demoulin

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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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.

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

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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.

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

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

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

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

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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.

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

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

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

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

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

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

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

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Title: Tracking Solar Active Region Outflow Plasma from Its Source
to the Near-Earth Environment
Authors: Culhane, J. L.; Brooks, D. H.; van Driel-Gesztelyi, L.;
Démoulin, P.; Baker, D.; DeRosa, M. L.; Mandrini, C. H.; Zhao, L.;
Zurbuchen, T. H.
2014SoPh..289.3799C Altcode: 2014SoPh..tmp...90C; 2014arXiv1405.2949C
Seeking to establish whether active-region upflow material contributes
to the slow solar wind, we examine in detail the plasma upflows from
Active Region (AR) 10978, which crossed the Sun's disc in the interval 8
to 16 December 2007 during Carrington rotation (CR) 2064. In previous
work, using data from the Hinode/EUV Imaging Spectrometer, upflow
velocity evolution was extensively studied as the region crossed the
disc, while a linear force-free-field magnetic extrapolation was used
to confirm aspects of the velocity evolution and to establish the
presence of quasi-separatrix layers at the upflow source areas. The
plasma properties, temperature, density, and first ionisation potential
bias [FIP-bias] were measured with the spectrometer during the disc
passage of the active region. Global potential-field source-surface
(PFSS) models showed that AR 10978 was completely covered by the
closed field of a helmet streamer that is part of the streamer
belt. Therefore it is not clear how any of the upflowing AR-associated
plasma could reach the source surface at 2.5 R⊙ and
contribute to the slow solar wind. However, a detailed examination of
solar-wind in-situ data obtained by the Advanced Composition Explorer
(ACE) spacecraft at the L1 point shows that increases in
O7+/O6+, C6+/C5+, and Fe/O -
a FIP-bias proxy - are present before the heliospheric current-sheet
crossing. These increases, along with an accompanying reduction in
proton velocity and an increase in density are characteristic of
both AR and slow-solar-wind plasma. Finally, we describe a two-step
reconnection process by which some of the upflowing plasma from the
AR might reach the heliosphere.

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

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

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

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

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

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

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Title: Coronal Magnetic Reconnection Driven by CME Expansion—the
2011 June 7 Event
Authors: van Driel-Gesztelyi, L.; Baker, D.; Török, T.; Pariat, E.;
Green, L. M.; Williams, D. R.; Carlyle, J.; Valori, G.; Démoulin,
P.; Kliem, B.; Long, D. M.; Matthews, S. A.; Malherbe, J. -M.
2014ApJ...788...85V Altcode: 2014arXiv1406.3153V
Coronal mass ejections (CMEs) erupt and expand in a magnetically
structured solar corona. Various indirect observational pieces of
evidence have shown that the magnetic field of CMEs reconnects with
surrounding magnetic fields, forming, e.g., dimming regions distant
from the CME source regions. Analyzing Solar Dynamics Observatory
(SDO) observations of the eruption from AR 11226 on 2011 June 7, we
present the first direct evidence of coronal magnetic reconnection
between the fields of two adjacent active regions during a CME. The
observations are presented jointly with a data-constrained numerical
simulation, demonstrating the formation/intensification of current
sheets along a hyperbolic flux tube at the interface between the CME
and the neighboring AR 11227. Reconnection resulted in the formation of
new magnetic connections between the erupting magnetic structure from
AR 11226 and the neighboring active region AR 11227 about 200 Mm from
the eruption site. The onset of reconnection first becomes apparent
in the SDO/AIA images when filament plasma, originally contained
within the erupting flux rope, is redirected toward remote areas in
AR 11227, tracing the change of large-scale magnetic connectivity. The
location of the coronal reconnection region becomes bright and directly
observable at SDO/AIA wavelengths, owing to the presence of down-flowing
cool, dense (1010 cm-3) filament plasma in its
vicinity. The high-density plasma around the reconnection region is
heated to coronal temperatures, presumably by slow-mode shocks and
Coulomb collisions. These results provide the first direct observational
evidence that CMEs reconnect with surrounding magnetic structures,
leading to a large-scale reconfiguration of the coronal magnetic field.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

---------------------------------------------------------
Title: The standard flare model in three dimensions. III. Slip-running
reconnection properties
Authors: Janvier, M.; Aulanier, G.; Pariat, E.; Démoulin, P.
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.

