MHD simulations and synthetic coronal images.

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Title: The role of small-scale surface motions in the transfer of
twist to a solar jet from a remote stable flux rope
Authors: Joshi, Reetika; Schmieder, Brigitte; Aulanier, Guillaume;
Bommier, Véronique; Chandra, Ramesh
2020A&A...642A.169J Altcode: 2020arXiv200806887J
Context. Jets often have a helical structure containing ejected plasma
that is both hot and also cooler and denser than the corona. Various
mechanisms have been proposed to explain how jets are triggered,
primarily attributed to a magnetic reconnection between the emergence
of magnetic flux and environment or that of twisted photospheric
motions that bring the system into a state of instability. 
Aims: Multi-wavelength observations of a twisted jet observed with
the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics
Observatory and the Interface Region Imaging Spectrograph (IRIS)
were used to understand how the twist was injected into the jet,
thanks to the IRIS spectrographic slit fortuitously crossing the
reconnection site at that time. Methods: We followed the
magnetic history of the active region based on the analysis of the
Helioseismic and Magnetic Imager vector magnetic field computed with
the UNNOFIT code. The nature and dynamics of the jet reconnection site
are characterised by the IRIS spectra. Results: This region
is the result of the collapse of two emerging magnetic fluxes (EMFs)
overlaid by arch filament systems that have been well-observed with AIA,
IRIS, and the New Vacuum Solar Telescope in Hα. In the magnetic field
maps, we found evidence of the pattern of a long sigmoidal flux rope
(FR) along the polarity inversion line between the two EMFs, which is
the site of the reconnection. Before the jet, an extension of the FR
was present and a part of it was detached and formed a small bipole
with a bald patch (BP) region, which dynamically became an X-current
sheet over the dome of one EMF where the reconnection took place. At
the time of the reconnection, the Mg II spectra exhibited a strong
extension of the blue wing that is decreasing over a distance of 10
Mm (from -300 km s-1 to a few km s-1). This
is the signature of the transfer of the twist to the jet. Conclusions: A comparison with numerical magnetohydrodynamics
simulations confirms the existence of the long FR. We conjecture that
there is a transfer of twist to the jet during the extension of the
FR to the reconnection site without FR eruption. The reconnection
would start in the low atmosphere in the BP reconnection region
and extend at an X-point along the current sheet formed above. Movies attached to Figs. 1, 3, 4, and 7 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202038562/olm">https://www.aanda.org</A>

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Title: The Solar Orbiter Science Activity Plan. Translating solar
and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
T.; Young, P. R.; Zhukov, A. N.
2020A&A...642A...3Z Altcode: 2020arXiv200910772Z
Solar Orbiter is the first space mission observing the solar plasma
both in situ and remotely, from a close distance, in and out of the
ecliptic. The ultimate goal is to understand how the Sun produces
and controls the heliosphere, filling the Solar System and driving
the planetary environments. With six remote-sensing and four in-situ
instrument suites, the coordination and planning of the operations are
essential to address the following four top-level science questions:
(1) What drives the solar wind and where does the coronal magnetic field
originate?; (2) How do solar transients drive heliospheric variability?;
(3) How do solar eruptions produce energetic particle radiation that
fills the heliosphere?; (4) How does the solar dynamo work and drive
connections between the Sun and the heliosphere? Maximising the
mission's science return requires considering the characteristics
of each orbit, including the relative position of the spacecraft
to Earth (affecting downlink rates), trajectory events (such
as gravitational assist manoeuvres), and the phase of the solar
activity cycle. Furthermore, since each orbit's science telemetry
will be downloaded over the course of the following orbit, science
operations must be planned at mission level, rather than at the level
of individual orbits. It is important to explore the way in which those
science questions are translated into an actual plan of observations
that fits into the mission, thus ensuring that no opportunities are
missed. First, the overarching goals are broken down into specific,
answerable questions along with the required observations and the
so-called Science Activity Plan (SAP) is developed to achieve this. The
SAP groups objectives that require similar observations into Solar
Orbiter Observing Plans, resulting in a strategic, top-level view of
the optimal opportunities for science observations during the mission
lifetime. This allows for all four mission goals to be addressed. In
this paper, we introduce Solar Orbiter's SAP through a series of
examples and the strategy being followed.

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Title: Case study of multi-temperature coronal jets for emerging
flux MHD models
Authors: Joshi, Reetika; Chandra, Ramesh; Schmieder, Brigitte;
Moreno-Insertis, Fernando; Aulanier, Guillaume; Nóbrega-Siverio,
Daniel; Devi, Pooja
2020A&A...639A..22J Altcode: 2020arXiv200506064J
Context. Hot coronal jets are a basic observed feature of the solar
atmosphere whose physical origin is still actively debated. 
Aims: We study six recurrent jets that occurred in active region NOAA
12644 on April 4, 2017. They are observed in all the hot filters
of AIA as well as cool surges in IRIS slit-jaw high spatial and
temporal resolution images. Methods: The AIA filters allow us
to study the temperature and the emission measure of the jets using
the filter ratio method. We studied the pre-jet phases by analysing
the intensity oscillations at the base of the jets with the wavelet
technique. Results: A fine co-alignment of the AIA and IRIS
data shows that the jets are initiated at the top of a canopy-like
double-chambered structure with cool emission on one and hot emission
on the other side. The hot jets are collimated in the hot temperature
filters, have high velocities (around 250 km s-1) and
are accompanied by cool surges and ejected kernels that both move
at about 45 km s-1. In the pre-phase of the jets, we find
quasi-periodic intensity oscillations at their base that are in phase
with small ejections; they have a period of between 2 and 6 min,
and are reminiscent of acoustic or magnetohydrodynamic waves. 
Conclusions: This series of jets and surges provides a good case study
for testing the 2D and 3D magnetohydrodynamic emerging flux models. The
double-chambered structure that is found in the observations corresponds
to the regions with cold and hot loops that are in the models below
the current sheet that contains the reconnection site. The cool surge
with kernels is comparable with the cool ejection and plasmoids that
naturally appears in the models. Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202037806/olm">https://www.aanda.org</A>

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Title: Quasi Periodic Oscillations in the Pre Phases of Recurrent
Jets Highlighting Plasmoids in Current Sheet
Authors: Joshi, Reetika; Chandra, Ramesh; Schmieder, Brigitte;
Aulanier, Guillaume; Devi, Pooja; Moreno-Insertis, Fernando;
Nóbrega-Siverio, Daniel
2020EGUGA..2222351J Altcode:
Solar jets observed at the limb are important to determine the location
of reconnection sites in the corona. In this study, we investigate
six recurrent hot and cool jets occurring in the active region NOAA
12644 as it is crossing the west limb on April 04, 2017. These jets
are observed in all the UV/EUV filters of SDO/AIA and in cooler
temperature formation lines in IRIS slit jaw images. The jets are
initiated at the top of a double chamber vault with cool loops on one
side and hot loops on the other side. The existence of such double
chamber vaults suggests the presence of emerging flux with cool
loops, the hot loops being the reconnected loops similarly as in the
models of Moreno-Insertiset al. 2008, 2013 and Nóbrega-Siverio et
al. 2016. In the preliminary phase of the main jets, quasi periodic
intensity oscillations accompanied by smaller jets are detected in the
bright current sheet between the vault and the preexisting magnetic
field. Individual kernels and plasmoids are ejected in open field lines
along the jets. Plasmoids may launch torsional Alfven waves and the
kernels would be the result of the untwist of the plasmoids in open
magnetic field as proposed in the model of Wyper et al. 2016.

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Title: Electric Current Evolution at the Footpoints of Solar Eruptions
Authors: Barczynski, Krzysztof; Aulanier, Guillaume; Janvier, Miho;
Schmieder, Brigitte; Masson, Sophie
2020ApJ...895...18B Altcode: 2020arXiv200407990B
Electric currents play a critical role in the triggering of solar
flares and their evolution. The aim of the present paper is to test
whether the surface electric current has a surface or subsurface
fixed source as predicted by the circuit approach of flare physics,
or is the response of the surface magnetic field to the evolution of
the coronal magnetic field as the MHD approach proposes? Out of all 19
X-class flares observed by SDO from 2011 to 2016 near the disk center,
we analyzed the only nine eruptive flares for which clear ribbon hooks
were identifiable. Flare ribbons with hooks are considered to be the
footprints of eruptive flux ropes in MHD flare models. For the first
time, fine measurements of the time evolution of electric currents
inside the hooks in the observations as well as in the OHM 3D MHD
simulation are performed. Our analysis shows a decrease of the electric
current in the area surrounded by the ribbon hooks during and after the
eruption. We interpret the decrease of the electric currents as due to
the expansion of the flux rope in the corona during the eruption. Our
analysis brings a new contribution to the standard flare model in 3D.

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Title: Energy and helicity fluxes in line-tied eruptive simulations
Authors: Linan, L.; Pariat, É.; Aulanier, G.; Moraitis, K.; Valori, G.
2020A&A...636A..41L Altcode: 2020arXiv200301698L
Context. Conservation properties of magnetic helicity and energy in
the quasi-ideal and low-β solar corona make these two quantities
relevant for the study of solar active regions and eruptions. 
Aims: Based on a decomposition of the magnetic field into potential
and nonpotential components, magnetic energy and relative helicity
can both also be decomposed into two quantities: potential and free
energies, and volume-threading and current-carrying helicities. In
this study, we perform a coupled analysis of their behaviors in a set
of parametric 3D magnetohydrodynamic (MHD) simulations of solar-like
eruptions. Methods: We present the general formulations for
the time-varying components of energy and helicity in resistive
MHD. We calculated them numerically with a specific gauge, and
compared their behaviors in the numerical simulations, which differ
from one another by their imposed boundary-driving motions. Thus,
we investigated the impact of different active regions surface flows
on the development of the energy and helicity-related quantities. Results: Despite general similarities in their overall behaviors,
helicities and energies display different evolutions that cannot be
explained in a unique framework. While the energy fluxes are similar
in all simulations, the physical mechanisms that govern the evolution
of the helicities are markedly distinct from one simulation to another:
the evolution of volume-threading helicity can be governed by boundary
fluxes or helicity transfer, depending on the simulation. 
Conclusions: The eruption takes place for the same value of the
ratio of the current-carrying helicity to the total helicity in all
simulations. However, our study highlights that this threshold can be
reached in different ways, with different helicity-related processes
dominating for different photospheric flows. This means that the
details of the pre-eruptive dynamics do not influence the eruption-onset
helicity-related threshold. Nevertheless, the helicity-flux dynamics
may be more or less efficient in changing the time required to reach
the onset of the eruption.

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Title: Observation of All Pre- and Post-reconnection Structures
Involved in Three-dimensional Reconnection Geometries in Solar
Eruptions
Authors: Dudík, Jaroslav; Lörinčík, Juraj; Aulanier, Guillaume;
Zemanová, Alena; Schmieder, Brigitte
2019ApJ...887...71D Altcode: 2019arXiv191008620D
We report on observations of the two newly identified reconnection
geometries involving erupting flux ropes. In 3D, a flux rope can
reconnect either with a surrounding coronal arcade (recently named
“ar-rf” reconnection) or with itself (“rr-rf” reconnection),
and both kinds of reconnection create a new flux-rope field line and a
flare loop. For the first time, we identify all four constituents of
both reconnections in a solar eruptive event, the filament eruption
of 2011 June 7 observed by Solar Dynamics Observatory/Atmospheric
Imaging Assembly. The ar-rf reconnection manifests itself as shift of
one leg of the filament by more than 25″ northward. At its previous
location, a flare arcade is formed, while the new location of the
filament leg previously corresponded to a footpoint of a coronal loop
in 171 Å. In addition, the evolution of the flare ribbon hooks is
also consistent with the occurrence of ar-rf reconnection as predicted
by MHD simulations. Specifically, the growing hook sweeps footpoints
of preeruptive coronal arcades, and these locations become inside the
hook. Furthermore, the rr-rf reconnection occurs during the peak phase
above the flare arcade, in an apparently X-type geometry involving a
pair of converging bright filament strands in the erupting filament. A
new flare loop forms near the leg of one of the strands, while a bright
blob, representing a remnant of the same strand, is seen ascending
into the erupting filament. All together, these observations vindicate
recent predictions of the 3D standard solar-flare model.

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Title: Manifestations of Three-dimensional Magnetic Reconnection
in an Eruption of a Quiescent Filament: Filament Strands Turning to
Flare Loops
Authors: Lörinčík, Juraj; Dudík, Jaroslav; Aulanier, Guillaume
2019ApJ...885...83L Altcode: 2019arXiv190903825L
We report on observations of the conversion of bright filament strands
into flare loops during the 2012 August 31 filament eruption. Prior
to the eruption, individual bright strands composing one of the legs
of the filament were observed in the 171 Å filter channel data of
the Atmospheric Imaging Assembly. After the onset of the eruption,
one of the hooked ribbons started to propagate and contract, sweeping
footpoints of the bright filament strands as well as coronal loops
located close by. Later on, hot flare loops appeared in regions
swept by the hook, where the filament strands were rooted. Timing
and localization of these phenomena suggest that they are caused by
reconnection of field lines composing the filament at the hook, which,
to our knowledge, has not been observed before. This process is not
included in the standard flare model (CSHKP), as it does not address
footpoints of erupting flux ropes and ribbon hooks. It has, however,
been predicted using the recent three-dimensional extensions to the
standard flare model. There, the erupting flux rope can reconnect with
surrounding coronal arcades as the hooked extensions of current ribbons
sweep its footpoints. This process results in formation of flare loops
rooted in previous footpoints of the flux rope. Our observations of
sweeping of filament footpoints are well described by this scenario. In
all observed cases, all of the footpoints of the erupting filament
became footpoints of flare loops. This process was observed to last
for about 150 minutes, throughout the whole eruption.

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Title: Bidirectional Reconnection Outflows in an Active Region
Authors: Ruan, Guiping; Schmieder, Brigitte; Masson, Sophie; Mein,
Pierre; Mein, Nicole; Aulanier, Guillaume; Chen, Yao
2019ApJ...883...52R Altcode:
We report on bidirectional coronal reconnection outflows reaching
±200 km s-1 as observed in an active region with the Si
IV and C II spectra of the Interface Region Imaging Spectrograph
(IRIS). The evolution of the active region with an emerging flux,
a failed filament eruption, and a jet is followed in Solar Dynamical
Observatory (SDO)/Atmospheric Imaging Assembly (AIA) filters from
304 to 94 Å, IRIS slit jaw images, and SDO/Helioseismic and Magnetic
Imager movies. The bidirectional outflow reconnection is located at
a bright point visible in multiwavelength AIA filters above an arch
filament system. This suggests that the reconnection occurs between
rising loops above the emergence of magnetic bipoles and the longer,
twisted magnetic field lines remnant of the failed filament eruption
one hour before. The reconnection occurs continuously in the corona
between quasi-parallel magnetic field lines, which is possible in a
3D configuration. The reconnection also triggers a jet with transverse
velocities around 60 km s-1. Blueshifts and redshifts along
its axis confirm the existence of a twist along the jet, which could
have been transferred from the filament flux rope. The jet finally
blows up the material of the filament before coming back during the
second phase. In the Hα Dopplergrams provided by the MSDP spectrograph,
we see more redshift than blueshift, indicating the return of the jet
and filament plasma.

---------------------------------------------------------
Title: Observations of a Footpoint Drift of an Erupting Flux Rope
Authors: Zemanová, Alena; Dudík, Jaroslav; Aulanier, Guillaume;
Thalmann, Julia K.; Gömöry, Peter
2019ApJ...883...96Z Altcode: 2019arXiv190802082Z
We analyze the imaging observations of an M-class eruptive flare of 2015
November 4. The pre-eruptive Hα filament was modeled by the nonlinear
force-free field model, which showed that it consisted of two helical
systems. Tether-cutting reconnection involving these two systems led
to the formation of a hot sigmoidal loop structure rooted in a small
hook that formed at the end of the flare ribbon. Subsequently, the hot
loops started to slip away from the small hook until it disappeared. The
loops continued slipping and the ribbon elongated itself by several
tens of arcseconds. A new and larger hook then appeared at the end of
the elongated ribbon with hot and twisted loops rooted there. After
the eruption of these hot loops, the ribbon hook expanded and later
contracted. We interpret these observations in the framework of
the recent three-dimensional (3D) extensions to the standard solar
flare model predicting the drift of the flux rope footpoints. The hot
sigmoidal loop is interpreted as the flux rope, whose footpoints drift
during the eruption. While the deformation and drift of the new hook can
be described by the model, the displacement of the flux rope footpoint
from the filament to that of the erupting flux rope indicate that the
hook evolution can be more complex than those captured by the model.

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Title: Velocities of Flare Kernels and the Mapping Norm of Field
Line Connectivity
Authors: Lörinčík, Juraj; Aulanier, Guillaume; Dudík, Jaroslav;
Zemanová, Alena; Dzifčáková, Elena
2019ApJ...881...68L Altcode: 2019arXiv190601880L
We report on observations of flare ribbon kernels during the 2012
August 31 filament eruption. In the 1600 and 304 Å channels of
the Atmospheric Imaging Assembly, flare kernels were observed to
move along flare ribbons at velocities v ∥ of up to
450 km s-1. Kernel velocities were found to be roughly
anticorrelated with strength of the magnetic field. An apparent
slipping motion of the flare loops was observed in the 131 Å only
for the slowest kernels moving through the strong-B region. In order
to interpret the observed relation between B LOS and v
∥, we examined the distribution of the norm N, a quantity
closely related to the slippage velocity. We calculated the norm N of
the quasi-separatrix layers (QSLs) in MHD model of a solar eruption
adapted to the magnetic environment that qualitatively agrees to that
of the observed event. We found that both the modeled N and velocities
of kernels reach their highest values in the same weak-field regions,
one located in the curved part of the ribbon hook and the other in
the straight part of the conjugate ribbon located close to a parasitic
polarity. Contrariwise, lower values of the kernel velocities are seen
at the tip of the ribbon hook, where the modeled N is low. Because the
modeled distribution of N matches the observed dynamics of kernels,
this supports the notion that the kernel motions can be interpreted
as a signature of QSL reconnection during the eruption.

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Title: Flare Reconnection-driven Magnetic Field and Lorentz Force
Variations at the Sun’s Surface
Authors: Barczynski, Krzysztof; Aulanier, Guillaume; Masson, Sophie;
Wheatland, Michael S.
2019ApJ...877...67B Altcode: 2019arXiv190405447B
During eruptive flares, vector magnetograms show an increasing
horizontal magnetic field and downward Lorentz force in the Sun’s
photosphere around the polarity-inversion line (PIL). This behavior
has often been associated with the implosion conjecture and has
been interpreted as the result of either momentum conservation while
the eruption moves upward or of the contraction of flare loops. We
characterize the physical origin of these observed behaviors by
analyzing a generic 3D magnetohydrodynamics simulation of an eruptive
flare. Even though the simulation was not designed to recover the
magnetic field and Lorentz force properties, it is fully consistent
with them, and it provides key additional information for understanding
them. The area where the magnetic field increases gradually develops
between current ribbons, which spread away from each other and are
connected to the coronal region. This area is merely the footprint of
the coronal post-flare loops, whose contraction increases their shear
field component and the magnetic energy density, in line with the ideal
induction equation. For simulated data, we computed the Lorentz force
density map by applying the method used in observations. We obtained an
increase in the downward component of the Lorentz force density around
the PIL, consistent with observations. However, this significantly
differs from the Lorentz force density maps that are obtained directly
from the 3D magnetic field and current. These results altogether
question previous interpretations that were based on the implosion
conjecture and momentum conservation with the coronal mass ejection,
and rather imply that the observed increases in photospheric horizontal
magnetic fields result from the reconnection-driven contraction of
sheared flare loops.

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Title: Sheared Magnetic Arcades and the Pre-eruptive Magnetic
Configuration of Coronal Mass Ejections: Diagnostics, Challenges
and Future Observables
Authors: Patsourakos, Spiros; Vourlidas, A.; Anthiochos, S. K.;
Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou, G.; Georgoulis,
M. K.; Green, L. M.; Kliem, B.; Leake, J.; Moore, R. L.; Nindos, A.;
Syntelis, P.; Torok, T.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J.
2019shin.confE.194P Altcode:
Our thinking about the pre-eruptive magnetic configuration of Coronal
Mass Ejections has been effectively dichotomized into two opposing
and often fiercely contested views: namely, sheared magnetic arcades
and magnetic flux ropes. Finding a solution to this issue will have
important implications for our understanding of CME initiation. We
first discuss the very value of embarking into the arcade vs. flux rope
dilemma and illustrate the corresponding challenges and difficulties to
address it. Next, we are compiling several observational diagnostics of
pre-eruptive sheared magnetic arcades stemming from theory/modeling,
discuss their merits, and highlight potential ambiguities that could
arise in their interpretation. We finally conclude with a discussion
of possible new observables, in the frame of upcoming or proposed
instrumentation, that could help to circumvent the issues we are
currently facing.

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Title: Modeling the Effect of Mass-draining on Prominence Eruptions
Authors: Jenkins, Jack M.; Hopwood, Matthew; Démoulin, Pascal; Valori,
Gherardo; Aulanier, Guillaume; Long, David M.; van Driel-Gesztelyi,
Lidia
2019ApJ...873...49J Altcode: 2019arXiv190110970J
Quiescent solar prominences are observed within the solar atmosphere
for up to several solar rotations. Their eruption is commonly preceded
by a slow increase in height that can last from hours to days. This
increase in the prominence height is believed to be due to their host
magnetic flux rope transitioning through a series of neighboring
quasi-equilibria before the main loss of equilibrium that drives
the eruption. Recent work suggests that the removal of prominence
mass from a stable, quiescent flux rope is one possible cause for
this change in height. However, these conclusions are drawn from
observations and are subject to interpretation. Here, we present a
simple model to quantify the effect of “mass-draining” during the
pre-eruptive height evolution of a solar flux rope. The flux rope is
modeled as a line current suspended within a background potential
magnetic field. We first show that the inclusion of mass, up to
1012 kg, can modify the height at which the line current
experiences loss of equilibrium by up to 14%. Next, we show that
the rapid removal of mass prior to the loss of equilibrium can allow
the height of the flux rope to increase sharply and without an upper
bound as it approaches its loss-of-equilibrium point. This indicates
that the critical height for the loss of equilibrium can occur at a
range of heights depending explicitly on the amount and evolution of
mass within the flux rope. Finally, we demonstrate that for the same
amount of drained mass, the effect on the height of the flux rope is
up to two orders of magnitude larger for quiescent prominences than
for active region prominences.

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Title: Generalization of the Magnetic Field Configuration of Typical
and Atypical Confined Flares
Authors: Joshi, Navin Chandra; Zhu, Xiaoshuai; Schmieder, Brigitte;
Aulanier, Guillaume; Janvier, Miho; Joshi, Bhuwan; Magara, Tetsuya;
Chandra, Ramesh; Inoue, Satoshi
2019ApJ...871..165J Altcode: 2018arXiv181101228J
Atypical flares cannot be naturally explained with standard models. To
predict such flares, we need to define their physical characteristics,
in particular, their magnetic environment, and identify pairs of
reconnected loops. Here, we present in detail a case study of a confined
flare preceded by flux cancellation that leads to the formation of a
filament. The slow rise of the noneruptive filament favors the growth
and reconnection of overlying loops. The flare is only of C5.0 class
but it is a long duration event. The reason is that it is comprised
of three successive stages of reconnection. A nonlinear force-free
field extrapolation and a magnetic topology analysis allow us to
identify the loops involved in the reconnection process and build a
reliable scenario for this atypical confined flare. The main result
is that a curved magnetic polarity inversion line in active regions
is a key ingredient for producing such atypical flares. A comparison
with previous extrapolations for typical and atypical confined flares
leads us to propose a cartoon for generalizing the concept.

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Title: Drifting of the line-tied footpoints of CME flux-ropes
Authors: Aulanier, Guillaume; Dudík, Jaroslav
2019A&A...621A..72A Altcode: 2018arXiv181104253A
Context. Bridging the gap between heliospheric and solar observations
of eruptions requires the mapping of interplanetary coronal mass
ejection (CME) footpoints down to the Sun's surface. But this not
straightforward. Improving the understanding of the spatio-temporal
evolutions of eruptive flares requires a comprehensive standard
model. But the current model is only two-dimensional and cannot
address the question of interplanetary CME footpoints. Aims:
Existing 3D extensions to the standard model show that flux-rope
footpoints are surrounded by curved-shaped quasi-separatrix layer (QSL)
footprints that can be related with hook-shaped flare-ribbons. We
build upon this finding and further address the joint questions of
their time-evolution, and of the formation of flare loops at the
ends of the flaring polarity inversion line (PIL) of the erupting
bipole, which are both relevant for flare understanding in general
and for interplanetary CME studies in particular. Methods:
We calculated QSLs and relevant field lines in an MHD simulation of a
torus-unstable flux-rope. The evolving QSL footprints are used to define
the outer edge of the flux rope at different times, and to identify and
characterize new 3D reconnection geometries and sequences that occur
above the ends of the flaring PIL. We also analyzed flare-ribbons as
observed in the extreme ultraviolet by SDO/AIA and IRIS during two
X-class flares. Results: The flux-rope footpoints are drifting
during the eruption, which is unexpected due to line-tying. This
drifting is due to a series of coronal reconnections that erode the
flux rope on one side and enlarge it on the other side. Other changes
in the flux-rope footpoint-area are due to multiple reconnections
of individual field lines whose topology can evolve sequentially from
arcade to flux rope and finally to flare loop. These are associated with
deformations and displacements of QSL footprints, which resemble those
of the studied flare ribbons. Conclusions: Our model predicts
continuous deformations and a drifting of interplanetary CME flux-rope
footpoints whose areas are surrounded by equally evolving hooked-shaped
flare-ribbons, as well as the formation of flare loops at the ends of
flaring PILs which originate from the flux-rope itself, both of which
being due to purely three-dimensional reconnection geometries. The
observed evolution of flare-ribbons in two events supports the model,
but more observations are required to test all its predictions.

