Author name code: demoulin ADS astronomy entries on 2022-09-14 author:"Demoulin, Pascal" ------------------------------------------------------------------------ Title: Over-expansion of coronal mass ejections modelled using 3D MHD EUHFORIA simulations Authors: Verbeke, Christine; Schmieder, Brigitte; Démoulin, Pascal; Dasso, Sergio; Grison, Benjamin; Samara, Evangelia; Scolini, Camilla; Poedts, Stefaan Bibcode: 2022AdSpR..70.1663V Altcode: 2022arXiv220703168V Coronal mass ejections (CMEs) are large scale eruptions observed close to the Sun. They are travelling through the heliosphere and possibly interacting with the Earth environment creating interruptions or even damaging new technology instruments. Most of the time their physical conditions (velocity, density, pressure) are only measured in situ at one point in space, with no possibility to have information on the variation of these parameters during their journey from Sun to Earth. Our aim is to understand the evolution of internal physical parameters of a set of three particular fast halo CMEs. These CMEs were launched between 15 and 18 July 2002. Surprisingly, the related interplanetary CMEs (ICMEs), observed near Earth, have a low, and in one case even very low, plasma density. We use the EUropean Heliosphere FORecasting Information Asset (EUHFORIA) model to simulate the propagation of the CMEs in the background solar wind by placing virtual spacecraft along the Sun--Earth line. We set up the initial conditions at 0.1 au, first with a cone model and then with a linear force free spheromak model. A relatively good agreement between simulation results and observations concerning the speed, density and arrival times of the ICMEs is obtained by adapting the initial CME parameters. In particular, this is achieved by increasing the initial magnetic pressure so that a fast expansion is induced in the inner heliosphere. This implied the develop First, we show that a magnetic configuration with an out of force balance close to the Sun mitigates the EUHFORIA assumptions related to an initial uniform velocity. Second, the over-expansion of the ejected magnetic configuration in the inner heliosphere is one plausible origin for the low density observed in some ICMEs at 1 au. The in situ observed very low density has a possible coronal origin of fast expansion for two of the three ICMEs. Title: Interpreting the Two-step Forbush Decrease with a closer look at the two substructures modulating Galactic Cosmic Rays within Coronal Mass Ejections Authors: Janvier, Miho; Dasso, Sergio; Demoulin, Pascal; Guo, Jingnan; Regnault, Florian; Perri, Barbara; Guttierez, Christian Bibcode: 2022cosp...44.1272J Altcode: Interplanetary Coronal Mass Ejections (CMEs) are magnetic structures emanating from the Sun. A consequence of their passage at planetary bodies can be seen as the reduction of galactic cosmic rays (GCRs), a phenomenon called a Forbush decrease. These decreases are routinely monitored with neutron detectors around the world, while ICMEs are measured directly in situ by spacecraft dedicated to the monitoring of the solar wind. In particular, these detections show that ICMEs may or not build a sheath of compressed solar wind at their front, preceded in some cases by a shock. Then, the question remains which substructure may, and how, drive the Forbush decrease. Here, we will discuss how statistical analyses such as superposed epoch studies can be applied to ICME-induced Forbush decreases. In particular, by selecting ICMEs with or without a sheath, we will show that magnetic ejecta alone can drive Forbush decreases as strong as those with a sheath. Different from previous studies, we find with such a study that it is the magnetic field intensity, rather than its fluctuations, that is the main driver of Forbush decreases. Finally, we will show how the passage of isolated magnetic ejecta reveal an anisotropy in the level of GCRs in the solar wind at 1 au, a finding that we explain as related to the gradient of the GCR flux found at different distances in the heliosphere, i.e., the GCR flux is slightly higher at a larger heliospheric distance. Title: Bayesian approach for modeling global magnetic parameters of solar active regions Authors: Mandrini, Cristina H.; Lopez Fuentes, Marcelo; Poisson, Mariano; Demoulin, Pascal; Grings, Francisco Bibcode: 2022cosp...44.2413M Altcode: Active regions (ARs) appear in the solar atmosphere as a consequence of the emergence of magnetic flux tubes. The magnetic field of these flux tubes acquires twist as it crosses the convection zone, building magnetic flux ropes (FRs). Due to the presence of twist, during the emergence of these FRs the photospheric line-of-sight (LOS) magnetograms show elongations of the AR polarities, also known as magnetic tongues. Since magnetic tongues can affect the measurement of AR characteristics during their emergence phase (e.g. their tilt angle, magnetic flux, and size, among others), direct estimations of the FR global quantities which do not consider this effect have to be revised. In this work we aim to model the emergence of ARs using a FR model based on a half-torus magnetic structure. We generate synthetic magnetograms introducing non-linear perturbations in order to reproduce the small scale features, asymmetries, and noise observed in real magnetograms. We characterize the half-torus model by generating 1000 synthetic AR magnetograms using a Bayesian scheme to infer the posterior probability distribution of the model parameters. We propose models introducing different temporal correlations of the parameters; this allows us to estimate expectation values for the tilt angle, magnetic helicity, and magnetic flux, which are consistent with the input parameters of the generated ARs. Title: Magnetic field lines configuration inside magnetic clouds: observations at 1 au Authors: Dasso, Sergio; Demoulin, Pascal; Janvier, Miho; Lanabere, Vanina Bibcode: 2022cosp...44.2435D Altcode: Flux ropes, which are twisted magnetic flux tubes, are of major interest in different space and astrophysical domains, such as the Sun, planetary environments, and stellar physics. In particular, these structures are observed in the solar photosphere, the corona, the interplanetary medium, and also in planetary magnetospheres. Magnetic flux ropes in the solar wind can reach huge sizes in the heliosphere, storing significant amounts of magnetic energy and helicity. Thus, interplanetary flux ropes (IFRs) transport these quantities from the Sun to the outer heliosphere. A few analytical models provide the IFR internal magnetic configuration, which can then be compared with in situ observations at 1 au. This provides hints (or information) on the associated coronal magnetic configuration at the origin of the event.The derived magnetic structure of IFRs has also implications to improve models for propagation of energetic particles inside IFRs. Finally, magnetic clouds are the clearest observed sub-set of IFRs, so that a detailed analysis and modelisation of the observed data can be performed to derive their magnetic twist profile. In this review talk we will present a summary of the state of the art about the quantification of the magnetic twist 
distribution in magnetic clouds from 'in-situ' observations at 1 au. Title: Evolution of Plasma Composition in an Eruptive Flux Rope Authors: Baker, Deborah; Demoulin, Pascal; Long, David; Janvier, Miho; Green, Lucie; Brooks, David; van Driel-Gesztelyi, Lidia; Mihailescu, Teodora; To, Andy S. H.; Yardley, Stephanie; Valori, Gherardo Bibcode: 2022cosp...44.1361B Altcode: Magnetic flux ropes are bundles of twisted magnetic field enveloping a central axis. They harbor free magnetic energy and can be progenitors of coronal mass ejections (CMEs). However, identifying flux ropes on the Sun can be challenging. One of the key coronal observables that has been shown to indicate the presence of a flux rope is a peculiar bright coronal structure called a sigmoid. In this work, we show Hinode EUV Imaging Spectrometer observations of sigmoidal active region (AR) 10977. We analyze the coronal plasma composition in the AR and its evolution as a sigmoid (flux rope) forms and erupts as a CME. Plasma with photospheric composition was observed in coronal loops close to the main polarity inversion line during episodes of significant flux cancellation, suggestive of the injection of photospheric plasma into these loops driven by photospheric flux cancellation. Concurrently, the increasingly sheared core field contained plasma with coronal composition. As flux cancellation decreased and a sigmoid/flux rope formed, the plasma evolved to an intermediate composition in between photospheric and typical AR coronal compositions. Finally, the flux rope contained predominantly photospheric plasma during and after a failed eruption preceding the CME. Hence, plasma composition observations of AR 10977 strongly support models of flux rope formation by photospheric flux cancellation forcing magnetic reconnection first at the photospheric level then at the coronal level. Title: Bayesian approach for modeling solar active region global magnetic parameters Authors: Poisson, M.; Grings, F.; Mandrini, C. H.; López-Fuentes, M.; Démoulin, P. Bibcode: 2022arXiv220705900P Altcode: Context. Active regions (ARs) appear in the solar atmosphere as a consequence of the emergence of magnetic flux tubes. The presence of elongated magnetic polarities in line-of-sight (LOS) magnetograms indicates the existence of twist in the flux tubes forming them. These polarity elongations, called magnetic tongues, bias the measurement of AR characteristics obtained during their emergence phase (e.g. their tilt angle and magnetic flux, among others). In particular, obtaining a good estimation of the tilt angle evolution plays a key role in constraining flux-transport dynamo models. Aims. In this work we aim to estimate the intrinsic properties of the twisted flux tubes, or flux ropes, that form ARs by quantitatively comparing observed LOS magnetograms with synthetic ones derived from a toroidal magnetic flux tube model. Methods. For this reason, we develop a Bayesian inference method to obtain the statistical distributions of the inferred model parameters. As an example, we apply the method to NOAA AR 10268. Next, we test the results using a synthetic-AR generator to quantify the effect of small scale perturbations over the inferred parameter distributions. Results. We conclude that this method can significantly remove the effects of magnetic tongues on the derived AR global characteristics, providing a better knowledge of the intrinsic properties of the emerging flux rope. Conclusions. These results provide a framework for future analysis of the physical properties of emerging ARs using Bayesian statistics. Title: Analysis of the Evolution of a Multi-Ribbon Flare and Failed Filament Eruption Authors: Joshi, Reetika; Mandrini, Cristina H.; Chandra, Ramesh; Schmieder, Brigitte; Cristiani, Germán D.; Mac Cormack, Cecilia; Démoulin, Pascal; Cremades, Hebe Bibcode: 2022SoPh..297...81J Altcode: 2022arXiv220600531J How filaments form and erupt are topics about which solar researchers have wondered for more than a century and they are still open to debate. We present observations of a filament formation, its failed eruption, and the associated flare (SOL2019-05-09T05:51) that occurred in active region (AR) 12740 using data from the Solar Dynamics Observatory (SDO), the Solar-Terrestrial Relations Observatory A (STEREO-A), the Interface Region Imaging Spectrograph (IRIS) and the Learmonth Solar Observatory (LSO) of the National Solar Observatory/Global Oscillation Network Group (NSO/GONG). AR 12740 was a decaying region formed by a very disperse following polarity and a strong leading spot, surrounded by a highly dynamic zone where moving magnetic features (MMFs) were seen constantly diverging from the spot. Our analysis indicates that the filament was formed by the convergence of fibrils at a location where magnetic flux cancellation was observed. Furthermore, we conclude that its destabilisation was also related to flux cancellation associated with the constant shuffling of the MMFs. A two-ribbon flare occurred associated with the filament eruption; however, because the large-scale magnetic configuration of the AR was quadrupolar, two additional flare ribbons developed far from the two main ones. We model the magnetic configuration of the AR using a force-free field approach at the AR scale size. This local model is complemented by a global potential-field source-surface one. Based on the local model, we propose a scenario in which the filament failed eruption and the flare are due to two reconnection processes, one occurring below the erupting filament, leading to the two-ribbon flare, and another one above it between the filament flux-rope configuration and the large-scale closed loops. Our computation of the reconnected magnetic flux added to the erupting flux rope, compared to that of the large-scale field overlying it, allows us to conclude that the latter was large enough to prevent the filament eruption. A similar conjecture can be drawn from the computation of the magnetic tension derived from the global field model. Title: Statistical Analysis of the Radial Evolution of the Solar Winds between 0.1 and 1 au, and their Semi-empirical Iso-poly Fluid Modeling Authors: Dakeyo; Maksimovic; Démoulin; Halekas; Stevens Bibcode: 2022arXiv220703898D Altcode: Statistical classification of the Helios solar wind observations into several populations sorted by bulk speed has revealed an outward acceleration of the wind. The faster the wind is, the smaller is this acceleration in the 0.3 - 1 au radial range (Maksimovic et al. 2020). In this article we show that recent measurements from the Parker Solar Probe (PSP) are compatible with an extension closer to the Sun of the latter Helios classification. For instance the well established bulk speed/proton temperature (u,Tp) correlation and bulk speed/electron temperature (u,Te) anti-correlation, together with the acceleration of the slowest winds, are verified in PSP data. We also model the combined PSP and Helios data, using empirical Parker-like models for which the solar wind undergoes an "iso-poly" expansion: isothermal in the corona, then polytropic at distances larger than the sonic point radius. The polytropic indices are derived from the observed temperature and density gradients. Our modelling reveals that the electron thermal pressure has a major contribution in the acceleration process of slow and intermediate winds (in the range of 300-500 km/s at 1 au), over a broad range of distances and that the global (electron and protons) thermal energy, alone, is able to explain the acceleration profiles. Moreover, we show that the very slow solar wind requires in addition to the observed pressure gradients, another source of acceleration. Title: Pressure balance of coronal mass ejections during their Sun-Earth journey modelled by 3D MHD EUHFORIA simulations Authors: Schmieder, Brigitte; Dasso, Sergio; Grison, Benjamin; Demoulin, Pascal; Verbeke, Christine; Scolini, Camilla; Samara, Evangelia; Poedts, Stefaan Bibcode: 2022cosp...44.2474S Altcode: The aim of this work is to understand the signatures of three coronal mass ejections (CMEs) at the Lagrange point L1 launched from the Sun between 15 and 18 July 2002. We use the EUropean Heliosphere FORecasting Information Asset (EUHFORIA) model to simulate their propagation and interaction in the background solar wind. The approach is to place virtual spacecraft along the Sun-Earth line. We set up the initial conditions at 0.1 au, modelling each CME using the linear force free spheromak model. We perform an analysis on the pressures acting within the first and the last CMEs of the series (CME1 and CME3) and investigate the role of pressure (un)balance in their expansion, while the second CME (CME2) was too compressed to be able to expand its ejecta during propagation. We find that the magnetic pressure within CME1 and CME3 was prominent at 0.1 au and rapidly decreased between 0.1 au and Earth, so that the gas pressure was progressively dominating in their extended ejecta. Title: Eruption of the EUV Hot Channel from the Solar Limb and Associated Moving Type IV Radio Burst Authors: Vemareddy, P.; Démoulin, P.; Sasikumar Raja, K.; Zhang, J.; Gopalswamy, N.; Vasantharaju, N. Bibcode: 2022ApJ...927..108V Altcode: 2022arXiv220106899V Using the observations from the Solar Dynamics Observatory, we study an eruption of a hot-channel flux rope (FR) near the solar limb on 2015 February 9. The pre-eruptive structure is visible mainly in EUV 131 Å images, with two highly sheared loop structures. They undergo a slow rising motion and then reconnect to form an eruptive hot channel, as in the tether-cutting reconnection model. The J-shaped flare ribbons trace the footpoint of the FR that is identified as the hot channel. Initially, the hot channel is observed to rise slowly at 40 km s-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. Title: A solar flare driven by thermal conduction observed in mid-infrared Authors: López, Fernando M.; Giménez de Castro, Carlos Guillermo; Mandrini, Cristina H.; Simões, Paulo J. A.; Cristiani, Germán D.; Gary, Dale E.; Francile, Carlos; Démoulin, Pascal Bibcode: 2022A&A...657A..51L Altcode: 2021arXiv211015751L Context. The mid-infrared (mid-IR) range has been mostly unexplored for the investigation of solar flares. It is only recently that new mid-IR flare observations have begun opening a new window into the response and evolution of the solar chromosphere. These new observations have been mostly performed by the AR30T and BR30T telescopes that are operating in Argentina and Brazil, respectively.