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

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

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

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

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

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

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

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

---------------------------------------------------------
Title: The standard flare model in three dimensions. II. Upper limit
on solar flare energy
Authors: Aulanier, G.; Démoulin, P.; Schrijver, C. J.; Janvier, M.;
Pariat, E.; Schmieder, B.
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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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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.

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

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

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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.

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

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

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

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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].

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Title: Long-Term Trend of Carbon Tetrachloride (CCl4)
from Ground-Based High Resolution Infrared Solar Spectra Recroded
at the Jungfraujoch
Authors: Rinsland, C.; Mahieu, E.; Demoulin, P.; Zander, R.; Chiou,
L.; Hartmann, J. -M.
2010mss..confEMJ10R Altcode:
The long-term trend of carbon tetrachloride (CCl4)
has been retrieved from infrared high resolution solar absorption
spectra encompassing the 1999 to 2010 time period. The measurements
were recorded with a Fourier transform spectrometer at the northern
mid-latitude, high altitude Jungfraujoch station in Switzerland
(46.5°N latitude, 8.0°E longitude, 3580 m altitude). Total
columns were derived from the region of the strong CCl4
\upsilon3 band at 794 cm-1 accounting for all
interfering molecules (e.g. H2O, O3) with
significant improvement in the residuals obtained by also taking
into account the line mixing in a nearby CO2 Q branch, a
procedure not implemented in previous remote sensing CCl4
retrievals though its importance has been noted in several papers. The
time series shows a statistically-significant long-term decrease in
the CCl4 total atmospheric burden of (-1.18 ±0.10 %/yr),
at the 95% confidence level, using 2005 as reference. Furthermore,
fit to the total column data set also reveals a seasonal cycle with
a peak-to-peak amplitude of 10.2%, with minimum and maximum values
found in mid-February and early August, respectively. This seasonal
modulation can however be attributed to tropopause height changes
throughout the season. The results quantify the continued impact of the
regulations implemented by the Montreal Protocol and its strengthening
amendments and adjustments for a molecule with high global warming
potential. Although a statistically significant decrease in the total
column is inferred, the CCl4 molecule remains an important
contributor to the stratospheric chlorine budget and burden.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

---------------------------------------------------------
Title: Nonlinear Force-free Field Modeling of a Solar Active Region
around the Time of a Major Flare and Coronal Mass Ejection
Authors: Schrijver, C. J.; DeRosa, M. L.; Metcalf, T.; Barnes, G.;
Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann, T.;
Wheatland, M. S.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann,
M.; Kusano, K.; Régnier, S.; Thalmann, J. K.
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: CME-related dimmings as a signature of interplanetary magnetic
cloud footpoints
Authors: Mandrini, Cristina H.; Soledad Nakwacki, Ms Maria; Attrill,
Gemma; van Driel-Gesztelyi, Lidia; Dasso, Sergio; Demoulin, Pascal
2008cosp...37.1900M Altcode: 2008cosp.meet.1900M
Coronal dimmings are often present on both sides of erupting magnetic
configurations. It has been suggested that dimmings mark the location
of the footpoints of ejected flux ropes and, thus, their magnetic
flux can be used as a proxy for the flux involved in the ejection. If
so, this quantity can be compared to the flux in the associated
interplanetary magnetic cloud to find clues about the origin of the
ejected flux rope. In the context of this physical interpretation,
we analyse several events, flares and coronal mass ejections (CMEs),
for which we can find their interplanetary counterpart. We combine
SOHO/Extreme Ultraviolet Imaging Telescope data and Michelson Doppler
Imager magnetic maps to identify and measure the flux in the dimming
regions. We model the associated clouds and compute their magnetic
flux using in situ observations. We find that the magnetic fluxes of
the dimmings and magnetic clouds are compatible in some cases; though
this is not the case for large-scale events and eruptions that occur
in regions that are not isolated from other flux concentrations. We
conclude that the interpretation of dimmings requires a deeper analysis
of the global magnetic field configuration, since at least a fraction
of the dimmed regions could be formed by reconnection between the
erupting field and the surrounding magnetic structures.