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Title: Fast velocities of flare ribbon kernels and ribbon elongation
in a quescent filament eruption of 2012 August 31 observed by SDO/AIA
Authors: Lörinčík, Juraj; Dudík, Jaroslav; Kašparová, Jana;
Aulanier, Guillaume; Zemanová, Alena; Dzifčáková, Elena
2018csc..confE..63L Altcode:
We report on SDO observations of an eruption of a quiescent filament
from 2012 August 31. In the 1600 Å filter channel of AIA, flare
ribbons were observed to elongate at velocities up to 480 km s^{-1}
and flare kernels move along a ribbon at velocity of ≈ 260 km
s^{-1}. In order to investigate the emission observed in the 1600 Å
channel, we used synthetic spectra modeled using CHIANTI and RADYN
models of flare atmospheres with beam parameters constrained using
fits of RHESSI spectra. We found out that depending on parameters of
heating of a flare model, thickness of a region where the emission
of the 1600 Å filter channel originates ranges between 10^{-2} and
10^{2} km. Information on dimensions of the formation region were
then utilized to estimate densities in flare ribbons using inversions
of the emission measure. These were found to range between 10^{10} -
4.10^{12} cm^{-3} for flare atmospheres heated by beams of different
parameters. Together with B_{LOS} data from SDO/HMI, diagnosed densities
were used to calculate Alfvén velocities in observed ribbons. These
can be as small as 17 km s^{-1} for flare ribbons observed in region of
weak magnetic field at latter stages of heating. This finding suggests
that elongation of ribbons and motion of kernels might not be related
to waves. Motions along the PIL are well-described in the 3D model of
solar eruptions of Aulanier et al. 2013 (A&amp;A, 543, 110). However,
EUV observations of flare loops revealed that velocity of their apparent
slipping motion is much lower than velocity of elongation of a ribbon,
which is observed in a close vicinity. Therefore, observed phenomena can
not be directly related to super-Alvénic regime of magnetic slipping
reconnection introduced in the 3D model.

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

---------------------------------------------------------
Title: Importance of the Hα Visibility and Projection Effects for
the Interpretation of Prominence Fine-structure Observations
Authors: Gunár, Stanislav; Dudík, Jaroslav; Aulanier, Guillaume;
Schmieder, Brigitte; Heinzel, Petr
2018ApJ...867..115G Altcode:
We construct a new 3D Whole-prominence Fine-structure (WPFS) model based
on a prominence magnetic field configuration designed to qualitatively
approximate the morphology of a quiescent prominence observed on 2010
June 22. The model represents an entire prominence with its numerous
fine structures formed by a prominence plasma located in dips in
the prominence magnetic field. We use the constructed 3D model and
employ a radiative-transfer-based Hα visualization method to analyze
the Hα visibility of prominence fine structures and its effect
on the perceived morphology of observed and modeled prominences. We
qualitatively compare three techniques used for visualization of modeled
prominences—visualizations drawing magnetic dips up to a height of
1 pressure scale height, drawing the full extent of magnetic dips,
and the synthetic Hα visualization—and discuss their suitability
for direct comparison between models and observations of prominences
and filaments. We also discuss the role of visibility of the prominence
fine structures in the estimation of the total height of prominences,
which may indicate the height of pre-erupting flux ropes. This
parameter is critical for the observational determination of the
flux-rope stability. In addition, we employ the WPFS model to assess
the effects caused by a projection of the naturally three-dimensional
and heterogeneous prominences onto a two-dimensional plane of the
sky. We discuss here how the morphological structures of prominences
differ when observed in projections from different viewing angles. We
also discuss the shapes of the dipped magnetic field lines and the
perceived projection of motions of prominence fine structures along
such field lines.

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Title: Flare reconnection driven magnetic field and Lorentz force
variations at the Sun's surface
Authors: Barczynski, Krzysztof; Aulanier, Guillaume; Masson, Sophie;
Wheatland, Michael S.
2018csc..confE..27B Altcode:
We show that the simulation is fully consistent with the observed
increase of the photospheric horizontal magnetic field and electric
currents around flaring PILs. The simulation also finds that the surface
integral coming from the volume integral of the Maxwell stress tensor,
as usually used in observational data analysis as the proxy of the
Lorentz force, shows an increased downard component in the photosphere,
as observed. But we also find that this proxy is significantly
different from the true Lorentz force, which does not reveal this
downward component. This result questions every previous interpretation
based on the implosion conjecture and momentum conservation. However
based on the analysis of the induction equation in the simulation,
we unveil that the increase of the horizontal magnetic filed around
active region PILs during eruptions is solely and exclusively result
of the flare reconnection-driven contraction of flare loops.

---------------------------------------------------------
Title: Signature of flux ropes before and after eruptions: electric
currents in active regions
Authors: Schmieder, Brigitte; Aulanier, Guillaume; Dalmasse, Kévin;
Janvier, Miho; Gilchrist, Stuart; Zhao, Jie; Dudik, Jaroslav
2018cosp...42E3026S Altcode:
Solar observations, nonlinear force-free field extrapolations relying
on these observations, and three-dimensional magnetohydrodynamic (MHD)
models indicate the presence of electric currents in the pre-eruption
state and in the course of eruptions of solar magnetic structures which
are interpreted as flux ropes (sigmoids, filaments, cavities).The MHD
models are able to explain the net currents in active regions by the
existence of strong magnetic shear along the polarity inversion lines,
thus confirming previous observations. The models have also captured
the essence of the behavior of electric currents in active regions
during solar eruptions, predicting current-density increases and
decreases inside flare ribbons and in the interior of expanding flux
ropes, respectively.The observed photospheric current-density maps,
inferred from vector magnetic field observations, exhibit whirling
ribbon patterns similar to the MHD model results, which are interpreted
as the signatures of flux ropes and of quasi-separatrix layers (QSLs)
between the magnetic systems in active regions. We will show how
observations can confirm enhancement of the total current in these
QSLs during the eruptions, and how these observations can be used
to investigate whether current density decrease can be seen at the
footpoints of erupting flux ropes

---------------------------------------------------------
Title: Can 3D whole-prominence fine structure models be used for
assessment of the prominence plasma mass and distribution prior to
the onset of CMEs?
Authors: Gunár, Stanislav; Schmieder, Brigitte; Aulanier, Guillaume;
Anzer, Ulrich; Heinzel, Petr; Mackay, Duncan; Dudik, Jaroslav
2018cosp...42E1316G Altcode:
Two complex 3D models of entire prominences including their numerous
fine structures were recently developed. The first 3D Whole-Prominence
Fine Structure (WPFS) model was developed by Gunár and Mackay. The
second 3D WPFS model was put forward by Gunár, Aulanier, Dudík,
Heinzel, and Schmieder. These 3D prominence models combine simulations
of the 3D magnetic field configuration of an entire prominence with a
detailed description of the prominence plasma. The plasma is located
in magnetic dips in hydrostatic equilibrium and is distributed
along hundreds of fine structures. The assumed prominence plasma
has realistic density and temperature distributions including the
prominence-corona transition region.These 3D WPFS models allow us
to study the distribution and the mass of the prominence plasma
contained in prominence magnetic field configurations. These can
be crucial during the onset and early evolution of CMEs. Moreover,
prominence plasma represents a bulk of the material ejected by CMEs
into the interplanetary space. Here, we investigate the potential of
using the 3D WPFS models for assessment of the role the prominence
plasma plays in the initiation and evolution of CMEs.

---------------------------------------------------------
Title: Interactions of Twisted Ω-loops in a Model Solar Convection
Zone
Authors: Jouve, L.; Brun, A. S.; Aulanier, G.
2018ApJ...857...83J Altcode: 2018arXiv180304709J
This study aims at investigating the ability of strong interactions
between magnetic field concentrations during their rise through
the convection zone to produce complex active regions at the solar
surface. To do so, we perform numerical simulations of buoyant magnetic
structures evolving and interacting in a model solar convection
zone. We first produce a 3D model of rotating convection and then
introduce idealized magnetic structures close to the bottom of the
computational domain. These structures possess a certain degree of
field line twist and they are made buoyant on a particular extension
in longitude. The resulting twisted Ω-loops will thus evolve inside a
spherical convective shell possessing large-scale mean flows. We present
results on the interaction between two such loops with various initial
parameters (mainly buoyancy and twist) and on the complexity of the
emerging magnetic field. In agreement with analytical predictions, we
find that if the loops are introduced with opposite handedness and same
axial field direction or the same handedness but opposite axial field,
they bounce against each other. The emerging region is then constituted
of two separated bipolar structures. On the contrary, if the loops are
introduced with the same direction of axial and peripheral magnetic
fields and are sufficiently close, they merge while rising. This more
interesting case produces complex magnetic structures with a high
degree of non-neutralized currents, especially when the convective
motions act significantly on the magnetic field. This indicates that
those interactions could be good candidates to produce eruptive events
like flares or CMEs.

---------------------------------------------------------
Title: On the Occurrence of Thermal Nonequilibrium in Coronal Loops
Authors: Froment, C.; Auchère, F.; Mikić, Z.; Aulanier, G.;
Bocchialini, K.; Buchlin, E.; Solomon, J.; Soubrié, E.
2018ApJ...855...52F Altcode: 2018arXiv180204010F
Long-period EUV pulsations, recently discovered to be common in active
regions, are understood to be the coronal manifestation of thermal
nonequilibrium (TNE). The active regions previously studied with
EIT/Solar and Heliospheric Observatory and AIA/SDO indicated that
long-period intensity pulsations are localized in only one or two
loop bundles. The basic idea of this study is to understand why. For
this purpose, we tested the response of different loop systems, using
different magnetic configurations, to different stratifications and
strengths of the heating. We present an extensive parameter-space study
using 1D hydrodynamic simulations (1020 in total) and conclude that the
occurrence of TNE requires specific combinations of parameters. Our
study shows that the TNE cycles are confined to specific ranges in
parameter space. This naturally explains why only some loops undergo
constant periodic pulsations over several days: since the loop geometry
and the heating properties generally vary from one loop to another in
an active region, only the ones in which these parameters are compatible
exhibit TNE cycles. Furthermore, these parameters (heating and geometry)
are likely to vary significantly over the duration of a cycle, which
potentially limits the possibilities of periodic behavior. This study
also confirms that long-period intensity pulsations and coronal rain are
two aspects of the same phenomenon: both phenomena can occur for similar
heating conditions and can appear simultaneously in the simulations.

---------------------------------------------------------
Title: Solar Active Region Electric Currents Before and During
Eruptive Flares
Authors: Schmieder, Brigitte; Aulanier, Guillaume
2018GMS...235..391S Altcode: 2019arXiv190304050S
This chapter discusses electric currents in the preeruption state and in
the course of eruptions of solar magnetic structures, using information
from solar observations, nonlinear force-free field extrapolations
relying on these observations, and three-dimensional magnetohydrodynamic
(MHD) models. The discussion addresses the issue of neutralized versus
nonneutralized currents in active regions and concludes that MHD models
are able to explain nonneutralized currents in active regions by the
existence of strong magnetic shear along the polarity inversion lines,
thus confirming previous observations that already contained this
result. The models have also captured the essence of the behavior of
electric currents in active regions during solar eruptions, predicting
current-density increases and decreases inside flare ribbons and
in the interior of expanding flux ropes, respectively. The observed
photospheric current-density maps, inferred from vector magnetic field
observations, exhibit whirling ribbon patterns similar to the MHD
model results, which are interpreted as the signatures of flux ropes
and of quasi-separatrix layers (QSLs) between the magnetic systems in
active regions. Enhancement of the total current in these QSLs during
the eruptions and decreasing current densities at the footpoint of
erupting flux ropes, has been confirmed in the observations.

---------------------------------------------------------
Title: Geoeffective events through solar cycles
Authors: Schmieder, Brigitte; Aulanier, Guillaume
2018IAUS..340..255S Altcode:
Extreme solar storms are well known in the historical databases. Since
the modern era, it has been possible to associate clearly
geomagnetic disturbances with solar events (flares, SEP, CMEs). In
the recent solar cycles the geoeffective events (number and strength)
are decreasing. As an example, in the 2002 maximum activity year,
we present how many flares, and CMEs were geoeffective. Based on
observations and simulations, we discuss on the size of sunspots and
the field strength to get more energetic flares (&gt; 1032
ergs) in the near future.

---------------------------------------------------------
Title: Slippage of Jets Explained by the Magnetic Topology of NOAA
Active Region 12035
Authors: Joshi, R.; Schmieder, B.; Chandra, R.; Aulanier, G.;
Zuccarello, F. P.; Uddin, W.
2017SoPh..292..152J Altcode: 2017arXiv170902791J
We present the investigation of 11 recurring solar jets that originated
from two different sites (site 1 and site 2) close to each other (≈11
Mm) in NOAA active region (AR) 12035 during 15 - 16 April 2014. The
jets were observed by the Atmospheric Imaging Assembly (AIA) telescope
on board the Solar Dynamics Observatory (SDO) satellite. Two jets
were observed by the telescope of the Aryabhatta Research Institute of
Observational Sciences (ARIES), Nainital, India, in Hα . On 15 April,
flux emergence is strong in site 1, while on 16 April, flux emergence
and cancellation mechanisms are involved in both sites. The jets of
both sites have parallel trajectories and move to the south with a
speed between 100 and 360 km s−1. The jets of site 2
occurred during the second day have a tendency to move toward the
jets of site 1 and merge with them. We conjecture that the slippage
of the jets could be explained by the complex topology of the region,
which included a few low-altitude null points and many quasi-separatrix
layers (QSLs), which could intersect with one another.

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

---------------------------------------------------------
Title: Transition from eruptive to confined flares in the same
active region
Authors: Zuccarello, F. P.; Chandra, R.; Schmieder, B.; Aulanier,
G.; Joshi, R.
2017A&A...601A..26Z Altcode: 2017arXiv170202477Z
Context. Solar flares are sudden and violent releases of magnetic
energy in the solar atmosphere that can be divided into two classes:
eruptive flares, where plasma is ejected from the solar atmosphere
resulting in a coronal mass ejection (CME), and confined flares,
where no CME is associated with the flare. Aims: We present
a case study showing the evolution of key topological structures,
such as spines and fans, which may determine the eruptive versus
non-eruptive behavior of the series of eruptive flares followed by
confined flares, which all originate from the same site. 
Methods: To study the connectivity of the different flux domains
and their evolution, we compute a potential magnetic field model of
the active region. Quasi-separatrix layers are retrieved from the
magnetic field extrapolation. Results: The change in behavior
of the flares from one day to the next - from eruptive to confined -
can be attributed to the change in orientation of the magnetic field
below the fan with respect to the orientation of the overlaying spine
rather than an overall change in the stability of the large-scale
field. Conclusions: Flares tend to be more confined when the
field that supports the filament and the overlying field gradually
becomes less anti-parallel as a direct result of changes in the
photospheric flux distribution, being themselves driven by continuous
shearing motions of the different magnetic flux concentrations. Movies associated to Figs. 2, 3, and 5 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201629836/olm">http://www.aanda.org</A>

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

---------------------------------------------------------
Title: Long-period Intensity Pulsations in Coronal Loops Explained
by Thermal Non-equilibrium Cycles
Authors: Froment, C.; Auchère, F.; Aulanier, G.; Mikić, Z.;
Bocchialini, K.; Buchlin, E.; Solomon, J.
2017ApJ...835..272F Altcode: 2017arXiv170101309F
In solar coronal loops, thermal non-equilibrium (TNE) is a phenomenon
that can occur when the heating is both highly stratified and
quasi-constant. Unambiguous observational identification of TNE
would thus permit us to strongly constrain heating scenarios. While
TNE is currently the standard interpretation of coronal rain, the
long-term periodic evolution predicted by simulations has never been
observed. However, the detection of long-period intensity pulsations
(periods of several hours) has been recently reported with the Solar
and Heliospheric Observatory/EIT, and this phenomenon appears to be very
common in loops. Moreover, the three intensity-pulsation events that we
recently studied with the Solar Dynamics Observatory/Atmospheric Imaging
Assembly (AIA) show strong evidence for TNE in warm loops. In this
paper, a realistic loop geometry from linear force-free field (LFFF)
extrapolations is used as input to 1D hydrodynamic simulations. Our
simulations show that, for the present loop geometry, the heating has
to be asymmetrical to produce TNE. We analyze in detail one particular
simulation that reproduces the average thermal behavior of one of the
pulsating loop bundle observed with AIA. We compare the properties of
this simulation with those deduced from the observations. The magnetic
topology of the LFFF extrapolations points to the presence of sites
of preferred reconnection at one footpoint, supporting the presence
of asymmetric heating. In addition, we can reproduce the temporal
large-scale intensity properties of the pulsating loops. This simulation
further strengthens the interpretation of the observed pulsations as
signatures of TNE. This consequently provides important information
on the heating localization and timescale for these loops.

---------------------------------------------------------
Title: Successive Magnetic Reconnections Observed during Sympathetic
Eruptions
Authors: Chandra Joshi, Navin; Schmieder, Brigitte; Magara, Tetsuya;
Guo, Yang; Aulanier, Guillaume
2017psio.confE.120C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar physics: When the tail wags the dog
Authors: Aulanier, Guillaume
2016NatPh..12..998A Altcode:
Solar eruptions are triggered by magnetic stress building up in the
corona due to the motion of the Sun's dense surface. New observations
reveal that these eruptions can, in turn, induce the rotational motion
of sunspots.

---------------------------------------------------------
Title: Long-period Intensity Pulsations as the Manifestation of the
Heating Stratification and Timescale in Coronal Loops
Authors: Froment, Clara; Auchère, Frédéric; Aulanier, Guillaume;
Mikić, Zoran; Bocchialini, Karine; Buchlin, Eric; Solomon, Jacques
2016usc..confE..47F Altcode:
In solar coronal loops, thermal non-equilibrium (TNE) is a phenomenon
that can occur when the heating is both highly-stratified and
quasi-constant. Unambiguous observational identification of TNE
would thus permit to strongly constrain heating scenarios. Up to
now, while TNE is the standard interpretation of coronal rain, it
was not believed to happen commonly in warm coronal loops. Recently,
the detection of long-period intensity pulsations (periods of several
hours) has been reported with SoHO/EIT. This phenomenon appears to be
very common in loops (Auchère et al. 2014). In Froment et al. 2015,
three intensity-pulsation events studied with SDO/AIA, show strong
evidence for TNE in warm loops. We use realistic loop geometries
from LFFF extrapolations for one of these events are used as input
to a 1D hydrodynamic simulation of TNE. A highly-stratified heating
function is chosen to reproduce the observed period of pulsation and
temperature of the loops. With these conditions, the heating function
has to be asymmetric. The magnetic topology of the LFFF extrapolations
points to the presence of sites of preferred reconnection at one
footpoint, supporting the presence of asymmetric heating. We compared
the properties of the simulated loop with the properties deduced
from observations. We found that the 1D hydrodynamic simulation
can reproduce the large temporal scale intensity properties of the
pulsating loops (Froment et al. 2016, submitted). This simulation
further strengthen the interpretation of the observed pulsations as
signatures of TNE. This implies that the heating for these loops is
highly-stratified and that the frequency of the heating events must
be high compared to the typical cooling time.

---------------------------------------------------------
Title: Evidence of flux rope and sigmoid in Active Regions prior
eruptions
Authors: Schmieder, Brigitte; Aulanier, Guillaume; Janvier, Miho;
Bommier, Veronique; Dudik, Jaroslav; Gilchrist, Stuart; Zhao, Jie
2016cosp...41E1750S Altcode:
In the solar corona, the magnetic field is dominant, and the current
density vector is nearly aligned with the magnetic field lines
for strong and stressed field regions. Stressed and highly twisted
flux ropes are at the origin of eruptive events such as flares and
coronal mass ejections, which inject material into the interplanetary
medium. The standard three dimensional (3D) flare model predicts
the complex evolution of flare loops and the flux rope before
the eruption. Flux ropes are not directly observed in the corona,
however it has started to be possible to detect their footprints
in the photosphere. Recent high spatial and temporal resolution
spectro-polarimeters have allowed us to compute the photospheric
electric currents and follow their evolution. Characteristics pattern
like J-shaped ribbons indicate the presence of a flux rope before
the flare. The results confirm the predictions of the 3D MHD standard
model of eruptive flares. It is interesting to compare the magnetic
helicity of the ejected flux rope with the in situ measurements of the
corresponding ICME at L1. We will show some examples (February 15 2011,
July 12 2012, Sept 10 2014).

---------------------------------------------------------
Title: Erratum: "Hooked Flare Ribbons and Flux-rope Related QSL
Footprints"<A href="/abs/2016ApJ...823...62Z">(2016, ApJ, 823, 62)</A>
Authors: Zhao, Jie; Gilchrist, Stuart A.; Aulanier, Guillaume;
Schmieder, Brigitte; Pariat, Etienne; Li, Hui
2016ApJ...825...80Z Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Hooked Flare Ribbons and Flux-rope-related QSL Footprints
Authors: Zhao, Jie; Gilchrist, Stuart A.; Aulanier, Guillaume;
Schmieder, Brigitte; Pariat, Etienne; Li, Hui
2016ApJ...823...62Z Altcode: 2016arXiv160307563Z
We studied the magnetic topology of active region 12158 on 2014
September 10 and compared it with the observations before and early in
the flare that begins at 17:21 UT (SOL2014-09-10T17:45:00). Our results
show that the sigmoidal structure and flare ribbons of this active
region observed by the Solar Dynamics Observatory/Atmospheric Imaging
Assembly can be well reproduced from a Grad-Rubin nonlinear force-free
field extrapolation method. Various inverse-S- and inverse-J-shaped
magnetic field lines, which surround a coronal flux rope, coincide with
the sigmoid as observed in different extreme-ultraviolet wavelengths,
including its multithreaded curved ends. Also, the observed distribution
of surface currents in the magnetic polarity where it was not prescribed
is well reproduced. This validates our numerical implementation and
setup of the Grad-Rubin method. The modeled double inverse-J-shaped
quasi-separatrix layer (QSL) footprints match the observed flare
ribbons during the rising phase of the flare, including their hooked
parts. The spiral-like shape of the latter may be related to a complex
pre-eruptive flux rope with more than one turn of twist, as obtained
in the model. These ribbon-associated flux-rope QSL footprints are
consistent with the new standard flare model in 3D, with the presence
of a hyperbolic flux tube located below an inverse-teardrop-shaped
coronal QSL. This is a new step forward forecasting the locations of
reconnection and ribbons in solar flares and the geometrical properties
of eruptive flux ropes.

---------------------------------------------------------
Title: Slipping Magnetic Reconnection, Chromospheric Evaporation,
Implosion, and Precursors in the 2014 September 10 X1.6-Class
Solar Flare
Authors: Dudík, Jaroslav; Polito, Vanessa; Janvier, Miho; Mulay,
Sargam M.; Karlický, Marian; Aulanier, Guillaume; Del Zanna, Giulio;
Dzifčáková, Elena; Mason, Helen E.; Schmieder, Brigitte
2016ApJ...823...41D Altcode: 2016arXiv160306092D
We investigate the occurrence of slipping magnetic reconnection,
chromospheric evaporation, and coronal loop dynamics in the 2014
September 10 X-class flare. Slipping reconnection is found to be present
throughout the flare from its early phase. Flare loops are seen to slip
in opposite directions toward both ends of the ribbons. Velocities
of 20-40 km s-1 are found within time windows where the
slipping is well resolved. The warm coronal loops exhibit expanding and
contracting motions that are interpreted as displacements due to the
growing flux rope that subsequently erupts. This flux rope existed and
erupted before the onset of apparent coronal implosion. This indicates
that the energy release proceeds by slipping reconnection and not via
coronal implosion. The slipping reconnection leads to changes in the
geometry of the observed structures at the Interface Region Imaging
Spectrograph slit position, from flare loop top to the footpoints in
the ribbons. This results in variations of the observed velocities of
chromospheric evaporation in the early flare phase. Finally, it is found
that the precursor signatures, including localized EUV brightenings as
well as nonthermal X-ray emission, are signatures of the flare itself,
progressing from the early phase toward the impulsive phase, with
the tether-cutting being provided by the slipping reconnection. The
dynamics of both the flare and outlying coronal loops is found to be
consistent with the predictions of the standard solar flare model in
three dimensions.

---------------------------------------------------------
Title: Chain Reconnections Observed in Sympathetic Eruptions
Authors: Joshi, Navin Chandra; Schmieder, Brigitte; Magara, Tetsuya;
Guo, Yang; Aulanier, Guillaume
2016ApJ...820..126J Altcode: 2016arXiv160207792J
The nature of various plausible causal links between sympathetic events
is still a controversial issue. In this work, we present multiwavelength
observations of sympathetic eruptions, associated flares, and coronal
mass ejections (CMEs) occurring on 2013 November 17 in two close active
regions. Two filaments, I.e., F1 and F2, are observed in between
the active regions. Successive magnetic reconnections, caused for
different reasons (flux cancellation, shear, and expansion) have been
identified during the whole event. The first reconnection occurred
during the first eruption via flux cancellation between the sheared
arcades overlying filament F2, creating a flux rope and leading to
the first double-ribbon solar flare. During this phase, we observed
the eruption of overlying arcades and coronal loops, which leads to
the first CME. The second reconnection is believed to occur between
the expanding flux rope of F2 and the overlying arcades of filament
F1. We suggest that this reconnection destabilized the equilibrium of
filament F1, which further facilitated its eruption. The third stage of
reconnection occurred in the wake of the erupting filament F1 between
the legs of the overlying arcades. This may create a flux rope and the
second double-ribbon flare and a second CME. The fourth reconnection
was between the expanding arcades of the erupting filament F1 and the
nearby ambient field, which produced the bi-directional plasma flows
both upward and downward. Observations and a nonlinear force-free
field extrapolation confirm the possibility of reconnection and the
causal link between the magnetic systems.

---------------------------------------------------------
Title: The Apparent Critical Decay Index at the Onset of Solar
Prominence Eruptions
Authors: Zuccarello, F. P.; Aulanier, G.; Gilchrist, S. A.
2016ApJ...821L..23Z Altcode:
A magnetic flux rope (MFR) embedded in a line-tied external magnetic
field that decreases with height as {z}-n is unstable
to perturbations if the decay index of the field n is larger
than a critical value. The onset of this instability, called torus
instability, is one of the main mechanisms that can initiate coronal
mass ejections. Since flux ropes often possess magnetic dips that
can support prominence plasma, this is also a valuable mechanism to
trigger prominence eruptions. Magnetohydrodynamic (MHD) simulations of
the formation and/or emergence of MFRs suggest a critical value for
the onset of the instability in the range [1.4-2]. However, detailed
observations of prominences suggest a value in the range [0.9-1.1]. In
this Letter, by using a set of MHD simulations, we show why the large
discrepancy between models and observations is only apparent. Our
simulations indeed show that the critical decay index at the onset of
the eruption is n=1.4+/- 0.1 when computed at the apex of the flux rope
axis, while it is n=1.1+/- 0.1 when it is computed at the altitude of
the topmost part of the distribution of magnetic dips. The discrepancy
only arises because weakly twisted curved flux ropes do not have dips
up to the altitude of their axis.