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 https://www.aanda.org Title: Evolution of Plasma Composition in an Eruptive Flux Rope Authors: Baker, D.; Green, L. M.; Brooks, D. H.; Démoulin, P.; van Driel-Gesztelyi, L.; Mihailescu, T.; To, A. S. H.; Long, D. M.; Yardley, S. L.; Janvier, M.; Valori, G. Bibcode: 2022ApJ...924...17B Altcode: 2021arXiv211011714B Magnetic flux ropes are bundles of twisted magnetic field enveloping a central axis. They harbor free magnetic energy and can be progenitors of coronal mass ejections (CMEs). However, identifying flux ropes on the Sun can be challenging. One of the key coronal observables that has been shown to indicate the presence of a flux rope is a peculiar bright coronal structure called a sigmoid. In this work, we show Hinode EUV Imaging Spectrometer observations of sigmoidal active region (AR) 10977. We analyze the coronal plasma composition in the AR and its evolution as a sigmoid (flux rope) forms and erupts as a CME. Plasma with photospheric composition was observed in coronal loops close to the main polarity inversion line during episodes of significant flux cancellation, suggestive of the injection of photospheric plasma into these loops driven by photospheric flux cancellation. Concurrently, the increasingly sheared core field contained plasma with coronal composition. As flux cancellation decreased and a sigmoid/flux rope formed, the plasma evolved to an intermediate composition in between photospheric and typical AR coronal compositions. Finally, the flux rope contained predominantly photospheric plasma during and after a failed eruption preceding the CME. Hence, plasma composition observations of AR 10977 strongly support models of flux rope formation by photospheric flux cancellation forcing magnetic reconnection first at the photospheric level then at the coronal level. Title: The Two-step Forbush Decrease: A Tale of Two Substructures Modulating Galactic Cosmic Rays within Coronal Mass Ejections Authors: Janvier, Miho; Démoulin, Pascal; Guo, Jingnan; Dasso, Sergio; Regnault, Florian; Topsi-Moutesidou, Sofia; Gutierrez, Christian; Perri, Barbara Bibcode: 2021ApJ...922..216J Altcode: 2021arXiv210914469J Interplanetary coronal mass ejections (ICMEs) are known to modify the structure of the solar wind as well as interact with the space environment of planetary systems. Their large magnetic structures have been shown to interact with galactic cosmic rays (GCRs), leading to the Forbush decrease (FD) phenomenon. We revisit in the present article the 17 yr of Advanced Composition Explorer spacecraft ICME detection along with two neutron monitors (McMurdo and Oulu) with a superposed epoch analysis to further analyze the role of the magnetic ejecta in driving FDs. We investigate in the following the role of the sheath and the magnetic ejecta in driving FDs, and we further show that for ICMEs without a sheath, a magnetic ejecta only is able to drive significant FDs of comparable intensities. Furthermore, a comparison of samples with and without a sheath with similar speed profiles enable us to show that the magnetic field intensity, rather than its fluctuations, is the main driver for the FD. Finally, the recovery phase of the FD for isolated magnetic ejecta shows an anisotropy in the level of the GCRs. We relate this finding at 1 au to the gradient of the GCR flux found at different heliospheric distances from several interplanetary missions. Title: Filament Eruption Driving EUV Loop Contraction and Then Expansion above a Stable Filament Authors: Chandra, Ramesh; Démoulin, Pascal; Devi, Pooja; Joshi, Reetika; Schmieder, Brigitte Bibcode: 2021ApJ...922..227C Altcode: 2021arXiv210907821C We analyze the observations of EUV loop evolution associated with the filament eruption located at the border of an active region (AR). The event SOL2013-03-16T14:00 was observed with a large difference in view point by the Solar Dynamics Observatory and Solar Terrestrial Relations Observatory. The filament height is fitted with the sum of a linear and exponential function. These two phases point to different physical mechanisms such as tether-cutting reconnection and a magnetic instability. While no X-ray emission is reported, this event presents classical eruption features like separation of double ribbons and the growth of flare loops. We report the migration of the southern foot of the erupting filament flux rope due to the interchange reconnection with encountered magnetic loops of a neighboring AR. Parallel to the erupting filament, a stable filament remains in the core of the AR. The specificity of this eruption is that coronal loops, located above the nearly joining ends of the two filaments, first contract in phase, then expand and reach a new stable configuration close to the one present at the eruption onset. Both contraction and expansion phases last around 20 minutes. The main difference with previous cases is that the PIL bent about 180° around the end of the erupting filament because the magnetic configuration is at least tripolar. These observations are challenging for models that interpreted previous cases of loop contraction within a bipolar configuration. New simulations are required to broaden the complexity of the configurations studied. Title: Plasma Upflows Induced by Magnetic Reconnection Above an Eruptive Flux Rope Authors: Baker, Deborah; Mihailescu, Teodora; Démoulin, Pascal; Green, Lucie M.; van Driel-Gesztelyi, Lidia; Valori, Gherardo; Brooks, David H.; Long, David M.; Janvier, Miho Bibcode: 2021SoPh..296..103B Altcode: 2021arXiv210616137B One of the major discoveries of Hinode's Extreme-ultraviolet Imaging Spectrometer (EIS) is the presence of upflows at the edges of active regions. As active regions are magnetically connected to the large-scale field of the corona, these upflows are a likely contributor to the global mass cycle in the corona. Here we examine the driving mechanism(s) of the very strong upflows with velocities in excess of 70 km s−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. Title: ICMEs and low plasma density in the solar wind observed at L1 Authors: Schmieder, Brigitte; Verbeke, Christine; Chané, Emmanuel; Démoulin, Pascal; Poedts, Stefaan; Grison, Benjamin Bibcode: 2021EGUGA..23.1799S Altcode: Different regimes of the solar wind have been observed at L1 during and after the passage of ICMEs, particularly anomalies with very low plasma density. From the observations at L1 (ACE) we identified different possible cases. A first case was explained by the evacuation of the plasma due over expansion of the ICME (May 2002). The second case on July 2002 is intriguing.In July 2002, three halo fast speed ICMEs, with their origin in the central part of the Sun, have surprisingly a poor impact on the magnetosphere (Dst > -28 nT). Analyzing the characteristics of the first ICME at L1, we conclude that the spacecraft crosses the ICME with a large impact (Bx component in GSE coordinates is dominant). The plasma density is low, just behind this first ICME. Next, we explore the generic conditions of low density formation in the EUHFORIA simulations.The very low density plasma after the sheath could be explained by the spacecraft crossing, on the side of the flux rope, while behind the front shock. We investigate two possible interpretations. The shock was able to compress and accelerate so much the plasma that a lower density is left behind. This can also be due to an effect of the sheath magnetic field which extends the flux rope effect on the sides of it, so a decrease of plasma density could occur like behind a moving object (here the sheath field). The following ICME, with also a low density, could be an intrinsic case with the formation in the corona of a cavity. Finally, we present some runs of EUHFORIA which fit approximately these data and argue in favor of the possible interpretations detailed above. Title: Over-expansion of a coronal mass ejection generates sub-Alfvénic plasma conditions in the solar wind at Earth Authors: Chané, E.; Schmieder, B.; Dasso, S.; Verbeke, C.; Grison, B.; Démoulin, P.; Poedts, S. Bibcode: 2021A&A...647A.149C Altcode: Context. From May 24-25, 2002, four spacecraft located in the solar wind at about 1 astronomical unit (au) measured plasma densities one to two orders of magnitude lower than usual. The density was so low that the flow became sub-Alfvénic for four hours, and the Alfvén Mach number was as low as 0.4. Consequently, the Earth lost its bow shock, and two long Alfvén wings were generated.
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. Title: Observations of a prominence eruption and loop contraction Authors: Devi, Pooja; Démoulin, Pascal; Chandra, Ramesh; Joshi, Reetika; Schmieder, Brigitte; Joshi, Bhuwan Bibcode: 2021A&A...647A..85D Altcode: 2021arXiv210107682D Context. Prominence eruptions provide key observations to understand the launch of coronal mass ejections as their cold plasma traces a part of the unstable magnetic configuration.
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 https://www.aanda.org Title: The Magnetic Environment of a Stealth Coronal Mass Ejection Authors: O'Kane, Jennifer; Mac Cormack, Cecilia; Mandrini, Cristina H.; Démoulin, Pascal; Green, Lucie M.; Long, David M.; Valori, Gherardo Bibcode: 2021ApJ...908...89O Altcode: 2020arXiv201203757O Interest in stealth coronal mass ejections (CMEs) is increasing due to their relatively high occurrence rate and space weather impact. However, typical CME signatures such as extreme-ultraviolet dimmings and post-eruptive arcades are hard to identify and require extensive image processing techniques. These weak observational signatures mean that little is currently understood about the physics of these events. We present an extensive study of the magnetic field configuration in which the stealth CME of 2011 March 3 occurred. Three distinct episodes of flare ribbon formation are observed in the stealth CME source active region (AR). Two occurred prior to the eruption and suggest the occurrence of magnetic reconnection that builds the structure that will become eruptive. The third occurs in a time close to the eruption of a cavity that is observed in STEREO-B 171 Å data; this subsequently becomes part of the propagating CME observed in coronagraph data. We use both local (Cartesian) and global (spherical) models of the coronal magnetic field, which are complemented and verified by the observational analysis. We find evidence of a coronal null point, with field lines computed from its neighborhood connecting the stealth CME source region to two ARs in the northern hemisphere. We conclude that reconnection at the null point aids the eruption of the stealth CME by removing the field that acted to stabilize the preeruptive structure. This stealth CME, despite its weak signatures, has the main characteristics of other CMEs, and its eruption is driven by similar mechanisms. Title: Magnetic twist distribution inside interplanetary flux ropes Authors: Dasso, Sergio; Rodriguez, Luciano; Demoulin, Pascal; Masias-Meza, Jimmy J.; Janvier, Miho; Lanabere, Vanina Bibcode: 2021cosp...43E1756D Altcode: Twisted magnetic flux tubes, also known as flux ropes, are ubiquitous in solar, stellar, and planetary environments. They are present in the photosphere of the Sun, the solar corona, the solar wind, and also in different locations of planetary magnetospheres and ionospheres. In particular, interplanetary flux ropes (IFRs) can store magnetic energy and, because their magnetic field lines are twisted around the tube axis, also can store important amounts of magnetic helicity. Thus, IFRs can transport these quantities from the Sun to the outer space of the heliosphere. The internal distribution of the magnetic twist forming the flux rope (i.e., the number of turns per unit length), is a key property to link IFRs with their solar origin and ejection processes, to improve the knowledge of coronal structures in equilibrium, and also to better understand the energetic particle propagation inside these interplanetary structures. Quantifying the magnetic twist distribution in IFRs from 'in-situ' observations of single events has a major difficulty produced by the significant field fluctuations in the interplanetary magnetic field. Magnetic clouds (MCs) are a sub-set of Interplanetary Coronal Ejections (ICMEs), which present clear signatures of flux ropes when 'in-situ' observed. In this work, we apply a superposed epoch analysis to a significant sample of MCs observed at 1 au, to extract their common features, and to remove the peculiarity and eventual high level of noise present in individual cases. From this analysis, we quantify the typical twist distribution inside the flux ropes forming MCs. As one of the main results, we find that the twist is nearly uniform in the core (central half part around the flux rope axis), and it increases moderately, up to a factor two, towards the MC boundaries. These results will allow to better understand these magnetic structures and to link them with their solar origin. Title: 20 years of ACE data: how superposed epoch analyses reveal generic features in interplanetary CME profiles Authors: Regnault, Florian; Dasso, Sergio; Auchere, Frederic; Demoulin, Pascal; Janvier, Miho; Strugarek, Antoine Bibcode: 2021cosp...43E1017R Altcode: Interplanetary Coronal Mass Ejections (ICMEs) result from solar flares occurring in our star's atmosphere. These large-scale magnetized structures propagate in the interplanetary medium where they can be probed by spacecraft. Depending on their speed, ICMEs may accumulate enough solar wind plasma to form a turbulent sheath ahead of them. They therefore consist of two main substructures : a sheath and a magnetic ejecta (ME). The magnetic ejecta is the main body of an ICME where the magnetic field is more intense and with less variance than that of the ambient solar wind. We present a statistical study using the superposed epoch analysis technique on a catalog of around 400 ICMEs where we consider the profiles of the physical parameters of the ICMEs (the magnetic field intensity, the speed, temperature, ...) seen at 1 AU by the ACE spacecraft. In particular, we investigate different possible classifications of ICMEs, for example based on their speeds, the phase of the solar cycle when they are detected, and the detection of an associated magnetic cloud (MCs, a subset of MEs with a clear rotation of the magnetic field as well as a low plasma temperature compared with the solar wind). We confirm that slow ICMEs have a more symmetric profile than fast ICMEs, therefore generalizing the work made on a sample of 44 ICMEs with clearly identified magnetic clouds by Masias-Meza et al. (2016). We also find that fast ICMEs show signs of compression in both their magnetic ejecta and in their sheath. Furthermore, we do not find any impact of the solar cycle on the generic features of ICMEs. However, more extreme events are observed during the active parts of the cycle, widening the distributions of all parameters. Finally, we find that ICMEs with or without a detected magnetic cloud show similar profiles, which confirms the hypothesis that both types of events correspond to similar ICMEs, and that the ones with no detected magnetic clouds may be observed when crossed sufficiently away from the flux rope core. Title: Initiation of CMEs and their geo-effectiveness Authors: Schmieder, Brigitte; Poedts, Stefaan; Grison, Benjamin; Demoulin, Pascal; Kim, Rok-Soon; Verbeke, Christine Bibcode: 2021cosp...43E1013S Altcode: Physical conditions of solar eruptions triggering coronal mass ejections (CMEs) have been determined by recent multi-wavelength observations as well by numerical simulations (e.g. OHM). CMEs and flares are the seeds of the Space Weather. Our analyze consists on a few case studies of CMEs which have all the good proxies for inducing geo-effectivity e.g. fast halo CME, central solar disk source. We follow the CMEs surfing in the solar wind as interplanetary coronal mass ejections (ICME) or magnetic clouds. We use numerical simulations (EUHFORIA) to investigate the geo-effectiveness of these ICMEs We study the degree of deviation of these halo CMEs from the Sun-Earth axis as well as their deformation and erosion due to their interaction with the ambient solar wind resulting in magnetic reconnections according to the input of parameters and their chance to hit other planets. The inhomogeneous nature of the solar wind and encounters are also important parameters influencing the impact of CMEs on planetary magnetospheres Title: A method to correct the effect of magnetic tongues and its application to measure active-region tilt angles Authors: Mandrini, Cristina H.; Lopez Fuentes, Marcelo; Poisson, Mariano; Demoulin, Pascal Bibcode: 2021cosp...43E1760M Altcode: The presence of elongated magnetic polarities in active-region (AR) line-of-sight (LOS) magnetograms indicates the existence of twist in the flux tube forming them. These elongations, called magnetic tongues, which are mostly visible during the emergence phase of ARs, affect the measurement of several AR characteristics; in particular, their tilt angles. Tilt angles have been measured thoroughly using LOS magnetograms and, historically speaking, long-term white-light (WL) databases, sometimes combined with magnetic field information. Since the influence of magnetic tongues on tilt measurements has not yet been taken into account in these measurements, we aim to investigate their impact on the different methods used to compute tilt values. We apply standard methods to WL data and LOS magnetograms, some developed by us and others used in long-term databases, and show that the computed tilt values are affected by the presence of magnetic tongues. Therefore, we apply the newly developed Core Field Fit Estimator (CoFFE) method to separate the magnetic flux in the tongues from that in the AR core when using LOS magnetograms. We compare all the determined tilt-angle values and find that, for ARs with low magnetic flux tongues, all of them report consistent values. But for ARs with high flux tongues, there are noticeable discrepancies between all methods, indicating that these features affect differently WL and magnetic data. However, in general, CoFFE achieves a better estimation of the main bipole tilt because it removes the effect of tongues, as well as the influence of the emergence of secondary bipoles. Title: Alfvénic Perturbations in a Sunspot Chromosphere Linked to Fractionated Plasma in the Corona Authors: Baker, Deborah; Stangalini, Marco; Valori, Gherardo; Brooks, David H.; To, Andy S. H.; van Driel-Gesztelyi, Lidia; Démoulin, Pascal; Stansby, David; Jess, David B.; Jafarzadeh, Shahin Bibcode: 2021ApJ...907...16B Altcode: 2020arXiv201204308B In this study, we investigate the spatial distribution of highly varying plasma composition around one of the largest sunspots of solar cycle 24. Observations of the photosphere, chromosphere, and corona are brought together with magnetic field modeling of the sunspot in order to probe the conditions that regulate the degree of plasma fractionation within loop populations of differing connectivities. We find that, in the coronal magnetic field above the sunspot umbra, the plasma has photospheric composition. Coronal loops rooted in the penumbra contain fractionated plasma, with the highest levels observed in the loops that connect within the active region. Tracing field lines from regions of fractionated plasma in the corona to locations of Alfvénic fluctuations detected in the chromosphere shows that they are magnetically linked. These results indicate a connection between sunspot chromospheric activity and observable changes in coronal plasma composition. Title: 20 Years of ACE Data: How Superposed Epoch Analyses Reveal Generic Features in Interplanetary CME Profiles Authors: Regnault, F.; Janvier, M.; Démoulin, P.; Auchère, F.; Strugarek, A.; Dasso, S.; Noûs, C. Bibcode: 2020JGRA..12528150R Altcode: 2020arXiv201105050R Interplanetary coronal mass ejections (ICMEs) are magnetic structures propagating from the Sun's corona to the interplanetary medium. With over 20 years of observations at the L1 libration point, ACE offers hundreds of ICMEs detected at different times during several solar cycles and with different features such as the propagation speed. We investigate a revisited catalog of more than 400 ICMEs using the superposed epoch method on the mean, median, and the most probable values of the distribution of magnetic and plasma parameters. We also investigate the effects of the speed of ICMEs relative to the solar wind, the solar cycle, and the existence of a magnetic cloud on the generic ICME profile. We find that fast-propagating ICMEs (relatively to the solar wind in front) still show signs of compression at 1 au, as seen by the compressed sheath and the asymmetric profile of the magnetic field. While the solar cycle evolution does not impact the generic features of ICMEs, there are more extreme events during the active part of the cycle, widening the distributions of all parameters. Finally, we find that ICMEs with or without a detected magnetic cloud show similar profiles, which confirms the hypothesis that ICMEs with no detected magnetic clouds are crossed further away from the flux rope core. Such a study provides a generic understanding of processes that shape the overall features of ICMEs in the solar wind and can be extended with future missions at different locations in the solar system. Title: Additivity of relative magnetic helicity in finite volumes Authors: Valori, Gherardo; Démoulin, Pascal; Pariat, Etienne; Yeates, Anthony; Moraitis, Kostas; Linan, Luis Bibcode: 2020A&A...643A..26V Altcode: 2020arXiv200800968V Context. Relative magnetic helicity is conserved by magneto-hydrodynamic evolution even in the presence of moderate resistivity. For that reason, it is often invoked as the most relevant constraint on the dynamical evolution of plasmas in complex systems, such as solar and stellar dynamos, photospheric flux emergence, solar eruptions, and relaxation processes in laboratory plasmas. However, such studies often indirectly imply that relative magnetic helicity in a given spatial domain can be algebraically split into the helicity contributions of the composing subvolumes, in other words that it is an additive quantity. A limited number of very specific applications have shown that this is not the case.