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

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

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

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

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

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

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

---------------------------------------------------------
Title: Progressive Transformation of a Flux Rope to an
ICME. Comparative Analysis Using the Direct and Fitted Expansion
Methods
Authors: Dasso, S.; Nakwacki, M. S.; Démoulin, P.; Mandrini, C. H.
2007SoPh..244..115D Altcode: 2007arXiv0706.2889D
The solar wind conditions at one astronomical unit (AU) can be strongly
disturbed by interplanetary coronal mass ejections (ICMEs). A subset,
called magnetic clouds (MCs), is formed by twisted flux ropes that
transport an important amount of magnetic flux and helicity, which
is released in CMEs. At 1 AU from the Sun, the magnetic structure
of MCs is generally modeled by neglecting their expansion during
the spacecraft crossing. However, in some cases, MCs present a
significant expansion. We present here an analysis of the huge
and significantly expanding MC observed by the Wind spacecraft
during 9 - 10 November 2004. This MC was embedded in an ICME. After
determining an approximate orientation for the flux rope using the
minimum variance method, we obtain a precise orientation of the cloud
axis by relating its front and rear magnetic discontinuities using a
direct method. This method takes into account the conservation of the
azimuthal magnetic flux between the inbound and outbound branches and
is valid for a finite impact parameter (i.e., not necessarily a small
distance between the spacecraft trajectory and the cloud axis). The
MC is also studied using dynamic models with isotropic expansion. We
have found (6.2±1.5)×1020 Mx for the axial flux and
(78±18)×1020 Mx for the azimuthal flux. Moreover, using
the direct method, we find that the ICME is formed by a flux rope (MC)
followed by an extended coherent magnetic region. These observations
are interpreted by considering the existence of a previously larger
flux rope, which partially reconnected with its environment in the
front. We estimate that the reconnection process started close to the
Sun. These findings imply that the ejected flux rope is progressively
peeled by reconnection and transformed to the observed ICME (with a
remnant flux rope in the front part).

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

---------------------------------------------------------
Title: Why to determine the magnetic helicity in corona and
interplanetary medium?
Authors: Luoni, M. L.; Dasso, S.; Mandrini, C. H.; van Driel-Gesztelyi,
L.; Démoulin, P.
2003BAAA...46....8L Altcode:
Magnetic clouds are huge objects that travel in the interplanetary
medium, transporting magnetic helicity (MH) produced by the Sun. Since
the dissipation time of MH is much larger than the typical time
associated with the dynamical processes in the solar corona and the
heliosphere, MH is the natural magnetohydrodinamic (MHD) magnitude
to compare interplanetary manifestations with the associated solar
processes. In this work we study an active region that produced a
coronal mass ejection (CME). We model the coronal magnetic field
using a linear force free approach, and we calculate the magnetic
flux and the variation of MH, before and after the ejection of
the CME. We model also the magnetic field configuration of the
associated interplanetary cloud, using several cylindrical models,
and estimate the flux and the content of MH. Finally, we compare the
coronal and the interplanetary values for the flux and the MH, and we
find a very good agreement. The coronal flux is 1022Mx,
while the magnetic flux for the cloud is around 1021Mx
(∼ 10% of the coronal flux, as typically observed). The variation
of the coronal MH turns out to be 3x1042Mx2,
while we obtain that the MH contained in the magnetic cloud is in the
range (2-8)x1042Mx2. Our results indicate that
MH is a very useful tool to link phenomena in very different regimes
and can be used to constrain both coronal and interplanetary models.