---------------------------------------------------------
Title: Role of "X point” in Flares and Filament Interactions
Authors: Schmieder, B.; Zuccarello, F. P.; Aulanier, G.; Chandra,
R.; Joshi, N. C.; Filippov, B.
2016CEAB...40...35S Altcode:
Explaining the trigger and energy release processes of flares is a
fundamental problem of solar physics. It is commonly held that magnetic
reconnection plays a key role in converting magnetic energy into other
forms of energy. In 2D magnetic field configurations, when oppositely
directed magnetic fields are brought together they may reconnect thereby
releasing stored magnetic energy eventually resulting in a flare. In
3D configurations, the magnetic topology should be considered and the
reconnection is favored at the intersection of magnetic quasi-separatrix
layers, which is an extension of what is called "X point" in 2D. The
evolution of key topological structures, such as null point, spines
and fans may determine the eruptive behavior of a flare. The presence
of a null point can be very important. We present a few examples, i.e.,
a flare with a circular flare ribbon and the interaction of two parallel
filaments. In the case of flux rope destabilization and triggering
eruption due to the torus instability, the important parameter is
the decay index and not the topology itself. However the complexity
of active regions leads to interpretations where different mechanisms
may be intermixed. The breakout mechanism, which requires a quadrupolar
configuration with QSLs and separator where the reconnection can occur,
is present in many models. That is not always a sufficient condition
to explain the eruptive flares. For one case study, the different
behaviour of a series of eruptive flares followed by confined flares,
all originating in the same site has been attributed to the change of
orientation of the magnetic field below the fan with respect to the
orientation of the spine. Flares tend to be more confined when the
two fields become less antiparallel.

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

---------------------------------------------------------
Title: Critical Decay Index at the Onset of Solar Eruptions
Authors: Zuccarello, F. P.; Aulanier, G.; Gilchrist, S. A.
2015ApJ...814..126Z Altcode: 2015arXiv151003713Z
Magnetic flux ropes are topological structures consisting of twisted
magnetic field lines that globally wrap around an axis. The torus
instability model predicts that a magnetic flux rope of major radius R
undergoes an eruption when its axis reaches a location where the decay
index -d({ln}{B}{ex})/d({ln}R) of the ambient magnetic field
Bex is larger than a critical value. In the current-wire
model, the critical value depends on the thickness and time evolution
of the current channel. We use magnetohydrodynamic simulations to
investigate whether the critical value of the decay index at the onset
of the eruption is affected by the magnetic flux rope’s internal
current profile and/or by the particular pre-eruptive photospheric
dynamics. The evolution of an asymmetric, bipolar active region is
driven by applying different classes of photospheric motions. We find
that the critical value of the decay index at the onset of the eruption
is not significantly affected by either the pre-erupitve photospheric
evolution of the active region or the resulting different magnetic
flux ropes. As in the case of the current-wire model, we find that
there is a “critical range” [1.3-1.5], rather than a “critical
value” for the onset of the torus instability. This range is in good
agreement with the predictions of the current-wire model, despite the
inclusion of line-tying effects and the occurrence of tether-cutting
magnetic reconnection.

---------------------------------------------------------
Title: Flare-CME Models: An Observational Perspective (Invited Review)
Authors: Schmieder, B.; Aulanier, G.; Vršnak, B.
2015SoPh..290.3457S Altcode: 2015SoPh..tmp...64S
Eruptions, flares, and coronal mass ejection (CMEs) are due to physical
phenomena mainly driven by an initially force-free current-carrying
magnetic field. We review some key observations relevant to the
current theoretical trigger mechanisms of the eruption and to the
energy release via reconnection. Sigmoids observed in X-rays and UV,
as well as the pattern (double J-shaped) of electric currents in
the photosphere show clear evidence of the existence of currents
parallel to the magnetic field and can be the signature of a flux
rope that is detectable in CMEs. The magnetic helicity of filaments
and active regions is an interesting indirectly measurable parameter
because it can quantify the twist of the flux rope. On the other hand,
the magnetic helicity of the solar structures allows us to associate
solar eruptions and magnetic clouds in the heliosphere. The magnetic
topology analysis based on the 3D magnetic field extrapolated from
vector magnetograms is a good tool for identifying the reconnection
locations (null points and/or the 3D large volumes - hyperbolic flux
tube, HFT). Flares are associated more with quasi-separatrix layers
(QSLs) and HFTs than with a single null point, which is a relatively
rare case. We review various mechanisms that have been proposed to
trigger CMEs and their observable signatures: by "breaking" the field
lines overlying the flux rope or by reconnection below the flux rope
to reduce the magnetic tension, or by letting the flux rope to expand
until it reaches a minimum threshold height (loss of equilibrium or
torus instability). Additional mechanisms are commonly operating in
the solar atmosphere. Examples of observations are presented throughout
the article and are discussed in this framework.

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

---------------------------------------------------------
Title: Slipping reconnection and chromospheric evaporation in the
10 September 2014 flare
Authors: Dudík, Jaroslav; Janvier, Miho; Polito, Vanessa; Mulay,
Sargam; Del Zanna, Giulio; Mason, Helen; Aulanier, Guillaume
2015IAUGA..2252237D Altcode:
We study the occurrence of slipping reconnection in the long-duration
X-class flare of 2014 September 10. From the start, the flare shows
apparent slippage of hot Fe XXI flare loops observed in the 131A
channel of SDO/AIA. Using the time-distance plots, we show that the
slipping motion of the flare loops proceeds in counter directions in
both flare ribbons. Simultaneous IRIS Fe XXI observations show the
occurrence of chromospheric evaporation at brightening kernels that are
involved in the slipping reconnection of AIA loops. This happens also
during a flux-rope breakout accompanied by a faint 'magnetic implosion'
of a coronal loop. Based on the 3D MHD flare model, we argue that the
'implosion' is caused by the erupting flux rope pushing the neighbouring
loops aside, with the low-lying loops being squeezed.

---------------------------------------------------------
Title: Formation of a rotating jet during the filament eruption on
2013 April 10-11
Authors: Filippov, B.; Srivastava, A. K.; Dwivedi, B. N.; Masson,
S.; Aulanier, G.; Joshi, N. C.; Uddin, W.
2015MNRAS.451.1117F Altcode: 2015MNRAS.451.5636F; 2015arXiv150501615F
We analyse multiwavelength and multiviewpoint observations of
a helically twisted plasma jet formed during a confined filament
eruption on 2013 April 10-11. Given a rather large-scale event with
its high spatial and temporal resolution observations, it allows us to
clearly understand some new physical details about the formation and
triggering mechanism of twisting jet. We identify a pre-existing flux
rope associated with a sinistral filament, which was observed several
days before the event. The confined eruption of the filament within
a null-point topology, also known as an Eiffel tower (or inverted-Y)
magnetic field configuration results in the formation of a twisted jet
after the magnetic reconnection near a null point. The sign of helicity
in the jet is found to be the same as that of the sign of helicity
in the filament. Untwisting motion of the reconnected magnetic field
lines gives rise to the accelerating plasma along the jet axis. The
event clearly shows the twist injection from the pre-eruptive magnetic
field to the jet.

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

---------------------------------------------------------
Title: Can we explain atypical solar flares?
Authors: Dalmasse, K.; Chandra, R.; Schmieder, B.; Aulanier, G.
2015A&A...574A..37D Altcode: 2014arXiv1410.8194D
Context. We used multiwavelength high-resolution data from ARIES,
THEMIS, and SDO instruments to analyze a non-standard, C3.3 class
flare produced within the active region NOAA 11589 on 2012 October
16. Magnetic flux emergence and cancellation were continuously detected
within the active region, the latter leading to the formation of
two filaments. Aims: Our aim is to identify the origins of
the flare taking the complex dynamics of its close surroundings into
account. Methods: We analyzed the magnetic topology of the active
region using a linear force-free field extrapolation to derive its 3D
magnetic configuration and the location of quasi-separatrix layers
(QSLs), which are preferred sites for flaring activity. Because the
active region's magnetic field was nonlinear force-free, we completed a
parametric study using different linear force-free field extrapolations
to demonstrate the robustness of the derived QSLs. Results:
The topological analysis shows that the active region presented a
complex magnetic configuration comprising several QSLs. The considered
data set suggests that an emerging flux episode played a key role in
triggering the flare. The emerging flux probably activated the complex
system of QSLs, leading to multiple coronal magnetic reconnections
within the QSLs. This scenario accounts for the observed signatures:
the two extended flare ribbons developed at locations matched by
the photospheric footprints of the QSLs and were accompanied with
flare loops that formed above the two filaments, which played no
important role in the flare dynamics. Conclusions: This is a
typical example of a complex flare that can a priori show standard
flare signatures that are nevertheless impossible to interpret with
any standard model of eruptive or confined flare. We find that a
topological analysis, however, permitted us to unveil the development
of such complex sets of flare signatures. Movies associated to
Figs. 1, 3, and 9 are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/574/A37">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/574/A37</A>

---------------------------------------------------------
Title: VizieR Online Data Catalog: Movies of 2012-10-16 solar flare
(Dalmasse+, 2015)
Authors: Dalmasse, K.; Chandra, R.; Schmieder, B.; Aulanier, G.
2015yCat..35740037D Altcode: 2015yCat..35749037D
Part of the observations of NOAA 11589 presented here were obtained
with the Atmospheric Imaging Assembly imager (AIA) and the Helioseismic
and Magnetic Imager (HMI) onboard the Solar Dynamic Observatory (SDO)
satellite. The AIA instrument observes the Sun over a wide range of
temperatures from the photosphere to the corona. The pixel size of the
AIA images is 0.6". In this study, we considered the 1600, 304, 193,
and 171Å data. The magnetic field in the AR was studied by using the
line-of-sight magnetograms of the HMI instrument, which observes the
full disk with a pixel size of 0.5". We also used ground-based
observations of the AR obtained with the Indian telescope from the
Aryabhatta Research Institute of observational Sciences (ARIES) and
with the French Telescope Heliographique pour l'Etude du Magnetisme
et des Instabilites Solaires (THEMIS). The 15-cm f/15 Coude telescope
of the ARIES, operating in Nainital (India), observes in the Hα line
with a spatial resolution of 0.58". The THEMIS telescope, operating
in Tenerife (Canary Islands), allows a simultaneous mapping of the
Hα emission and the full Stokes parameters in the Fe 6302.5Å of a
field of view of about 240"x100" in one hour. (2 data files).

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

---------------------------------------------------------
Title: Distribution of electric currents in source regions of solar
eruptions
Authors: Torok, Tibor; Leake, James E.; Titov, Viacheslav; Archontis,
Vasilis; Mikic, Zoran; Linton, Mark; Dalmasse, Kevin; Aulanier,
Guillaume; Kliem, Bernhard
2014AAS...22431202T Altcode:
There has been a long-lasting debate on the question of whether or
not electric currents in the source regions of solar eruptions are
neutralized. That is, whether or not the direct coronal currents
connecting the photospheric polarities in such regions are surrounded
by return currents of equal amount and opposite direction. In order to
address this question, we consider several mechanisms of source region
formation (flux emergence, photospheric shearing/twisting flows,
and flux cancellation) and quantify the evolution of the electric
currents, using 3D MHD simulations. For the experiments conducted so
far, we find a clear dominance of the direct currents over the return
currents in all cases in which the models produce significant magnetic
shear along the source region's polarity inversion line. This suggests
that pre-eruptive magnetic configurations in strongly sheared active
regions and filament channels carry substantial net currents. We discuss
the implications of this result for the modeling of solar eruptions.

---------------------------------------------------------
Title: Detection of Coherent Structures in Photospheric Turbulent
Flows
Authors: Chian, Abraham C. -L.; Rempel, Erico L.; Aulanier, Guillaume;
Schmieder, Brigitte; Shadden, Shawn C.; Welsch, Brian T.; Yeates,
Anthony R.
2014ApJ...786...51C Altcode: 2013arXiv1312.2405C
We study coherent structures in solar photospheric flows in a plage in
the vicinity of the active region AR 10930 using the horizontal velocity
data derived from Hinode/Solar Optical Telescope magnetograms. Eulerian
and Lagrangian coherent structures (LCSs) are detected by computing
the Q-criterion and the finite-time Lyapunov exponents of the velocity
field, respectively. Our analysis indicates that, on average, the
deformation Eulerian coherent structures dominate over the vortical
Eulerian coherent structures in the plage region. We demonstrate the
correspondence of the network of high magnetic flux concentration to the
attracting Lagrangian coherent structures (aLCSs) in the photospheric
velocity based on both observations and numerical simulations. In
addition, the computation of aLCS provides a measure of the local rate
of contraction/expansion of the flow.

---------------------------------------------------------
Title: Slipping Magnetic Reconnection during an X-class Solar Flare
Observed by SDO/AIA
Authors: Dudík, J.; Janvier, M.; Aulanier, G.; Del Zanna, G.;
Karlický, M.; Mason, H. E.; Schmieder, B.
2014ApJ...784..144D Altcode: 2014arXiv1401.7529D
We present SDO/AIA observations of an eruptive X-class flare of
2012 July 12, and compare its evolution with the predictions of a
three-dimensional (3D) numerical simulation. We focus on the dynamics of
flare loops that are seen to undergo slipping reconnection during the
flare. In the Atmospheric Imaging Assembly (AIA) 131 Å observations,
lower parts of 10 MK flare loops exhibit an apparent motion with
velocities of several tens of km s-1 along the developing
flare ribbons. In the early stages of the flare, flare ribbons consist
of compact, localized bright transition-region emission from the
footpoints of the flare loops. A differential emission measure analysis
shows that the flare loops have temperatures up to the formation of
Fe XXIV. A series of very long, S-shaped loops erupt, leading to a
coronal mass ejection observed by STEREO. The observed dynamics are
compared with the evolution of magnetic structures in the "standard
solar flare model in 3D." This model matches the observations well,
reproducing the apparently slipping flare loops, S-shaped erupting
loops, and the evolution of flare ribbons. All of these processes are
explained via 3D reconnection mechanisms resulting from the expansion
of a torus-unstable flux rope. The AIA observations and the numerical
model are complemented by radio observations showing a noise storm
in the metric range. Dm-drifting pulsation structures occurring
during the eruption indicate plasmoid ejection and enhancement of the
reconnection rate. The bursty nature of radio emission shows that the
slipping reconnection is still intermittent, although it is observed
to persist for more than an hour.

---------------------------------------------------------
Title: Distribution of Electric Currents in Solar Active Regions
Authors: Török, T.; Leake, J. E.; Titov, V. S.; Archontis, V.;
Mikić, Z.; Linton, M. G.; Dalmasse, K.; Aulanier, G.; Kliem, B.
2014ApJ...782L..10T Altcode: 2014arXiv1401.2931T
There has been a long-standing debate on the question of whether or
not electric currents in solar active regions are neutralized. That
is, whether or not the main (or direct) coronal currents connecting
the active region polarities are surrounded by shielding (or return)
currents of equal total value and opposite direction. Both theory and
observations are not yet fully conclusive regarding this question, and
numerical simulations have, surprisingly, barely been used to address
it. Here we quantify the evolution of electric currents during the
formation of a bipolar active region by considering a three-dimensional
magnetohydrodynamic simulation of the emergence of a sub-photospheric,
current-neutralized magnetic flux rope into the solar atmosphere. We
find that a strong deviation from current neutralization develops
simultaneously with the onset of significant flux emergence into the
corona, accompanied by the development of substantial magnetic shear
along the active region's polarity inversion line. After the region
has formed and flux emergence has ceased, the strong magnetic fields
in the region's center are connected solely by direct currents, and
the total direct current is several times larger than the total return
current. These results suggest that active regions, the main sources
of coronal mass ejections and flares, are born with substantial net
currents, in agreement with recent observations. Furthermore, they
support eruption models that employ pre-eruption magnetic fields
containing such currents.

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

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

---------------------------------------------------------
Title: A confined flare above filaments
Authors: Dalmasse, K.; Chandra, R.; Schmieder, B.; Aulanier, G.
2014IAUS..300..227D Altcode: 2013arXiv1310.0667D
We present the dynamics of two filaments and a C-class flare observed
in NOAA 11589 on 2012 October 16. We used the multi-wavelength
high-resolution data from SDO, as well as THEMIS and ARIES ground-based
observations. The observations show that the filaments are progressively
converging towards each other without merging. We find that the
filaments have opposite chirality which may have prevented them from
merging. On October 16, a C3.3 class flare occurred without the eruption
of the filaments. According to the standard solar flare model, after
the reconnection, post-flare loops form below the erupting filaments
whether the eruption fails or not. However, the observations show
the formation of post-flare loops above the filaments, which is not
consistent with the standard flare model. We analyze the topology of
the active region's magnetic field by computing the quasi-separatrix
layers (QSLs) using a linear force-free field extrapolation. We find
a good agreement between the photospheric footprints of the QSLs and
the flare ribbons. We discuss how slipping or slip-running reconnection
at the QSLs may explain the observed dynamics.

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

---------------------------------------------------------
Title: The physical mechanisms that initiate and drive solar eruptions
Authors: Aulanier, Guillaume
2014IAUS..300..184A Altcode: 2013arXiv1309.7329A
Solar eruptions are due to a sudden destabilization of force-free
coronal magnetic fields. But the detailed mechanisms which can bring the
corona towards an eruptive stage, then trigger and drive the eruption,
and finally make it explosive, are not fully understood. A large
variety of storage-and-release models have been developed and opposed
to each other since 40 years. For example, photospheric flux emergence
vs. flux cancellation, localized coronal reconnection vs. large-scale
ideal instabilities and loss of equilibria, tether-cutting vs. breakout
reconnection, and so on. The competition between all these approaches
has led to a tremendous drive in developing and testing all these
concepts, by coupling state-of-the-art models and observations. Thanks
to these developments, it now becomes possible to compare all these
models with one another, and to revisit their interpretation in
light of their common and their different behaviors. This approach
leads me to argue that no more than two distinct physical mechanisms
can actually initiate and drive prominence eruptions: the magnetic
breakout and the torus instability. In this view, all other processes
(including flux emergence, flux cancellation, flare reconnection and
long-range couplings) should be considered as various ways that lead
to, or that strengthen, one of the aforementioned driving mechanisms.

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

---------------------------------------------------------
Title: Hot Spine Loops and the Nature of a Late-phase Solar Flare
Authors: Sun, Xudong; Hoeksema, J. Todd; Liu, Yang; Aulanier,
Guillaume; Su, Yingna; Hannah, Iain G.; Hock, Rachel A.
2013ApJ...778..139S Altcode: 2013arXiv1310.1438S
The fan-spine magnetic topology is believed to be responsible for
many curious features in solar explosive events. A spine field line
links distinct flux domains, but direct observation of such a feature
has been rare. Here we report a unique event observed by the Solar
Dynamic Observatory where a set of hot coronal loops (over 10 MK)
connected to a quasi-circular chromospheric ribbon at one end and
a remote brightening at the other. Magnetic field extrapolation
suggests that these loops are partly tracers of the evolving spine
field line. Continuous slipping- and null-point-type reconnections
were likely at work, energizing the loop plasma and transferring
magnetic flux within and across the fan quasi-separatrix layer. We
argue that the initial reconnection is of the "breakout" type, which
then transitioned to a more violent flare reconnection with an eruption
from the fan dome. Significant magnetic field changes are expected
and indeed ensued. This event also features an extreme-ultraviolet
(EUV) late phase, i.e., a delayed secondary emission peak in warm EUV
lines (about 2-7 MK). We show that this peak comes from the cooling
of large post-reconnection loops beside and above the compact fan,
a direct product of eruption in such topological settings. The long
cooling time of the large arcades contributes to the long delay;
additional heating may also be required. Our result demonstrates the
critical nature of cross-scale magnetic coupling—topological change
in a sub-system may lead to explosions on a much larger scale.

---------------------------------------------------------
Title: Twisting solar coronal jet launched at the boundary of an
active region
Authors: Schmieder, B.; Guo, Y.; Moreno-Insertis, F.; Aulanier, G.;
Yelles Chaouche, L.; Nishizuka, N.; Harra, L. K.; Thalmann, J. K.;
Vargas Dominguez, S.; Liu, Y.
2013A&A...559A...1S Altcode: 2013arXiv1309.6514S
 Aims: A broad jet was observed in a weak magnetic field area
at the edge of active region NOAA 11106 that also produced other
nearby recurring and narrow jets. The peculiar shape and magnetic
environment of the broad jet raised the question of whether it was
created by the same physical processes of previously studied jets
with reconnection occurring high in the corona. Methods:
We carried out a multi-wavelength analysis using the EUV images
from the Atmospheric Imaging Assembly (AIA) and magnetic fields
from the Helioseismic and Magnetic Imager (HMI) both on-board the
Solar Dynamics Observatory, which we coupled to a high-resolution,
nonlinear force-free field extrapolation. Local correlation tracking
was used to identify the photospheric motions that triggered the jet,
and time-slices were extracted along and across the jet to unveil its
complex nature. A topological analysis of the extrapolated field was
performed and was related to the observed features. Results:
The jet consisted of many different threads that expanded in around 10
minutes to about 100 Mm in length, with the bright features in later
threads moving faster than in the early ones, reaching a maximum speed
of about 200 km s-1. Time-slice analysis revealed a striped
pattern of dark and bright strands propagating along the jet, along with
apparent damped oscillations across the jet. This is suggestive of a
(un)twisting motion in the jet, possibly an Alfvén wave. Bald patches
in field lines, low-altitude flux ropes, diverging flow patterns, and a
null point were identified at the basis of the jet. Conclusions:
Unlike classical λ or Eiffel-tower-shaped jets that appear to be caused
by reconnection in current sheets containing null points, reconnection
in regions containing bald patches seems to be crucial in triggering
the present jet. There is no observational evidence that the flux
ropes detected in the topological analysis were actually being ejected
themselves, as occurs in the violent phase of blowout jets; instead,
the jet itself may have gained the twist of the flux rope(s) through
reconnection. This event may represent a class of jets different from
the classical quiescent or blowout jets, but to reach that conclusion,
more observational and theoretical work is necessary.

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

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Title: Hot Spine Loops and the Nature of a Late-Phase Solar Flare
Authors: Sun, Xudong; Hoeksema, J. T.; Liu, Y.; Aulanier, G.; Su,
Y.; Hannah, I.; Hock, R.
2013SPD....4420103S Altcode:
The fan-spine magnetic topology is believed to be responsible for
many curious emission signatures in solar explosive events. A spine
field line links topologically distinct flux domains and possibly
their evolutionary trends, but direct observation of such structure
has been rare. Here we report a unique event observed by the Solar
Dynamic Observatory (SDO) where a set of hot coronal loops (over 10
MK) that developed during the rising phase of the flare connected to a
quasi-circular chromospheric ribbon at one end and a remote brightening
at the other. Magnetic field extrapolation suggests these loops
are partly tracers of the evolving spine field line. The sequential
brightening of the ribbon, the apparent shuffling loop motion, and the
increasing volume occupied by the hot loops suggest that continuous
slipping- and null-point-type reconnections were at work, energizing
the loop plasma and transferring magnetic flux within and across
the dome-shaped, fan quasi-separatrix layer (QSL). We argue that the
initial reconnection is of the "break-out" type, which transitioned to
more violent flare reconnection nearing the flare peak with an eruption
from the fan dome. Significant magnetic field changes are expected and
indeed ensued, which include a shift of the QSL footprint, an increase
of the horizontal photospheric field, and de-shearing of the coronal
loops. This event also features an extreme-ultraviolet (EUV) late phase
-- a second emission peak observed in the warm EUV lines (about 2--7 MK)
up to 1--2 hours after the soft X-ray peak. We show that this peak comes
from the large post-flare arcades beside and above the compact fan dome,
a direct product of eruption in such topological settings. Cooling
of these large arcades naturally explains the sequential delay of the
late-phase peaks in increasingly cooler EUV lines, and the estimated
theoretical cooling time is compatible with observation. Our result
demonstrates the critical nature of cross-scale magnetic coupling --
minor topological change in a sub-system may lead to explosions on a
much larger scale.

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

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Title: SDO/AIA Prominence physical conditions
Authors: Schmieder, B.; Parenti, S.; Dudik, J.; Aulanier, G.; Heinzel,
P.; Zapior, M.; Golub, L.
2013enss.confE..27S Altcode:
SDO/AIA has carried out continuous observations of prominences in
multiple wavelengths, with high spatial and temporal resolution. These
data provide us an opportunity to understand the physical conditions
and dynamics of prominences. The surprising brightness of prominences
in some coronal lines has been well explained by the presence of
transition region lines in the bandpass of the filters (171 A, 131 A),
a result that leads us to revise our model of the transition region
of prominences and to consider a relatively dense transition region in
some prominence evolutionary phases or in some viewing orientation. An
additional aspect of prominence dynamics will be presented with a new
quasi-static MHD model proposed for bubbles and plumes. We propose
an alternative to the interpretation that thermal instabilities are
responsible for the formation of bubbles. The bubbles are found to
correspond to magnetic separatrices formed by emerging magnetic field
close to prominence footpoints.

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Title: Behavior of the vertical current during the X2 flare of 2011
February 15 observed by SDO/HMI, compared to a line-tied zero-beta
resistive MHD simulation
Authors: Bommier, Veronique; Aulanier, Guillaume
2013enss.confE..79B Altcode:
The level-1 data of SDO/HMI have been inverted with the UNNOFIT
inversion code (Bommier et al., 2007, A&amp;A, 464, 323), which differs
from VFISV about the magnetic filling factor modeling. More realistic
field inclinations are obtained outside the active region. The spatial
resolution seems to be also better. UNNOFIT is enabled for the taking
into account of gradients of radial velocity, responsible for asymmetry
of the Stokes profiles (Molodij et al., 2011, A&amp;A, 531, A139). The
ambiguity has been solved with the ME0 code of Metcalf, Leka, Barnes
&amp; Crouch. We present the movie of 4 hours of observation, the
flare occurring at middle. Two current ribbons of opposite polarity
are visible along the magnetic neutral line, in the vertical density
current map. The negative one strengthens and radially expands from
the flare center at the eruption moment. A similar current ribbon pair
is visible in a 3D line-tied zero-beta resistive MHD flare simulation
with the OHM code (Aulanier et al. , 2012, A&amp;A, 543, A110). The
two ribbons part from the flare center during the flare, similarly to
what observed on 2011 February 15 at 02:00 with SDO/HMI.