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. Bibcode: 2020SPD....5121005O Altcode: Interest in Stealth Coronal Mass Ejections (CMEs) is increasing due to their relatively high occurrence rate and space weather impact. However, typical CME signatures such as EUV dimmings and post-eruptive arcades are hard to identify for stealth CMEs and require extensive image processing techniques. These weak observational signatures mean little is currently understood about the physics of these events. We present an extensive study of the magnetic field configuration in which the stealth CME of 3 March 2011 occurred. The magnetic field prior to the eruption is evaluated using a Linear Force Free Field (LFFF) model and a Potential Field Source Surface (PFSS) model, and complemented by in-depth observational analysis. The models are verified using observations of plasma emission structures in the stealth CME source region and trans-equatorial loops. We find evidence of a high-altitude null point in both the LFFF model and the PFSS model, with surrounding field lines connecting two active regions on the solar disk. One of these active regions in the Southern Hemisphere is shown to be the source region of the stealth CME. Three distinct episodes of flare ribbon formation are observed in AIA 304Å. Two occurred prior to the eruption and suggest the occurrence of magnetic reconnection that builds the eruptive structure. The third occurs at the same time as an erupting cavity is observed in STEREO-B 171Å data; this subsequently becomes part of the propagating CME observed in COR1. We conclude that reconnection at the null point, driven by eruptive activity in the complex northern active region, aids the eruption of the stealth CME by removing field that acted to stabilise the pre-eruptive structure. Title: Contribution of the ageing effect to the observed asymmetry of interplanetary magnetic clouds Authors: Démoulin, P.; Dasso, S.; Lanabere, V.; Janvier, M. Bibcode: 2020A&A...639A...6D Altcode: 2020arXiv200505049D Context. Large magnetic structures are launched away from the Sun during solar eruptions. They are observed as (interplanetary) coronal mass ejections (ICMEs or CMEs) with coronal and heliospheric imagers. A fraction of them are observed in situ as magnetic clouds (MCs). Fitting these structures properly with a model requires a better understanding of their evolution.
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. Bibcode: 2020ApJ...894..131P Altcode: 2020arXiv200407345P The presence of elongations in active-region (AR) polarities, called magnetic tongues, is mostly visible during their emergence phase. AR tilts have been measured thoroughly using long-term white-light (WL) databases, sometimes combined with magnetic-field information. Since the influence of magnetic tongues on WL tilt measurements has not been taken into account before, we aim to investigate their role in tilt-angle values and to compare them with those derived from LOS magnetograms. We apply four methods to compute the tilt angle of generally bipolar ARs: one applies the k-means algorithm to WL data, a second one includes the magnetic-field sign of the polarities to WL data, and a third one uses the magnetic flux-weighted center of each polarity. The tilt values computed in any of these ways are affected by the presence of magnetic tongues. Therefore, we apply the newly developed Core Field Fit Estimator (CoFFE) method to separate the magnetic flux in the tongues from that in the AR core. We compare the four computed tilt-angle values, as well as these with the ones reported in long-term WL databases. For ARs with low-magnetic-flux tongues, the different methods report consistent tilt-angle values. But for ARs with high-flux tongues, there are noticeable discrepancies between all methods, indicating that magnetic tongues differently affect WL and magnetic data. However, in general, CoFFE achieves a better estimation of the main bipole tilt because it removes both the effect of tongues as well as the emergence of secondary bipoles when it occurs in between the main bipole magnetic polarities. Title: Can Subphotospheric Magnetic Reconnection Change the Elemental Composition in the Solar Corona? Authors: Baker, Deborah; van Driel-Gesztelyi, Lidia; Brooks, David H.; Démoulin, Pascal; Valori, Gherardo; Long, David M.; Laming, J. Martin; To, Andy S. H.; James, Alexander W. Bibcode: 2020ApJ...894...35B Altcode: 2020arXiv200303325B Within the coronae of stars, abundances of those elements with low first ionization potential (FIP) often differ from their photospheric values. The coronae of the Sun and solar-type stars mostly show enhancements of low-FIP elements (the FIP effect) while more active stars such as M dwarfs have coronae generally characterized by the inverse-FIP effect (I-FIP). Here we observe patches of I-FIP effect solar plasma in AR 12673, a highly complex βγδ active region. We argue that the umbrae of coalescing sunspots, and more specifically strong light bridges within the umbrae, are preferential locations for observing I-FIP effect plasma. Furthermore, the magnetic complexity of the active region and major episodes of fast flux emergence also lead to repetitive and intense flares. The induced evaporation of the chromospheric plasma in flare ribbons crossing umbrae enables the observation of four localized patches of I-FIP effect plasma in the corona of AR 12673. These observations can be interpreted in the context of the ponderomotive force fractionation model which predicts that plasma with I-FIP effect composition is created by the refraction of waves coming from below the chromosphere. We propose that the waves generating the I-FIP effect plasma in solar active regions are generated by subphotospheric reconnection of coalescing flux systems. Although we only glimpse signatures of I-FIP effect fractionation produced by this interaction in patches on the Sun, on highly active M stars it may be the dominant process. Title: Using Forbush decreases at Earth and Mars to measure the radial evolution of ICMEs Authors: von Forstner, Johan; Guo, Jingnan; Wimmer-Schweingruber, Robert F.; Dumbović, Mateja; Janvier, Miho; Démoulin, Pascal; Veronig, Astrid; Temmer, Manuela; Papaioannou, Athanasios; Dasso, Sergio; Hassler, Donald M.; Zeitlin, Cary J. Bibcode: 2020EGUGA..22.7838V Altcode: Interplanetary coronal mass ejections (ICMEs), large clouds of plasma and magnetic field regularly expelled from the Sun, are one of the main drivers of space weather effects in the solar system. While the prediction of their arrival time at Earth and other locations in the heliosphere is still a complex task, it is also necessary to further understand the time evolution of their geometric and magnetic structure, which is even more challenging considering the limited number of available observation points.Forbush decreases (FDs), short-term drops in the flux of galactic cosmic rays (GCR), can be caused by the shielding from strong and/or turbulent magnetic structures in the solar wind, such as ICMEs and their associated shock/sheath regions. In the past, FD observations have often been used to determine the arrival times of ICMEs at different locations in the solar system, especially where sufficient solar wind plasma and magnetic field measurements are not (or not always) available. One of these locations is Mars, where the Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory (MSL) mission's Curiosity rover has been continuously measuring GCRs and FDs on the surface for more than 7 years.In this work, we investigate whether FD data can be used to derive additional information about the ICME properties than just the arrival time by performing a statistical study based on catalogs of FDs observed at Earth or Mars. In particular, we find that the linear correlation between the FD amplitude and the maximum steepness, which was already seen at Earth by previous authors (Belov et al., 2008, Abunin et al., 2012), is likewise present at Mars, but with a different proprtionality factor.By consulting physics-based analytical models of FDs, we find that this quantity is not expected to be influenced by the different energy ranges of GCR particles observed by the instruments at Earth and Mars. Instead, we suggest that the difference in FD characteristics at the two planets is caused by the radial enlargement of the ICMEs, and particularly their sheath regions, as they propagate from Earth (1 AU) to Mars (~ 1.5 AU). This broadening factor derived from our analysis extends observations for the evolution closer to the Sun by Janvier et al. (2019, JGR Space Physics) to larger heliocentric distances and is consistent with these results. Title: Low Geo-Effectiveness of Fast Halo CMEs Related to the 12 X-Class Flares in 2002 Authors: Schmieder, B.; Kim, R. -S.; Grison, B.; Bocchialini, K.; Kwon, R. -Y.; Poedts, S.; Démoulin, P. Bibcode: 2020JGRA..12527529S Altcode: 2020arXiv200310777S It is generally accepted that extreme space weather events tend to be related to strong flares and fast halo coronal mass ejections (CMEs). In the present paper, we carefully identify the chain of events from the Sun to the Earth induced by all 12 X-class flares that occurred in 2002. In this small sample, we find an unusual high rate (58%) of solar sources with a longitude larger than 74°. Yet all 12 X-class flares are associated with at least one CME. The fast halo CMEs (50%) are related to interplanetary CMEs (ICMEs) at L1 and weak Dst minimum values (more than -51 nT), while five (41%) of the 12 X-class flares are related to solar proton events (SPEs). We conclude that (i) all 12 analyzed solar events, even those associated with fast halo CMEs originating from the central disk region, and those ICMEs and SPEs were not very geo-effective. This unexpected result demonstrates that the suggested events in the chain (fast halo CME, X-class flares, central disk region, ICME, and SPE) are not infallible proxies for geo-effectiveness. (ii) The low value of integrated and normalized southward component of the interplanetary magnetic field (Bz*) may explain the low geo-effectiveness for this small sample. In fact, Bz* is well correlated to the weak Dst and low auroral electrojet activity. Hence, the only space weather impact at Earth in 2002 we can explain is based on Bz* at L1. Title: Magnetic twist profile inside magnetic clouds derived with a superposed epoch analysis Authors: Lanabere, V.; Dasso, S.; Démoulin, P.; Janvier, M.; Rodriguez, L.; Masías-Meza, J. J. Bibcode: 2020A&A...635A..85L Altcode: 2020arXiv200210606L Context. Magnetic clouds (MCs) are large-scale interplanetary transient structures in the heliosphere that travel from the Sun into the interplanetary medium. The internal magnetic field lines inside the MCs are twisted, forming a flux rope (FR). This magnetic field structuring is determined by its initial solar configuration, by the processes involved during its eruption from the Sun, and by the dynamical evolution during its interaction with the ambient solar wind.
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. Bibcode: 2020JGRA..12527662F Altcode: 2020arXiv200303157V Forbush decreases (FDs), which are short-term drops in the flux of galactic cosmic rays, are caused by the shielding from strong and/or turbulent magnetic structures in the solar wind, especially interplanetary coronal mass ejections (ICMEs) and their associated shocks, as well as corotating interaction regions. Such events can be observed at Earth, for example, using neutron monitors, and also at many other locations in the solar system, such as on the surface of Mars with the Radiation Assessment Detector instrument onboard Mars Science Laboratory. They are often used as a proxy for detecting the arrival of ICMEs or corotating interaction regions, especially when sufficient in situ solar wind measurements are not available. We compare the properties of FDs observed at Earth and Mars, focusing on events produced by ICMEs. We find that FDs at both locations show a correlation between their total amplitude and the maximum hourly decrease, but with different proportionality factors. We explain this difference using theoretical modeling approaches and suggest that it is related to the size increase of ICMEs, and in particular their sheath regions, en route from Earth to Mars. From the FD data, we can derive the sheath broadening factor to be between about 1.5 and 1.9, agreeing with our theoretical considerations. This factor is also in line with previous measurements of the sheath evolution closer to the Sun. Title: Correcting the effect of magnetic tongues on the tilt angle of bipolar active regions Authors: Poisson, M.; López Fuentes, M. C.; Mandrini, C. H.; Démoulin, P.; MacCormack, C. Bibcode: 2020A&A...633A.151P Altcode: 2019arXiv191212990P Context. The magnetic polarities of bipolar active regions (ARs) exhibit elongations in line-of-sight magnetograms during their emergence. These elongations are referred to as magnetic tongues and attributed to the presence of twist in the emerging magnetic flux-ropes (FRs) that form ARs.
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 https://www.aanda.org Title: Comparing the Properties of ICME-Induced Forbush Decreases at Earth and Mars Authors: Freiherr von Forstner, J. L.; Guo, J.; Wimmer-Schweingruber, R. F.; Dumbovic, M.; Janvier, M.; Demoulin, P.; Veronig, A.; Temmer, M.; Hassler, D.; Zeitlin, C. Bibcode: 2019AGUFMSH41D3339F Altcode: Forbush decreases (FDs), short-term drops in the flux of galactic cosmic rays (GCR), can be caused by the shielding from strong and/or turbulent magnetic structures in the solar wind, i.e. interplanetary coronal mass ejections (ICMEs) and their associated shocks as well as corotating interaction regions (CIRs). FDs are often used as a proxy for detecting the arrival of ICMEs or CIRs at locations where sufficient in situ solar wind measurements are not or not always available, such as at Mars. The Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory (MSL) mission's Curiosity rover has been continuously measuring the GCR environment on the surface of Mars for more than 7 years since its landing in August 2012 and is thus an excellent source for measurements of FDs at Mars (see e.g. Guo et al. 2018, A&A).