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

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

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

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

---------------------------------------------------------
Title: The Magnetic Helicity Budget of a cme-Prolific Active Region
Authors: Green, L. M.; López fuentes, M. C.; Mandrini, C. H.;
Démoulin, P.; Van Driel-Gesztelyi, L.; Culhane, J. L.
2002SoPh..208...43G Altcode:
Coronal mass ejections (CMEs) are thought to be the way by which the
solar corona expels accumulated magnetic helicity which is injected
into the corona via several methods. DeVore (2000) suggests that a
significant quantity is injected by the action of differential rotation,
however Démoulin et al. (2002b), based on the study of a simple bipolar
active region, show that this may not be the case. This paper studies
the magnetic helicity evolution in an active region (NOAA 8100) in
which the main photospheric polarities rotate around each other during
five Carrington rotations. As a result of this changing orientation of
the bipole, the helicity injection by differential rotation is not a
monotonic function of time. Instead, it experiences a maximum and even
a change of sign. In this particular active region, both differential
rotation and localized shearing motions are actually depleting the
coronal helicity instead of building it. During this period of five
solar rotations, a high number of CMEs (35 observed, 65 estimated)
erupted from the active region and the helicity carried away has
been calculated, assuming that each can be modeled by a twisted flux
rope. It is found that the helicity injected by differential rotation
(≈−7×1042 Mx2) into the active region cannot
provide the amount of helicity ejected via CMEs, which is a factor 5
to 46 larger and of the opposite sign. Instead, it is proposed that
the ejected helicity is provided by the twist in the sub-photospheric
part of the magnetic flux tube forming the active region.

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

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

---------------------------------------------------------
Title: The distribution of peculiar active regions along two solar
cycles
Authors: Mandrini, C. H.; López Fuentes, M. C.; Démoulin, P.;
van Driel-Gesztelyi, L.
2002ESASP.477...27M Altcode: 2002scsw.conf...27M
We perform a statistical study of the spatial and temporal distribution
of "peculiar" active regions (ARs) along solar cycles 21 and 22. ARs
usually appear in the photosphere in the form of bipolar concentrations
of magnetic flux, by "peculiar" we mean regions in which the the
main polarities rotate one around the other along several solar
rotations. Our results show that these regions are spatially distributed
as usual ARs when no selection on their magnetic flux is applied. When
classified according to their flux, the latitudinal distribution of
ARs above 1022 Mx closely follow the butterfly diagram;
while those with lower flux are more randomly distributed. The number
of rotating ARs follow the activity cycle, with a tendency to dual-peak
maxima.

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

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

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

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

---------------------------------------------------------
Title: Energetics of the 18 May 1994 brightening event
Authors: Tang, Y. H.; Li, Y. N.; Fang, C.; Schmieder, B.; Aulanier,
G.; Demoulin, P.
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: Surges y Arch Filament Systems: Una topología inusual
Authors: Mandrini, C. H.; Démoulin, P.; Schmieder, B.; Deng, Y. Y.;
Rudawy, P.
2002BAAA...45...17M Altcode:
Active region (AR) NOAA 7968 was observed during its solar disk transit
by several instruments on ground and on board satellites (Yohkoh and
SOHO). During its emergence Arch Filament Systems (AFS) linking the
polarities of the main bipole were observed. During its decay a surge
(a chromospheric confined mass ejection) occurred to the South of the
positive polarity of this bipole. We model the AR magnetic field in the
magnetohydrostatic approach and compute its topology. We find that the
evolution of both events, AFS and surge, agrees with magnetic field
reconnection occurring in field lines that are tangentially touching
the photosphere. These lines define the so called “bald patches”
(BPs). In previous studies these topological structures have been found
to be related to small flares and transition region brightenings. Our
results point out the importance of BPs in a wider phenomenological
context and show that current sheets can develop and efficiently
dissipate in the chromosphere.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