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Title: Global dynamics of subsurface solar active regions
Authors: Jouve, L.; Brun, A. S.; Aulanier, G.
2013ApJ...762....4J Altcode: 2012arXiv1211.7251J
We present three-dimensional numerical simulations of a magnetic
loop evolving in either a convectively stable or unstable rotating
shell. The magnetic loop is introduced into the shell in such a
way that it is buoyant only in a certain portion in longitude, thus
creating an Ω-loop. Due to the action of magnetic buoyancy, the loop
rises and develops asymmetries between its leading and following legs,
creating emerging bipolar regions whose characteristics are similar
to those of observed spots at the solar surface. In particular, we
self-consistently reproduce the creation of tongues around the spot
polarities, which can be strongly affected by convection. We further
emphasize the presence of ring-shaped magnetic structures around our
simulated emerging regions, which we call "magnetic necklace" and
which were seen in a number of observations without being reported
as of today. We show that those necklaces are markers of vorticity
generation at the periphery and below the rising magnetic loop. We also
find that the asymmetry between the two legs of the loop is crucially
dependent on the initial magnetic field strength. The tilt angle of the
emerging regions is also studied in the stable and unstable cases and
seems to be affected both by the convective motions and the presence
of a differential rotation in the convective cases.

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Title: The standard flare model in three dimensions. II. Upper limit
on solar flare energy
Authors: Aulanier, G.; Démoulin, P.; Schrijver, C. J.; Janvier, M.;
Pariat, E.; Schmieder, B.
2013A&A...549A..66A Altcode: 2012arXiv1212.2086A
Context. Solar flares strongly affect the Sun's atmosphere as well as
the Earth's environment. Quantifying the maximum possible energy of
solar flares of the present-day Sun, if any, is thus a key question in
heliophysics. Aims: The largest solar flares observed over the
past few decades have reached energies of a few times 1032
erg, possibly up to 1033 erg. Flares in active Sun-like
stars reach up to about 1036 erg. In the absence of direct
observations of solar flares within this range, complementary methods
of investigation are needed to assess the probability of solar flares
beyond those in the observational record. Methods: Using
historical reports for sunspot and solar active region properties
in the photosphere, we scaled to observed solar values a realistic
dimensionless 3D MHD simulation for eruptive flares, which originate
from a highly sheared bipole. This enabled us to calculate the magnetic
fluxes and flare energies in the model in a wide paramater space. 
Results: Firstly, commonly observed solar conditions lead to modeled
magnetic fluxes and flare energies that are comparable to those
estimated from observations. Secondly, we evaluate from observations
that 30% of the area of sunspot groups are typically involved in
flares. This is related to the strong fragmentation of these groups,
which naturally results from sub-photospheric convection. When the
model is scaled to 30% of the area of the largest sunspot group ever
reported, with its peak magnetic field being set to the strongest value
ever measured in a sunspot, it produces a flare with a maximum energy of
~6 × 1033 erg. Conclusions: The results of the model
suggest that the Sun is able to produce flares up to about six times as
energetic in total solar irradiance fluence as the strongest directly
observed flare of Nov. 4, 2003. Sunspot groups larger than historically
reported would yield superflares for spot pairs that would exceed tens
of degrees in extent. We thus conjecture that superflare-productive
Sun-like stars should have a much stronger dynamo than in the Sun.

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Title: Magnetic Topology of Bubbles in Quiescent Prominences
Authors: Dudík, J.; Aulanier, G.; Schmieder, B.; Zapiór, M.;
Heinzel, P.
2012ApJ...761....9D Altcode:
We study a polar-crown prominence with a bubble and its plume observed
in several coronal filters by the SDO/AIA and in Hα by the MSDP
spectrograph in Białków (Poland) to address the following questions:
what is the brightness of prominence bubbles in EUV with respect to the
corona outside of the prominence and the prominence coronal cavity? What
is the geometry and topology of the magnetic field in the bubble? What
is the nature of the vertical threads seen within prominences? We
find that the brightness of the bubble and plume is lower than the
brightness of the corona outside of the prominence, and is similar to
that of the coronal cavity. We constructed linear force-free models of
prominences with bubbles, where the flux rope is perturbed by inclusion
of parasitic bipoles. The arcade field lines of the bipole create the
bubble, which is thus devoid of magnetic dips. Shearing the bipole or
adding a second one can lead to cusp-shaped prominences with bubbles
similar to the observed ones. The bubbles have complex magnetic
topology, with a pair of coronal magnetic null points linked by a
separator outlining the boundary between the bubble and the prominence
body. We conjecture that plume formation involves magnetic reconnection
at the separator. Depending on the viewing angle, the prominence can
appear either anvil-shaped with predominantly horizontal structures,
or cusp-shaped with predominantly vertical structuring. The latter
is an artifact of the alignment of magnetic dips with respect to the
prominence axis and the line of sight.

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Title: X-ray and ultraviolet investigation into the magnetic
connectivity of a solar flare
Authors: Reid, H. A. S.; Vilmer, N.; Aulanier, G.; Pariat, E.
2012A&A...547A..52R Altcode: 2012arXiv1210.2916R
We investigate the X-ray and UV emission detected by RHESSI and TRACE
in the context of a solar flare on the 16th November 2002 with the goal
of better understanding the evolution of the flare. We analysed the
characteristics of the X-ray emission in the 12-25 and 25-50 keV energy
range while we looked at the UV emission at 1600 Å . The flare appears
to have two distinct phases of emission separated by a 25-s time delay,
with the first phase being energetically more important. We found good
temporal and spatial agreement between the 25-50 keV X-rays and the
most intense areas of the 1600 Å UV emission. We also observed an
extended 100-arcsec &lt; 25 keV source that appears coronal in nature
and connects two separated UV ribbons later in the flare. Using the
observational properties in X-ray and UV wavelengths, we propose two
explanations for the flare evolution in relation to the spine/fan
magnetic field topology and the accelerated electrons. We find that
a combination of quasi separatrix layer reconnection and null-point
reconnection is required to account for the observed properties of
the X-ray and UV emission.

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

---------------------------------------------------------
Title: Comparison of a Magnetohydrodynamical Simulation and a
Non-Linear Force-Free Field Model of a Sigmoidal Active Region.
Authors: Pariat, Etienne; DeLuca, Edward; Van Ballegooijen, Adriaan;
Aulanier, Guillaume; Savcheva, Antonia
2012cosp...39.1448P Altcode: 2012cosp.meet.1448P
Sigmoids are solar magnetic structures where highly non-potential
fields (strong shear/twist) are believed to be present. Thanks to
the high level of free magnetic energy, active regions with sigmoids
possess a higher eruptivity. In the present study, we will present
a comparive topological analysis between a Non-Linear Force Free
Field (NLFFF) model of sigmoid region, and a three-dimensional (3D)
magnetohydrodynamics numerical simulation of the formation and eruption
of such a structure. The MHD simulation is based on an idealized
magnetic field distribution and the sigmoidal flux rope is built by
means of shearing motions and magnetic polarity diffusion. The NLFFF
model is based on the flux rope insertion method which utilizes line of
sight magnetograms and X-ray observations of the region to constrain the
models. We compare the geometrical and topological properties of the 3D
magnetic fields given by both methods in their pre-eruptive phases. We
arrive at a consistent picture for the evolution and eruption of the
sigmoid by using the idealized MHD simulation as a context for the more
specific observationally-constrained NLFFF models and data. Although,
the two models are very different in their setups, we identify strong
similarities between the two models and understandable differences. By
computing the squashing factor in different horizontal maps at various
heights above the photosphere and in vertical cuts in the domains,
we demonstrate the existence of key Quasi-Separatrix Layers (QSL)
eventually involved in the dynamic of the structure. We also show that
there are electric current concentrations coinciding with the main
QSLs. Finally, we perform torus instability analysis and show that
a combination between reconnection at the main QSL and the resulting
expansion of the flux rope into the torus instability domain is the
cause of the CME in both models. This study finally highlights the
interest of the use of in-depth topological tools to study highly
non-potential magnetic fields.

---------------------------------------------------------
Title: Can bubbles in quiescent prominences be purely magnetic
phenomena?
Authors: Dudik, Jaroslav; Schmieder, Brigitte; Aulanier, Guillaume;
Zapior, Maciej; Heinzel, Petr
2012cosp...39..486D Altcode: 2012cosp.meet..486D
We present a model of the magnetic field constituting quiescent
prominences. The model assumes a linear force-free field with a
weakly twisted flux-tube in an OX/OF topology perturbed by presence
of parasitic polarities within the filament channel. The parasitic
polarities locally create the cusp-shaped prominences with bubbles
exactly as those observed by the SDO/AIA and Bialkow Observatory. We
find that the observations are best reproduced if the parasitic bipoles
are sheared with respect to the main inversion line. We show that
the bubbles are in fact constituted by the arcade-like field lines,
as opposed to that of the prominence, which is created by magnetic
dips. A pair of null points is always associated with the parasitic
bipole. These null points are connected by a separator passing through
the prominence bubble. We show how the presence of an additional
parasitic bipole moves the separator to the boundary between the bubble
and the rest of the prominence, producing a topology favorable for
reconnection and possibly for the formation of plumes.

---------------------------------------------------------
Title: The standard flare model in three dimensions. I. Strong-to-weak
shear transition in post-flare loops
Authors: Aulanier, G.; Janvier, M.; Schmieder, B.
2012A&A...543A.110A Altcode:
Context. The standard CSHKP model for eruptive flares is
two-dimensional. Yet observational interpretations of photospheric
currents in pre-eruptive sigmoids, shear in post-flare loops, and
relative positioning and shapes of flare ribbons, all together require
three-dimensional extensions to the model. Aims: We focus on
the strong-to-weak shear transition in post-flare loops, and on the
time-evolution of the geometry of photospheric electric currents, which
occur during the development of eruptive flares. The objective is to
understand the three-dimensional physical processes, which cause them,
and to know how much the post-flare and the pre-eruptive distributions
of shear depend on each other. Methods: The strong-to-weak shear
transition in post-flare loops is identified and quantified in a flare
observed by STEREO, as well as in a magnetohydrodynamic simulation
of CME initiation performed with the OHM code. In both approaches,
the magnetic shear is evaluated with field line footpoints. In the
simulation, the shear is also estimated from ratios between magnetic
field components. Results: The modeled strong-to-weak shear
transition in post-flare loops comes from two effects. Firstly,
a reconnection-driven transfer of the differential magnetic shear,
from the pre- to the post-eruptive configuration. Secondly, a vertical
straightening of the inner legs of the CME, which induces an outer shear
weakening. The model also predicts the occurrence of narrow electric
current layers inside J-shaped flare ribbons, which are dominated
by direct currents. Finally, the simulation naturally accounts for
energetics and time-scales for weak and strong flares, when typical
scalings for young and decaying solar active regions are applied. Conclusions: The results provide three-dimensional extensions to
the standard flare model. These extensions involve MHD processes that
should be tested with observations.

---------------------------------------------------------
Title: How to build-up realistic 3D magnetic field environments for
eruptive flares?
Authors: Aulanier, Guillaume
2012cosp...39...71A Altcode: 2012cosp.meet...71A
The standard model in 2D for solar eruptive flares is based on
magnetic reconnection at an X-point between open field lines, which
produces closed post-flare loops at the footpoints of which ribbons
emissions take place. So as to understand the observed morphology
and dynamics of postflare loops and ribbons, it is required to go
beyond the standard model. This implies to know the 3D geometry of
the reconnecting magnetic fields. This passes through the modeling
of the dynamic expansion of current-carrying loops, which eventually
turn into a coronal mass ejection (CME). On the one hand the first
model proposed for CME triggering -the loss of equilibrium model- used
the physical approach of electric wires and Laplace. But on the other
hand, the wire approach must be replaced by the physics of MHD in the
solar corona. Therefore, this paradigm has led to some uncertainty for
several decades, regarding the nature of the most physically viable
eruptions mechanisms for CMEs. A large variety of semi-analytical and
numerical storage-and-release MHD models have been developped in the
past 20 years or so. While all these models rely on the slow increase
of currents and/or the slow decrease of the restraining magnetic tension
preceding the eruption, they all put the emphazis on different physical
mechanisms, both to achieve the pre-eruptive evolution, and to suddenly
trigger and later drive the eruption. Nevertheless, all the models
share many common features. And all the later describe many individual
observed aspects of solar eruptions. It is therefore not always clear
which of all the suggested mechanisms, if any, do really account for
the triggering of observed events in general. Also, these mechanisms
should arguably not be as numerous as the models themselves, owing
to the common occurence of eruptions. In order to shed some light on
this challenging -but still unripe- topic, I will first compare the
driving and stabilizing forces in both the wire and the MHD views. I
will then discuss the applicability of the MHD models to the Sun, and
most of all I will re-order the most sensitive ones ina common frame,
so as to find common denominators. I will end on a brief report of
the shape of post-flare loops and ribbons, as they develop in one of
these CME models.

---------------------------------------------------------
Title: Slip-running reconnection and evolution of shear in post-flare
loops
Authors: Janvier, Miho; Schmieder, Brigitte; Pariat, Etienne;
Aulanier, Guillaume
2012cosp...39..816J Altcode: 2012cosp.meet..816J
We analyze the physical mechanisms of an eruptive flare via 3D
magnetohydrodynamic simulations of a flux rope. We focus on the
relaxation process associated with the reconnection of magnetic field
lines driven by the free expansion of the magnetic field. First, the
origin of the shearing of post-flare magnetic loops is investigated
in relation to the pre-flare geometry of the magnetic field. Indeed,
space-borne satellites can observe the temporal changes of post-flare
structures that are important observational manifestations of the
solar flare phenomenon. As such, understanding the evolution of
post-flare loops can reveal the characteristics of the pre-flare
magnetic field. Here, we introduce different proxies to quantify
the shear angle. We show that strong geometrical similarities exist
between the initial magnetic field and the post-flare loops. Analysis
of the eruption dynamics shows that magnetic reconnection at the origin
of the post-flare field lines forms less and less sheared magnetic
loops on top of one another. We confirm this tendency by direct
measurements of the shear angle seen in flare events such as that
of May 9, 2011 recorded by STEREO-B/EUVI. Our results also highlight
that vertical stretching of the magnetic field lines may play a role
in the shear angle evolution of post-flare loops. The analysis of
the eruptive flare evolution is followed by a detailed investigation
of the flux rope growth and of the post-flare loops formation due to
coronal slip-running reconnection. For that, we study the dynamics of
different regions around two ribbons of opposite current. We find that
these ribbons correspond to quasi-separatrix layers (QSLs), associated
with J-shaped pre-flare magnetic field lines, reconnected S-shaped
flux rope lines and post-flare loops. Simulations with very small time
steps are required so as to show the detailed time evolution of those
QSLs as well as the time variations of the slip-running velocities. Our
results provide a fully 3D extension of the standard 2D flare model.

---------------------------------------------------------
Title: Moving towards a comprehensive model for active region outflows
Authors: Aulanier, Guillaume; Del Zanna, Giulio; Bradshaw, Stephen
2012cosp...39...72A Altcode: 2012cosp.meet...72A
Coronal outflows located at the edges of strong magnetic flux
concentrations seem to be a common and persistent property of solar
active regions. They have been reported and discussed using both direct
imaging in EUV and SXR, as well as using Doppler measurements from
EUV spectroscopy. Due to their potential role in feeding the solar
wind with extra mass and momentum, which is one of the primary goal of
the upcoming Solar Orbiter mission, coronal outflows have received a
broad attention since more than a decade. But for the genuine reader,
the nature of the observed motions, as well as their physical origins,
still look to be very unclear. I will review some of the most debated
interpretations for these features, such as : Do the `warm' outflows,
reported in imagery, which are in fact associated with redshifts seen in
spectroscopy, correspond to upward-traveling waves ? Do the redshifts
indicate a global mass circulation along the chromosphere-coronal axis
? Do the non-steady, quasi-periodic, and relatively faster disturbances,
that are superposed on quasi-steady and relatively-slower upflows,
correspond to magnetoacoustic waves, to spicule transient jets, or to
some other bulk flows ? More generally, do the assymetric `hot' line
profiles reported in several observations really highlight different
plasmas along the LOS, and thus require the development of specific
models ? Do the increasing Dopplershifts with line temperature formation
indicate accelerating upflows, or do they simply show different flows
along different flux tubes ? Do all the observed outflows feed the
solar wind, or do some of them end up as downflows ? In the latter
case, does the mass fall back at remote coronal locations, or right
towards the underlying chromosphere ? Is the continuing growth of
active regions responsible for the flows, and if yes are the flows
induced by high-altitude reconnection or by low altitude squashing of
the plasma ? Owing to the intrinsic limitations of the EUV spectroscopic
observations, new studies have investigated this intriguing phenomenon,
using others methods of investigation : magnetic field extrapolations,
topological analyses, radiative hydrodynamic simulations, calculation of
synthetic line profiles, and last but not least, radio observations as
well as in-situ solar wind plasma measurements. I will argue that these
studies, when reviewed alltogether, appear to provide an important
step towards an integrated model for coronal outflows, even though
they do not solve all the aforementioned issues.

---------------------------------------------------------
Title: Resistive magnetic flux emergence and formation of solar
active regions
Authors: Pariat, E.; Schmieder, B.; Masson, S.; Aulanier, G.
2012EAS....55..115P Altcode:
Magnetic flux emergence as the mechanism leading to the formation of
magnetized structures in the solar atmosphere plays a key role in the
dynamic of the Sun. Observed as a whole, emerging flux regions show
clear signs of twisted structure, bearing the magnetic free energy
necessary to power active events. The high resolution observations
of the recent solar observatories (e.g. Hinode, SDO) have revealed
how intermittent the magnetic field appears and how various active
events induced by flux emergence are. Magnetic field reconstructions
methods show that the topology of the field in interspot regions
presents a serpentine structure, i.e. field lines having successive U
and Ω parts. Associated with the appearance of magnetic polarities,
a tremendous number of brief small scale brightening are observed
in different photospheric and chromospheric lines, e.g. Ellerman
Bombs, along with small scale jet-like structures. These events are
believed to be the observational signatures of the multiple magnetic
reconnections which enable the magnetic field to emerge further up
and magnetically structure the corona above active region. Meanwhile
a world-wide effort to numerically model the emergence of magnetic
field forming solar active region is been carried on. Using different
types of physical paradigm - e.g. idealized magnetohydrodynamic model,
advanced treatment of the physical equations, data-driven simulations
- these numerical experiments highlight how electric currents can
build-up during flux emergence, lead to reconnection and thus explain
the formation of the different observed transients.

---------------------------------------------------------
Title: What are the physical mechanisms of eruptions and CMEs?
Authors: Schmieder, Brigitte; Aulanier, Guillaume
2012AdSpR..49.1598S Altcode:
CMEs are due to physical phenomena that drive both, eruptions and
flares in active regions. Eruptions/CMEs must be driven from initially
force-free current-carrying magnetic field. Twisted flux ropes,
sigmoids, current lanes and pattern in photospheric current maps show
a clear evidence of currents parallel to the magnetic field. Eruptions
occur starting from equilibria which have reached some instability
threshold. Revisiting several data sets of CME observations we
identified different mechanisms leading to this unstable state from a
force free field. Boundary motions related to magnetic flux emergence
and shearing favor the increase of coronal currents leading to the
large flares of November 2003. On the other hand, we demonstrated by
numerical simulations that magnetic flux emergence is not a sufficient
condition for eruptions. Filament eruptions are interpreted either
by a torus instability for an event occurring during the minimum of
solar activity either by the diffusion of the magnetic flux reducing
the tension of the restraining arcade. We concluded that CME models
(tether cutting, break out, loss of equilibrium models) are based on
these basic mechanisms for the onset of CMEs.

---------------------------------------------------------
Title: Electric current density and related sigmoid in an active
region
Authors: Joulin, V.; Schmieder, B.; Aulanier, G.; Bommier, V.
2012EAS....55..143J Altcode:
Using THEMIS vector magnetograms we measured vertical electric current
density in the leading sunspot of NOAA 11127 active region during
its disk passage. The current structures evolve versus time. MHD
modelling allows us to explain the spiral pattern by torsion. We found
observational visible counterparts in the SDO/AIA 335 A images. The
field lines are visible as loops in the AIA images. When the torsion
is increasing, a sigmoid is observed. In the present event observed
on November 24th 2010, we find that reconnection is also necessary to
explain their sigmoidal shape.

---------------------------------------------------------
Title: New perspectives on solar prominences
Authors: Schmieder, B.; Aulanier, G.
2012EAS....55..149S Altcode:
Recent observations of prominences obtained with high spatial and
temporal resolution instruments, on board satellites (Hinode, SDO) as
well as on the ground (SST) have provided very intriguing movies and
open a new area for understanding the nature of prominences. The main
topics are still debate: formation, dynamics, and characteristics of the
plasma in the core and in the transition zone between the prominence
and corona. We will review briefly the recent advances made in these
topics, observationally as well as theoretically.

---------------------------------------------------------
Title: Sigmoidal Active Region on the Sun: Comparison of a
Magnetohydrodynamical Simulation and a Nonlinear Force-free Field
Model
Authors: Savcheva, A.; Pariat, E.; van Ballegooijen, A.; Aulanier,
G.; DeLuca, E.
2012ApJ...750...15S Altcode:
In this paper we show that when accurate nonlinear force-free
field (NLFFF) models are analyzed together with high-resolution
magnetohydrodynamic (MHD) simulations, we can determine the physical
causes for the coronal mass ejection (CME) eruption on 2007 February
12. We compare the geometrical and topological properties of the
three-dimensional magnetic fields given by both methods in their
pre-eruptive phases. We arrive at a consistent picture for the
evolution and eruption of the sigmoid. Both the MHD simulation and
the observed magnetic field evolution show that flux cancellation
plays an important role in building the flux rope. We compute the
squashing factor, Q, in different horizontal maps in the domains. The
main shape of the quasi-separatrix layers (QSLs) is very similar
between the NLFFF and MHD models. The main QSLs lie on the edge of
the flux rope. While the QSLs in the NLFFF model are more complex due
to the intrinsic large complexity in the field, the QSLs in the MHD
model are smooth and possess lower maximum value of Q. In addition,
we demonstrate the existence of hyperbolic flux tubes (HFTs) in both
models in vertical cross sections of Q. The main HFT, located under the
twisted flux rope in both models, is identified as the most probable
site for reconnection. We also show that there are electric current
concentrations coinciding with the main QSLs. Finally, we perform torus
instability analysis and show that a combination between reconnection
at the HFT and the resulting expansion of the flux rope into the torus
instability domain is the cause of the CME in both models.

---------------------------------------------------------
Title: Topological Tools For The Analysis Of Active Region Filament
Stability
Authors: DeLuca, Edward E.; Savcheva, A.; van Ballegooijen, A.;
Pariat, E.; Aulanier, G.; Su, Y.
2012AAS...22020207D Altcode:
The combination of accurate NLFFF models and high resolution MHD
simulations allows us to study the changes in stability of an active
region filament before a CME. Our analysis strongly supports the
following sequence of events leading up to the CME: first there is a
build up of magnetic flux in the filament through flux cancellation
beneath a developing flux rope; as the flux rope develops a hyperbolic
flux tube (HFT) forms beneath the flux rope; reconnection across
the HFT raises the flux rope while adding addition flux to it; the
eruption is triggered when the flux rope becomes torus-unstable. The
work applies topological analysis tools that have been developed over
the past decade and points the way for future work on the critical
problem of CME initiation in solar active regions. We will present
the uses of this approach, current limitations and future prospects.

---------------------------------------------------------
Title: On the Nature of Prominence Bubbles and Plumes
Authors: Schmieder, B.; Zapior, M.; Heinzel, P.; Aulanier, G.
2012ASPC..456...77S Altcode:
An example of bubble and related plume, using time series in
selected SDO/AIA channels and co-temporal MSDP observations in the
Hα line obtained at Wroclaw-Bialkow observatory on April 20, 2011 is
presented. The formation of bubbles may be due to emerging arcades in
the filament channel, below the prominence. After discussing on MHD
modeling, we conclude that bubbles and plumes are parts of the corona
observed through gaps/windows in the prominence.

---------------------------------------------------------
Title: 3D MHD Simulation of Current Intensification along Serpentine
Emerging Magnetic Fields
Authors: Pariat, E.; Masson, S.; Aulanier, G.
2012ASPC..455..177P Altcode:
The high resolution observations of the Hinode instruments have
revealed many important features of the magnetic flux evolution and its
interaction with the solar plasma in emerging flux regions. The high
intermittency of the magnetic field distribution in interspot regions
confirms the serpentine topology adopted by the magnetic field as it
cross the solar photosphere. Precise information about the evolution
of localized brightenings, usually called Ellerman bombs (EBs), typical
events of emerging flux regions, have been gathered by Hinode: the link
between EBs and the magnetic topology, the EBs detailed spectral time
evolution and their relation with other dynamic events such as small
scale jets, etc. Ellerman bombs are believed to be the observational
signatures of the multiple magnetic reconnections which enable
the magnetic field to emerge further up and magnetically structure
the corona above active regions. This work is part of a world-wide
effort to model the emergence of magnetic field forming solar active
regions. Using a data-driven, three-dimensional (3D) magnetohydrodynamic
(MHD) numerical simulation of a flux emergence region, we study the
development of 3D electric current sheets. We show that these currents
buildup along the 3D serpentine magnetic-field structure as a result
of photospheric diverging horizontal line-tied motions that emulate
the observed photospheric evolution. We study which types of motion
and magnetic topology lead to the highest current intensification
and therefore to the highest reconnection probability. We discuss how
these currents can explain the formation of Ellerman bombs, facilitate
the flux emergence, and account for some observed pattern of emerging
flux regions.

---------------------------------------------------------
Title: Topological tools for the analysis of active region filament
stability
Authors: DeLuca, Edward E.; Savcheva, A.; van Ballegooijen, A.;
Pariat, E.; Aulanier, G.; Su, Y.
2012decs.confE..64D Altcode:
The combination of accurate NLFFF models and high resolution MHD
simulations allows us to study the changes in stability of an active
region filament before a CME. Our analysis strongly supports the
following sequence of events leading up to the CME: first there is a
build up of magnetic flux in the filament through flux cancellation
beneath a developing flux rope; as the flux rope develops a hyperbolic
flux tube (HFT) forms beneath the flux rope; reconnection across
the HFT raises the flux rope while adding addition flux to it; the
eruption is triggered when the flux rope becomes torus-unstable. The
work applies topological analysis tools that have been developed over
the past decade and points the way for future work on the critical
problem of CME initiation in solar active regions. We will discuss
the uses of this approach, current limitations and future prospects.