Based on the large catalog of FDs at Mars compiled by Papaioannou et al. (2019, Solar Physics) as well as results from our previous work (Freiherr von Forstner et al., 2019, Space Weather), 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 (Belov et al., 2008, Abunin et al., 2012). 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 <a href="https://doi.org/10.1029/2018JA025949>Janvier et al. (2019, JGR Space Physics). Title: Re-analysis of Lepping's Fitting Method for Magnetic Clouds: Lundquist Fit Reloaded Authors: Démoulin, Pascal; Dasso, Sergio; Janvier, Miho; Lanabere, Vanina Bibcode: 2019SoPh..294..172D Altcode: 2019arXiv191209829D Magnetic clouds (MCs) are a subset of ejecta, launched from the Sun as coronal mass ejections. The coherent rotation of the magnetic field vector observed in MCs leads to envision MCs as formed by flux ropes (FRs). Among all the methods used to analyze MCs, Lepping's method (Lepping, Burlaga, and Jones in J. Geophys. Res.95, 11957, 1990) is the broadest used. While this fitting method does not require the axial field component to vanish at the MC boundaries, this idea is largely spread in publications. We revisit Lepping's method to emphasize its hypothesis and the meaning of its output parameters. As originally defined, these parameters imply a fitted FR which could be smaller or larger than the studied MC. We rather provide a re-interpretation of Lepping's results with a fitted model limited to the observed MC interval. We find that typically the crossed FRs are asymmetric with a larger side both in size and magnetic flux before or after the FR axis. At the boundary of the largest side we find an axial magnetic field component distributed around zero which we justify by the physics of solar eruptions. In contrast, at the boundary of the smaller side the axial field distribution is shifted to positive values, as expected with erosion acting during the interplanetary travel. This new analysis of Lepping's results has several implications. First, global quantities, such as magnetic fluxes and helicity, need to be revised depending on the aim (estimating global properties of FRs just after the solar launch or at 1 au). Second, the deduced twist profiles in MCs range quasi-continuously from nearly uniform, to increasing away from the FR axis, up to a reversal near the MC boundaries. There is no trace of outsider cases, but a continuum of cases. Finally, the impact parameter of the remaining FR crossed at 1 au is revised. Its distribution is compatible with weakly flattened FR cross-sections. Title: Do Current and Magnetic Helicities Have the Same Sign? Authors: Russell, A. J. B.; Demoulin, P.; Hornig, G.; Pontin, D. I.; Candelaresi, S. Bibcode: 2019ApJ...884...55R Altcode: Current helicity, H 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 < 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. Title: Definition of the Spatial Propagator and Implications for Magnetic Field Properties Authors: Edmondson, Justin K.; Démoulin, Pascal Bibcode: 2019SoPh..294...76E Altcode: We present a theoretical framework to analyze the 3D coronal vector magnetic-field structure. We assume that the vector magnetic field exists and is a priori smooth. We introduce a generalized connectivity phase space associated with the vector magnetic field in which the basic elements are the field line and its linearized variation: the Spatial Propagator. We provide a direct formulation of these elements in terms of the vector magnetic field and its spatial derivatives, constructed with respect to general curvilinear coordinates and the equivalence class of general affine parameterizations. The Spatial Propagator describes the geometric organization of the local bundle of field lines, equivalent to the kinematic deformation of a propagated volume tied to the bundle. The Spatial Propagator's geometric properties are characterized by dilation, anisotropic stretch, and rotation. Extreme singular values of the Spatial Propagator describe quasi-separatrix layers (QSLs), while true separatrix surfaces and separator lines are identified by the vanishing of one and two singular values, respectively. Finally, we show that, among other possible applications, the squashing factor [Q ] is easily constructed from an analysis of particular sub-matrices of the Spatial Propagator. Title: Transient Inverse-FIP Plasma Composition Evolution within a Solar Flare Authors: Baker, Deborah; van Driel-Gesztelyi, Lidia; Brooks, David H.; Valori, Gherardo; James, Alexander W.; Laming, J. Martin; Long, David M.; Démoulin, Pascal; Green, Lucie M.; Matthews, Sarah A.; Oláh, Katalin; Kővári, Zsolt Bibcode: 2019ApJ...875...35B Altcode: 2019arXiv190206948B Understanding elemental abundance variations in the solar corona provides an insight into how matter and energy flow from the chromosphere into the heliosphere. Observed variations depend on the first ionization potential (FIP) of the main elements of the Sun’s atmosphere. High-FIP elements (>10 eV) maintain photospheric abundances in the corona, whereas low-FIP elements have enhanced abundances. Conversely, inverse FIP (IFIP) refers to the enhancement of high-FIP or depletion of low-FIP elements. We use spatially resolved spectroscopic observations, specifically the Ar XIV/Ca XIV intensity ratio, from Hinode’s Extreme-ultraviolet Imaging Spectrometer to investigate the distribution and evolution of plasma composition within two confined flares in a newly emerging, highly sheared active region. During the decay phase of the first flare, patches above the flare ribbons evolve from the FIP to the IFIP effect, while the flaring loop tops show a stronger FIP effect. The patch and loop compositions then evolve toward the preflare basal state. We propose an explanation of how flaring in strands of highly sheared emerging magnetic fields can lead to flare-modulated IFIP plasma composition over coalescing umbrae which are crossed by flare ribbons. Subsurface reconnection between the coalescing umbrae leads to the depletion of low-FIP elements as a result of an increased wave flux from below. This material is evaporated when the flare ribbons cross the umbrae. Our results are consistent with the ponderomotive fractionation model for the creation of IFIP-biased plasma. Title: Modeling the Effect of Mass-draining on Prominence Eruptions Authors: Jenkins, Jack M.; Hopwood, Matthew; Démoulin, Pascal; Valori, Gherardo; Aulanier, Guillaume; Long, David M.; van Driel-Gesztelyi, Lidia Bibcode: 2019ApJ...873...49J Altcode: 2019arXiv190110970J Quiescent solar prominences are observed within the solar atmosphere for up to several solar rotations. Their eruption is commonly preceded by a slow increase in height that can last from hours to days. This increase in the prominence height is believed to be due to their host magnetic flux rope transitioning through a series of neighboring quasi-equilibria before the main loss of equilibrium that drives the eruption. Recent work suggests that the removal of prominence mass from a stable, quiescent flux rope is one possible cause for this change in height. However, these conclusions are drawn from observations and are subject to interpretation. Here, we present a simple model to quantify the effect of “mass-draining” during the pre-eruptive height evolution of a solar flux rope. The flux rope is modeled as a line current suspended within a background potential magnetic field. We first show that the inclusion of mass, up to 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. Title: Generic Magnetic Field Intensity Profiles of Interplanetary Coronal Mass Ejections at Mercury, Venus, and Earth From Superposed Epoch Analyses Authors: Janvier, Miho; Winslow, Reka M.; Good, Simon; Bonhomme, Elise; Démoulin, Pascal; Dasso, Sergio; Möstl, Christian; Lugaz, Noé; Amerstorfer, Tanja; Soubrié, Elie; Boakes, Peter D. Bibcode: 2019JGRA..124..812J Altcode: 2019arXiv190109921J We study interplanetary coronal mass ejections (ICMEs) measured by probes at different heliocentric distances (0.3-1 AU) to investigate the propagation of ICMEs in the inner heliosphere and determine how the generic features of ICMEs change with heliospheric distance. Using data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER), Venus Express and ACE spacecraft, we analyze with the superposed epoch technique the profiles of ICME substructures, namely, the sheath and the magnetic ejecta. We determine that the median magnetic field magnitude in the sheath correlates well with ICME speeds at 1 AU, and we use this proxy to order the ICMEs at all spacecraft. We then investigate the typical ICME profiles for three categories equivalent to slow, intermediate, and fast ICMEs. Contrary to fast ICMEs, slow ICMEs have a weaker solar wind field at the front and a more symmetric magnetic field profile. We find the asymmetry to be less pronounced at Earth than at Mercury, indicating a relaxation taking place as ICMEs propagate. We also find that the magnetic field intensities in the wake region of the ICMEs do not go back to the pre-ICME solar wind intensities, suggesting that the effects of ICMEs on the ambient solar wind last longer than the duration of the transient event. Such results provide an indication of physical processes that need to be reproduced by numerical simulations of ICME propagation. The samples studied here will be greatly improved by future missions dedicated to the exploration of the inner heliosphere, such as Parker Solar Probe and Solar Orbiter. Title: Physical Processes Involved in the EUV "Surge" Event of 9 May 2012 Authors: López Fuentes, Marcelo; Mandrini, Cristina H.; Poisson, Mariano; Démoulin, Pascal; Cristiani, Germán; López, Fernando M.; Luoni, Maria Luisa Bibcode: 2018SoPh..293..166L Altcode: 2018arXiv181012403L We study an extreme ultraviolet (EUV) confined ejection observed on 9 May 2012 in Active Region (AR) NOAA 11476. For the analysis we use observations in multiple wavelengths (EUV, X-rays, Hα , and magnetograms) from a variety of ground- and space-based instruments. The magnetic configuration showed two rotating bipoles within the following polarity of the AR. This evolution was present some tens of hours before the studied event and continued thereafter. During this period, the magnetic flux of both bipoles continuously decreased. A mini-filament with a length of ≈30″ lay along the photospheric inversion line of the largest bipole. The mini-filament was observed to erupt, accompanied by an M4.7 flare (SOL20120509T12:23:00). This injected dense material as well as twist along closed loops in the form of a very broad ejection whose morphology resembled that of typical Hα surges. We conclude that the flare and eruption can be explained as due to two reconnection processes, one occurring below the erupting mini-filament, and another above it. This second process injects the mini-filament plasma within the reconnected closed loops linking the main AR polarities. By analyzing the magnetic topology using a force-free model of the coronal field, we identify the location of quasi-separatix layers, where reconnection is prone to occur, and present a detailed interpretation of the chromospheric and coronal eruption observations. In particular, this event, in contrast to what has been proposed in several models explaining surges and/or jets, is not produced by magnetic flux emergence, but by magnetic flux cancellation accompanied by the rotation of the bipoles. In fact, the conjunction of these two processes, flux cancellation and bipole rotations, is at the origin of a series of events, homologous to the event we analyze in this article, which occurred in AR 11476 from 8 to 10 May 2012. Title: Recurrent eruptions by converging and shearing polarities in a solar AR 12371 Authors: Vemareddy, P.; Demoulin, P. Bibcode: 2018csc..confE..67V Altcode: Solar eruptions, which include flares and CMEs, influence the heliosphere and planetary atmosphere in a wide range of physical phenomena. Powerful, spectacular eruptions occur in active regions (ARs) with distinct evolving conditions. In the space weather perspective, they are of great scientific interest compared to non-eruptive ARs. To this end, we consider the AR 12371 producing faster CMEs recurrently in a week time of observation. Coronal observations from AIA/SDO reveal inverse S-sigmoid morphology to the magnetic structure. The HMI/SDO magnetic field observations show converging and shearing motion of opposite polarity regions co-spatial with the twisted core flux system of the sigmoid. From these observations, we propose continuous shearing and submerging motion of opposite polarity regions lead to formation of sheared arcade, which upon slow reconnection forms flux rope being erupted by tether-cutting reconnection. Various magnetic non-potential parameters support this scenario of energy build up and release by eruptions. We further analyzed modeling aspect of AR magnetic structure and feasibility conditions for eruption. We further study the magnetic structure of successively erupting sigmoid in active region (AR) 12371 by modeling the quasi-static coronal field evolution with non-linear force-free field (NLFFF) equilibria. The modelled structure captured major features of sigmoid-to-arcade-to-sigmoid transformation, that is being recurrent under continuous photospheric flux motions. Calculations of the field line twist reveal a fractional increase followed by a decrease of the number of pixels having a range of twist. This traces the buildup process of twisted core field by slow photospheric motions and the relaxation after eruption, respectively. Our study infers that the large eruptivity of this AR is due to a steep decrease of the overlying coronal field meeting the torus instability criteria from a significantly lower height (≈50 Mm) in contrast to non-eruptive ARs. Title: The nature of imploding loops during solar eruptions as revealed by MHD simulations and AIA observations Authors: Aulanier, Guillaume; Dudik, Jaroslav; Zucarello, F. P.; Demoulin, Pascal; Schmieder, Brigitte Bibcode: 2018csc..confE..19A Altcode: Over the last years AIA revealed the frequent occurence of contracting loops at the flanks of erupting active regions. Those have often been interpreted as an evidence of the implosion conjecture that relates magnetic energy decreases with volume contractions in the Sun's corona. So as to unveil the physical nature of these features we carried out observational analyses of two solar eruptions observed with AIA with different projection angles, which we coupled with new analyses of a generic zero-beta MHD simulation of an asymmetric eruption driven by the torus instability, that was not designed for this particular study. The simulation does display contracting loops in general. And the synthetic time-slices of the simulation, when rotated to the right projections, do match the observed ones. But in the simulation these inward motions are not due to any volume contraction. Instead they are associated with two large-scale quasi-incompressible coronal-vortices. Those develop at the flanks of the erupting flux ropes, as most of the compressive component of the flow is evacuated away by an Alfven wave in the early stages of the eruption. We argue that this behavior is merely a magnetic version of the usual pressure-driven formation of vortex rings in hydrodyanmics. This result implies that during a solar eruption, the free magnetic-energy from the pre-erupting active-region is converted not only in the flare and the CME, but is also "lost" in the generation of these two large-scale coronal vortices. Title: Exploring the biases of a new method based on minimum variance for interplanetary magnetic clouds Authors: Démoulin, P.; Dasso, S.; Janvier, M. Bibcode: 2018A&A...619A.139D Altcode: 2018arXiv180900522D Context. Magnetic clouds (MCs) are twisted magnetic structures ejected from the Sun and probed by in situ instruments. They are typically modeled as flux ropes (FRs).