---------------------------------------------------------
Title: Magnetic Field and Plasma Scaling Laws: Their Implications
for Coronal Heating Models
Authors: Mandrini, C. H.; Démoulin, P.; Klimchuk, J. A.
2000ApJ...530..999M Altcode:
In order to test different models of coronal heating, we have
investigated how the magnetic field strength of coronal flux
tubes depends on the end-to-end length of the tube. Using
photospheric magnetograms from both observed and idealized
active regions, we computed potential, linear force-free, and
magnetostatic extrapolation models. For each model, we then
determined the average coronal field strength, &lt;B&gt;, in
approximately 1000 individual flux tubes with regularly spaced
footpoints. Scatter plots of &lt;B&gt; versus length, L, are
characterized by a flat section for small L and a steeply declining
section for large L. They are well described by a function of the form
log=C1+C2logL+C3/2log(L2+S2),
where C2~0, -3&lt;=C3&lt;=-1, and 40&lt;=S&lt;=240
Mm is related to the characteristic size of the active region. There
is a tendency for the magnitude of C3 to decrease as the
magnetic complexity of the region increases. The average magnetic
energy in a flux tube, &lt;B2&gt;, exhibits a similar
behavior, with only C3 being significantly different. For
flux tubes of intermediate length, 50&lt;=L&lt;=300 Mm, corresponding
to the soft X-ray loops in a study by Klimchuk &amp; Porter (1995),
we find a universal scaling law of the form ~Lδ, where
δ=-0.88+/-0.3. By combining this with the Klimchuk &amp; Porter result
that the heating rate scales as L-2, we can test different
models of coronal heating. We find that models involving the gradual
stressing of the magnetic field, by slow footpoint motions, are in
generally better agreement with the observational constraints than are
wave heating models. We conclude, however, that the theoretical models
must be more fully developed and the observational uncertainties must
be reduced before any definitive statements about specific heating
mechanisms can be made.

---------------------------------------------------------
Title: Brightening Event in Hα and Soft X-Ray on May 18, 1994
Authors: Tang, Y. H.; Li, Y. N.; Schmieder, B.; Aulanier, G.; Demoulin,
P.; Fang, C.; Sakurai, T.
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: Structuring of the Solar Plasma by the Magnetic Field
Authors: Demoulin, Pascal; Klein, Karl-Ludwig
2000LNP...553...99D Altcode: 2000tech.conf...99D
This paper presents a simplified overview of the role of the magnetic
field in the solar atmosphere. The magnetic field emanating from
the solar interior governs energy transport and plasma motions in
the outer solar atmosphere. Thereby it creates structure, such as
coronal holes, loops and prominences, and the dynamical phenomena
known as coronal mass ejections and flares. The magnetic field is also
thought to be at the origin of the coronal heating, so of the corona
itself. An overview of atmospheric structure is presented, followed
by illustrations on present ideas on the interaction between plasma
and magnetic field. The physical conditions in the corona are briefly
compared to those in the magnetosphere. The emphasis is then put on the
energetic processes from the largest ones (coronal mass ejections) over
flares and X-ray bright points to coronal heating. In all cases magnetic
reconnection is likely to play a key role. Solar prominences are then
described because their observations provide important information on
the surrounding coronal magnetic field. Finally the implications of
processes in the convection zone on the physics of the corona and of
the interplanetary medium are illustrated for the case of formation,
storage and ejection of twisted magnetic flux tubes.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