---------------------------------------------------------
Title: Interchange Slip-Running Reconnection and Sweeping SEP Beams
Authors: Masson, S.; Aulanier, G.; Pariat, E.; Klein, K. -L.
2012SoPh..276..199M Altcode: 2011arXiv1109.5678M
We present a new model to explain how particles (solar energetic
particles; SEPs), accelerated at a reconnection site that is not
magnetically connected to the Earth, could eventually propagate
along the well-connected open flux tube. Our model is based on the
results of a low-β resistive magnetohydrodynamics simulation of a
three-dimensional line-tied and initially current-free bipole, which
is embedded in a non-uniform open potential field. The topology of
this configuration is that of an asymmetric coronal null point, with
a closed fan surface and an open outer spine. When driven by slow
photospheric shearing motions, field lines, initially fully anchored
below the fan dome, reconnect at the null point, and jump to the open
magnetic domain. This is the standard interchange mode as sketched and
calculated in 2D. The key result in 3D is that reconnected open field
lines located in the vicinity of the outer spine keep reconnecting
continuously, across an open quasi-separatrix layer, as previously
identified for non-open-null-point reconnection. The apparent slipping
motion of these field lines leads to formation of an extended narrow
magnetic flux tube at high altitude. Because of the slip-running
reconnection, we conjecture that if energetic particles would be
traveling through, or be accelerated inside, the diffusion region,
they would be successively injected along continuously reconnecting
field lines that are connected farther and farther from the spine. At
the scale of the full Sun, owing to the super-radial expansion of
field lines below 3 R⊙, such energetic particles could
easily be injected in field lines slipping over significant distances,
and could eventually reach the distant flux tube that is well-connected
to the Earth.

---------------------------------------------------------
Title: Large Field-of-View Spectropolarimetric Observations with a
Large Aperture Telescope
Authors: Molodij, G.; Aulanier, G.
2012SoPh..276..451M Altcode:
In the context of the increasing interest in large-aperture telescopes
dedicated to the Sun, we present a study to evaluate the adaptive-optics
system limitations on the requirements expected for magnetic-field
extrapolations and data-driven MHD simulations of active regions. The
questions we address include: What is the size of the field of view
at high spatial resolution for a four-meter class telescope with a
spectrograph? What is the impact of the selected spectral domain on the
performance in relation to the aforementioned scientific goals? We show
that the visible-wavelength domain remains difficult to explore with
ground-based telescopes using classical adaptive optics systems. The
field of view obtained will be only a few arcseconds at the diffraction
limit for most of the time. We review alternative configurations of
adaptive-optics systems for different telescope apertures and wavelength
domains which could be considered for practical implementation in
derivations of the magnetic field from polarimetric observations.

---------------------------------------------------------
Title: Adaptive optics system performances and large field of view
spectropolarimetric observations
Authors: Aulanier, G.; Molodij, G.
2011sf2a.conf..395A Altcode:
In the context of the increasing interest for large aperture telescope
dedicated to the Sun such as EST or ATST projects, we (the Guillaumes)
present a study to evaluate the adaptive optics system limitations
in regard of the scientific requirements expected for magnetic field
extrapolations and data-driven MHD simulations of active regions. The
questions we address are: what is the size of the field of view at high
spatial resolution for a 4 meter class telescope with a spectrograph,
what is the impact of the selected spectral domain on the performances
in relation to the scientific goals aforementioned ? We show that
the visible wavelength domain still remains difficult to explore with
ground-based telescope using a classical adaptive optics system. The
field of view obtained will be only few arcsecs at diffraction limit
for the most part of the observation time.

---------------------------------------------------------
Title: A Reconnection-driven Rarefaction Wave Model for Coronal
Outflows
Authors: Bradshaw, S. J.; Aulanier, G.; Del Zanna, G.
2011ApJ...743...66B Altcode:
We conduct numerical experiments to determine whether interchange
reconnection at high altitude coronal null points can explain the
outflows observed as blueshifts in coronal emission lines at the
boundaries between open and closed magnetic field regions. In this
scenario, a strong, post-reconnection pressure gradient forms in the
field-aligned direction when dense and hot, active region core loops
reconnect with neighboring tenuous and cool, open field lines. We
find that the pressure gradient drives a supersonic outflow and a
rarefaction wave develops in both the open and closed post-reconnection
magnetic field regions. We forward-model the spectral line profiles
for a selection of coronal emission lines to predict the spectral
signatures of the rarefaction wave. We find that the properties of
the rarefaction wave are consistent with the observed velocity versus
temperature structure of the corona in the outflow regions, where
the velocity increases with the formation temperature of the emission
lines. In particular, we find excellent agreement between the predicted
and observed Fe XII 195.119 Å spectral line profiles in terms of the
blueshift (10 km s-1), full width at half-maximum (83 mÅ)
and symmetry. Finally, we find that Ti &lt; Te in
the open field region, which indicates that the interchange reconnection
scenario may provide a viable mechanism and source region for the slow
solar wind.

---------------------------------------------------------
Title: The 2011 February 15 X2 Flare, Ribbons, Coronal Front, and
Mass Ejection: Interpreting the Three-dimensional Views from the
Solar Dynamics Observatory and STEREO Guided by Magnetohydrodynamic
Flux-rope Modeling
Authors: Schrijver, Carolus J.; Aulanier, Guillaume; Title, Alan M.;
Pariat, Etienne; Delannée, Cecile
2011ApJ...738..167S Altcode:
The 2011 February 15 X2.2 flare and associated Earth-directed halo
coronal mass ejection were observed in unprecedented detail with
high resolution in spatial, temporal, and thermal dimensions by the
Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory,
as well as by instruments on the two STEREO spacecraft, then at
near-quadrature relative to the Sun-Earth line. These observations
enable us to see expanding loops from a flux-rope-like structure over
the shearing polarity-inversion line between the central δ-spot groups
of AR 11158, developing a propagating coronal front ("EIT wave"),
and eventually forming the coronal mass ejection moving into the inner
heliosphere. The observations support the interpretation that all of
these features, including the "EIT wave," are signatures of an expanding
volume traced by loops (much larger than the flux rope only), surrounded
by a moving front rather than predominantly wave-like perturbations;
this interpretation is supported by previously published MHD models
for active-region and global scales. The lateral expansion of the
eruption is limited to the local helmet-streamer structure and halts
at the edges of a large-scale domain of connectivity (in the process
exciting loop oscillations at the edge of the southern polar coronal
hole). The AIA observations reveal that plasma warming occurs within
the expansion front as it propagates over quiet Sun areas. This warming
causes dimming in the 171 Å (Fe IX and Fe X) channel and brightening
in the 193 and 211 Å (Fe XII-XIV) channels along the entire front,
while there is weak 131 Å (Fe VIII and Fe XXI) emission in some
directions. An analysis of the AIA response functions shows that
sections of the front running over the quiet Sun are consistent with
adiabatic warming; other sections may require additional heating which
MHD modeling suggests could be caused by Joule dissipation. Although
for the events studied here the effects of volumetric expansion are
much more obvious than true wave phenomena, we discuss how different
magnetic environments within and around the erupting region can lead
to the signatures of either or both of these aspects.

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

---------------------------------------------------------
Title: Coronal heating and flaring in QSLs
Authors: Aulanier, Guillaume
2011IAUS..273..233A Altcode:
Quasi-Separatrix Layers (QSLs) are 3D geometrical objects that define
narrow volumes across which magnetic field lines have strong, but
finite, gradients of connectivity from one footpoint to another. QSLs
extend the concept of separatrices, that are topological objects across
which the connectivity is discontinuous. Based on analytical arguments,
and on magnetic field extrapolations of the Sun's coronal force-free
field above observed active regions, it has long since been conjectured
that QSLs are favorable locations for current sheet (CS) formation, as
well as for magnetic reconnection, and therefore are good predictors
for the locations of magnetic energy release in flares and coronal
heating. It is only up to recently that numerical MHD simulations and
solar observations, as well as a laboratory experiment, have started
to address the validity of these conjectures. When put all together,
they suggest that QSL reconnection is involved in the displacement
of EUV and SXR brightenings along chromospheric flare ribbons, that
it is related with the heating of EUV coronal loops, and that the
dissipation of QSL related CS may be the cause of coronal heating in
initially homogeneous, braided and turbulent flux tubes, as well as in
coronal arcades rooted in the slowly moving and numerous small-scale
photospheric flux concentrations, both in active region faculae and
in the quiet Sun. The apparent ubiquity of QSL-related CS in the
Sun's corona, which will need to be quantified with new generation
solar instruments, also suggests that QSLs play an important role
in stellar's atmospheres, when their surface radial magnetic fields
display complex patterns.

---------------------------------------------------------
Title: Interchange slip-running reconnection and sweeping SEP beams
Authors: Masson, Sophie; Aulanier, G.; Pariat, E.; Klein, K. -L.
2011shin.confE..38M Altcode:
We present a new model to explain how particles, accelerated at a
reconnection site that is not magnetically connected to the Earth,
could eventually propagate along the well-connected open flux tube. Our
model is based on the results of a low beta resistive MHD simulation of
a 3D line-tied and initially current-free bipole, that is embedded in
a non-uniform open potential field. The topology of this configuration
is that of an asymmetric coronal null-point, with a closed fan surface
and an open outer spine. When driven by slow photospheric shearing
motions, field lines initially anchored at both feet below the fan dome
reconnect at the null point, and jump to the open magnetic domain. This
is the standard interchange mode as sketched and calculated in 2D. The
key result in 3D is that, after the interchange, and just as found
earlier in non-open null-point reconnection, reconnected open field
lines located in the vicinity of the outer spine keep reconnecting
continuously, across an open quasi-separatrix layer. The apparent
slipping motion of these field lines leads to forming an extended
narrow magnetic flux tube at high altitude. Because of the slip-running
reconnection, we conjecture that if energetic particles would be
traveling through, or be accelerated inside, the diffusion region,
they would be successively injected along continuously reconnecting
field lines, that are connected farther and farther from the spine. At
the scale of the full Sun, owing to the super-radial expansion of field
lines below 3 Rs, such energetic particles could easily be injected in
field lines slipping over significant distances, and could eventually
reach the distant flux tube that is well connected to the Earth.

---------------------------------------------------------
Title: Interchange Slip-running Reconnection and Sweeping SEP Beams
Authors: Masson, Sophie; Aulanier, G.; Pariat, E.; Klein, K.
2011SPD....42.1403M Altcode: 2011BAAS..43S.1403M
We present a new model to explain how particles, accelerated at a
reconnection site that is not magnetically connected to the Earth,
could eventually propagate along the well-connected open flux tube. Our
model is based on the results of a low beta resistive MHD simulation of
a 3D line-tied and initially current-free bipole, that is embedded in
a non-uniform open potential field. The topology of this configuration
is that of an asymmetric coronal null-point, with a closed fan surface
and an open outer spine. When driven by slow photospheric shearing
motions, field lines initially anchored at both feet below the fan dome
reconnect at the null point, and jump to the open magnetic domain. This
is the standard interchange mode as sketched and calculated in 2D. The
key result in 3D is that, after the interchange, and just as found
earlier in non-open null-point reconnection, reconnected open field
lines located in the vicinity of the outer spine keep reconnecting
continuously, across an open quasi-separatrix layer. The apparent
slipping motion of these field lines leads to forming an extended
narrow magnetic flux tube at high altitude. Because of the slip-running
reconnection, we conjecture that if energetic particles would be
traveling through, or be accelerated inside, the diffusion region,
they would be successively injected along continuously reconnecting
field lines, that are connected farther and farther from the spine. At
the scale of the full Sun, owing to the super-radial expansion of field
lines below 3 Rs, such energetic particles could easily be injected in
field lines slipping over significant distances, and could eventually
reach the distant flux tube that is well connected to the Earth.

---------------------------------------------------------
Title: A single picture for solar coronal outflows and radio noise
storms
Authors: Del Zanna, G.; Aulanier, G.; Klein, K. -L.; Török, T.
2011A&A...526A.137D Altcode:
We propose a unified interpretation for persistent coronal outflows
and metric radio noise storms, two phenomena typically observed in
association with quiescent solar active regions. Our interpretation
is based on multi-wavelength observations of two such regions as
they crossed the meridian in May and July 2007. For both regions,
we observe a persistent pattern of blue-shifted coronal emission in
high-temperature lines with Hinode/EIS, and a radio noise storm with the
Nançay Radioheliograph. The observations are supplemented by potential
and linear force-free extrapolations of the photospheric magnetic
field over large computational boxes, and by a detailed analysis of
the coronal magnetic field topology. We find true separatrices in the
coronal field and null points high in the corona, which are preferential
locations for magnetic reconnection and electron acceleration. We
suggest that the continuous growth of active regions maintains a steady
reconnection across the separatrices at the null point. This interchange
reconnection occurs between closed, high-density loops in the core of
the active region and neighbouring open, low-density flux tubes. Thus,
the reconnection creates strong pressure imbalances which are the main
drivers of plasma upflows. Furthermore, the acceleration of low-energy
electrons in the interchange reconnection region sustains the radio
noise storm in the closed loop areas, as well as weak type III emission
along the open field lines. For both active regions studied, we find a
remarkable agreement between the observed places of persistent coronal
outflows and radio noise storms with their locations as predicted by
our interpretation.

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

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

---------------------------------------------------------
Title: Multiwavelength Observations of Small-scale Reconnection
Events Triggered by Magnetic Flux Emergence in the Solar Atmosphere
Authors: Guglielmino, S. L.; Bellot Rubio, L. R.; Zuccarello, F.;
Aulanier, G.; Vargas Domínguez, S.; Kamio, S.
2010ApJ...724.1083G Altcode: 2010arXiv1007.4657G
The interaction between emerging magnetic flux and the pre-existing
ambient field has become a "hot" topic for both numerical simulations
and high-resolution observations of the solar atmosphere. The appearance
of brightenings and surges during episodes of flux emergence is believed
to be a signature of magnetic reconnection processes. We present an
analysis of a small-scale flux emergence event in NOAA 10971, observed
simultaneously with the Swedish 1 m Solar Telescope on La Palma and the
Hinode satellite during a joint campaign in 2007 September. Extremely
high-resolution G-band, Hα, and Ca II H filtergrams, Fe I and Na
I magnetograms, EUV raster scans, and X-ray images show that the
emerging region was associated with chromospheric, transition region
and coronal brightenings, as well as with chromospheric surges. We
suggest that these features were caused by magnetic reconnection
at low altitude in the atmosphere. To support this idea, we perform
potential and linear force-free field extrapolations using the FROMAGE
service. The extrapolations show that the emergence site is cospatial
with a three-dimensional null point, from which a spine originates. This
magnetic configuration and the overall orientation of the field lines
above the emerging flux region are compatible with the structures
observed in the different atmospheric layers and remain stable against
variations of the force-free field parameter. Our analysis supports
the predictions of recent three-dimensional numerical simulations that
energetic phenomena may result from the interaction between emerging
flux and the pre-existing chromospheric and coronal field.

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

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

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Title: Physics of Solar Prominences: II—Magnetic Structure and
Dynamics
Authors: Mackay, D. H.; Karpen, J. T.; Ballester, J. L.; Schmieder,
B.; Aulanier, G.
2010SSRv..151..333M Altcode: 2010SSRv..tmp...32M; 2010arXiv1001.1635M
Observations and models of solar prominences are reviewed. We focus on
non-eruptive prominences, and describe recent progress in four areas of
prominence research: (1) magnetic structure deduced from observations
and models, (2) the dynamics of prominence plasmas (formation and
flows), (3) Magneto-hydrodynamic (MHD) waves in prominences and (4)
the formation and large-scale patterns of the filament channels in
which prominences are located. Finally, several outstanding issues in
prominence research are discussed, along with observations and models
required to resolve them.

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

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Title: A Flaring Twisted Emerging Flux Region
Authors: Chandra, R.; Schmieder, B.; Aulanier, G.; Malherbe, J. M.
2010ASSP...19..523C Altcode: 2010mcia.conf..523C
We present signatures of the emergence of a twisted flux tube in
decaying active region NOAA AR10365 on 27 May 2003. When the magnetic
flux tube is twisted, an asymmetry appears in the magnetogram because
of the contribution of the azimuthal component to the observed vertical
component of the field. In this case, the vertical component produces
two "tongues" (Fig. 1, left). The twist of the flux tube is revealed
by the photospheric longitudinalmagnetic field pattern: diverging
flows of opposite polarities, elongated polarities with a "tongue"
shape. The asymmetry of the opposite polarities is interpreted as
right-hand twist of the emerging flux tube.

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

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Title: What triggers coronal mass ejections ?
Authors: Aulanier, Guillaume
2010cosp...38.1854A Altcode: 2010cosp.meet.1854A
Coronal mass ejections (CMEs) are large clouds of highly magnetized
plasma. They are ac-celerated from the solar atmosphere into
interplanetary space by the Lorentz force, which is associated to their
strong current-carrying magnetic fields. Both theory and observations
lead to the inevitable conclusion that the launch of a CME must result
from the sudden release of free magnetic energy, which has slowly been
accumulated in the corona for a long time before the eruption. Since the
incomplete, but seminal, loss-of-equilibrium model was proposed by van
Tend and Kuperus (1978), a large variety of analytical and numerical
storage-and-release MHD models has been put forward in the past 20
years or so. All these models rely on the slow increase of currents
and/or the slow decrease of the restraining magnetic tension preceding
the eruption. But they all put the emphazis on different physical
mechanisms to achieve this preeruptive evolution, and to suddenly
trigger and later drive a CME. Nevertheless, all these models actually
share many common features, which all describe many individual observed
aspects of solar eruptions. It is therefore not always clear which of
all the suggested mecha-nisms do really account for the triggering of
observed CMEs in general. Also, these mechanisms should arguably not
be as numerous as the models themselves, owing to the common occurence
of CMEs. In order to shed some light on this challenging, but unripe,
topic, I will attempt to rediscuss the applicability of the models
to the Sun, and to rethink the most sensitive ones in a common frame,
so as to find their common denominator. I will elaborate on the idea
that many of the proposed triggering mechanisms may actually only be
considered as different ways to apply a "last push", which puts the
system beyond its eruptive threshold. I will argue that, in most cases,
the eruptive threshold is determined by the vertical gradient of the
magnetic field in the low-β corona, just like the usual convection
threshold is determined by the temperature gradient in a stratified
medium.

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Title: How skeletons turn into quasi-separatrix layers in source
models
Authors: Restante, A. L.; Aulanier, G.; Parnell, C. E.
2009A&A...508..433R Altcode:
Context: In situations where there are no magnetic null points located
above a reference photospheric plane, and when the photospheric
magnetic field is modeled by discrete flux concentrations, the
magnetic connectivity is defined by the magnetic skeleton of the
configuration. For a continuous distribution of non-zero photospheric
flux, the connectivity is defined by quasi-separatrix layers
(QSLs). Both the magnetic skeleton and QSLs can account for current
sheet formation and dissipation. Observationally, though, only some
portions of the skeleton are found to be related to flare ribbons,
which are generally associated with QSL footpoints. Aims:
In potential magnetic source models, a transition from the skeleton
to QSLs has been shown to occur when the sources are displaced below
the photospheric plane. The objective of this paper is to understand
the topological and geometrical nature of this transition, and to
derive rules to predict which parts of a given skeleton will give
rise to QSLs. Methods: We consider magnetic configurations,
derived from potential magnetic sources, which possess no coronal null
points. We have calculated their skeletons, composed of null points,
spine field lines and separatrix (fan) surfaces. Choosing a reference
photospheric plane above the sources, we have calculated their QSL
footprints. Results: As already known, the latter mostly match
with subphotospheric spine field lines since, above these lines, field
lines tend to diverge as a result of approaching a null and lying either
side of the separatrix surface extending out of from this null. However,
many non-spine related QSL footprints are also found, which we call
branches. They correspond to the intersection with the photosphere of
portions of fan field lines which “branch” away from the sources and
result in QSLs due to the inclination of the coronal field lines. 
Conclusions: Our findings allow a better geometrical understanding of
the relations between QSLs and skeletons. We show that in the absence
of coronal null points, spines, as well as specific portions of fans
as calculated in standard potential source models, are good predictors
for the location of QSL footprints and of flare ribbons.

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Title: Formation, Interaction and Merger of an Active Region and a
Quiescent Filament Prior to Their Eruption on 19 May 2007
Authors: Bone, L. A.; van Driel-Gesztelyi, L.; Culhane, J. L.;
Aulanier, G.; Liewer, P.
2009SoPh..259...31B Altcode:
We report observations of the formation of two filaments - one
active and one quiescent, and their subsequent interactions prior to
eruption. The active region filament appeared on 17 May 2007, followed
by the quiescent filament about 24 hours later. In the 26 hour interval
preceding the eruption, which occurred at around 12:50 UT on 19 May
2007, we see the two filaments attempting to merge and filament material
is repeatedly heated suggesting magnetic reconnection. The filament
structure is observed to become increasingly dynamic preceding the
eruption with two small hard X-ray sources seen close to the active
part of the filament at around 01:38 UT on 19 May 2007 during one of
the activity episodes. The final eruption on 19 May at about 12:51 UT
involves a complex CME structure, a flare and a coronal wave. A magnetic
cloud is observed near Earth by the STEREO-B and WIND spacecraft about
2.7 days later. Here we describe the behaviour of the two filaments
in the period prior to the eruption and assess the nature of their
dynamic interactions.

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Title: Fan-Spine Topology Formation Through Two-Step Reconnection
Driven by Twisted Flux Emergence
Authors: Török, T.; Aulanier, G.; Schmieder, B.; Reeves, K. K.;
Golub, L.
2009ApJ...704..485T Altcode: 2009arXiv0909.2235T
We address the formation of three-dimensional nullpoint topologies
in the solar corona by combining Hinode/X-ray Telescope (XRT)
observations of a small dynamic limb event, which occurred beside
a non-erupting prominence cavity, with a three-dimensional (3D)
zero-β magnetohydrodynamics (MHD) simulation. To this end, we model
the boundary-driven "kinematic" emergence of a compact, intense,
and uniformly twisted flux tube into a potential field arcade that
overlies a weakly twisted coronal flux rope. The expansion of the
emerging flux in the corona gives rise to the formation of a nullpoint
at the interface of the emerging and the pre-existing fields. We unveil
a two-step reconnection process at the nullpoint that eventually yields
the formation of a broad 3D fan-spine configuration above the emerging
bipole. The first reconnection involves emerging fields and a set of
large-scale arcade field lines. It results in the launch of a torsional
MHD wave that propagates along the arcades, and in the formation of
a sheared loop system on one side of the emerging flux. The second
reconnection occurs between these newly formed loops and remote arcade
fields, and yields the formation of a second loop system on the opposite
side of the emerging flux. The two loop systems collectively display
an anenome pattern that is located below the fan surface. The flux that
surrounds the inner spine field line of the nullpoint retains a fraction
of the emerged twist, while the remaining twist is evacuated along
the reconnected arcades. The nature and timing of the features which
occur in the simulation do qualititatively reproduce those observed
by XRT in the particular event studied in this paper. Moreover, the
two-step reconnection process suggests a new consistent and generic
model for the formation of anemone regions in the solar corona.

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Title: Surface magnetic fields on two accreting TTauri stars: CVCha
and CRCha
Authors: Hussain, G. A. J.; Collier Cameron, A.; Jardine, M. M.;
Dunstone, N.; Ramirez Velez, J.; Stempels, H. C.; Donati, J. -F.;
Semel, M.; Aulanier, G.; Harries, T.; Bouvier, J.; Dougados, C.;
Ferreira, J.; Carter, B. D.; Lawson, W. A.
2009MNRAS.398..189H Altcode: 2009arXiv0905.0914H; 2009MNRAS.tmp..997H
We have produced brightness and magnetic field maps of the surfaces of
CVCha and CRCha: two actively accreting G- and K-type TTauri stars in
the ChamaeleonI star-forming cloud with ages of 3-5Myr. Our magnetic
field maps show evidence for strong, complex multipolar fields
similar to those obtained for young rapidly rotating main-sequence
stars. Brightness maps indicate the presence of dark polar caps and
low-latitude spots - these brightness maps are very similar to those
obtained for other pre-main-sequence and rapidly rotating main-sequence
stars. Only two other classical TTauri stars have been studied
using similar techniques so far: V2129Oph and BPTau. CVCha and CRCha
show magnetic field patterns that are significantly more complex than
those recovered for BPTau, a fully convective TTauri star. We
discuss possible reasons for this difference and suggest that the
complexity of the stellar magnetic field is related to the convection
zone; with more complex fields being found in TTauri stars with
radiative cores (V2129Oph, CVCha and CRCha). However, it is clearly
necessary to conduct magnetic field studies of TTauri star systems,
exploring a wide range of stellar parameters in order to establish how
they affect magnetic field generation, and thus how these magnetic
fields are likely to affect the evolution of TTauri star systems as
they approach the main sequence.

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Title: Evidence of Magnetic Helicity in Emerging Flux and Associated
Flare
Authors: Chandra, R.; Schmieder, B.; Aulanier, G.; Malherbe, J. M.
2009SoPh..258...53C Altcode: 2009arXiv0906.1210C
The aim of this paper is to look at the magnetic helicity structure
of an emerging active region and show that both emergence and flaring
signatures are consistent with a same sign for magnetic helicity. We
present a multiwavelength analysis of an M1.6 flare occurring in the
NOAA active region 10365 on 27 May 2003, in which a large new bipole
emerges in a decaying active region. The diverging flow pattern and the
"tongue" shape of the magnetic field in the photosphere with elongated
polarities are highly suggestive of the emergence of a twisted flux
tube. The orientation of these tongues indicates the emergence of a flux
tube with a right-hand twist (i.e., positive magnetic helicity). The
flare signatures in the chromosphere are ribbons observed in Hα
by the MSDP spectrograph in the Meudon solar tower and in 1600 Å by
TRACE. These ribbons have a J shape and are shifted along the inversion
line. The pattern of these ribbons suggests that the flare was triggered
by magnetic reconnection at coronal heights below a twisted flux tube of
positive helicity, corresponding to that of the observed emergence. It
is the first time that such a consistency between the signatures of
the emerging flux through the photosphere and flare ribbons has been
clearly identified in observations. Another type of ribbons observed
during the flare at the periphery of the active region by the MSDP and
SOHO/EIT is related to the existence of a null point, which is found
high in the corona in a potential field extrapolation. We discuss
the interpretation of these secondary brightenings in terms of the
"breakout" model and in terms of plasma compression/heating within
large-scale separatrices.