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. Bibcode: 2018ApJ...862..117D Altcode: 2018arXiv180700020D We describe and analyze observations by the Solar Dynamics Observatory of the emergence of a small, bipolar active region within an area of unipolar magnetic flux that was surrounded by a circular, quiescent filament. Within only 8 hours from the start of the emergence, a partial splitting of the filament and two consecutive coronal mass ejections took place. We argue that all three dynamic events occurred as a result of particular magnetic-reconnection episodes between the emerging bipole and the pre-existing coronal magnetic field. To substantiate our interpretation, we consider 3D magnetohydrodynamic simulations that model the emergence of magnetic flux in the vicinity of a large-scale coronal flux rope. The simulations qualitatively reproduce most of the reconnection episodes suggested by the observations, as well as the filament splitting, the first eruption, and the formation of sheared/twisted fields that may have played a role in the second eruption. Our results suggest that the position of emerging flux with respect to the background magnetic configuration is a crucial factor for the resulting evolution, while previous results suggest that parameters such as the orientation or the amount of emerging flux are important as well. This poses a challenge for predicting the onset of eruptions that are triggered by flux emergence, and calls for a detailed survey of the relevant parameter space by means of numerical simulations. Title: Manifestation of Coronal Mass Ejections near Earth: A review Authors: Dasso, Sergio; Rodriguez, . Luciano, , dr.; Demoulin, Pascal; Masias-Meza, Jimmy J.; Janvier, Miho; Lanabere, Vanina Bibcode: 2018cosp...42E.768D Altcode: Coronal Mass Ejections (CMEs) are launched from the Sun, as a result of magnetic instabilities, carrying away a huge amount of magnetic flux and helicity. Interplanetary CMEs (ICMEs) are their manifestations observed further away in the heliosphere. ICMEs contain different plasma and magnetic field properties, compared with those of the ambient solar wind. From the large number of observed ICMEs in the past years, we significantly increased our knowledge on several of their properties such as: their global 3D shape, the identification of the composing sub-structures, the amount of magnetohydrodynamical quantities transported, as well as how the plasma and magnetic field are typically distributed inside them.In the present talk we will present a general review of these aspects of ICMEs. In particular we will focus on the total amount of magnetic flux and helicity ejected by CMEs from the Sun along a solar cycle, and on plasma and magnetic properties of their shock/sheath/flux-rope/wake. These results can help to understand their interaction with the ambient solar wind and with planetary magnetic environments. They are particularly crucial for a better understanding of the Sun-Earth coupling. Title: The effect of magnetic tongues in the determination of Joy's law Authors: Poisson, Mariano; Mandrini, Cristina H.; Lopez Fuentes, Marcelo; Demoulin, Pascal Bibcode: 2018cosp...42E2706P Altcode: We study the emergence of 186 bipolar active regions (ARs) to determine the relation between the tilt angle formed with respect to the E-W direction and the latitude of emergence. This relation, known as Joy's law, plays a fundamental role to test the ability of dynamo models to explain, among other things, the equatorial flux cancelation and the inversion of the poloidal magnetic field between solar cycles. The methods used in recent works to determine this law are based on the automatic computation of the tilt angle from line-of-sight (LOS) magnetograms (Stenflo & Kosovichev 2012; Wang et al. 2015). However, since those results show a large dispersion, the precise latitudinal depedence on the tilt is still a topic of discussion. We consider that an important part of this dispersion can be due to the effect of the so called magnetic tongues. These are produced by the line of sight projection of the azimuthal magnetic field of the twisted emerging flux-tubes that form ARs. The tongues are observed in LOS magnetograms as an elongation of the magnetic polarities. In Poisson et al. (2016, Solar Phys., 291, 1625-1646) we showed that the magnetic tongues affect the photospheric field distribution observed in LOS magnetograms and, consequently, impact on the determination of the tilt angle. In this work we test a novel method to remove the effect of the tongues on the tilt angle determination and we quantify the effect of this correction on Joy's law. Furthermore, we study the relation of the latitudinal dependence of the corrected tilt with other AR properties such as the magnetic helicity sign, the hemisphere of emergence, and the sense of rotation of the bipoles. Title: Constructing a Generic Icme from the Sun to Earth from Statistical Studies of in Situ Data Authors: Janvier, Miho; Dasso, Sergio; Demoulin, Pascal Bibcode: 2018cosp...42E1600J Altcode: Interplanetary Coronal Mass Ejections (ICMEs) are detected in situ by instruments measuring the magnetic field and plasma properties of the ambient solar wind. In particular, a subset of ICMEs, referred to as Magnetic Clouds (MCs), is well defined by the presence of a rotating magnetic field, indicative of a twisted magnetic structure. Shocks, on the other hand, are also well defined in the interplanetary medium as sharp discontinuities in the plasma and magnetic properties. Both structures then allow defining the presence of a sheath region between the shock and the MC. Over the past years, we have proposed and refined new statistical methods aiming at analyzing ICME properties, so as to assess the existence of a generic shape and a generic internal profile of ICMEs at different distances from the Sun. These methods rely on the computation from the data of the distribution of the shock normal and the flux-rope axis directions. From these analysis, we were able to constrain an analytical shape that describes best these observed distributions. Another method is a superposed epoch analysis so as to obtain typical profiles of ICME substructures at different distances from the Sun. Next, we compare such generic features of ICMEs to numerical simulations and heliospheric images of CMEs. We will discuss the commonalities, then the discrepancies that need to be further understood between the models and the constraints given by the in situ data. This is important in completing the scenario of the evolution of solar eruptive flares, from their start in the Sun's atmosphere to their evolution in the solar wind. Title: Coronal Elemental Abundances in Solar Emerging Flux Regions Authors: Baker, Deborah; Brooks, David H.; van Driel-Gesztelyi, Lidia; James, Alexander W.; Démoulin, Pascal; Long, David M.; Warren, Harry P.; Williams, David R. Bibcode: 2018ApJ...856...71B Altcode: 2018arXiv180108424B The chemical composition of solar and stellar atmospheres differs from the composition of their photospheres. Abundances of elements with low first ionization potential (FIP) are enhanced in the corona relative to high-FIP elements with respect to the photosphere. This is known as the FIP effect and it is important for understanding the flow of mass and energy through solar and stellar atmospheres. We used spectroscopic observations from the Extreme-ultraviolet Imaging Spectrometer on board the Hinode observatory to investigate the spatial distribution and temporal evolution of coronal plasma composition within solar emerging flux regions inside a coronal hole. Plasma evolved to values exceeding those of the quiet-Sun corona during the emergence/early-decay phase at a similar rate for two orders of magnitude in magnetic flux, a rate comparable to that observed in large active regions (ARs) containing an order of magnitude more flux. During the late-decay phase, the rate of change was significantly faster than what is observed in large, decaying ARs. Our results suggest that the rate of increase during the emergence/early-decay phase is linked to the fractionation mechanism that leads to the FIP effect, whereas the rate of decrease during the later decay phase depends on the rate of reconnection with the surrounding magnetic field and its plasma composition. Title: Studying the Transfer of Magnetic Helicity in Solar Active Regions with the Connectivity-based Helicity Flux Density Method Authors: Dalmasse, K.; Pariat, É.; Valori, G.; Jing, J.; Démoulin, P. Bibcode: 2018ApJ...852..141D Altcode: 2017arXiv171204691D In the solar corona, magnetic helicity slowly and continuously accumulates in response to plasma flows tangential to the photosphere and magnetic flux emergence through it. Analyzing this transfer of magnetic helicity is key for identifying its role in the dynamics of active regions (ARs). The connectivity-based helicity flux density method was recently developed for studying the 2D and 3D transfer of magnetic helicity in ARs. The method takes into account the 3D nature of magnetic helicity by explicitly using knowledge of the magnetic field connectivity, which allows it to faithfully track the photospheric flux of magnetic helicity. Because the magnetic field is not measured in the solar corona, modeled 3D solutions obtained from force-free magnetic field extrapolations must be used to derive the magnetic connectivity. Different extrapolation methods can lead to markedly different 3D magnetic field connectivities, thus questioning the reliability of the connectivity-based approach in observational applications. We address these concerns by applying this method to the isolated and internally complex AR 11158 with different magnetic field extrapolation models. We show that the connectivity-based calculations are robust to different extrapolation methods, in particular with regard to identifying regions of opposite magnetic helicity flux. We conclude that the connectivity-based approach can be reliably used in observational analyses and is a promising tool for studying the transfer of magnetic helicity in ARs and relating it to their flaring activity. Title: Field distribution of magnetograms from simulations of active region formation Authors: Dacie, S.; van Driel-Gesztelyi, L.; Démoulin, P.; Linton, M. G.; Leake, J. E.; MacTaggart, D.; Cheung, M. C. M. Bibcode: 2017A&A...606A..34D Altcode: Context. The evolution of the photospheric magnetic field distributions (probability densities) has previously been derived for a set of active regions. Photospheric field distributions are a consequence of physical processes that are difficult to determine from observations alone.
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 Bibcode: 2017SPD....4811206D Altcode: Analyzing the transfer of magnetic helicity in active regions is a key component for understanding the nature of its coronal storage and release and for identifying its role in the coronal dynamics of active regions. We recently developed a method for studying the photospheric flux of magnetic helicity in both 2D and 3D. The method takes into account the 3D nature of magnetic helicity by explicitly using knowledge of the magnetic field connectivity. Since the coronal magnetic field in active regions is not measured, we rely on the non-unique 3D solution obtained from force-free coronal magnetic field extrapolations to derive the magnetic field connectivity. In this poster, we apply the method to the complex and highly-flaring active region NOAA 11158 using the magnetic field connectivity derived from different force-free extrapolation models and implementations. We show that the calculations of photospheric flux of magnetic helicity are robust to different extrapolation methods and assumptions, in particular with regards to identifying regions of opposite magnetic helicity flux. Finally, we discuss the implications of our results for tracking the transfer of magnetic helicity in active regions and relate it to their flaring activity. Title: Expanding and Contracting Coronal Loops as Evidence of Vortex Flows Induced by Solar Eruptions Authors: Dudík, J.; Zuccarello, F. P.; Aulanier, G.; Schmieder, B.; Démoulin, P. Bibcode: 2017ApJ...844...54D Altcode: 2017arXiv170604783D Eruptive solar flares were predicted to generate large-scale vortex flows at both sides of the erupting magnetic flux rope. This process is analogous to a well-known hydrodynamic process creating vortex rings. The vortices lead to advection of closed coronal loops located at the peripheries of the flaring active region. Outward flows are expected in the upper part and returning flows in the lower part of the vortex. Here, we examine two eruptive solar flares, the X1.1-class flare SOL2012-03-05T03:20 and the C3.5-class SOL2013-06-19T07:29. In both flares, we find that the coronal loops observed by the Atmospheric Imaging Assembly in its 171 Å, 193 Å, or 211 Å passbands show coexistence of expanding and contracting motions, in accordance with the model prediction. In the X-class flare, multiple expanding and contracting loops coexist for more than 35 minutes, while in the C-class flare, an expanding loop in 193 Å appears to be close by and cotemporal with an apparently imploding loop arcade seen in 171 Å. Later, the 193 Å loop also switches to contraction. These observations are naturally explained by vortex flows present in a model of eruptive solar flares. Title: Studying the transfer of magnetic helicity in solar active regions Authors: Dalmasse, Kévin; Jing, J.; Pariat, E.; Valori, G.; Démoulin, P. Bibcode: 2017shin.confE.160D Altcode: Analyzing the transfer of magnetic helicity in active regions is a key component for understanding the nature of its coronal storage and release and for identifying its role in the coronal dynamics of active regions. We recently developed a method for studying the photospheric flux of magnetic helicity in both 2D and 3D. The method takes into account the 3D nature of magnetic helicity by explicitly using knowledge of the magnetic field connectivity. Since the coronal magnetic field in active regions is not measured, we rely on the approximate 3D solution obtained from force-free coronal magnetic field extrapolations to derive the magnetic field connectivity. In this poster, we apply the method to the complex and highly-flaring active region NOAA 11158 using the magnetic field connectivity derived from different force-free extrapolation models and implementations. We show that the calculations of photospheric flux of magnetic helicity are robust to different extrapolation methods and assumptions, in particular with regards to identifying regions of opposite magnetic helicity flux. Finally, we discuss the implications of our results for tracking the transfer of magnetic helicity in active regions and relate it to their flaring activity. Title: A study of the long term evolution in active region upflows Authors: Harra, Louise K.; Ugarte-Urra, Ignacio; De Rosa, Marc; Mandrini, Cristina; van Driel-Gesztelyi, Lidia; Baker, Deborah; Culhane, J. Leonard; Démoulin, Pascal Bibcode: 2017PASJ...69...47H Altcode: Since their discovery, upflows at the edges of active regions have attracted a lot of interest, primarily as they could potentially contribute to the slow solar wind. One aspect that has not been studied yet is how the long term evolution of active regions impacts the upflows. In this work, we analyze one active region that survives three solar rotations. We track how the flows change with time. We use local and global modeling of the decaying active region to determine how the age of the active region will impact the extent of the open magnetic fields, and then how some of the upflows could become outflows. We finish with a discussion of how these results, set in a broader context, can be further developed with the Solar Orbiter mission. Title: Apparent and Intrinsic Evolution of Active Region Upflows Authors: Baker, Deborah; Janvier, Miho; Démoulin, Pascal; Mandrini, Cristina H. Bibcode: 2017SoPh..292...46B Altcode: 2017arXiv170206022B We analyze the evolution of Fe XII coronal plasma upflows from the edges of ten active regions (ARs) as they cross the solar disk using the Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) to do this. Confirming the results of Démoulin et al. (Sol. Phys.283, 341, 2013), we find that for each AR there is an observed long-term evolution of the upflows. This evolution is largely due to the solar rotation that progressively changes the viewpoint of dominantly stationary upflows. From this projection effect, we estimate the unprojected upflow velocity and its inclination to the local vertical. AR upflows typically fan away from the AR core by 40° to nearly vertical for the following polarity. The span of inclination angles is more spread out for the leading polarity, with flows angled from −29° (inclined toward the AR center) to 28° (directed away from the AR). In addition to the limb-to-limb apparent evolution, we identify an intrinsic evolution of the upflows that is due to coronal activity, which is AR dependent. Furthermore, line widths are correlated with Doppler velocities only for the few ARs with the highest velocities. We conclude that for the line widths to be affected by the solar rotation, the spatial gradient of the upflow velocities must be large enough such that the line broadening exceeds the thermal line width of Fe XII. Finally, we find that upflows occurring in pairs or multiple pairs are a common feature of ARs observed by Hinode/EIS, with up to four pairs present in AR 11575. This is important for constraining the upflow-driving mechanism as it implies that the mechanism is not local and does not occur over a single polarity. AR upflows originating from reconnection along quasi-separatrix layers between overpressure AR loops and neighboring underpressure loops is consistent with upflows occurring in pairs, unlike other proposed mechanisms that act locally in one polarity. Title: Vortex and Sink Flows in Eruptive Flares as a Model for Coronal Implosions Authors: Zuccarello, F. P.; Aulanier, G.; Dudík, J.; Démoulin, P.; Schmieder, B.; Gilchrist, S. A. Bibcode: 2017ApJ...837..115Z Altcode: 2017arXiv170200199Z Eruptive flares are sudden releases of magnetic energy that involve many phenomena, several of which can be explained by the standard 2D flare model and its realizations in 3D. We analyze a 3D magnetohydrodynamics simulation, in the framework of this model, that naturally explains the contraction of coronal loops in the proximity of the flare sites, as well as the inflow toward the region above the cusp-shaped loops. We find that two vorticity arcs located along the flanks of the erupting magnetic flux rope are generated as soon as the eruption begins. The magnetic arcades above the flux rope legs are then subjected to expansion, rotation, or contraction depending on which part of the vortex flow advects them. In addition to the vortices, an inward-directed magnetic pressure gradient exists in the current sheet below the magnetic flux rope. It results in the formation of a sink that is maintained by reconnection. We conclude that coronal loop apparent implosions observed during eruptive flares are the result of hydromagnetic effects related to the generation of vortex and sink flows when a flux rope moves in a magnetized environment. Title: Successive injection of opposite magnetic helicity in solar active region NOAA 11928 Authors: Vemareddy, P.; Démoulin, P. Bibcode: 2017A&A...597A.104V Altcode: 2016arXiv161100699V
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. Bibcode: 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. Bibcode: 2016AGUFMSH53A..03J Altcode: Coronal Mass Ejections (CMEs) are the result of magnetic instabilities in the Sun's atmosphere, which are consequently launched into the heliosphere. As their interplanetary counterparts (ICMEs) propagate in the interplanetary medium, they can interact with the magnetized environment of planets and other objects in the solar system. They are believed to be the main drivers of space weather. Over the past decades, the multiplication of space missions has led to a gold mine in ICME data, allowing us to deepen our knowledge on their properties and evolution from the Sun to the Earth. In particular, the identification of substructures such as shocks and magnetic clouds and their typical profiles, as well as their properties, can be traced at different locations away from the Sun. Here, we will review different aspects of ICMEs, such as their 3D generic shape, the transported physical quantities as well as their evolution (such as the expansion) in the inner heliosphere. These aspects can be quantified by in situ data, and consequently they can provide useful information to constrain analytical and numerical models as well as remote-sensing data interpretation. They also provide key questions to be addressed by the future Solar Orbiter and Solar Probe Plus missions. Title: Quantitative model for the generic 3D shape of ICMEs at 1 AU Authors: Démoulin, P.; Janvier, M.; Masías-Meza, J. J.; Dasso, S. Bibcode: 2016A&A...595A..19D Altcode: 2016arXiv160808550D Context. Interplanetary imagers provide 2D projected views of the densest plasma parts of interplanetary coronal mass ejections (ICMEs), while in situ measurements provide magnetic field and plasma parameter measurements along the spacecraft trajectory, that is, along a 1D cut. The data therefore only give a partial view of the 3D structures of ICMEs.
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 Bibcode: 2016SoPh..291.1739P Altcode: 2016arXiv160505704P; 2016SoPh..tmp..101P Coronal magnetic null points exist in abundance, as demonstrated by extrapolations of the coronal field, and have been inferred to be important for a broad range of energetic events. These null points and their associated separatrix and spine field lines represent discontinuities of the field line mapping, making them preferential locations for reconnection. This field line mapping also exhibits strong gradients adjacent to the separatrix (fan) and spine field lines, which can be analysed using the "squashing factor", Q . In this article we analyse in detail the distribution of Q in the presence of magnetic nulls. While Q is formally infinite on both the spine and fan of the null, the decay of Q away from these structures is shown in general to depend strongly on the null-point structure. For the generic case of a non-radially-symmetric null, Q decays most slowly away from the spine or fan in the direction in which |B | increases most slowly. In particular, this demonstrates that the extended elliptical high-Q halo around the spine footpoints observed by Masson et al. (Astrophys. J.700, 559, 2009) is a generic feature. This extension of the Q halos around the spine or fan footpoints is important for diagnosing the regions of the photosphere that are magnetically connected to any current layer that forms at the null. In light of this, we discuss how our results can be used to interpret the geometry of observed flare ribbons in circular ribbon flares, in which typically a coronal null is implicated. We conclude that both the physics in the vicinity of the null and how this is related to the extension of Q away from the spine or fan can be used in tandem to understand observational signatures of reconnection at coronal null points. Title: Properties of Magnetic Tongues over a Solar Cycle Authors: Poisson, Mariano; Démoulin, Pascal; López Fuentes, Marcelo; Mandrini, Cristina H. Bibcode: 2016SoPh..291.1625P Altcode: 2016arXiv160900329P; 2016SoPh..tmp..109P The photospheric spatial distribution of the main magnetic polarities of bipolar active regions (ARs) present during their emergence deformations are known as magnetic tongues. They are attributed to the presence of twist in the toroidal magnetic-flux tubes that form the ARs. The aim of this article is to study the twist of newly emerged ARs from the evolution of magnetic tongues observed in photospheric line-of-sight magnetograms. We apply the procedure described by Poisson et al. (Solar Phys.290, 727, 2015a) to ARs observed over the full Solar Cycle 23 and the beginning of Cycle 24. Our results show that the hemispherical rule obtained using the tongues as a proxy of the twist has a weak sign dominance (53 % in the southern hemisphere and 58 % in the northern hemisphere). By defining the variation of the tongue angle, we characterize the strength of the magnetic tongues during different phases of the AR emergence. We find that there is a tendency of the tongues to be stronger during the beginning of the emergence and to become weaker as the AR reaches its maximum magnetic flux. We compare this evolution with the emergence of a toroidal flux-rope model with non-uniform twist. The variety of evolution of the tongues in the analyzed ARs can only be reproduced when using a broad range of twist profiles, in particular having a large variety of twist gradients in the direction vertical to the photosphere. Although the analytical model used is a special case, selected to minimize the complexity of the problem, the results obtained set new observational constraints to theoretical models of flux-rope emergence that form bipolar ARs. Title: Superposed epoch study of ICME sub-structures near Earth and their effects on Galactic cosmic rays Authors: Masías-Meza, J. J.; Dasso, S.; Démoulin, P.; Rodriguez, L.; Janvier, M. Bibcode: 2016A&A...592A.118M Altcode: 2016arXiv160508130M Context. Interplanetary coronal mass ejections (ICMEs) are the interplanetary manifestations of solar eruptions. The overtaken solar wind forms a sheath of compressed plasma at the front of ICMEs. Magnetic clouds (MCs) are a subset of ICMEs with specific properties (e.g. the presence of a flux rope). When ICMEs pass near Earth, ground observations indicate that the flux of Galactic cosmic rays (GCRs) decreases.