---------------------------------------------------------
Title: Bright Points and Subflares in Ultraviolet Lines and X-Rays
Authors: Rovira, M.; Schmieder, B.; Démoulin, P.; Simnett, G. M.;
Hagyard, M. J.; Reichmann, E.; Tandberg-Hanssen, E.
1999ApJ...510..474R Altcode:
We have analyzed an active region which was observed in Hα
(Multichannel Subtractive Double Pass Spectrograph), in UV lines
(SMM/UVSP), and in X-rays (SMM/HXIS). In this active region there
were only a few subflares and many small bright points visible in UV
and in X-rays. Using an extrapolation based on the Fourier transform,
we have computed magnetic field lines connecting different photospheric
magnetic polarities from ground-based magnetograms. Along the magnetic
inversion lines we find two different zones: (1) a high-shear region
(&gt;70°) where subflares occur, and (2) a low-shear region along
the magnetic inversion line where UV bright points are observed. In
these latter regions the magnetic topology is complex with a mixture
of polarities. According to the velocity field observed in the Si IV
λ1402 line and the extrapolation of the magnetic field, we notice that
each UV bright point is consistent with emission from low-rising loops
with downflows at both ends. We notice some hard X-ray emissions above
the bright-point regions with temperatures up to 8 × 106 K,
which suggests some induced reconnection due to continuous emergence of
new flux. This reconnection is also enhanced by neighboring subflares.

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

---------------------------------------------------------
Title: The NOAA AR 6718 magnetic field extrapolation with localized
current filaments.
Authors: Karlický, M.; Démoulin, P.; Aulanier, G.; van
Driel-Gesztelyi, L.; Hénoux, J. C.; Jirička, K.
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: The Effect of Curvature on Flux-Rope Models of Coronal Mass
Ejections
Authors: Lin, J.; Forbes, T. G.; Isenberg, P. A.; Démoulin, P.
1998ApJ...504.1006L Altcode:
The large-scale curvature of a flux rope can help propel it outward
from the Sun. Here we extend previous two-dimensional flux-rope models
of coronal mass ejections to include the curvature force. To obtain
analytical results, we assume axial symmetry and model the flux rope as
a torus that encircles the Sun. Initially, the flux rope is suspended
in the corona by a balance between magnetic tension, compression,
and curvature forces, but this balance is lost if the photospheric
sources of the coronal field slowly decay with time. The evolution of
the system shows catastrophic behavior as occurred in previous models,
but, unlike the previous models, flux ropes with large radii are more
likely to erupt than ones with small radii. The maximum total magnetic
energy that can be stored before equilibrium is lost is 1.53 times the
energy of the potential field, and this value is less than the limiting
value of 1.662 for the fully opened field. As a consequence, the loss
of ideal MHD equilibrium that occurs in the model cannot completely
open the magnetic field. However, the loss of equilibrium does lead
to the sudden formation of a current sheet, and if rapid reconnection
occurs in this sheet, then the flux rope can escape from the Sun. We
also find that the field can gradually become opened without suffering
any loss of equilibrium if the photospheric field strength falls
below a critical value. This behavior is analogous to the opening of
a spherically symmetric arcade in response to a finite amount of shear.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