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Title: Current Buildup in Emerging Serpentine Flux Tubes
Authors: Pariat, E.; Masson, S.; Aulanier, G.
2009ApJ...701.1911P Altcode:
The increase of magnetic flux in the solar atmosphere during
active-region formation involves the transport of the magnetic field
from the solar convection zone through the lowest layers of the solar
atmosphere, through which the plasma β changes from &gt;1 to &lt;1 with
altitude. The crossing of this magnetic transition zone requires the
magnetic field to adopt a serpentine shape also known as the sea-serpent
topology. In the frame of the resistive flux-emergence model, the
rising of the magnetic flux is believed to be dynamically driven by
a succession of magnetic reconnections which are commonly observed
in emerging flux regions as Ellerman bombs. Using a data-driven,
three-dimensional (3D) magnetohydrodynamic numerical simulation of flux
emergence occurring in active region 10191 on 2002 November 16-17,
we study the development of 3D electric current sheets. We show
that these currents buildup along the 3D serpentine magnetic-field
structure as a result of photospheric diverging horizontal line-tied
motions that emulate the observed photospheric evolution. We observe
that reconnection can not only develop following a pinching evolution
of the serpentine field line, as usually assumed in two-dimensional
geometry, but can also result from 3D shearing deformation of the
magnetic structure. In addition, we report for the first time on the
observation in the UV domain with the Transition Region and Coronal
Explorer (TRACE) of extremely transient loop-like features, appearing
within the emerging flux domain, which link several Ellermam bombs
with one another. We argue that these loop transients can be explained
as a consequence of the currents that build up along the serpentine
magnetic field.

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Title: The Nature of Flare Ribbons in Coronal Null-Point Topology
Authors: Masson, S.; Pariat, E.; Aulanier, G.; Schrijver, C. J.
2009ApJ...700..559M Altcode:
Flare ribbons are commonly attributed to the low-altitude impact, along
the footprints of separatrices or quasi-separatrix layers (QSLs),
of particle beams accelerated through magnetic reconnection. If
reconnection occurs at a three-dimensional coronal magnetic null
point, the footprint of the dome-shaped fan surface would map a closed
circular ribbon. This paper addresses the following issues: does the
entire circular ribbon brighten simultaneously, as expected because
all fan field lines pass through the null point? And since the spine
separatrices are singular field lines, do spine-related ribbons look
like compact kernels? What can we learn from these observations about
current sheet formation and magnetic reconnection in a null-point
topology? The present study addresses these questions by analyzing
Transition Region and Coronal Explorer and Solar and Heliospheric
Observatory/Michelson Doppler Imager observations of a confined flare
presenting a circular ribbon. Using a potential field extrapolation,
we linked the circular shape of the ribbon with the photospheric
mapping of the fan field lines originating from a coronal null
point. Observations show that the flare ribbon outlining the fan lines
brightens sequentially along the counterclockwise direction and that
the spine-related ribbons are elongated. Using the potential field
extrapolation as initial condition, we conduct a low-β resistive
magnetohydrodynamics simulation of this observed event. We drive the
coronal evolution by line-tied diverging boundary motions, so as to
emulate the observed photospheric flow pattern associated with some
magnetic flux emergence. The numerical analysis allows us to explain
several observed features of the confined flare. The vorticity induced
in the fan by the prescribed motions causes the spines to tear apart
along the fan. This leads to formation of a thin current sheet and
induces null-point reconnection. We also find that the null point
and its associated topological structure is embedded within QSLs,
already present in the asymmetric potential field configuration. We
find that the QSL footprints correspond to the observed elongated
spine ribbons. Finally, we observe that before and after reconnecting
at the null point, all field lines undergo slipping and slip-running
reconnection within the QSLs. Field lines, and therefore particle
impacts, slip or slip-run according to their distance from the spine,
in directions and over distances that are compatible with the observed
dynamics of the ribbons.

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

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Title: Evidence for a Pre-Eruptive Twisted Flux Rope Using the Themis
Vector Magnetograph
Authors: Canou, A.; Amari, T.; Bommier, V.; Schmieder, B.; Aulanier,
G.; Li, H.
2009ApJ...693L..27C Altcode:
Although there is evidence that twisted structures form during
large-scale eruptive events, it is not yet clear whether these exist in
the pre-eruptive phase as twisted flux ropes (TFRs) in equilibrium. This
question has become a major issue since several theoretical mechanisms
can lead to the formation of TFRs. These models consider either the
evolution of a coronal configuration driven by photospheric changes or
the emergence of TFR from the convection zone. We consider as a target
for addressing this issue the active region NOAA AR 10808 known at
the origin of several large-scale eruptive phenomena, and associated
with the emergence of a δ-spot. Using the THEMIS vector magnetogram
as photospheric boundary conditions for our nonlinear force-free
reconstruction model of the low corona and without any other assumption,
we show that the resulting pre-eruptive configuration exhibits a TFR
above the neutral line of the emerging δ-spot. In addition, the free
magnetic energy of this configuration could even be large enough to
explain such resulting large-scale eruptive events.

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Title: Solar prominences
Authors: Schmieder, Brigitte; Aulanier, Guillaume; Török, Tibor
2009IAUS..257..223S Altcode:
Solar filaments (or prominences) are magnetic structures in the
corona. They can be represented by twisted flux ropes in a bipolar
magnetic environment. In such models, the dipped field lines of the
flux rope carry the filament material and parasitic polarities in the
filament channel are responsible for the existence of the lateral feet
of prominences. Very simple laws do exist for the chirality of
filaments, the so-called “filament chirality rules”: commonly
dextral/sinistral filaments corresponding to left- (resp. right)
hand magnetic twists are in the North/South hemisphere. Combining
these rules with 3D weakly twisted flux tube models, the sign of the
magnetic helicity in several filaments were identified. These rules
were also applied to the 180° disambiguation of the direction of the
photospheric transverse magnetic field around filaments using THEMIS
vector magnetograph data (López Ariste et al. 2006). Consequently,
an unprecedented evidence of horizontal magnetic support in filament
feet has been observed, as predicted by former magnetostatic and
recent MHD models. The second part of this review concerns the
role of emerging flux in the vicinity of filament channels. It has been
suggested that magnetic reconnection between the emerging flux and the
pre-existing coronal field can trigger filament eruptions and CMEs. For
a particular event, observed with Hinode/XRT, we observe signatures of
such a reconnection, but no eruption of the filament. We present a 3D
numerical simulation of emerging flux in the vicinity of a flux rope
which was performed to reproduce this event and we briefly discuss,
based on the simulation results, why the filament did not erupt.

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Title: Magnetic helicity and solar prominence formation
Authors: Aulanier, G.; Schmieder, B.
2008sf2a.conf..543A Altcode:
Simple laws have long-since been put forward from the chirality of
observed features to derive the direction of the axial magnetic field
inside solar filaments. These are the so-called “filament chirality
rules”. Here, we report on two uses of these rules applied to THEMIS
and SVST observations and to MHD simulations. Being the first to
apply these rules to the 180° disambiguation of the direction of
the photospheric transverse magnetic field around filaments, we found
the unprecedented evidence of magnetic support in filament feet, as
predicted by former magnetostatic and recent MHD models. By combining
these rules with 3D weakly twisted flux tube models, we identified
the sign of the magnetic helicity in several filaments. Following
their interactions with one another over a few days, we found that the
observational condition for two filaments to merge is that their flux
tubes must have the same helicity sign. We theoretically recovered
these results, by conducting a parametric study of 3D numerical MHD
simulations of sheared bipoles. This study also provided new conditions
for filament merging, in yet-unobserved configurations in which sheared
bipoles are oppositely oriented.

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Title: Magnetic reconnection and particle accelerationinitiated by
flux emergence
Authors: Masson, S.; Aulanier, G.; Pariat, E.; Klein, K. -L.;
Schrijver, C. J.
2008sf2a.conf..555M Altcode:
So as to perform an MHD simulation of the evolution of the corona driven
by the evolution of the photosphere, a key aspect is the definition of
the boundary conditions for reaching a good compromise between physical
conditions and numerical constraints. In this work, we focused on the
simulation of a confined flare observed on Nov 16, 2002. As initial
configuration, we considered a uniform temperature corona, with a
magnetic field resulting from a 3D potential field extrapolation
from a SOHO/MDI magnetogram. We prescribed a velocity field at the
photospheric boundary of the domain, so as to mimic the observed flow
pattern associated to a flux emergence. This resulted in a combination
of “slipping reconnection” in a halo of QSLs surrounding a 3D null
point, through which a “fan reconnection” regime took place. This
simplified approach of flux emergence has successfully reproduced
the main characteristics of the observed flare: the flare ribbons
observed in the EUV with TRACE being due to the chromospheric impact
of particles accelerated along reconnecting field lines, this bimodal
regime could explain both the shapes and dynamics of these ribbons. We
foresee that this kind of modeling should be able to simulate the
evolution of slipping magnetic flux tubes in open configurations,
allowing to predict the spatio-temporal evolution of particle beams
injected into the heliosphere.

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Title: Photospheric flows around a quiescent filament at Large and
small scale and their ffects on filament destabilization
Authors: Roudier, Th.; Malherbe, J. M.; Švanda, M.; Molodij, G.;
Keil, S.; Sütterlin, P.; Schmieder, B.; Bommier, V.; Aulanier, G.;
Meunier, N.; Rieutord, M.; Rondi, S.
2008sf2a.conf..569R Altcode:
We study the influence of large and small scales photospheric
motions on the destabilization of an eruptive filament, observed
on October 6, 7, and 8, 2004 as part of an international observing
campaign (JOP 178). Large-scale horizontal flows are invetigated
from a series of MDI/SOHO full-disc Dopplergrams and magnetograms
from THEMIS. Small-scale horizontal flows were derived using local
correlation tracking on TRACE satellite, Dutch Open Telescope (DOT)
and The Dunn Solar telescope (DST) data. The topology of the flow field
changed significantly during the filament eruptive phase, suggesting
a possible coupling between the surface flow field and the coronal
magnetic field. We measured an increase of the shear below the point
where the eruption starts and a decrease in shear after the eruption. We
conclude that there is probably a link between changes in surface flow
and the disappearance of the eruptive filament.

---------------------------------------------------------
Title: The MHD coupling between coronal dynamics and photospheric
motions
Authors: Grappin, R.; Aulanier, G.; Pinto, R.
2008A&A...490..353G Altcode:
Context: Whether it be the heating problem or the destabilization of
coronal structures, use is often made of the so-called “line-tying”
boundary conditions, which amounts to imposing the photospheric
velocity at the photosphere as a boundary condition for coronal
dynamics. Directly coupling the low beta coronal evolution to prescribed
photospheric motions of the magnetic footpoints allows strong magnetic
energy accumulation in the corona. But this amounts to ignoring
possible feedback from the coronal loops on photospheric motions,
a neglect that is commonly justified by the strong density contrast
between the photosphere and the corona. On the other hand, the energy
injected into the corona comes from the photosphere, so in principle
the coronal loop might act as a conduit communicating photospheric
dynamics from one region to another. Aims: Our objective is
to test the degree of validity of this line-tying approximation
by considering the role of the dense photosphere explicitly. Methods: We consider here a 1.5D MHD model of a magnetic loop
including a strongly stratified solar-like atmosphere and consider
free (instead of prescribed/line-tied) boundary conditions applied
deep in the photosphere, so as to quantify the coupling between the
photosphere and corona as determined by stratification. We give an
initial kick to one of the footpoints in the form of an upwardly
propagating Alfvénic perturbation rising from the lower boundary,
and then allow waves to freely escape the numerical domain from the
boundaries, seated deep in the photosphere. Results: We find that
the response of the loop differs in many aspects from what is predicted
by the line-tied condition. a) The magnetic energy density available in
the corona is limited to a value equal to the kinetic energy density
in the photospheric motion. b) The initial velocity shear between the
opposite loop footpoints vanishes after a time proportional to the loop
length. The shear between the coronal boundaries on opposite sides
of the loop is quasi-uniform and is relaxed slowly by Alfvén waves
propagating downwards through the high-β photospheric layers. This
process is insensitive to details of the thermal structure. c) Coronal
loops are thus shown to exert a strong feedback on the photospheric
dynamics, intermediate between friction and diffusion, instead of no
reaction at all.

---------------------------------------------------------
Title: Magnetic field changes preceding filament eruptions and
coronal mass ejections
Authors: Schmieder, B.; Török, T.; Aulanier, G.
2008AIPC.1043..260S Altcode:
Solar filaments (or prominences) can be represented by twisted flux
ropes in a bipolar magnetic environment. In such models, the dipped
field lines of the flux rope carry the filament material and parasitic
polarities in the filament channel are responsible for the existence
of the lateral feet of filaments. Most filaments eventually erupt, in
many cases as part of a coronal mass ejection (CME). Such eruptions are
often preceded by detectable changes in the photospheric magnetic field
in the vicinity of the filament. We first review recent observations of
such changes due to large-scale flows or variations of the background
magnetic field, and we discuss their role in eruptions. We then focus
on emerging flux in the vicinity of filament channels. It has been
suggested that magnetic reconnection between the emerging flux and
the pre-existing coronal field can trigger filament eruptions and
CMEs. For a particular event, observed with Hinode/XRT, we observe
signatures of such reconnection, but no eruption of the filament. We
present a numerical simulation of this event and we briefly argue why
no eruption took place in this case.

---------------------------------------------------------
Title: Multiple Ribbons of a M1.6 Flare Related to the Magnetic
Configuration of the NOAA AR 365
Authors: Chandra, R.; Schmieder, B.; Aulanier, G.; Malherbe, M. J.
2008ESPM...12.2.65C Altcode:
The aim of this paper is to understand the magnetic configuration
of an active region NOAA 365 and its evolution before and after the
occurrence of a M1.6 flare in order to understand the magnetic origin
of the flare and its development at particularly the ribbons. We analyze a M1.6 flare occurring in the active region NOAA 365,
using space instruments (SOHO/MDI, EIT, TRACE, RHESSI) as well as
ground based instruments i.e. the MSDP spectrograph of the Meudon
solar tower. The analysis of the magnetic topology of the region is
done by using a force-free field linear extrapolation code of the
photospheric field proposed in the database FROMAGE. Two series
of ribbons are identified, signature of the reconnection, the main
ribbons in the center of the active region and secondary ribbons at
the periphery of the active region. The main ribbons have a `J' shape,
typical shape for large emerging flux tube. The secondary ribbons are
explained by the magnetic configuration.

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

---------------------------------------------------------
Title: Topological Departures from Translational Invariance along
a Filament Observed by THEMIS
Authors: Dudík, J.; Aulanier, G.; Schmieder, B.; Bommier, V.;
Roudier, T.
2008SoPh..248...29D Altcode: 2008SoPh..tmp...53D
We study the topology of the 3D magnetic field in a filament channel
to address the following questions: Is a filament always formed in a
single flux tube? How does the photospheric magnetic field lead to
filament interruptions and to feet formation? What is the relation
between feet-related field lines and the parasitic polarities? What
can topological analyses teach us about EUV filament channels? To do
so, we consider a filament observed on 6 October 2004 with THEMIS/MTR,
in Hα with the full line profile simultaneously and cospatially with
its photospheric vector magnetic field. The coronal magnetic field
was calculated from a "linear magnetohydrostatic" extrapolation of a
composite THEMIS-MDI magnetogram. Its free parameters were adjusted
to get the best match possible between the distribution of modeled
plasma-supporting dips and the Hα filament morphology. The model
results in moderate plasma β≤1 at low altitudes in the filament,
in conjunction with non-negligible departures from force-freeness
measured by various metrics. The filament here is formed by a split
flux tube. One part of the flux tube is rooted in the photosphere aside
an observed interruption in the filament. This splitted topology is
due to strong network polarities on the edge of the filament channel,
not to flux concentrations closer to the filament. We focus our study
to the northwest portion of the filament. The related flux tube is
highly fragmented at low altitudes. This fragmentation is due to small
flux concentrations of two types. First, some locally distort the
tube, leading to noticeable thickness variations along the filament
body. Second, parasitic polarities, associated with filament feet,
result in secondary dips above the related local inversion line. These
dips belong to long field lines that pass below the flux tube. Many
of these field lines are not rooted near the related foot. Finally,
the present model shows that the coronal void interpretation cannot
be ruled out to interpret the wideness of EUV filament channels.

---------------------------------------------------------
Title: Nonlinear Force-free Field Modeling of a Solar Active Region
around the Time of a Major Flare and Coronal Mass Ejection
Authors: Schrijver, C. J.; DeRosa, M. L.; Metcalf, T.; Barnes, G.;
Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann, T.;
Wheatland, M. S.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann,
M.; Kusano, K.; Régnier, S.; Thalmann, J. K.
2008ApJ...675.1637S Altcode: 2007arXiv0712.0023S
Solar flares and coronal mass ejections are associated with rapid
changes in field connectivity and are powered by the partial dissipation
of electrical currents in the solar atmosphere. A critical unanswered
question is whether the currents involved are induced by the motion of
preexisting atmospheric magnetic flux subject to surface plasma flows or
whether these currents are associated with the emergence of flux from
within the solar convective zone. We address this problem by applying
state-of-the-art nonlinear force-free field (NLFFF) modeling to the
highest resolution and quality vector-magnetographic data observed
by the recently launched Hinode satellite on NOAA AR 10930 around
the time of a powerful X3.4 flare. We compute 14 NLFFF models with
four different codes and a variety of boundary conditions. We find
that the model fields differ markedly in geometry, energy content,
and force-freeness. We discuss the relative merits of these models in
a general critique of present abilities to model the coronal magnetic
field based on surface vector field measurements. For our application
in particular, we find a fair agreement of the best-fit model field
with the observed coronal configuration, and argue (1) that strong
electrical currents emerge together with magnetic flux preceding the
flare, (2) that these currents are carried in an ensemble of thin
strands, (3) that the global pattern of these currents and of field
lines are compatible with a large-scale twisted flux rope topology,
and (4) that the ~1032 erg change in energy associated with
the coronal electrical currents suffices to power the flare and its
associated coronal mass ejection.

---------------------------------------------------------
Title: A New Model for Propagating Parts of EIT Waves: A Current
Shell in a CME
Authors: Delannée, C.; Török, T.; Aulanier, G.; Hochedez, J. -F.
2008SoPh..247..123D Altcode:
EIT waves are observed in EUV as bright fronts. Some of these bright
fronts propagate across the solar disk. EIT waves are all associated
with a flare and a CME and are commonly interpreted as fast-mode
magnetosonic waves. Propagating EIT waves could also be the direct
signature of the gradual opening of magnetic field lines during a
CME. We quantitatively addressed this alternative interpretation. Using
two independent 3D MHD codes, we performed nondimensional numerical
simulations of a slowly rotating magnetic bipole, which progressively
result in the formation of a twisted magnetic flux tube and its fast
expansion, as during a CME. We analyse the origins, the development,
and the observability in EUV of the narrow electric currents sheets that
appear in the simulations. Both codes give similar results, which we
confront with two well-known SOHO/EIT observations of propagating EIT
waves (7 April and 12 May 1997), by scaling the vertical magnetic field
components of the simulated bipole to the line of sight magnetic field
observed by SOHO/MDI and the sign of helicity to the orientation of the
soft X-ray sigmoids observed by Yohkoh/SXT. A large-scale and narrow
current shell appears around the twisted flux tube in the dynamic phase
of its expansion. This current shell is formed by the return currents
of the system, which separate the twisted flux tube from the surrounding
fields. It intensifies as the flux tube accelerates and it is co-spatial
with weak plasma compression. The current density integrated over the
altitude has the shape of an ellipse, which expands and rotates when
viewed from above, reproducing the generic properties of propagating
EIT waves. The timing, orientation, and location of bright and faint
patches observed in the two EIT waves are remarkably well reproduced. We
conjecture that propagating EIT waves are the observational signature of
Joule heating in electric current shells, which separate expanding flux
tubes from their surrounding fields during CMEs or plasma compression
inside this current shell. We also conjecture that the bright edges
of halo CMEs show the plasma compression in these current shells.

---------------------------------------------------------
Title: Slipping Magnetic Reconnection in Coronal Loops
Authors: Aulanier, Guillaume; Golub, Leon; DeLuca, Edward E.; Cirtain,
Jonathan W.; Kano, Ryouhei; Lundquist, Loraine L.; Narukage, Noriyuki;
Sakao, Taro; Weber, Mark A.
2007Sci...318.1588A Altcode:
Magnetic reconnection of solar coronal loops is the main process that
causes solar flares and possibly coronal heating. In the standard
model, magnetic field lines break and reconnect instantaneously at
places where the field mapping is discontinuous. However, another mode
may operate where the magnetic field mapping is continuous but shows
steep gradients: The field lines may slip across each other. Soft
x-ray observations of fast bidirectional motions of coronal loops,
observed by the Hinode spacecraft, support the existence of this
slipping magnetic reconnection regime in the Sun’s corona. This
basic process should be considered when interpreting reconnection,
both on the Sun and in laboratory-based plasma experiments.

---------------------------------------------------------
Title: What can We learn about Filaments from Vector Magnetograms?
Authors: Schmieder, B.; Aulanier, G.; Lopez Ariste, A.
2007ASPC..369..137S Altcode:
Theoretical MHD models of filaments have predicted the existence
of dips in magnetic field lines supporting the cool filament
plasma. Condensation would be one of the possible mechanism of filament
formation. The controversy is still alive. Filament fine structures are
of dynamical nature and injection of cold material (like surges) from
the photosphere would be the proposed mechanism. With the presence of
dips, the magnetic lines are predicted to be tangent to the photosphere,
near the barbs, footpoints of the prominences. The injection model
predicted nearly vertical structures of the barbs rooted in the
minority polarities. Measurements of vector magnetic field in
filament channels can answer to these questions and will be possible
with Solar-B. Recent results have been obtained with THEMIS vector
magnetograph in Tenerife, suggesting that dips are really present in
filament channel leading to the conclusion that the observed magnetic
topology in the photosphere fully supports models of prominences based
on dips.

---------------------------------------------------------
Title: Eruptive and Compact Flares
Authors: Schmieder, B.; Aulanier, G.; Delannée, C.; Berlicki, A.
2007AIPC..934...22S Altcode:
Solar two ribbon flares are commonly explained by magnetic field
reconnections in the high corona. During the reconnection energetic
particles (electrons and protons) are accelerated from the reconnection
site. These particles are following the magnetic field lines down
to the chromosphere. As the plasma density is higher in these lower
layers, there are collisions and emission of radiation. Thus after
the flare bright ribbons are observed at both ends of loops. These
ribbons are typically observed in Hα and in EUV with SoHO and
TRACE. As the time is going, these ribbons are expanding away of each
other. In most studied models, the reconnection site is an X-point,
where two magnetic separatrices intersect. They define four distinct
connectivity domains, across which the magnetic connectivity changes
discontinuously. In this paper, we present a generalization of this
model to 3D complex magnetic topologies where there are no null points,
but quasi-separatrices layers instead. In that case, while the ribbons
spread away during reconnection, we show that magnetic field lines
can quickly slip along them. We propose that this new phenomenon could
explain fast extension of Hα and TRACE 1600 Å ribbons, fast moving
HXR footpoints as observed by RHESSI, and that it is observed in soft
X rays with Hinode/XRT. We also show how this concept can be applied
to model the non-wave nature of EIT waves.

---------------------------------------------------------
Title: Unveiling the Magnetic Field Topology of Prominences
Authors: López Ariste, A.; Aulanier, G.
2007ASPC..368..291L Altcode:
A renewed effort is being dedicated to infer magnetic fields in
prominences through spectropolarimetry of emission lines like the He
D3 and 10830 Å lines. We will briefly review those present
observational efforts pointing at how do they improve or disregard past
attempts to measure magnetic fields in prominences and at how they try
to answer some of the standing questions from theoretical models. A
brief and gentle introduction to the Hanle effect and other subtle
quantum phenomena is given, as they are key to present diagnostic
techniques and, finally, an overview of future observational goals
and wishes is presented.

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

---------------------------------------------------------
Title: Stationary parts of an EIT and Moreton wave: a topological
model
Authors: Delannée, C.; Hochedez, J. -F.; Aulanier, G.
2007A&A...465..603D Altcode:
Context: EIT and Moreton waves came into focus in 1997, when a
propagating disturbance on a large area of the solar disc was
discovered. The process generating the EIT and Moreton waves has
been frequently discussed. Aims: On May 2, 1998, a halo CME
was observed related to an EIT wave, a Moreton wave, a X1 flare,
radio emission sources, and dimmings. We studied this event to find
the relation between all these structures. Methods: We use
and co-align multi-wavelength observations and the online potential
field source surface (pfss) package. Results: The observed EIT
and Moreton waves present some brightenings that remain at the same
location. We relate the connectivity of the coronal potential magnetic
field to the stationary brightenings. We find that the areas where the
magnetic field lines have drastic jumps of connectivity are cospatial
to the stationary brightenings of the waves. Conclusions: .We
conclude that the EIT and Moreton waves may be due to Joule heating
resulting from the generation of electric currents in the neighboring
area of the drastic jumps of magnetic connectivity, while the magnetic
field lines are opening during a CME.

---------------------------------------------------------
Title: Magnetic flux tubes observed with THEMIS/MSDP
Authors: Mein, P.; Mein, N.; Faurobert, M.; Aulanier, G.; Malherbe,
J. -M.
2007A&A...463..727M Altcode:
Aims:We use spectro-polarimetric THEMIS/MSDP data to investigate the 3D
structure of solar magnetic-flux tubes across the upper photosphere. Methods: Profiles of the sodium D1 line 589.6 nm are analysed by
the bisector method at different wavelengths from the core to the
wings, for several bright features. They are compared to synthetic
profiles derived from 2D magnetic models of flux tubes and from the
MULTI code for NLTE line profiles. Three different magnetic models of
flux tubes are investigated. Model (I) consists of a single flux tube
that compensates for the horizontal Lorentz forces exactly, while model
(II) uses a compromise between horizontal and vertical components. Model
(III), a conglomerate of thinner flux tubes, leads to the best agreement
with observations. Results: (1) The combination of seeing effects
(small filling factor) with slopes of line profiles, which are different
in the flux tubes and the neighbouring quiet sun, account for the
decrease in observed magnetic field from line core to line wings in
central parts of magnetic features, as well as the decrease in magnetic
fluxes integrated over the whole magnetic features. (2) The expansion
with height of single magnetic flux tubes (models I and II) accounts for
the increase in the size of magnetic features from line wings to line
core. (3) Pure thermodynamical criteria characterising Dopplershifts
and line-intensity fluctuations of magnetic and non-magnetic features
have been proven by observations. Conclusions: . We could account
for differential Zeeman effects along the D1 line profile by combining
expansion of flux tubes with height, low gas pressure inside flux tubes,
and small filling factor due to seeing effects. Better agreement with
observations, in particular with respect to magnetic field amplitudes,
will probably need 3D models that take velocity fields and horizontal
gradients of temperature into account.