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. Bibcode: 2016SoPh..291.2145R Altcode: 2016SoPh..tmp..113R Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs). They are important because of their simple internal magnetic field configuration, which resembles a magnetic flux rope, and because they represent one of the most geoeffective types of solar transients. In this study, we analyze their internal structure using a superposed epoch method on 63 events observed at L1 by the Advance Composition Explorer (ACE), between 1998 and 2006. In this way, we obtain an average profile for each plasma and magnetic field parameter at each point of the cloud. Furthermore, we take a fixed time-window upstream and downstream from the MC to also sample the regions preceding the cloud and the wake trailing it. We then perform a detailed analysis of the internal characteristics of the clouds and their surrounding solar wind environments. We find that the parameters studied are compatible with log-normal distribution functions. The plasma β and the level of fluctuations in the magnetic field vector are the best parameters to define the boundaries of MCs. We find that one third of the events shows a peak in plasma density close to the trailing edge of the flux ropes. We provide several possible explanations for this result and investigate if the density peak is of a solar origin (e.g. erupting prominence material) or formed during the magnetic cloud travel from the Sun to 1 AU. The most plausible explanation is the compression due to a fast overtaking flow, coming from a coronal hole located to the east of the solar source region of the magnetic cloud. Title: Manifestation of Coronal Mass Ejections near Earth: A review Authors: Dasso, Sergio; Rodriguez, Luciano; Demoulin, Pascal; Masías-Meza, Jimmy J.; Janvier, Miho Bibcode: 2016cosp...41E.405D Altcode: Coronal Mass Ejections (CMEs) are launched from the Sun, as a result of magnetic instabilities, carrying away a huge amount of magnetic flux and helicity. Interplanetary CMEs (ICMEs) are their manifestation observed further away in the heliosphere. ICMEs produce important changes of plasma and magnetic field properties in the interplanetary medium, with respect to the ones of the ambient solar wind. From the large number of observed ICMEs, in the past years we significantly increased our kwnoledge on several of their properties, such as: the identification of the composing sub-structures and their local properties, their global 3D shape, the amount of magnetohydrodynamical quantities transported in the heliosphere by the associated flux ropes, as well as how the plasma and magnetic field are distributed inside them. In the present talk we will present a general review of these aspects of ICMEs. In particular we will focuss on the total amount of magnetic flux and helicity ejected by CMEs from the Sun along a solar cycle, and on plasma and magnetic properties of their shock-sheath-flux_rope-wake. These results can help to understand their interaction with the ambient solar wind and with planetary magnetic environments. They are particularly crucial for a better understanding of the Sun-Earth coupling. Title: Why are flare ribbons generically elongated in configurations with magnetic null points? Authors: Pontin, David Iain; Galsgaard, Klaus; Demoulin, Pascal Bibcode: 2016SPD....47.0625P Altcode: Coronal magnetic null points exist in abundance as demonstrated by extrapolations of the coronal field, and have been inferred to be important for a broad range of energetic events. These null points and their associated separatrix and spine field lines represent discontinuities of the field line mapping, making them preferential locations for reconnection in the corona. In addition, the field line mapping in the vicinity of these null points exhibits strong gradients as measured by the “squashing factor”, Q. We demonstrate that the extension of the Q halos around the spine/fan footpoints is in general important for diagnosing the regions of the photosphere that are magnetically connected to any current layer that forms at the null. In light of this, we discuss the extent to which our results can be used to interpret the geometry of observed flare ribbons in events in which a coronal null is implicated. We conclude that together the physics in the vicinity of the null and how this is related to the extension of Q away from the spine/fan can be used in tandem to understand observational signatures of reconnection at coronal null points. Title: Homologous Solar Events on 2011 January 27: Build-up and Propagation in a Complex Coronal Environment Authors: Pick, M.; Stenborg, G.; Démoulin, P.; Zucca, P.; Lecacheux, A. Bibcode: 2016ApJ...823....5P Altcode: In spite of the wealth of imaging observations at the extreme-ultraviolet (EUV), X-ray, and radio wavelengths, there are still relatively few cases where all of the imagery is available to study the full development of a coronal mass ejection (CME) event and its associated shock. The aim of this study is to contribute to the understanding of the role of the coronal environment in the development of CMEs and the formation of shocks, and their propagation. We have analyzed the interactions of a couple of homologous CME events with ambient coronal structures. Both events were launched in a direction far from the local vertical, and exhibited a radical change in their direction of propagation during their progression from the low corona into higher altitudes. Observations at EUV wavelengths from the Atmospheric Imaging Assembly instrument on board the Solar Dynamic Observatory were used to track the events in the low corona. The development of the events at higher altitudes was followed by the white-light coronagraphs on board the Solar and Heliospheric Observatory. Radio emissions produced during the development of the events were well recorded by the Nançay solar instruments. Thanks to their detection of accelerated electrons, the radio observations are an important complement to the EUV imaging. They allowed us to characterize the development of the associated shocks, and helped to unveil the physical processes behind the complex interactions between the CMEs and ambient medium (e.g., compression, reconnection). Title: Magnetic Flux and Helicity of Magnetic Clouds Authors: Démoulin, P.; Janvier, M.; Dasso, S. Bibcode: 2016SoPh..291..531D Altcode: 2015SoPh..tmp..183D; 2015arXiv150901068D Magnetic clouds (MCs) are formed by flux ropes (FRs) launched from the Sun as part of coronal mass ejections (CMEs). They carry away a large amount of magnetic flux and helicity. The main aim of this study is to quantify these amounts from in situ measurements of MCs at 1 AU. The fit of these data by a local FR model provides the axial magnetic field strength, the radius, the magnetic flux, and the helicity per unit length along the FR axis. We show that these quantities are statistically independent of the position along the FR axis. We then derive the generic shape and length of the FR axis from two sets of MCs. These results improve the estimation of magnetic helicity. Next, we evaluate the total magnetic flux and helicity that cross the sphere of radius of 1 AU, centred at the Sun, per year and during a solar cycle. We also include in the study two sets of small FRs that do not have all the typical characteristics of MCs. While small FRs are at least ten times more numerous than MCs, the magnetic flux and helicity are dominated by the contribution from the larger MCs. In one year they carry away the magnetic flux of about 25 large active regions and the magnetic helicity of 200 of them. MCs carry away an amount of unsigned magnetic helicity similar to the amount estimated for the solar dynamo and that measured in emerging active regions. Title: Erratum to: The Magnetic Helicity Budget of a CME-Prolific Active Region Authors: Green, L. M.; López Fuentes, M.; Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.; Culhane, J. L. Bibcode: 2016SoPh..291..335G Altcode: 2015SoPh..tmp..179G No abstract at ADS Title: From Coronal Observations to MHD Simulations, the Building Blocks for 3D Models of Solar Flares (Invited Review) Authors: Janvier, M.; Aulanier, G.; Démoulin, P. Bibcode: 2015SoPh..290.3425J Altcode: 2015SoPh..tmp...63J; 2015arXiv150505299J Solar flares are energetic events taking place in the Sun's atmosphere, and their effects can greatly impact the environment of the surrounding planets. In particular, eruptive flares, as opposed to confined flares, launch coronal mass ejections into the interplanetary medium, and as such, are one of the main drivers of space weather. After briefly reviewing the main characteristics of solar flares, we summarise the processes that can account for the build-up and release of energy during their evolution. In particular, we focus on the development of recent 3D numerical simulations that explain many of the observed flare features. These simulations can also provide predictions of the dynamical evolution of coronal and photospheric magnetic field. Here we present a few observational examples that, together with numerical modelling, point to the underlying physical mechanisms of the eruptions. Title: Active-Region Twist Derived from Magnetic Tongues and Linear Force-Free Extrapolations Authors: Poisson, Mariano; López Fuentes, Marcelo; Mandrini, Cristina H.; Démoulin, Pascal Bibcode: 2015SoPh..290.3279P Altcode: 2015SoPh..tmp..183P The main aim of this study is to compare the amount of twist present in emerging active regions (ARs) from photospheric and coronal data. We use linear force-free field models of the observed coronal structure of ARs to determine the global twist. The coronal twist is derived, on one hand, from the force-free parameter [α ] of the model and, on the other, from the computed coronal magnetic helicity normalized by the magnetic flux squared. We compare our results, for the same set of ARs, with those of Poisson et al. (Solar Phys.290, 727, 2015), in which the twist was estimated using the so-called magnetic tongues observed in line-of-sight magnetograms during AR emergence. We corroborate the agreement between the photospheric and coronal twist-sign and the presence of magnetic tongues as an early proxy of the AR non-potentiality. We find a globally linear relationship between the coronal twist and the one previously deduced for the emerging AR flux rope at the photospheric level. The coronal-twist value is typically lower by a factor of six than the one deduced for the emerging flux rope. We interpret this result as due to the partial emergence of the flux rope that forms the region. Title: The Origin of Net Electric Currents in Solar Active Regions Authors: Dalmasse, K.; Aulanier, G.; Démoulin, P.; Kliem, B.; Török, T.; Pariat, E. Bibcode: 2015ApJ...810...17D Altcode: 2015arXiv150705060D There is a recurring question in solar physics regarding whether or not electric currents are neutralized in active regions (ARs). This question was recently revisited using three-dimensional (3D) magnetohydrodynamic (MHD) numerical simulations of magnetic flux emergence into the solar atmosphere. Such simulations showed that flux emergence can generate a substantial net current in ARs. Other sources of AR currents are photospheric horizontal flows. Our aim is to determine the conditions for the occurrence of net versus neutralized currents with this second mechanism. Using 3D MHD simulations, we systematically impose line-tied, quasi-static, photospheric twisting and shearing motions to a bipolar potential magnetic field. We find that such flows: (1) produce both direct and return currents, (2) induce very weak compression currents—not observed in 2.5D—in the ambient field present in the close vicinity of the current-carrying field, and (3) can generate force-free magnetic fields with a net current. We demonstrate that neutralized currents are in general produced only in the absence of magnetic shear at the photospheric polarity inversion line—a special condition that is rarely observed. We conclude that photospheric flows, as magnetic flux emergence, can build up net currents in the solar atmosphere, in agreement with recent observations. These results thus provide support for eruption models based on pre-eruption magnetic fields that possess a net coronal current. Title: Parallel Evolution of Quasi-separatrix Layers and Active Region Upflows Authors: Mandrini, C. H.; Baker, D.; Démoulin, P.; Cristiani, G. D.; van Driel-Gesztelyi, L.; Vargas Domínguez, S.; Nuevo, F. A.; Vásquez, A. M.; Pick, M. Bibcode: 2015ApJ...809...73M Altcode: 2015arXiv150701264M Persistent plasma upflows were observed with Hinode’s EUV Imaging Spectrometer (EIS) at the edges of active region (AR) 10978 as it crossed the solar disk. We analyze the evolution of the photospheric magnetic and velocity fields of the AR, model its coronal magnetic field, and compute the location of magnetic null-points and quasi-sepratrix layers (QSLs) searching for the origin of EIS upflows. Magnetic reconnection at the computed null points cannot explain all of the observed EIS upflow regions. However, EIS upflows and QSLs are found to evolve in parallel, both temporarily and spatially. Sections of two sets of QSLs, called outer and inner, are found associated to EIS upflow streams having different characteristics. The reconnection process in the outer QSLs is forced by a large-scale photospheric flow pattern, which is present in the AR for several days. We propose a scenario in which upflows are observed, provided that a large enough asymmetry in plasma pressure exists between the pre-reconnection loops and lasts as long as a photospheric forcing is at work. A similar mechanism operates in the inner QSLs; in this case, it is forced by the emergence and evolution of the bipoles between the two main AR polarities. Our findings provide strong support for the results from previous individual case studies investigating the role of magnetic reconnection at QSLs as the origin of the upflowing plasma. Furthermore, we propose that persistent reconnection along QSLs does not only drive the EIS upflows, but is also responsible for the continuous metric radio noise-storm observed in AR 10978 along its disk transit by the Nançay Radio Heliograph. Title: Testing magnetic helicity conservation in a solar-like active event Authors: Pariat, E.; Valori, G.; Démoulin, P.; Dalmasse, K. Bibcode: 2015A&A...580A.128P Altcode: 2015arXiv150609013P Context. Magnetic helicity has the remarkable property of being a conserved quantity of ideal magnetohydrodynamics (MHD). Therefore, it could be used as an effective tracer of the magnetic field evolution of magnetized plasmas.