---------------------------------------------------------
Title: 3D Magnetic Reconnection at an X-Ray Bright Point
Authors: Mandrini, C. H.; Démoulin, P.; Van Driel-Gesztelyi, L.;
Schmieder, B.; Cauzzi, G.; Hofmann, A.
1996SoPh..168..115M Altcode:
On May 1, 1993, a flaring X-ray bright point (XBP) was observed for
about 16 hours in the old, disintegrating, bipolar active region (AR)
NOAA 7493. During this period, a minor magnetic bipole (1020
Mx) emerged in the region. We have found observational evidence showing
that the XBP brightenings were due to magnetic reconnection between
the new bipole and pre-existing plage fields. The aim of the present
work is to substantiate with magnetic modelling what has been shown
by the observations. For this purpose we extrapolate the observed
photospheric magnetic fields in the linear force-free approximation
and follow its evolution during the lifetime of the XBP. From the
computed coronal field lines we determine the location of regions of
drastic change in field-line linkage, called `quasi-separatrix layers'
or QSLs. QSLs are open layers that behave physically like separatrices:
the break down of ideal magnetohydrodynamics and the release of free
magnetic energy may occur at these locations when their thickness
is small enough. The extrapolated field lines, with photospheric
footpoints on both sides of QSLs, match the observed chromospheric and
coronal structures (arch filament system, XBP and faint X-ray loops
(FXL)). We study also the evolution of the width of the QSL located
over the new negative polarity pore: the calculated QSL is very thin
(typically less than 100 m) during the lifetime of the XBP, but becomes
much thicker (≥ 104 m) after the XBP has faded. Furthermore
we show that peaks in X-ray brightness propagate along the FXL with a
velocity of ≈ 670 km s-1, starting from the XBP location,
implying that the energy is released where the emerging bipole impacts
against pre-existing coronal loops. We discuss the possible mechanism
of energy transport and conclude that the energy is conducted to the
remote footpoints of the FXL by a thermal front. These results strongly
support the supposition that the XBP brightness and flaring are due
to the interaction of different flux systems, through 3D magnetic
reconnection, at QSLs.

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

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

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

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

---------------------------------------------------------
Title: Las fulguraciones como manifestación de reconexión en el
campo magnético solar
Authors: Bagalá, L. G.; Mandrini, M. C.; Rovira, M. G.; Démoulin, P.
1996BAAA...40R...2B Altcode:
Las fulguraciones solares son fenómenos transitorios de liberación
de energía que se desarrollan en las estructuras magnéticas
de las regiones activas del Sol. Las fulguraciones pueden llegar
a liberar hasta 1032 erg en 100 seg. en todo el rango
electromagnético, y acelerar partículas. En este trabajo mostramos que
la ubicación de los abrillantamientos en Hα de diversas fulguraciones
está relacionado con las propiedades de las conexiones de las
líneas del campo magnético de la región, como se espera por las
teorías de reconexión en 3D recientemente desarrolladas (Démoulin
et al, 1996a). El campo magnético coronal se extrapola del campo
fotosférico observado suponiendo una configuración libre de fuerzas
lineal. Por medio de un algoritmo se determinan las regiones donde
existe un cambio drástico en la conectividad de las líneas de campo
(límites “cuasi-discontinuos”, o cuasi-separatrices CS). Las CS
son bandas abiertas que identifican zonas donde el campo magnético se
reconectará con más probabilidad y, siempre que las mismas sean lo
suficientemente finas, se producirá allíla liberación de energía
proveniente del campo magnético. Hemos encontrado que en todas las
regiones fulgurantes estudiadas (Démoulin et al, 1996b) existen CS
en los mismos lugares donde se observaron los abrillantamientos en
Hα. Allídonde coinciden los abrillantamientos con las CS, éstas
tienen un espesor menor que 1 Mm. Las líneas de campo coronales
extrapoladas de nuestro modelo tienen sus orígenes fotosféricos a
ambos lados de las CS, como se espera dados los recientes estudios
de reconexión magnética en 3D. Estos resultados ponen a prueba los
modelos presentes sobre fulguraciones solares.