---------------------------------------------------------
Title: Magnetic flux tubes observed with THEMIS/MSDP .
Authors: Mein, P.; Mein, N.; Faurobert, M.; Aulanier, G.; Malherbe,
J. -M.
2007MmSAI..78...92M Altcode:
We use 2D spectro-polarimetric data of the NaD1 line to investigate
magnetic flux tubes at several levels of the solar photosphere: -
magnetic and non-magnetic bright features can be discriminated by simple
criteria of intensities and dopplershifts. - 2D magnetic models
and NLTE line profiles are compared to observations : combination of
seeing effects and departures between slopes of line profiles in flux
tubes and neighbouring photosphere account for vertical gradients of
line-of-sight (LOS) magnetic field measurements. - Best qualitative
agreements are obtained with clusters of magnetic flux tubes.

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

---------------------------------------------------------
Title: Evolving Photospheric Flux Concentrations and Filament
Dynamic Changes
Authors: Schmieder, B.; Aulanier, G.; Mein, P.; Ariste, A. López
2006SoPh..238..245S Altcode: 2006SoPh..tmp...64S
We analyze the role of weak photospheric flux concentrations that
evolve in a filament channel, in the triggering of dynamic changes in
the shape of a filament. The high polarimetric sensitivity of THEMIS
allowed us to detect weak flux concentrations (few Gauss) associated
with the filament development. The synoptic instruments (MDI, SOLIS)
even if their sensitivity is much less than THEMIS were useful to
follow any subsequent strengthening of these flux concentrations after
their identification in the THEMIS magnetograms. We found that (1)
the northern part of the filament develops an Hα barb at the same
time that weak minority polarity elements develop near a plage; (2)
a section in the southern part of the Hα filament gradually disappears
and later reforms at the same time that several mixed-polarity magnetic
elements appear, then subsequently cancel or spread away from each
other. These changes correspond to increases in EUV emission, as
observed by TRACE, EIT, and CDS. This suggests that the plasma is
temporarily heated along the filament spine. An idealized sequence of
force-free models of this filament channel, based on plasma-supporting
magnetic dips occurring in the windings of a very weakly twisted flux
tube, naturally explains the evolution of its southern part as being
due to changes in the topology of the coronal magnetic field as the
photospheric flux concentrations evolve.

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

---------------------------------------------------------
Title: First observation of bald patches in a filament channel and
at a barb endpoint
Authors: López Ariste, A.; Aulanier, G.; Schmieder, B.; Sainz
Dalda, A.
2006A&A...456..725L Altcode:
The 3D magnetic field topology of solar filaments/prominences is
strongly debated, because it is not directly measureable in the
corona. Among various prominence models, several are consistent
with many observations, but their related topologies are very
different. We conduct observations to address this paradigm. We
measure the photospheric vector magnetic field in several small
flux concentrations surrounding a filament observed far from disc
center. Our objective is to test for the presence/absence of magnetic
dips around/below the filament body/barb, which is a strong constraint
on prominence models, and that is still untested by observations. Our
observations are performed with the THEMIS/MTR instrument. The four
Stokes parameters are extracted, from which the vector magnetic fields
are calculated using a PCA inversion. The resulting vector fields
are then deprojected onto the photospheric plane. The 180° ambiguity
is then solved by selecting the only solution that matches filament
chirality rules. Considering the weakness of the resulting magnetic
fields, a careful analysis of the inversion procedure and its error
bars was performed, to avoid over-interpretation of noisy or ambiguous
Stokes profiles. Thanks to the simultaneous multi-wavelength THEMIS
observations, the vector field maps are coaligned with the Hα image of
the filament. By definition, photospheric dips are identifiable where
the horizontal component of the magnetic field points from a negative
toward a positive polarity. Among six bipolar regions analyzed in the
filament channel, four at least display photospheric magnetic dips,
i.e. bald patches. For barbs, the topology of the endpoint is that of
a bald patch located next to a parasitic polarity, not of an arcade
pointing within the polarity. The observed magnetic field topology in
the photosphere tends to support models of prominence based on magnetic
dips located within weakly twisted flux tubes. Their underlying and
lateral extensions form photospheric dips both within the channel and
below barbs.

---------------------------------------------------------
Title: Is Pre-Eruptive Null Point Reconnection Required for Triggering
Eruptions?
Authors: Li, Hui; Schmieder, Brigitte; Aulanier, Guillaume; Berlicki,
Arkadiusz
2006SoPh..237...85L Altcode: 2006SoPh..tmp...22L; 2006SoPh..tmp...18L
We study the magnetic field evolution and topology of the active
region NOAA 10486 before the 3B/X1.2 flare of October 26, 2003,
using observational data from the French-Italian THEMIS telescope,
the Michelson Doppler Imager (MDI) onboard Solar and Heliospheric
Observatory (SOHO), the Solar Magnetic Field Telescope (SMFT) at
Huairou Solar Observation Station (HSOS), and the Transition Region
and Coronal Explorer (TRACE). Three dimensional (3D) extrapolation of
photospheric magnetic field, assuming a potential field configuration,
reveals the existence of two magnetic null points in the corona above
the active region. We look at their role in the triggering of the main
flare, by using the bright patches observed in TRACE 1600 Å images as
tracers at the solar surface of energy release associated with magnetic
reconnection at the null points. All the bright patches observed before
the flare correspond to the low-altitude null point. They have no
direct relationship with the X1.2 flare because the related separatrix
is located far from the eruptive site. No bright patch corresponds
to the high-altitude null point before the flare. We conclude that
eruptions can be triggered without pre-eruptive coronal null point
reconnection, and the presence of null points is not a sufficient
condition for the occurrence of flares. We propose that this eruptive
flare results from the loss of equilibrium due to persistent flux
emergence, continuous photospheric motion and strong shear along the
magnetic neutral line. The opening of the coronal field lines above
the active region should be a byproduct of the large 3B/X1.2 flare
rather than its trigger.

---------------------------------------------------------
Title: Solar Prominence Merging
Authors: Aulanier, Guillaume; DeVore, C. Richard; Antiochos, Spiro K.
2006ApJ...646.1349A Altcode:
In a recent paper, we described MHD simulations of the interaction
between a pair of distinct prominences formed by the photospheric
line-tied shearing of two separated dipoles. One case was typical of
solar observations of prominence merging, in which the prominences
have the same axial field direction and sign of magnetic helicity. For
that configuration, we reported the formation of linkages between the
prominences due to magnetic reconnection of their sheared fields. In
this paper, we analyze the evolution of the plasma-supporting
magnetic dips in this configuration. As the photospheric flux is
being progressively sheared, dip-related chromospheric fibrils and
high-altitude threads form and develop into the two prominences, which
undergo internal oscillations. As the prominences are stretched farther
along their axes, they come into contact and their sheared fluxes
pass each other, and new dips form in the interaction region. The
distribution of these dips increasingly fills the volume between
the prominences, so that the two progenitors gradually merge into
a single prominence. Our model reproduces typical observational
properties reported from both high-cadence and daily observations at
various wavelengths. We identify the multistep mechanism, consisting
of a complex coupling between photospheric shear, coronal magnetic
reconnection without null points, and formation of quasi bald patches,
that is responsible for the prominence merging through dip creation. The
resulting magnetic topology differs significantly from that of a
twisted flux tube.

---------------------------------------------------------
Title: Electron Acceleration and Transport During the November 5,
1998 Solar Flare At ∼13:34 UT
Authors: Trottet, G.; Correia, E.; Karlický, M.; Aulanier, G.; Yan,
Y.; Kaufmann, P.
2006SoPh..236...75T Altcode:
This paper deals with a detailed analysis of spectral and imaging
observations of the November 5, 1998 (Hα 1B, GOES M1.5) flare
obtained over a large spectral range, i.e., from hard X-rays to
radiometric wavelengths. These observations allowed us to probe electron
acceleration and transport over a large range of altitudes that is to
say within small-scale (a few 103 km) and large-scale (a few
105 km) magnetic structures. The observations combined with
potential and linear force-free magnetic field extrapolations allow
us to show that: (i) Flare energy release and electron acceleration
are basically driven by loop-loop interactions at two independent, low
lying, null points of the active region magnetic field; (ii) &lt;300 keV
hard X-ray-producing electrons are accelerated by a different process
(probably DC field acceleration) than relativistic electrons that
radiate the microwave emission; and (iii) although there is evidence
that hard X-ray and decimetric/metric radio-emitting electrons are
produced by the same accelerator, the present observations and analysis
did not allow us to find a clear and direct magnetic connection between
the hard X-ray emitting region and the radio-emitting sources in the
middle corona.

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

---------------------------------------------------------
Title: Magnetic Topology before a 3B/X1.2 Flare and the Associated CME
Authors: Li, H.; Schmieder, B.; Aulanier, G.; Berlicki, A.
2006IAUS..233..399L Altcode:
We extrapolated observed photospheric magnetic field before the 3B/X1.2
flare occurred in NOAA 10486 on 2003 October 26. Two magnetic null
points exist above the active region, which have no crucial role in
triggering the flare, even though enhanced TRACE EUV/UV emission was
observed before the main flare due to magnetic reconnection near the
lower-altitude null point. We conclude that this flare results from the
loss of equilibrium due to persistent flux emergence and photospheric
motion, and strong shear. The accompanying fast CME with velocity of
∼ 800 km s^{-1} shows quick mass pickup and energy increase in the low
corona. Its kinetic energy is always larger than its potential energy.

---------------------------------------------------------
Title: Can we finally solve the problems of "Coronal Heating " and
"Solar Wind Acceleration" in the Cosmic Vision era ?
Authors: Maksimovic, M.; Appourchaux, T.; Aulanier, G.; Chust, T.;
Dudok de Wit, T.; Klein, K. L.; Krasnoselskikh, V.; Louarn, P.; Roux,
A.; Vial, J. C.
2006cosp...36.2999M Altcode: 2006cosp.meet.2999M
Since the discovery of the corona s million-degree temperature in the
1940s and the supersonic solar wind in the early 1960s major efforts
have been made to discover the physical mechanisms that could explain
these two observations These efforts have led to a tremendous increase
in our knowledge of our neighbour star the inner heliosphere and the
Sun-Earth connections Unfortunately these efforts haven t allowed to
provide a definitive answer to these questions Why such a situation On
one hand the remote-sensing strategy has tried to probe the coronal
properties by basically analysing the photons emitted or absorbed
by the Sun s atmosphere With this regards limitations occur on both
theoretical ground physics of the coupling between photons and plasma
and experimental ground limited number of observables such as spectral
lines or the hardly solvable problem of the line of sight integration
On the other hand solar wind in-situ measurements have had access to
the very detailed state of the local plasma properties full particles
velocity distribution functions observations of the electromagnetic
plasma fluctuations over a huge frequency range but at locations
far from the corona and the solar wind acceleration regions Moreover
it has been realized more recently that the magnetic field plays a
fundamental role in shaping the low corona and channelling the energy
inputs Unfortunately the measurement of the full magnetic vector in
the corona is a very difficult enterprise and this lack of information
hampers all on-going modelling efforts Given

---------------------------------------------------------
Title: Emergence of undulatory magnetic flux tubes by small scale
reconnections
Authors: Pariat, E.; Aulanier, G.; Schmieder, B.; Georgoulis, M. K.;
Rust, D. M.; Bernasconi, P. N.
2006AdSpR..38..902P Altcode:
With Flare Genesis Experiment (FGE), a balloon borne observatory
launched in Antarctica on January 2000, series of high spatial
resolution vector magnetograms, Dopplergrams, and Hα filtergrams
have been obtained in an emerging active region (AR 8844). Previous
analyses of this data revealed the occurence of many short-lived
and small-scale H α brightenings called 'Ellerman bombs'
(EBs) within the AR. We performed an extrapolation of the field above
the photosphere using the linear force-free field approximation. The
analysis of the magnetic topology reveals a close connexion between
the loci of EBs and the existence of "Bald patches" (BP) regions
(BPs are regions where the vector magnetic field is tangential to
the photosphere). Some of these EBs/BPs are magnetically connected
by low-lying field lines, presenting a serpentine shape. This results
leads us to conjecture that arch filament systems and active regions
coronal loops do not result from the smooth emergence of large scale
Ω-loops, but rather from the rise of flat undulatory flux tubes which
get released from their photospheric anchorage by reconnection at BPs,
which observational signature is Ellerman bombs.

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

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

---------------------------------------------------------
Title: Observation of Small Scale Reconnection Role in Undulated
Flux Tube Emergence
Authors: Pariat, E.; Aulanier, G.; Schmieder, B.; Georgoulis, M. K.;
Rust, D. M.; Bernasconi, P. N.
2005ESASP.596E..34P Altcode: 2005ccmf.confE..34P
No abstract at ADS

---------------------------------------------------------
Title: Observational Evidence of Photoshperic Magnetic Dips in
Filament Channels
Authors: Schmieder, B.; López Ariste, A.; Aulanier, G.
2005ESASP.596E..19S Altcode: 2005ccmf.confE..19S
No abstract at ADS

---------------------------------------------------------
Title: Solar Prominence Interactions
Authors: DeVore, C. Richard; Antiochos, Spiro K.; Aulanier, Guillaume
2005ApJ...629.1122D Altcode:
We report numerical simulations of the formation, interaction, and
magnetic reconnection between pairs of solar prominences within the
sheared-arcade model. Our experiments consider the four possible basic
combinations of chiralities (identical or opposite) and axial magnetic
fields (aligned or opposed) between the participating prominences. When
the topology of the global flux system comprising the prominences
and arcades is bipolar, so that a single polarity inversion line is
shared by the two structures, then identical chiralities necessarily
imply aligned axial fields, while opposite chiralities imply opposed
axial fields. In the former case, external magnetic reconnections
forming field lines linking the two prominences occur; in the latter,
such reconnections are disfavored, and no linkage takes place. These
results concur with empirical rules for prominence interactions. When
the topology instead is quadrupolar, so that a second polarity
inversion line crossing the first lies between the prominences,
then the converse relation holds between chirality and axial-field
alignment. External reconnections forming linking field lines now occur
between prominences with opposite chiralities; they also occur, but
result only in footpoint exchanges, between prominences with identical
chiralities. These findings conflict with the accepted empirical rules
but may not have been tested in observations to date. All of our model
prominences, especially those that undergo linking reconnections,
contain substantial magnetic shear and twist. Nevertheless, none
exhibits any sign of onset of instability or loss of equilibrium that
might culminate in an eruption.

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

---------------------------------------------------------
Title: Research on a complex CME event including Hα, LASCO, radio
and MDI observations
Authors: Wang, S. J.; Maia, D.; Pick, M.; Aulanier, G.; Malherbe,
J. -M.; Delaboudinière, J. -P.
2005AdSpR..36.2273W Altcode:
We present our research on a fast and decelerating partial halo
coronal mass ejection (CME) event detected in multi-wavelengths
in the chromosphere and the corona on 14 October, 1999. The event
involved a whole complex active area which spanned more than 40°
of heliolongitude. It included a strong solar flare (XI/1N) and a
complex eruptive filament within an active region of the entire
complex. Especially, several radio sources were detected in the
decimetric range prior to the CME by the Nançay Radioheliograph
(NRH). A linear force-free field extrapolation of the Michelson Doppler
Imager (MDI) magnetogram was performed to calculate the magnetic
topology of the complex prior to the triggering of the event. The
presence of a coronal null point combined with the occurrence of two
distant and nearly simultaneous radio sources put strong arguments
in favor of the generalized breakout model for the triggering of the
eruption. The analysis of the subsequent development of the event
suggests that large interconnecting loops were ejected together with
the CME.

---------------------------------------------------------
Title: Flux tube emergence, from photosphere to corona
Authors: Pariat, E.; Schmieder, B.; Aulanier, G.
2004sf2a.conf..103P Altcode: 2004sf2a.confE.339P
From a campaign of multi-wavelength observations of an emerging active
region, we have studied the dynamics of the solar atmosphere due to
this emergence and the magnetic field topology of the active region. In
addition with the observations obtained with Yohkoh, SOHO and TRACE,
a balloon borne 80 cm telescope (Flare Genesis Experiment) provided us
a series of high spatial resolution vector magnetograms. For the first
time we highlight that magnetic flux tubes do not directly emerge with
a large Omega-loop shape, as suggest the TRACE observations of the
corona, but rather within an undulatory shape. We demonstrated that
the resistive Parker instability allows the flux tube to go through
the low atmosphere. This result has been obtained by performing
an extrapolation of the field above the active region.

---------------------------------------------------------
Title: Resistive Emergence of Undulatory Flux Tubes
Authors: Pariat, E.; Aulanier, G.; Schmieder, B.; Georgoulis, M. K.;
Rust, D. M.; Bernasconi, P. N.
2004ApJ...614.1099P Altcode:
During its 2000 January flight, the Flare Genesis Experiment observed
the gradual emergence of a bipolar active region, by recording a series
of high-resolution photospheric vector magnetograms and images in the
blue wing of the Hα line. Previous analyses of these data revealed the
occurrence of many small-scale, transient Hα brightenings identified
as Ellerman bombs (EBs). They occur during the flux emergence,
and many of them are located near moving magnetic dipoles in which
the vector magnetic field is nearly tangential to the photosphere. A
linear force-free field extrapolation of one of the magnetograms was
performed to study the magnetic topology of small-scale EBs and their
possible role in the flux emergence process. We found that 23 out of 47
EBs are cospatial with bald patches (BPs), while 15 are located at the
footpoints of very flat separatrix field lines passing through distant
BPs. We conclude that EBs can be due to magnetic reconnection, not only
at BP locations, but also along their separatrices, occurring in the
low chromosphere. The topological analysis reveals, for the first time,
that many EBs and BPs are linked by a hierarchy of elongated flux tubes
showing aperiodic spatial undulations, whose wavelengths are typically
above the threshold of the Parker instability. These findings suggest
that arch filament systems and coronal loops do not result from the
smooth emergence of large-scale Ω-loops from below the photosphere,
but rather from the rise of undulatory flux tubes whose upper parts
emerge because of the Parker instability and whose dipped lower parts
emerge because of magnetic reconnection. EBs are then the signature
of this resistive emergence of undulatory flux tubes.

---------------------------------------------------------
Title: Evolution and magnetic topology of the M 1.0 flare of October
22, 2002
Authors: Berlicki, A.; Schmieder, B.; Vilmer, N.; Aulanier, G.;
Del Zanna, G.
2004A&A...423.1119B Altcode:
In this paper we analyse an M 1.0 confined flare observed mainly
during its gradual phase. We use the data taken during a coordinated
observational campaign between ground based instruments (THEMIS and
VTT) and space observatories (SoHO/CDS and MDI, TRACE and RHESSI). We
use these multi-wavelength observations to study the morphology
and evolution of the flare, to analyse its gradual phase and to
understand the role of various heating mechanisms. During the flare,
RHESSI observed emission only within the 3-25 keV spectral range. The
RHESSI spectra indicate that the emission of the flare was mainly of
thermal origin with a small non-thermal component observed between
10 and 20 keV. Nevertheless, the energy contained in the non-thermal
electrons is negligible compared to the thermal energy of the flaring
plasma. The temperature of plasma obtained from the fitting of the
RHESSI X-ray spectra was between 8.5 and 14 MK. The lower temperature
limit is typical for a plasma contained in post flare loops observed
in X-rays. Higher temperatures were observed during a secondary peak
of emission corresponding to a small impulsive event. The SoHO/CDS
observations performed in EUV Fe XIX line also confirm the presence
of a hot plasma at temperatures similar to those obtained from RHESSI
spectra. The EUV structures were located at the same place as RHESSI
X-ray emission. The magnetic topology analysis of the AR coming from a
linear force-free field extrapolation explains the observed features
of the gradual phase of the flare i.e. the asymmetry of the ribbons
and their fast propagation. The combination of the multi-wavelength
observations with the magnetic model further suggests that the onset
of the flare would be due to the reconnection of an emerging flux in
a sheared magnetic configuration.

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

---------------------------------------------------------
Title: Emergence of undulatory magnetic flux tubes by small scale
reconnections
Authors: Pariat, E.; Aulanier, G.; Schmieder, B.; Georgoulis, M. K.;
Rust, D. M.; Bernasconi, P. N.
2004cosp...35.1482P Altcode: 2004cosp.meet.1482P
With Flare Genesis Experiment (FGE), a balloon borne observatory
launched in Antarctica on January 2000, series of high spatial
resolution vector magnetograms, Dopplergrams, and Hα filtergrams
have been obtained in an emerging active region (AR 8844). Previous
analyses of this data revealed the occurence of many short-lived and
small-scale Hα brightenings called 'Ellerman bombs' (EBs) within the
AR. We performed an extrapolation of the field above the photosphere
using the linear force-free field approximation. The analysis of the
magnetic topology reveals a close connexion between the loci of EBs
and the existence of “Bald patches” regions (BPs are regions where
the vector magnetic field is tangential to the photosphere). Among
47 identified EBs, we found that 23 are co-spatial with a BP, while
19 are located at the footpoint of very flat separatrix field lines
passing throught a distant BP. We reveal for the first time that
some of these EBs/BPs are magneticaly connected by low-lying lines,
presenting a 'sea-serpent' shape. This results leads us to conjecture
that arch filament systems and active regions coronal loops do not
result from the smooth emergence of large scale Ω loops, but rather
from the rise of flat undulatory flux tubes which get released from
their photospheric anchorage by reconnection at BPs, whose observational
signature is Ellerman bombs.

---------------------------------------------------------
Title: Flare evolution and magnetic configuration study
Authors: Berlicki, A.; Schmieder, B.; Aulanier, G.; Vilmer, N.; Yan,
Y. H.
2004cosp...35.2200B Altcode: 2004cosp.meet.2200B
We will present the analysis of M1.0 confined flare emission and
evolution in the context of the topology of the coronal magnetic
field. This flare was observed in NOAA 0162 on 22 October 2002. The
multiwavelength data were taken during a coordinated observational
campaign between ground based instruments and space observatories. The
photospheric line-of-sight magnetic field observations were obtained
with THEMIS and SOHO/MDI. We used these data to perform linear
force-free field extrapolation of magnetic field into the corona. Our
extrapolation provides an explanation of the appearance of H-alpha
flare ribbons. An elongated shape of X-ray emission observed by Reuven
Ramaty High Energy Solar Spectroscopic Imager (RHESSI) also follow
the predicted shape of extrapolated field lines. Moreover, the X-ray
emission observed by RHESSI permit to see thermal emission of coronal
loops heated probably by non-thermal electrons, accelerated during the
reconnection processes. The presence of non-thermal particles can be
deduced from RHESSI X-ray spectra reconstructed during the gradual phase
of the flare. On Huairou vector magnetograms of the AR we see that there
was strong shear between one of main negative spot and the north small
positive spot. The extrapolation with non-constant alpha force-free
field model did not obtain any loop to connect these two spots.

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

---------------------------------------------------------
Title: Interpretation of a complex CME event: Coupling of scales in
multiple flux systems
Authors: Maia, D.; Aulanier, G.; Wang, S. J.; Pick, M.; Malherbe,
J. -M.; Delaboudinière, J. -P.
2003A&A...405..313M Altcode:
Using multi-wavelength observations, in particular in imagery, recorded
by SOHO/LASCO-MDI, Yohkoh/SXT, the Meudon spectroheliograph and the
Nançay radioheliograph, and performing a linear force-free field
extrapolation, we analyzed the triggering and the development of a
complex eruptive event in the chromosphere and in the corona. This
event included an X1 class flare and an eruptive filament within an
active region, but it also involved a whole active complex spanning over
40 degrees of heliolongitude. It resulted in a fast and decelerating
partial halo CME, associated with a Moreton wave and a complex series
of metric, decimetric and microwave radio bursts. The presence of a
coronal null point combined with the occurrence of two distant and
nearly simultaneous radio sources give strong arguments in favor of
the generalized breakout model for the triggering of the eruption. The
observations are consistent with the occurrence of magnetic reconnection
at the null point three minutes before the start of the eruption,
which is consistent with other observed CME precursors. The analysis
of the subsequent development of the event suggests that large
interconnecting loops were ejected together with the CME, and that
secondary reconnections at low altitude probably occurred remotely in
the active complex. Our results show that the triggering and evolution
of this complex CME involved multiple magnetic flux systems over a
large coronal volume surrounding the flare site, and that it resulted
from the coupling of scales from narrow reconnection current sheets
to very large inter active region magnetic connections.

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

---------------------------------------------------------
Title: Na I D1 Stokes V Asymmetries and Velocity Structure
Around Sunspots
Authors: Eibe, M. T.; Sánchez Almeida, J.; Mein, P.; Aulanier, G.;
Malherbe, J. M.
2003ASPC..307..374E Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetic field measurements with THEMIS
Authors: Aulanier, G.
2003sf2a.conf...83A Altcode: 2003sf2a.confE..40A
Some recent observations have shown that dark and wide EUV filament
extensions observed on the disc at lambda &lt; 912 A are due to the
absorption of coronal and transition region lines in cool plasma
condensations, located aside of filaments, that are unobservable in
Hα. We present the results of our 3D magnetohydrostatic model for
filaments, here applied to THEMIS and SoHO observations of such a wide
EUV filament channel. The model was calculated from a MDI magnetogram
as lower boundary conditions. We discuss the results of the model in
terms of predictions for (i) the mass loading of CMEs during filament
eruptions and (ii) the detectability of real filaments within dark,
but possibly filamentless, EUV channels. We believe that both these
issues will be relevant in the definition of future space instruments
dedicated to 'space weather oriented' solar observations in EUV.

---------------------------------------------------------
Title: Spectropolarimetry of Solar Prominences
Authors: Paletou, F.; Aulanier, G.
2003ASPC..307..458P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the Need of High-Resolution Spectropolarimetric Observations
of Prominences
Authors: Paletou, F.; Aulanier, G.
2003ASPC..286...45P Altcode: 2003ctmf.conf...45P
No abstract at ADS

---------------------------------------------------------
Title: What can we learn from lfff magnetic extrapolations
Authors: Schmieder, B.; Aulanier, G.
2003AdSpR..32.1875S Altcode:
Observations of the Sun is done, up to now, in 2D and magnetic field is
measured mainly in the photosphere. Magnetic extrapolation techniques
allow us nevertheless to have a 3D view of the magnetic field. Different
methods are available today. We present in this paper interesting
and exploitable results obtained with linear force-free-field methods
(lfff). The α parameter is assumed to be constant in the whole volume
of computations. The results concern the global potential field in the
corona (e.g. example of transequatorial loops), the magnetic topology
of flaring active regions (e.g. flares and bald patch regions), twisted
magnetic fields in filaments, and magnetic reconnection in emerging
active region (e.g. Ellerman Bombs). We discuss on the limits of the
validity of the methods.