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 (<2.2%), in particular compared to the relative dissipation of magnetic energy (>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 http://www.aanda.org Title: Strong coronal channelling and interplanetary evolution of a solar storm up to Earth and Mars Authors: Möstl, Christian; Rollett, Tanja; Frahm, Rudy A.; Liu, Ying D.; Long, David M.; Colaninno, Robin C.; Reiss, Martin A.; Temmer, Manuela; Farrugia, Charles J.; Posner, Arik; Dumbović, Mateja; Janvier, Miho; Démoulin, Pascal; Boakes, Peter; Devos, Andy; Kraaikamp, Emil; Mays, Mona L.; Vršnak, Bojan Bibcode: 2015NatCo...6.7135M Altcode: 2015arXiv150602842M; 2015NatCo...6E7135M The severe geomagnetic effects of solar storms or coronal mass ejections (CMEs) are to a large degree determined by their propagation direction with respect to Earth. There is a lack of understanding of the processes that determine their non-radial propagation. Here we present a synthesis of data from seven different space missions of a fast CME, which originated in an active region near the disk centre and, hence, a significant geomagnetic impact was forecasted. However, the CME is demonstrated to be channelled during eruption into a direction +37+/-10° (longitude) away from its source region, leading only to minimal geomagnetic effects. In situ observations near Earth and Mars confirm the channelled CME motion, and are consistent with an ellipse shape of the CME-driven shock provided by the new Ellipse Evolution model, presented here. The results enhance our understanding of CME propagation and shape, which can help to improve space weather forecasts. Title: Comparing generic models for interplanetary shocks and magnetic clouds axis configurations at 1 AU Authors: Janvier, M.; Dasso, S.; Démoulin, P.; Masías-Meza, J. J.; Lugaz, N. Bibcode: 2015JGRA..120.3328J Altcode: 2015arXiv150306128J Interplanetary coronal mass ejections (ICMEs) are the manifestation of solar transient eruptions, which can significantly modify the plasma and magnetic conditions in the heliosphere. They are often preceded by a shock, and a magnetic flux rope is detected in situ in a third to half of them. The main aim of this study is to obtain the best quantitative shape for the flux rope axis and for the shock surface from in situ data obtained during spacecraft crossings of these structures. We first compare the orientation of the flux rope axes and shock normals obtained from independent data analyses of the same events, observed in situ at 1 AU from the Sun. Then we carry out an original statistical analysis of axes/shock normals by deriving the statistical distributions of their orientations. We fit the observed distributions using the distributions derived from several synthetic models describing these shapes. We show that the distributions of axis/shock orientations are very sensitive to their respective shape. One classical model, used to analyze interplanetary imager data, is incompatible with the in situ data. Two other models are introduced, for which the results for axis and shock normals lead to very similar shapes; the fact that the data for MCs and shocks are independent strengthens this result. The model which best fits all the data sets has an ellipsoidal shape with similar aspect ratio values for all the data sets. These derived shapes for the flux rope axis and shock surface have several potential applications. First, these shapes can be used to construct a consistent ICME model. Second, these generic shapes can be used to develop a quantitative model to analyze imager data, as well as constraining the output of numerical simulations of ICMEs. Finally, they will have implications for space weather forecasting, in particular, for forecasting the time arrival of ICMEs at the Earth. Title: Electric current neutralization in solar active regions Authors: Dalmasse, Kévin; Aulanier, Guillaume; Török, Tibor; Démoulin, Pascal; Pariat, Etienne; Kliem, Bernhard Bibcode: 2015TESS....111303D Altcode: There is a recurring question in solar physics of whether or not photospheric vertical electric currents are neutralized in solar active regions, i.e., whether or not the total electric current integrated over a single magnetic polarity of an active region vanishes. While different arguments have been proposed in favor of, or against, the neutralization of electric currents, both theory and observations are still not fully conclusive. Providing the answer to this question is crucial for theoretical models of solar eruptions. Indeed, if currents are neutralized in active regions, then any eruption model based on net - i.e., non-zero - electric currents, such as the torus instability, requires further consideration. We address the question of electric current neutralization in active regions using 3D zero-beta MHD simulations of line-tied, slow photospheric driving motions imposed on an initially potential magnetic field. We compare our results to a recent study of the build-up of coronal electric currents in an MHD simulation of the emergence of a current-neutralized twisted flux tube into the solar atmosphere. Our parametric study shows that, in accordance with the flux emergence simulation, photospheric motions are associated with the formation of both direct and return currents. It further shows that both processes (flux emergence and photospheric flows) can lead to the formation of strong net currents in the solar corona, and that the non-neutralization of electric currents is related to the presence of magnetic shear at the polarity inversion line. We discuss the implications of our results for the observations and for theoretical models of solar eruptions. Title: FIP Bias Evolution in a Decaying Active Region Authors: Baker, D.; Brooks, D. H.; Démoulin, P.; Yardley, S. L.; van Driel-Gesztelyi, L.; Long, D. M.; Green, L. M. Bibcode: 2015ApJ...802..104B Altcode: 2015arXiv150107397B Solar coronal plasma composition is typically characterized by first ionization potential (FIP) bias. Using spectra obtained by Hinode’s EUV Imaging Spectrometer instrument, we present a series of large-scale, spatially resolved composition maps of active region (AR)11389. The composition maps show how FIP bias evolves within the decaying AR during the period 2012 January 4-6. Globally, FIP bias decreases throughout the AR. We analyzed areas of significant plasma composition changes within the decaying AR and found that small-scale evolution in the photospheric magnetic field is closely linked to the FIP bias evolution observed in the corona. During the AR’s decay phase, small bipoles emerging within supergranular cells reconnect with the pre-existing AR field, creating a pathway along which photospheric and coronal plasmas can mix. The mixing timescales are shorter than those of plasma enrichment processes. Eruptive activity also results in shifting the FIP bias closer to photospheric in the affected areas. Finally, the FIP bias still remains dominantly coronal only in a part of the AR’s high-flux density core. We conclude that in the decay phase of an AR’s lifetime, the FIP bias is becoming increasingly modulated by episodes of small-scale flux emergence, i.e., decreasing the AR’s overall FIP bias. Our results show that magnetic field evolution plays an important role in compositional changes during AR development, revealing a more complex relationship than expected from previous well-known Skylab results showing that FIP bias increases almost linearly with age in young ARs. Title: Strong coronal deflection of a CME and its interplanetary evolution to Earth and Mars Authors: Möstl, Christian; Rollett, Tanja; Frahm, Rudy A.; Liu, Ying D.; Long, David M.; Colaninno, Robin C.; Reiss, Martin A.; Temmer, Manuela; Farrugia, Charles J.; Posner, Arik; Dumbovic, Mateja; Janvier, Miho; Demoulin, Pascal; Boakes, Peter; Devos, Andy; Kraaikamp, Emil; Mays, Mona L.; Vrsnak, Bojan Bibcode: 2015EGUGA..17.1366M Altcode: We discuss multipoint imaging and in situ observations of the coronal mass ejection (CME) on January 7 2014 which resulted in a major false alarm. While the source region was almost at disk center facing Earth, the eruption was strongly deflected in the corona, and in conjunction with its particular orientation this CME missed Earth almost entirely, leading to no significant geomagnetic effects. We demonstrate this by a synthesis of data from 7 different heliospheric and planetary space missions (STEREO-A/B, SOHO, SDO, Wind, Mars Express, Mars Science Laboratory). The CMEs ecliptic part was deflected by 37 ± 10° in heliospheric longitude, a value larger than previously thought. Multipoint in situ observations at Earth and Mars confirm the deflection, and are consistent with an elliptical interplanetary shock shape of aspect ratio 1.4 ± 0.4. We also discuss our new method, the Ellipse Evolution (ElEvo) model, which allows us to optimize the global shape of the CME shock with multipoint in situ observations of the interplanetary CME arrival. ElEvo, which is an extension to the Drag-Based-Model by Vrsnak et al., may also be used for real time space weather forecasting. The presented results enhance our understanding of CME deflection and shape, which are fundamental ingredients for improving space weather forecasts. Title: Evidence of Twisted Flux-Tube Emergence in Active Regions Authors: Poisson, M.; Mandrini, C. H.; Démoulin, P.; López Fuentes, M. Bibcode: 2015SoPh..290..727P Altcode: 2015arXiv150501805P; 2014SoPh..tmp..196P Elongated magnetic polarities are observed during the emergence phase of bipolar active regions (ARs). These extended features, called magnetic tongues, are interpreted as a consequence of the azimuthal component of the magnetic flux in the toroidal flux-tubes that form ARs. We develop a new systematic and user-independent method to identify AR tongues. Our method is based on determining and analyzing the evolution of the AR main polarity inversion line (PIL). The effect of the tongues is quantified by measuring the acute angle [τ] between the orientation of the PIL and the direction orthogonal to the AR main bipolar axis. We apply a simple model to simulate the emergence of a bipolar AR. This model lets us interpret the effect of magnetic tongues on parameters that characterize ARs (e.g. the PIL inclination and the tilt angles, and their evolution). In this idealized kinematic emergence model, τ is a monotonically increasing function of the twist and has the same sign as the magnetic helicity. We systematically apply our procedure to a set of bipolar ARs (41 ARs) that were observed emerging in line-of-sight magnetograms over eight years. For most of the cases studied, the tongues only have a small influence on the AR tilt angle since tongues have a much lower magnetic flux than the more concentrated main polarities. From the observed evolution of τ, corrected for the temporal evolution of the tilt angle and its final value when the AR is fully emerged, we estimate the average number of turns in the subphotospherically emerging flux-rope. These values for the 41 observed ARs are below unity, except for one. This indicates that subphotospheric flux-ropes typically have a low amount of twist, i.e. highly twisted flux-tubes are rare. Our results demonstrate that the evolution of the PIL is a robust indicator of the presence of tongues and constrains the amount of twist in emerging flux-tubes. Title: Statistical study of magnetic cloud erosion by magnetic reconnection Authors: Ruffenach, A.; Lavraud, B.; Farrugia, C. J.; Démoulin, P.; Dasso, S.; Owens, M. J.; Sauvaud, J. -A.; Rouillard, A. P.; Lynnyk, A.; Foullon, C.; Savani, N. P.; Luhmann, J. G.; Galvin, A. B. Bibcode: 2015JGRA..120...43R Altcode: recent studies suggest that magnetic reconnection is able to erode substantial amounts of the outer magnetic flux of interplanetary magnetic clouds (MCs) as they propagate in the heliosphere. We quantify and provide a broader context to this process, starting from 263 tabulated interplanetary coronal mass ejections, including MCs, observed over a time period covering 17 years and at a distance of 1 AU from the Sun with Wind (1995-2008) and the two STEREO (2009-2012) spacecraft. Based on several quality factors, including careful determination of the MC boundaries and main magnetic flux rope axes, an analysis of the azimuthal flux imbalance expected from erosion by magnetic reconnection was performed on a subset of 50 MCs. The results suggest that MCs may be eroded at the front or at rear and in similar proportions, with a significant average erosion of about 40% of the total azimuthal magnetic flux. We also searched for in situ signatures of magnetic reconnection causing erosion at the front and rear boundaries of these MCs. Nearly ~30% of the selected MC boundaries show reconnection signatures. Given that observations were acquired only at 1 AU and that MCs are large-scale structures, this finding is also consistent with the idea that erosion is a common process. Finally, we studied potential correlations between the amount of eroded azimuthal magnetic flux and various parameters such as local magnetic shear, Alfvén speed, and leading and trailing ambient solar wind speeds. However, no significant correlations were found, suggesting that the locally observed parameters at 1 AU are not likely to be representative of the conditions that prevailed during the erosion which occurred during propagation from the Sun to 1 AU. Future heliospheric missions, and in particular Solar Orbiter or Solar Probe Plus, will be fully geared to answer such questions. Title: Magnetic Flux Erosion and Redistribution during CME Propagation Authors: Lavraud, B.; Ruffenach, A.; Manchester, W.; Farrugia, C. J.; Demoulin, P.; Dasso, S.; Sauvaud, J. A.; Rouillard, A. P.; Foullon, C.; Owens, M. J.; Savani, N.; Kajdic, P.; Luhmann, J. G.; Galvin, A. B. Bibcode: 2014AGUFMSH22A..01L Altcode: We will review recent works which highlight the occurrence of magnetic flux erosion and redistribution at the front of coronal mass ejections (when they have the structure of a well-defined magnetic cloud). Two main processes have been found and will be presented. The first comes from the occurrence of magnetic reconnection between the magnetic cloud and its sheath ahead, leading to magnetic flux erosion and redistribution, with associated large scale topological changes. The second may occur when dense filament material in the coronal mass ejection pushes its way through the structure and comes in direct contact with the shocked plasma in the sheath ahead. This leads to diverging non-radial flows in front of the CME which transport poloidal flux of the flux rope to the sides of the magnetic cloud. Title: How Can Active Region Plasma Escape into the Solar Wind from Below a Closed Helmet Streamer? Authors: Mandrini, C. H.; Nuevo, F. A.; Vásquez, A. M.; Démoulin, P.; van Driel-Gesztelyi, L.; Baker, D.; Culhane, J. L.; Cristiani, G. D.; Pick, M. Bibcode: 2014SoPh..289.4151M Altcode: 2014arXiv1409.7369M; 2014SoPh..tmp..115M Recent studies show that active-region (AR) upflowing plasma, observed by the EUV-Imaging Spectrometer (EIS) onboard Hinode, can gain access to open-field lines and be released into the solar wind (SW) via magnetic-interchange reconnection at magnetic null-points in pseudo-streamer configurations. When only one bipolar AR is present on the Sun and is fully covered by the separatrix of a streamer, such as AR 10978 in December 2007, it seems unlikely that the upflowing AR plasma can find its way into the slow SW. However, signatures of plasma with AR composition have been found at 1 AU by Culhane et al. (Solar Phys.289, 3799, 2014) that apparently originated west of AR 10978. We present a detailed topology analysis of AR 10978 and the surrounding large-scale corona based on a potential-field source-surface (PFSS) model. Our study shows that it is possible for the AR plasma to move around the streamer separatrix and be released into the SW via magnetic reconnection, which occurs in at least two main steps. We analyse data from the Nançay Radioheliograph (NRH) in a search for evidence of the chain of magnetic reconnections that we propose. We find a noise storm above the AR and several varying sources at 150.9 MHz. Their locations suggest that they might be associated with particles accelerated during the first-step reconnection process at a null point well outside of the AR. We find no evidence of the second reconnection step in the radio data, however. Our results demonstrate that even when it appears highly improbable for the AR plasma to reach the SW, indirect channels involving a sequence of reconnections can make it possible. Title: Understanding Coronal Mass Ejections and Associated Shocks in the Solar Corona by Merging Multiwavelength Observations Authors: Zucca, P.; Pick, M.; Démoulin, P.; Kerdraon, A.; Lecacheux, A.; Gallagher, P. T. Bibcode: 2014ApJ...795...68Z Altcode: 2014arXiv1409.3691Z Using multiwavelength imaging observations, in EUV, white light and radio, and radio spectral data over a large frequency range, we analyzed the triggering and development of a complex eruptive event. This one includes two components, an eruptive jet and a coronal mass ejection (CME), which interact during more than 30 minutes, and can be considered as physically linked. This was an unusual event. The jet is generated above a typical complex magnetic configuration that has been investigated in many former studies related to the build-up of eruptive jets; this configuration includes fan-field lines originating from a corona null point above a parasitic polarity, which is embedded in one polarity region of a large active region. The initiation and development of the CME, observed first in EUV, does not show usual signatures. In this case, the eruptive jet is the main actor of this event. The CME appears first as a simple loop system that becomes destabilized by magnetic reconnection between the outer part of the jet and the ambient medium. The progression of the CME is closely associated with the occurrence of two successive type II bursts from a distinct origin. An important part of this study is the first radio type II burst for which the joint spectral and imaging observations were allowed: (1) to follow, step by step, the evolution of the spectrum and of the trajectory of the radio burst, in relationship with the CME evolution and (2) to obtain, without introducing an electronic density model, the B field and the Alfvén speed. Title: Tracking Solar Active Region Outflow Plasma from Its Source to the Near-Earth Environment Authors: Culhane, J. L.; Brooks, D. H.; van Driel-Gesztelyi, L.; Démoulin, P.; Baker, D.; DeRosa, M. L.; Mandrini, C. H.; Zhao, L.; Zurbuchen, T. H. Bibcode: 2014SoPh..289.3799C Altcode: 2014SoPh..tmp...90C; 2014arXiv1405.2949C Seeking to establish whether active-region upflow material contributes to the slow solar wind, we examine in detail the plasma upflows from Active Region (AR) 10978, which crossed the Sun's disc in the interval 8 to 16 December 2007 during Carrington rotation (CR) 2064. In previous work, using data from the Hinode/EUV Imaging Spectrometer, upflow velocity evolution was extensively studied as the region crossed the disc, while a linear force-free-field magnetic extrapolation was used to confirm aspects of the velocity evolution and to establish the presence of quasi-separatrix layers at the upflow source areas. The plasma properties, temperature, density, and first ionisation potential bias [FIP-bias] were measured with the spectrometer during the disc passage of the active region. Global potential-field source-surface (PFSS) models showed that AR 10978 was completely covered by the closed field of a helmet streamer that is part of the streamer belt. Therefore it is not clear how any of the upflowing AR-associated plasma could reach the source surface at 2.5 R⊙ 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. Title: Recurrent Coronal Jets Induced by Magnetic Emergence in the Solar Atmosphere Authors: Guo, Y.; Démoulin, P.; Schmieder, B.; Ding, M. D.; Vargas Domínguez, S.; Liu, Y. Bibcode: 2014RMxAC..44...45G Altcode: Jets are part of the observed phenomenology in the solar corona. They are thought to be a consequence of magnetic reconnection but the physics involved is not completely understood. We study some recurrent jetting events with unprecedented temporal and spatial resolutions. Title: In situ properties of small and large