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

---------------------------------------------------------
Title: Reconexión magnética en una región activa en decaimiento
Authors: Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.;
Schmieder, B.; Bagalá, L. G.; Rovira, M. G.
1996BAAA...40....5M Altcode:
Se han obtenido observaciones desde Tierra (Hα y magnetogramas)
coordinadas con el Soft X-ray Telescope (SXT), a bordo del satélite
japonés Yohkoh, de una región activa bipolar en decaimiento. Estos
datos constituyen la base para el estudio de un punto brillante en rayos
X (PBX) y de la actividad relacionada con el mismo en distintas capas
de la atmósfera solar. Las observaciones muestran que el PBX está
relacionado con la aparición de un bipolo menor (~ 1020 Mx)
y que su abrillantamiento continuo, así como sus aumentos de brillo
esporádicos (“fulguraciones"), son el resultado de la reconexión
entre el pequeño arco emergente (visto en Hα como un sistema de
filamentos arqueados, SFA) y arcos mayores asociados al campo facular
preexistente. Se ha extrapolado el campo magnético observado en la
aproximación libre de fuerzas lineal y se ha seguido su evolución
a lo largo de la vida del PBX. Se ha calculado la posición de las
cuasiseparatrices (CSs) a partir del campo modelado. Las líneas de
campo extrapoladas, cuyas bases fotosféricas se encuentran a ambos
lados de las CSs, están de acuerdo con las estructuras cromosféricas
y coronales observadas. Se ha calculado el espesor de la CD ubicada
a lo largo de la polaridad negativa emergente, encontrándose que su
variación está de acuerdo con la evolución de la intensidad del PBX;
la CS es muy delgada durante la vida del PBX (~ 100 m), mientras que
su espesor aumenta considerablemente (&gt;= 10^4 m) cuando el PBX
desaparece de las imágenes del SXT. Estos resultados señalan que
el abrillantamiento y las “fulguraciones" de este PBX se deben al
proceso de reconexión en 3D que tiene lugar en las CSs.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

---------------------------------------------------------
Title: Ground-Based Infrared Measurements of HNO3 Total
Column Abundances: Long-Term Trend and Variability
Authors: Rinsland, C. P.; Zander, R.; Demoulin, P.
1991JGR....96.9379R Altcode:
The long-term trend and variability of the total column amount of
atmospheric nitric acid (HNO3) have been investigated
based on time series of infrared solar absorption spectra recorded
at two remote high-altitude sites, the International Scientific
Station of the Jungfraujoch (ISSJ) in the Swiss Alps (altitude
3.6 km, latitude 46.5°N, longitude 8.0°E) and the National Solar
Observatory McMath solar telescope facility on Kitt Peak (altitude
2.1 km, latitude 31.9°N, longitude 111.6°W), southwest of Tucson,
Arizona. The HNO3 ν5 band Q branch at 879.1 cm-1
and three P branch manifolds near 869 cm-1 were analyzed
using a nonlinear least squares spectral fitting technique and a
consistent set of spectroscopic line parameters. The ISSJ measurements
evaluated in the present work consist of two solar spectra recorded
with a grating spectrometer in June 1951 and a set of observations
obtained with a high-resolution Fourier transform spectrometer between
June 1986 and June 1990. The modern ISSJ measurements show a ∼20%
peak-to-peak amplitude seasonal cycle with a winter maximum superimposed
on significant variability and a summer minimum; the June results
from 1986 to 1990 are both higher and lower than the two retrieved
June 1951 HNO3 total column amounts. The fitted trend,
(-0.16±0.50)% yr-1, 2σ, indicates that there has been no
detectable change in the HNO3 total column over the last 4
decades. The Kitt Peak measurements, recorded with a high-resolution
Fourier transform spectrometer between December 1980 and June 1990,
also show marked variability in the HNO3 total column,
but in contrast to the ISSJ measurements, no obvious seasonal cycle
is observed. The deduced trend in the total column above Kitt Peak,
(-0.8±1.6)% yr-1, 2σ, is consistent with the ISSJ time
series of measurements, in that no significant HNO3 long-term
trend has been found. The sets of measurements from the two sites
are compared with each other and with previously published results,
with emphasis on the reported variability of HNO3 and the
changes in the HNO3 total column with season and latitude.

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

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

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

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

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

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

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

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

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

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

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

---------------------------------------------------------
Title: Structure et stabilité thermique et magnétique des
protubérances solaires

---------------------------------------------------------
Title: Structure et stabilité thermique et
magnétique des protubérances solaires

---------------------------------------------------------
Title: Thermal and magnetic
structure and stability of solar prominences;
Authors: Démoulin, Pascal
1989PhDT.......141D Altcode:
No abstract at ADS

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

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

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

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

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

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

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

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

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

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

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

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

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