---------------------------------------------------------
Title: The "careers in solar physics" session of the SPM10 meeting
Authors: Aulanier, G.; Parenti, S.; Krijger, J. M.
2002ESASP.506..981A Altcode: 2002ESPM...10..981A; 2002svco.conf..981A
During the SPM10 meeting held in Prague (Czech Republic) on September
9-14, 2002, a half-day 'young session' was organized on the topic
of careers in solar physics. Several young researchers and senior
scientists were invited to give oral contributions on the current
advantages and difficulties attached to the current system for
post-doctoral contracts. A scientist from USA also presented the
American system for contractors, and an ESA representative presented
the official position of ESA regarding funding researchers. From
the talks as well as from the long open discussion which followed,
it was widely agreed that several typical rules for EU post-doc
contracts (their short duration, their mandatory mobility, their
age limit and their administrative and financial difficulties) not
only lead to serious problems in the private life of postdocs, but
essentially can have serious drawbacks on the follow-up of long-term
scientific developments, and could quickly result in a dramatic loss
of expertise, from the scale of individual institutes to the European
scientific community at large. Many participants and most of the young
researchers naturally agreed that new longer-term, renewable and stable
contracts are necessary. In order to create such types of contracts,
several fund raising initiative achieveable by the scientific community
were discussed. The development of better public outreach initiatives
on the European scale was a possibility which federated most of the
participants. The resulting conclusion on this session were transmitted
to the new board of the Solar Physics Section of the EAS/SPS.

---------------------------------------------------------
Title: Flare Genesis Experiment: magnetic topology of Ellerman bombs
Authors: Schmieder, B.; Pariat, E.; Aulanier, G.; Georgoulis, M. K.;
Rust, D. M.; Bernasconi, P. N.
2002ESASP.506..911S Altcode: 2002svco.conf..911S; 2002ESPM...10..911S
Flare Genesis Experiment (FGE), a balloon borne Observatory was launched
in Antarctica on January 10, 2000 and flew during 17 days. FGE consists
of an 80 cm Cassegrain telescope with an F/1.5 ultra-low-expansion
glass primary mirror and a crystalline silicon secondary mirror. A
helium-filled balloon carried the FGE to an altitude of 37 km
(Bernasconi et al. 2000, 2001). We select among all the observations a
set of high spatial and temporal resolution observations of an emerging
active region with numerous Ellerman bombs (EBs). Statistical and
morphology analysis have been performed. We demonstrate that Ellerman
bombs are the result of magnetic reconnection in the low chromosphere
by a magnetic topology analysis. The loci of EBs coincide with "bald
patches" (BPs). BPs are regions where the vector field is tangential to
the boundary (photosphere) along an inversion line. We conclude that
emerging flux through the photosphere is achieved through resistive
emergence of U loops connecting small Ω loops before rising in the
chromosphere and forming Arch Filament System (AFS).

---------------------------------------------------------
Title: Vector magnetic field observations of flux tube emergence
Authors: Schmieder, B.; Aulanier, G.; Pariat, E.; Georgoulis, M. K.;
Rust, D. M.; Bernasconi, P. N.
2002ESASP.505..575S Altcode: 2002IAUCo.188..575S; 2002solm.conf..575S
With Flare Genesis Experiment (FGE), a balloon borne Observatory high
spatial and temporal resolution vector magnetograms have been obtained
in an emerging active region. The comparison of the observations
(FGE and TRACE) with a linear force-free field analysis of the region
shows where the region is non-force-free. An analysis of the magnetic
topology furnishes insights into the existence of "bald patches"
regions (BPs are regions where the vector field is tangential to the
boundary (photosphere) along an inversion line). Magnetic reconnection
is possible and local heating of the chromopshere is predicted near the
BPs. Ellerman bombs (EBs) were found to coincide with few BPs computed
from a linear force-free extrapolation of the observed longitudinal
field. But when the actual observations of transverse fields were used
to identify BPs, then the correspondence with EB positions improved
significantly. We conclude that linear force-free extrapolations must
be done with the true observed vertical fields, which require the
measurement of the three components of the magnetic field.

---------------------------------------------------------
Title: Simulations of Interactions and Magnetic Reconnection Between
Solar Filaments
Authors: DeVore, C. R.; Antiochos, S. K.; Aulanier, G.
2002AAS...200.3720D Altcode: 2002BAAS...34..698D
It has long been known that pairs of filaments near each other on the
Sun's disk sometimes come into contact and interact. Under favorable
conditions, the two structures apparently link up to form a single,
larger filament. When conditions are unfavorable, on the other hand,
the filaments appear to avoid each other and retain their distinct
identities. Recent ground-based observational studies have shown
that a key requirement for linkage to occur is that the two filaments
possess the same chirality, or handedness. We have performed detailed
numerical experiments of pairs of interacting filaments within the
sheared-arcade model. In this model, the filament plasma resides in
the magnetic hammock formed in a strongly sheared field held down by an
overlying arcade. We considered four cases: like or unlike chirality of
the two filaments, and like or unlike polarity of the vertical magnetic
fields at their approaching ends. Only the case of like chirality and
unlike polarity produces any significant reconfiguration. The magnetic
structure is substantially modified, with reconnected field lines
extending over the entire combined length of the filaments. Low, closed
arcade fields form in the reconnection zone, forcing the newly linked
filament fields above them to rise and form a magnetic 'aneurysm.' Our
simple, bipolar configuration relaxes to a new equilibrium, consistent
with those cases in which the linked structure is observed to persist
stably after the interaction has passed. In the much more complex
magnetic environment of the solar corona, on the other hand, newly
linked filaments with such aneurysms sometimes are observed to erupt
promptly and violently. The removal of the restraining arcade fields, by
reconnection with the external field of the corona, is likely necessary
for eruption to occur. This research was supported by NASA and ONR.

---------------------------------------------------------
Title: The magnetic nature of wide EUV filament channels and their
role in the mass loading of CMEs
Authors: Aulanier, G.; Schmieder, B.
2002A&A...386.1106A Altcode:
Previous works have shown that dark and wide EUV filament channels
observed at lambda &lt; 912 Å, are due to absorption of EUV lines in
cool plasma condensations that are not observed in Hα . We extend this
interpretation and we address the issue of the possible injection of
their mass into CMEs, through the magneto-hydrostatic modeling in 3D
of one filament observed both in Hα and in EUV. The model parameters
are fixed so as to match the Hα observations only. Further comparison
of the model with the EUV observations reveal the magnetic nature of
the absorbing plasma condensations. They are formed in magnetic dips,
as for the filament itself. Opacity ratios and the hydrostatic condition
imply that the dips must be filled by cool material up to 1700 km, which
increases the filament mass by 50% as compared to Hα estimations. Far
from the filament, the absorbing condensations are located below 4 Mm
in altitude above the photosphere, on the edge of weak photospheric
parasitic polarities, within the lower parts of long field lines
overlaying the filament. By physical analogy with Hα filament feet,
we redefined these extended regions as EUV feet. The broadening of the
EUV filament channel is dominated by EUV feet, while the larger filling
of dips plays a non-negligible but minor role. Further implications
from this work are discussed, on the visibility and the geometry of
the condensations, on the existence of EUV filament channels in the
absence of filaments, on the loading of cool material into filament feet
through bald patch reconnection and on the complex geometry of the upper
prominence-corona transition region. The magnetic topology implies that
during the filament eruption, the mass of its wide EUV feet will not
contribute to the CME, whereas the extra mass provided by the large
filling of dips in the filament flux tube will be loaded into the CME.

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

---------------------------------------------------------
Title: Prominence Magnetic Dips in Three-Dimensional Sheared Arcades
Authors: Aulanier, G.; DeVore, C. R.; Antiochos, S. K.
2002ApJ...567L..97A Altcode:
We calculate the distribution of field-line dips in the
three-dimensional sheared arcade model for prominence/filament magnetic
fields. We consider both moderately and highly sheared configurations
computed by fully time-dependent three-dimensional MHD simulations
in which the field was relaxed to a static equilibrium end state. In
agreement with previous low spatial resolution measurements of the
magnetic field inside prominences, we find that for all configurations,
the field in the great majority of the calculated dips exhibits inverse
polarity. But for each configuration we also find well-defined narrow
regions with stable dips of normal polarity. These tend to be located
on the edges of the filament ends and at the top of the central part
of the prominence. This distinctive mixture of normal/inverse polarity
dips that we find in sheared arcades is not likely to be present in
twisted flux rope prominence models. Therefore, our results provide a
rigorous and unique observational test that can distinguish between
the two classes of models, as well as new predictions for future
high spatial resolution spectropolarimetric observations of filaments
and prominences.

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

---------------------------------------------------------
Title: Vertical structure of sunspots from THEMIS observations
Authors: Eibe, M. T.; Aulanier, G.; Faurobert, M.; Mein, P.; Malherbe,
J. M.
2002A&A...381..290E Altcode:
We have analysed two-dimensional spectro-polarimetric data taken
with the MSDP observing mode of THEMIS in the Na I D1
line to investigate the height variation of the magnetic field
in sunspot umbrae. From the Zeeman-induced circular polarization
measured at individual MSDP channels within the line profile, maps of
the longitudinal magnetic field have been computed. A method based
on Response Functions has been developed to estimate the depth in
the atmosphere at which the Zeeman measurements are originated,
thus providing the line-of-sight field at different altitudes
in the photosphere. The magnetogram corresponding to the deepest
level has served as a boundary condition to perform the potential
field extrapolation into the corona. We have found that the spatial
distribution of vertical field gradient contours predicted from
extrapolation is in qualitatively good agreement with that inferred from
observations. Quantitatively, however, the longitudinal field gradients
obtained with both methods differ about one order of magnitude, being
larger for observations. The origin of this discrepancy has been
discussed with respect to possible observation biases, as well as to
idealizations used for field extrapolation. This is a crucial problem
to be addressed in future work, and may have important implications
for the physics of how the magnetic field evolves through sunspots
and how the flux is distributed in the corona.

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

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

---------------------------------------------------------
Title: What can we learn from magnetic extrapolation above active
region and filament?
Authors: Schmieder, B.; Aulanier, G.
2002cosp...34E.458S Altcode: 2002cosp.meetE.458S
Observations of the Sun is done up to now in 2D. Magnetic
extrapolation technique allows us to have a 3D view of the magnetic
field lines. Global 3D structures can be visualized by using
such computations. Assuming linear force-free-field configuration
we have analyzed different active regions and filaments. In the
lfff approximation thevalue is constant for all the field lines
and is chosen in order to give the best global or local fit to the
structures projected on the solar surface observed in H, in UV lines
(EIT, TRACE) or in X rays (Yohkoh/SXT). With some examples we will
show some important results that we have obtained: 1. the existence
of a vertical gradient of the magnetic shear above active region
with filament (Schmieder et al 1996). 2. the existence of the same
value offitting the sheared filament and the spiral structure around
a sunspot, the existence of dips in the magnetic field strength at the
location of the filament channel in an AR (Schmieder et al 1991). 3. the
validity of chirality laws with dextral/sinistral filaments and negative
/positiveparameter according to the hemisphere (Aulanier et al 1999,
2000, Aulanier and Schmieder 2002)

---------------------------------------------------------
Title: Multi-wavelength research for the solar flare and associated
coronal mass ejection event on 1999 October 14
Authors: Wang, S.; Maia, D.; Pick, M.; Aulanier, G.
2002cosp...34E.102W Altcode: 2002cosp.meetE.102W
We present the results of our investigation on multi-wavelength
observations of the strong solar flare (X1/1N) that occured in complex
active regions on October 14, 1999. In association with this event
a partial halo coronal mass ejection (CME) is observed by the Solar
and Helospheric Observatory Large-Angle Spectrometric coronagraph
(LASCO/SOHO). The observation of the CME is preceded by radio
bursts detected by the Nançay radioheliograph (NRH) and other radio
telescapes. In the decimeter range, the radioheliograph shows two noise
storm (NS) sources prior to the event. After the onset of the flare four
emitting sources are detected contributing to the radio outburst. Two
of them were close to the two NS sources, but the other two were in
the west part of the complex active regions. Also a Moreton wave is
indentified in Hα data which propagated closely associated in time
with the position evolution of the radio emitting source in southeast
direction. The manifestations of global radio spectrum from 7.6 GHz to
1 MHz are a series of fast drifring bursts, metric wave type II burst
and some type III bursts. The time of the CME at one solar radius is
inferred that indicate the fact the CME is launched in close temporal
proximity with the flare and the radio bursts. Then a line force-free
field extrapolation is preformed using the Michelson Doppler Imager
(MDI) data as boundary conditions. The topology of the reconstruction
fields coincide well with the radio emitting sources. We interpret this
event including CME as the results of a certain magnetic instability.

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

---------------------------------------------------------
Title: Is the CME magnetic energy stored in coronal flux ropes ?
Authors: Aulanier, G.
2001AGUSM..SH41C06A Altcode:
MHD theory, coronograph and in situ solar wind observations are
consistent with a flux rope like topology for many CME's. However,
this does not permit to conclude that the pre-eruptive coronal
magnetic field does have this topology. This is because any erupting
fields must lead to the formation of a vertical current sheet, in
which reconnection can form the so-called coronal postflare loops,
as well as a large flux rope which surrounds the erupting fields,
which are ejected alltogether. The only physical property of the
pre-eruptive fields which is required for triggering a CME is that
they must be “stressed”, i.e. they must contain strong electric
currents. As prominences are the largest and best observed stressed
magnetic configurations of the solar atmosphere, and as they often
lead to CME's, they provide a unique opportunity for studying the
pre-CME magnetic field topology. Based on a compilation of old and
recent results, I will show that both magnetic and multi-wavelength
observations strongly support a uniform flux rope like topology for
prominences. Then, I will compare the predicted flux/twist/helicity
with the values measured in interplanetary magnetic clouds, and I
will discuss the role of the large scale fields for the development of
CME's. I will end on possible theoretical and observational prospectives
which should be achieved for the study of stressed fields in prominences
and in active regions (e.g. delta-spots).

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

---------------------------------------------------------
Title: Model Prediction for an Observed Filament
Authors: Aulanier, G.; Srivastava, N.; Martin, S. F.
2000ApJ...543..447A Altcode:
This paper presents the results of a “blind test” for modeling
the structure of an observed filament using the three-dimensional
magnetohydrostatic model recently developed by Aulanier et al. in
1999. The model uses a constant shear α, and it takes into account the
effects of pressure and gravity. The test consisted of predicting the
structure of a filament (observed in the southern hemisphere) with
a minimum observational input: only a line-of-sight magnetogram,
with a straight line drawn on it to show the location of the
filament, was provided. The filament was chosen by the observers
(N. S. and S. F. M.) because it had a definite overall left-handed
structural pattern known as sinistral, but the direction of component
of the magnetic field along the filament axis was uncertain from the
combination of Hα data and magnetograms. The modeler (G. A.) evaluated
and fixed the values of some of the free parameters of the model
while some others were varied in reasonable ranges. The Hα image
of the filament was revealed only after the modeling. For α&gt;0,
the three-dimensional distribution of magnetic dips computed by the
model fairly well reproduces the structure of the filament and its
barbs. Moreover, the models for which α&lt;0 do not match well the
observations. This study then shows the first successful theoretical
prediction for the magnetic field of an observed filament. It shows
that the method based on the Aulanier et al. model is a powerful tool,
not only for purposes of modeling, but also for prediction of the
chirality, helicity, and morphology of observed filaments.

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

---------------------------------------------------------
Title: The Topology and Evolution of the Bastille Day Flare
Authors: Aulanier, G.; DeLuca, E. E.; Antiochos, S. K.; McMullen,
R. A.; Golub, L.
2000ApJ...540.1126A Altcode:
On 1998 July 14, a class M3 flare occurred at 12:55 UT in AR 8270
near disk center. Kitt Peak line-of-sight magnetograms show that the
flare occurred in a δ spot. Mees vector magnetograms show a strong
shear localized near a portion of the closed neutral line around the
parasitic polarity of the δ spot. Observations of the flare in 171,
195, and 1600 Å have been obtained by TRACE, with ~=40 s temporal
and 0.5" spatial resolutions. They reveal that small-scale preflare
loops above the sheared region expanded and disappeared for more than
1 hr before flare maximum. During the flare, bright loops anchored in
bright ribbons form and grow. This occurs while large-scale dimmings,
associated with large expanding loops, develop on both sides of
the active region. This suggests that the flare was eruptive and
was accompanied by a coronal mass ejection (CME). Magnetic field
extrapolations reveal the presence of a null point in the corona, with
its associated “spine” field line, and its “fan” surface surrounding
the parasitic polarity. We show that while the whole event occurs,
the intersections of the “fan” and the “spine” with the photosphere
brighten and move continuously. The interpretation of the event shows
that the magnetic evolution of the eruptive flare is strongly coupled
with its surrounding complex topology. We discuss evidence supporting a
“magnetic breakout” process for triggering this eruptive flare. We
finally conclude that multipolar fields cannot be neglected in the
study and modeling of the origin of CMEs in the corona.

---------------------------------------------------------
Title: Hα and Soft X-Ray Brightening Events Caused by Emerging Flux
Authors: Tang, Y. H.; Li, Y. N.; Fang, C.; Aulanier, G.; Schmieder,
B.; Demoulin, P.; Sakurai, T.
2000ApJ...534..482T Altcode:
By using Yohkoh soft X-ray images, vector magnetograms, and Hα
filtergrams, the brightening event that occurred on 1994 May 18 has
been studied in detail. It occurred in a nearly potential large-scale
magnetic configuration as shown by the comparison between the magnetic
extrapolation (linear force-free field) and the large-scale soft
X-ray loops. This event is related to the emergence of a new magnetic
flux of about 3×1020 Mx. The impulsive enhancement of
the emerging flux occurs about 20 minutes before the peaks of the
Hα and soft X-ray brightening and lasts for about 10 minutes. This
brightening may be a signature of reconnection taking place between the
preexisting nonpotential loops and the new emerging small loops. The
magnetic energy provided by reconnection is likely to be stored in
the nonpotential loops and the emerging flux as implied by the vector
magnetograms. By using the electron temperature and the electron density
of the brightening event derived from the analysis of the Yohkoh data,
an energy budget has been estimated. The result indicates that the
energy needed can be reasonably provided by magnetic reconnection.

---------------------------------------------------------
Title: The Topology and Evolution of the Bastille Day Flare Observed
by TRACE
Authors: Aulanier, G.; Antiochos, S. K.; DeLuca, E. E.; McMullen,
R. A.; Golub, L.
2000SPD....31.1402A Altcode: 2000BAAS...32..846A
On July 14, 1998, a class M3 flare occurred at 12:55 UT in AR 8270
near disc center. Kitt Peak line-of-sight magnetograms show that the
flare occurred in a δ -spot. Mees vector magnetograms show a strong
shear localized near a portion of the closed neutral line around the
parasitic polarity of the δ -spot. Observations of the flare in 171
Angstroms, 195 Angstroms and 1600 Angstroms have been obtained by TRACE,
with ~= 40 s temporal and 0.5 arcsec spatial resolutions. They reveal
that small-scale pre-flare loops above the sheared region expanded and
disappeared for more than one hour before flare maximum. During the
flare, bright loops anchored in bright ribbons form and grow. This
occurs while large-scale dimmings, associated with large expanding
loops, develop on both sides of the AR. This suggests that the
flare was eruptive, and was accompanied by a coronal mass ejection
(CME). Magnetic field extrapolations reveal the presence of a null
point in the corona, with its associated “spine” field line, and
its “fan” surface surrounding the parasitic polarity. We show that
while the whole event occurs, the intersections of the “fan” and the
“spine” with the photosphere brighten and move continuously. The
interpretation of the event shows that the magnetic evolution of
the eruptive flare is strongly coupled with its surrounding complex
topology. We discuss evidence supporting a “magnetic breakout”
process for triggering this eruptive flare. We finally conclude that
multipolar fields cannot be neglected in the study and modeling of
the origin of CMEs in the corona. This work is supported, at SAO by
a NASA contract to Lockheed-Martin, and at NRL by NASA and ONR.

---------------------------------------------------------
Title: Brightening Event in Hα and Soft X-Ray on May 18, 1994
Authors: Tang, Y. H.; Li, Y. N.; Schmieder, B.; Aulanier, G.; Demoulin,
P.; Fang, C.; Sakurai, T.
2000AdSpR..25.1829T Altcode:
By using Yohkoh soft X-ray images, vector magnetograms and Hα
filtergrams, a brightening event that occurred on May 18, 1994 has
been studied in detail. It occurred in a nearly potential large-scale
magnetic configuration as shown by the comparisons between the magnetic
extrapolations (linear force-free field) and the large-scale soft
X-ray loops. This brightening event observed in Hα line and soft
X-ray seems to be related to new emerging magnetic flux with an
amount of photospheric magnetic flux of about 3× 1020
Mx. The emerging flux increases obviously about 20 minutes before the
Hα and soft X-ray brightening, and lasts for about 103
s. This brightening may be a signature of reconnection taking place
between the pre-existing loop and the new emerging small loops

---------------------------------------------------------
Title: 3-D Magnetic Configurations for Filaments and Flares: The
Role of “Magnetic Dips” and “Bald Patches”
Authors: Aulanier, G.; Schmieder, B.; van Driel-Gesztelyi, L.; Kucera,
T.; Démoulin, P.; Fang, C.; Mein, N.; Vial, J. -C.; Mein, P.; Tang,
Y. H.; Deforest, C.
2000AdSpR..26..485A Altcode:
The 3-D magnetic configuration of a filament and of a low energy
flare is reconstructed, using linear mag- netohydrostatic (lmhs)
extrapolations. In both cases, we find observational signatures
of energy release at the locations of computed “bald patches”
separatrices, characterised by field lines which are tangent to
the photosphere.The filament was observed on Sept. 25, 1996, in Hα
with the MSDP on the German VTT, Tenerife, as well as in Si IV with
SOHO/SUMER. It is modeled as a twisted flux-tube deformed by the
magnetic polarities observed with SOHO/MDI. The shape and location of
the computed dipped field lines are in good agreement with the shape of
the filament and its feet observed in Hα. Some “bald patches” (BPs)
are present where the distribution of dips reaches the photosphere. We
show that some of the large scale field lines rooted in BPs can be
related to bright fine structures in Si IV. We propose that the plasma
there is heated by ohmic dissipation from the currents expected to be
present along the BP separatrices.The flare was observed on May 18,
1994, in soft X-rays with Yohkoh/SXT, and in Hα at Mitaka (Japan). The
magnetic field is directly extrapolated from a photospheric magnetogram
from Kitt Peak Observatory. The intersections with the photosphere of
the computed separatrices match well the bright Hα ribbons. The later
are associated to three BPs, with overlaying dipped field lines. We
show that enhanced densities are present in these dips, which can be
correlated with dark Hα fibrils.Both cases show the importance of
dipped field lines and BPs in the solar atmosphere. Energy release
via ohmic dissipation as well as reconnection along BP separatrices
is proposed to provide heating observed as UV brightenings in filament
channels and even as small flares

---------------------------------------------------------
Title: Cme Associated with Transequatorial Loops and a Bald Patch
Flare
Authors: Delannée, C.; Aulanier, G.
1999SoPh..190..107D Altcode:
We study a flare which occurred on 3 November 1997 at 10:31 UT in
the vicinity of a parasitic polarity of AR 8100. Using SOHO/EIT 195
Å observations, we identify the brightening of thin transequatorial
loops connecting AR 8100 and AR 8102, and dimmings located between
the two active regions. Difference images highlight the presence
of a loop-like structure rooted near the flare location usually
called an EIT wave. The coronal magnetic field derived from potential
extrapolations from a SOHO/MDI magnetogram shows that the topology is
complex near the parasitic polarity. There, a `bald patch' (defined as
the locations where the magnetic field is tangent to the photosphere) is
present. We conclude that the flare was a `bald patch flare'. Moreover,
the extrapolation confirms that there is a large coronal volume filled
with transequatorial field lines interconnecting AR 8100 and AR 8102,
and overlaying the bald patch.

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

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

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

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

---------------------------------------------------------
Title: Filament channel structures in a SI IV line related to a 3d
magnetic model
Authors: Kucera, T. A.; Aulanier, G.; Schmieder, B.; Mein, N.; Vial,
J. -C.
1999SoPh..186..259K Altcode:
A recent 3D magnetic model of filament support (Aulanier and Démoulin,
1998) has shown that specific morphologies derived from the model, based
on SOHO/MDI magnetograms, match quite well with the observations of a
filament observed in Hα and Ca ii lines with the German telescope VTT
in Tenerife on 25 September 1996 (Aulanier et al., 1998, 1999a). Some
predictions of this model concern the filament channel. To continue the
comparison of model and data, we have investigated the same filament
region observed in ultraviolet by the SOHO spectrometers SUMER and
CDS. The elongated EUV fine structures in the filament channel observed
in the Si iv 1393.76 Å line by SUMER have similar orientations
and locations to features predicted by the model of Aulanier et
al. (1999a). These regions are near the bases of field lines which
tangentially join to the photosphere in so called 'bald patches' and
are parts of large arcades above the filament channel. In addition,
we consider the Si iv Doppler shifts in these structures and compare
them to what might be expected from the model field structure. Our
study also suggests that the filament has a very low opacity in Si iv,
lower than that of the O v line observed by CDS.

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

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

---------------------------------------------------------
Title: The NOAA AR 6718 magnetic field extrapolation with localized
current filaments.
Authors: Karlický, M.; Démoulin, P.; Aulanier, G.; van
Driel-Gesztelyi, L.; Hénoux, J. C.; Jirička, K.
1999joso.proc...97K Altcode:
The 3-D extrapolation of magnetic field lines of the July 11, 1991
Kitt Peak magnetogram shows a differential magnetic field shear in
the NOAA 6718 active region. A new combined extrapolation technique,
which includes localized current filaments is suggested and applied in
modelling of this shear. First, the potential field extrapolation is
made and then force-free current paths for several current filaments
in specific positions are computed. It is shown that with the electric
current increase the localized magnetic field shear is increasing. The
total electric current in 16 current filaments is considered up to
1.2×1012A.

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

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

---------------------------------------------------------
Title: Modelisation tridimensionnelle de configurations magnetiques
a l'equilibre appliquees aux observations d'eruptions et de
protuberances solaires

---------------------------------------------------------
Title: Modelisation tridimensionnelle de
configurations magnetiques a l'equilibre appliquees aux observations
d'eruptions et de protuberances solaires

---------------------------------------------------------
Title: Three-dimensional
modeling of equilibrium magnetic configurations applied to
observations of solar eruptions and protuberances;
Authors: Aulanier, Guillaume
1998PhDT.......229A Altcode:
No abstract at ADS

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

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

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

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

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

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

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

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

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

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

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