flux ropes in the solar wind Authors: Janvier, M.; Démoulin, P.; Dasso, S. Bibcode: 2014JGRA..119.7088J Altcode: 2014arXiv1408.5520J Two populations of twisted magnetic field tubes, or flux ropes (hereafter, FRs), are detected by in situ measurements in the solar wind. While small FRs are crossed by the observing spacecraft within few hours, with a radius typically less than 0.1 AU, larger FRs, or magnetic clouds (hereafter, MCs), have durations of about half a day. The main aim of this study is to compare the properties of both populations of FRs observed by the Wind spacecraft at 1 AU. To do so, we use standard correlation techniques for the FR parameters, as well as histograms and more refined statistical methods. Although several properties seem at first different for small FRs and MCs, we show that they are actually governed by the same propagation physics. For example, we observe no in situ signatures of expansion for small FRs, contrary to MCs. We demonstrate that this result is in fact expected: small FRs expand similar to MCs, as a consequence of a total pressure balance with the surrounding medium, but the expansion signature is well hidden by velocity fluctuations. Next, we find that the FR radius, velocity, and magnetic field strength are all positively correlated, with correlation factors than can reach a value >0.5. This result indicates a remnant trace of the FR ejection process from the corona. We also find a larger FR radius at the apex than at the legs (up to 3 times larger at the apex), for FR observed at 1 AU. Finally, assuming that the detected FRs have a large-scale configuration in the heliosphere, we derived the mean axis shape from the probability distribution of the axis orientation. We therefore interpret the small FR and MC properties in a common framework of FRs interacting with the solar wind, and we disentangle the physics present behind their common and different features. Title: Distribution of Electric Currents in Sunspots from Photosphere to Corona Authors: Gosain, Sanjay; Démoulin, Pascal; López Fuentes, Marcelo Bibcode: 2014ApJ...793...15G Altcode: We present a study of two regular sunspots that exhibit nearly uniform twist from the photosphere to the corona. We derive the twist parameter in the corona and in the chromosphere by minimizing the difference between the extrapolated linear force-free field model field lines and the observed intensity structures in the extreme-ultraviolet images of the Sun. The chromospheric structures appear more twisted than the coronal structures by a factor of two. Further, we derive the vertical component of electric current density, 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. Bibcode: 2014SoPh..289.2633J Altcode: 2014SoPh..tmp...26J; 2014arXiv1401.6812J Flux ropes are twisted magnetic structures that can be detected by in-situ measurements in the solar wind. However, different properties of detected flux ropes suggest different types of flux-rope populations. As such, are there different populations of flux ropes? The answer is positive and is the result of the analysis of four lists of flux ropes, including magnetic clouds (MCs), observed at 1 AU. The in-situ data for the four lists were fitted with the same cylindrical force-free field model, which provides an estimate of the local flux-rope parameters such as its radius and orientation. Since the flux-rope distributions have a broad dynamic range, we went beyond a simple histogram analysis by developing a partition technique that uniformly distributes the statistical fluctuations across the radius range. By doing so, we found that small flux ropes with radius R<0.1 AU have a steep power-law distribution in contrast to the larger flux ropes (identified as MCs), which have a Gaussian-like distribution. Next, from four CME catalogs, we estimated the expected flux-rope frequency per year at 1 AU. We found that the predicted numbers are similar to the frequencies of MCs observed in-situ. However, we also found that small flux ropes are at least ten times too abundant to correspond to CMEs, even to narrow ones. Investigating the different possible scenarios for the origin of these small flux ropes, we conclude that these twisted structures can be formed by blowout jets in the low corona or in coronal streamers. Title: Electric Currents in Flare Ribbons: Observations and Three-dimensional Standard Model Authors: Janvier, M.; Aulanier, G.; Bommier, V.; Schmieder, B.; Démoulin, P.; Pariat, E. Bibcode: 2014ApJ...788...60J Altcode: 2014arXiv1402.2010J We present for the first time the evolution of the photospheric electric currents during an eruptive X-class flare, accurately predicted by the standard three-dimensional (3D) flare model. We analyze this evolution for the 2011 February 15 flare using Helioseismic and Magnetic Imager/Solar Dynamics Observatory magnetic observations and find that localized currents in J-shaped ribbons increase to double their pre-flare intensity. Our 3D flare model, developed with the OHM code, suggests that these current ribbons, which develop at the location of extreme ultraviolet brightenings seen with Atmospheric Imaging Assembly imagery, are driven by the collapse of the flare's coronal current layer. These findings of increased currents restricted in localized ribbons are consistent with the overall free energy decrease during a flare, and the shapes of these ribbons also give an indication of how twisted the erupting flux rope is. Finally, this study further enhances the close correspondence obtained between the theoretical predictions of the standard 3D model and flare observations, indicating that the main key physical elements are incorporated in the model. Title: Topological Analysis of Emerging Bipole Clusters Producing Violent Solar Events Authors: Mandrini, C. H.; Schmieder, B.; Démoulin, P.; Guo, Y.; Cristiani, G. D. Bibcode: 2014SoPh..289.2041M Altcode: 2013arXiv1312.3359M During the rising phase of Solar Cycle 24 tremendous activity occurred on the Sun with rapid and compact emergence of magnetic flux leading to bursts of flares (C to M and even X-class). We investigate the violent events occurring in the cluster of two active regions (ARs), NOAA numbers 11121 and 11123, observed in November 2010 with instruments onboard the Solar Dynamics Observatory and from Earth. Within one day the total magnetic flux increased by 70 % with the emergence of new groups of bipoles in AR 11123. From all the events on 11 November, we study, in particular, the ones starting at around 07:16 UT in GOES soft X-ray data and the brightenings preceding them. A magnetic-field topological analysis indicates the presence of null points, associated separatrices, and quasi-separatrix layers (QSLs) where magnetic reconnection is prone to occur. The presence of null points is confirmed by a linear and a non-linear force-free magnetic-field model. Their locations and general characteristics are similar in both modelling approaches, which supports their robustness. However, in order to explain the full extension of the analysed event brightenings, which are not restricted to the photospheric traces of the null separatrices, we compute the locations of QSLs. Based on this more complete topological analysis, we propose a scenario to explain the origin of a low-energy event preceding a filament eruption, which is accompanied by a two-ribbon flare, and a consecutive confined flare in AR 11123. The results of our topology computation can also explain the locations of flare ribbons in two other events, one preceding and one following the ones at 07:16 UT. Finally, this study provides further examples where flare-ribbon locations can be explained when compared to QSLs and only, partially, when using separatrices. Title: The evolution of writhe in kink-unstable flux ropes and erupting filaments Authors: Török, T.; Kliem, B.; Berger, M. A.; Linton, M. G.; Démoulin, P.; van Driel-Gesztelyi, L. Bibcode: 2014PPCF...56f4012T Altcode: 2014arXiv1403.1565T The helical kink instability of a twisted magnetic flux tube has been suggested as a trigger mechanism for solar filament eruptions and coronal mass ejections (CMEs). In order to investigate if estimations of the pre-emptive twist can be obtained from observations of writhe in such events, we quantitatively analyze the conversion of twist into writhe in the course of the instability, using numerical simulations. We consider the line tied, cylindrically symmetric Gold-Hoyle flux rope model and measure the writhe using the formulae by Berger and Prior which express the quantity as a single integral in space. We find that the amount of twist converted into writhe does not simply scale with the initial flux rope twist, but depends mainly on the growth rates of the instability eigenmodes of higher longitudinal order than the basic mode. The saturation levels of the writhe, as well as the shapes of the kinked flux ropes, are very similar for considerable ranges of initial flux rope twists, which essentially precludes estimations of pre-eruptive twist from measurements of writhe. However, our simulations suggest an upper twist limit of ∼6π for the majority of filaments prior to their eruption. Title: Coronal Magnetic Reconnection Driven by CME Expansion—the 2011 June 7 Event Authors: van Driel-Gesztelyi, L.; Baker, D.; Török, T.; Pariat, E.; Green, L. M.; Williams, D. R.; Carlyle, J.; Valori, G.; Démoulin, P.; Kliem, B.; Long, D. M.; Matthews, S. A.; Malherbe, J. -M. Bibcode: 2014ApJ...788...85V Altcode: 2014arXiv1406.3153V Coronal mass ejections (CMEs) erupt and expand in a magnetically structured solar corona. Various indirect observational pieces of evidence have shown that the magnetic field of CMEs reconnects with surrounding magnetic fields, forming, e.g., dimming regions distant from the CME source regions. Analyzing Solar Dynamics Observatory (SDO) observations of the eruption from AR 11226 on 2011 June 7, we present the first direct evidence of coronal magnetic reconnection between the fields of two adjacent active regions during a CME. The observations are presented jointly with a data-constrained numerical simulation, demonstrating the formation/intensification of current sheets along a hyperbolic flux tube at the interface between the CME and the neighboring AR 11227. Reconnection resulted in the formation of new magnetic connections between the erupting magnetic structure from AR 11226 and the neighboring active region AR 11227 about 200 Mm from the eruption site. The onset of reconnection first becomes apparent in the SDO/AIA images when filament plasma, originally contained within the erupting flux rope, is redirected toward remote areas in AR 11227, tracing the change of large-scale magnetic connectivity. The location of the coronal reconnection region becomes bright and directly observable at SDO/AIA wavelengths, owing to the presence of down-flowing cool, dense (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. Bibcode: 2014A&A...565A..99J Altcode: Context. Shocks are frequently detected by spacecraft in the interplanetary space. However, the in situ data of a shock do not provide direct information on its overall properties even when a following interplanetary coronal mass ejection (ICME) is detected.
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 Bibcode: 2014cosp...40E.637D Altcode: Interplanetary Coronal Mass Ejections (ICMEs) are meso-scale transient objects in the heliosphere, ejected by the Sun from the destabilisation of a portion of coronal magnetic field. They imply large modifications of the heliospheric plasma and magnetic field properties. Then, an ICME passing nearby Earth generates strong variations of the input of energy, momentum and particles, from the interplanetary medium to the terrestrial environment. The study of ICMEs has greatly advanced in the last few years, thanks to multi-spacecraft observations of the solar corona and the solar wind, combined with high performance numerical modelling. The comparisons between models and recent observations now answer several open questions, such as the typical configuration (internal and global) of ICMEs, as well as how they are affected due to their interaction with the ambient solar wind during their propagation in the interplanetary medium. This talk will provide a summary of recent advances in the field of ICMEs, and will present several aspects of the interaction with the ambient solar wind that have serious consequences on the level of Sun-Earth coupling. Title: Structure of ICMEs and their driven shocks at 1 AU, and consequences on Forbush decreases Authors: Dasso, Sergio; Janvier, Miho; Demoulin, Pascal; Masias-Meza, Jimmy J. Bibcode: 2014cosp...40E.636D Altcode: Solar wind structures, such as interplanetary (IP) shocks, can affect the transport of energetic particles in the heliosphere. In particular, the presence of IP shocks driven by interplanetary coronal mass ejections (ICMEs) is typically associated with a transient variation of the energetic particles flux (e.g., Forbush decreases, FDs). A FD can present two steps: one of them produced by a diffusive barrier associated with the turbulent region behind the shock, and the another one produced by the ICME itself. However, not every IP shock driven by an ICME is followed by a two-step FD, and it is under debate what are the properties of the solar wind for determining the presence of a two-step Forbush decrease, the presence of a single-step FD, or even the absence of a FD after the passage of the ICME. Magnetic clouds (MCs) are a subset of ICMEs, which present clear evidence in favor of the presence of an interplanetary flux rope in the solar wind. We recently found constraints to the geometrical shape of ICME shocks from a statistical study of shock orientations, and found constraints to the global shape of MCs from a statistical study of main axis orientation of a large sample of magnetic clouds, both at one astronomical unit from the Sun. The main aim of this study is to establish the link between Forbush decreases and the MC/shock properties, taking into account these geometrical shapes of MC axis and shocks surfaces. We present here a combined analysis of events MC-shock-FD, in order to better understand the effects of interplanetary structures on the propagation of energetic particles in the heliosphere. Title: Constraining magnetic flux emergence from a timeseries of helicitigrams Authors: Dalmasse, Kévin; Pariat, Etienne; Green, Lucie M.; Aulanier, Guillaume; Demoulin, Pascal; Valori, Gherardo Bibcode: 2014cosp...40E.612D Altcode: Magnetic helicity quantifies how globally twisted and/or sheared is the magnetic field in a volume. Observational studies have reported the injection of large amounts of magnetic helicity associated with the emergence of magnetic flux into the solar atmosphere. Because magnetic helicity is conserved in the convection zone, the injection of magnetic helicity into the solar corona reflects the helicity content of emerging magnetic flux tubes. Mapping the photospheric injection of magnetic helicity thus seems to be a key tool for constraining the parameters of the emerging flux tubes in numerical case-studies of observed active regions. We recently developed a method to compute the distribution of magnetic helicity flux. Contrary to previous proxies, this method takes into account the 3D nature of magnetic helicity, and is thus, better-suited to study the distribution of helicity flux. After introducing this method, we will present the results of its application to the NOAA AR 11158. We will show that, the distribution of helicity flux is complex, with patterns of real mixed signals of helicity flux related to the specific topology of the active region's magnetic field. Finally, we will discuss the implications of our results on the evolution and dynamics of this active region. Title: Magnetic flux emergence, flares, and coronal mass ejections Authors: Mandrini, Cristina H.; Schmieder, Brigitte; Cristiani, Germán; Demoulin, Pascal; Guo, Yang Bibcode: 2014cosp...40E1980M Altcode: We study the violent events occurring in the cluster of two active regions (ARs), NOAA numbers 11121 and 11123, observed in November 2010 with instruments onboard the Solar Dynamics Observatory and from Earth. Within one day the total magnetic flux increased by 70 per cent with the emergence of new groups of bipoles in AR 11123. These emergences led to a very complex magnetic configuration in which around ten solar flares, some of them accompanied by coronal mass ejections (CMEs), occurred. A magnetic-field topology somputation indicates the presence of null points, associated separatrices and quasi-separatrix layers (QSLs) where magnetic reconnection is prone to occur. Based on this analysis, we propose a scenario to explain the origin of a low-energy event preceding a filament eruption, which is accompanied by a two-ribbon flare and CME, and a consecutive confined flare in AR 11123. The results of our topology computation can also explain the locations of flare ribbons in two other events, one preceding and one following the ones just mentioned. Title: Electric current variations and 3D magnetic configuration of coronal jets Authors: Schmieder, Brigitte; Harra, Louise K.; Aulanier, Guillaume; Guo, Yang; Demoulin, Pascal; Moreno-Insertis, Fernando, , Prof Bibcode: 2014cosp...40E2928S Altcode: Coronal jets (EUV) were observed by SDO/AIA on September 17, 2010. HMI and THEMIS measured the vector magnetic field from which we derived the magnetic flux, the phostospheric velocity and the vertical electric current. The magnetic configuration was computed with a non linear force-free approach. The phostospheric current pattern of the recurrent jets were associated with the quasi-separatrix layers deduced from the magnetic extrapolation. The large twisted near-by Eiffel-tower-shape jet was also caused by reconnection in current layers containing a null point. This jet cannot be classified precisely within either the quiescent or the blowout jet types. We will show the importance of the existence of bald patches in the low atmosphere Title: Flux rope axis geometry of magnetic clouds deduced from in situ data Authors: Janvier, Miho; Démoulin, Pascal; Dasso, Sergio Bibcode: 2014IAUS..300..265J Altcode: Magnetic clouds (MCs) consist of flux ropes that are ejected from the low solar corona during eruptive flares. Following their ejection, they propagate in the interplanetary medium where they can be detected by in situ instruments and heliospheric imagers onboard spacecraft. Although in situ measurements give a wide range of data, these only depict the nature of the MC along the unidirectional trajectory crossing of a spacecraft. As such, direct 3D measurements of MC characteristics are impossible. From a statistical analysis of a wide range of MCs detected at 1 AU by the Wind spacecraft, we propose different methods to deduce the most probable magnetic cloud axis shape. These methods include the comparison of synthetic distributions with observed distributions of the axis orientation, as well as the direct integration of observed probability distribution to deduce the global MC axis shape. The overall shape given by those two methods is then compared with 2D heliospheric images of a propagating MC and we find similar geometrical features. Title: FIP bias in a sigmoidal active region Authors: Baker, D.; Brooks, D. H.; Démoulin, P.; van Driel-Gesztelyi, Lidia; Green, L. M.; Steed, K.; Carlyle, J. Bibcode: 2014IAUS..300..222B Altcode: We investigate first ionization potential (FIP) bias levels in an anemone active region (AR) - coronal hole (CH) complex using an abundance map derived from Hinode/EIS spectra. The detailed, spatially resolved abundance map has a large field of view covering 359'' × 485''. Plasma with high FIP bias, or coronal abundances, is concentrated at the footpoints of the AR loops whereas the surrounding CH has a low FIP bias, ~1, i.e. photospheric abundances. A channel of low FIP bias is located along the AR's main polarity inversion line containing a filament where ongoing flux cancellation is observed, indicating a bald patch magnetic topology characteristic of a sigmoid/flux rope configuration. Title: Active region helicity properties from magnetic tongues. Authors: Poisson, Mariano; Mandrini, Cristina H.; Lopez Fuentes, Marcelo; Demoulin, Pascal Bibcode: 2014cosp...40E2579P Altcode: We study the evolution of photospheric magnetic tongues to infer the magnetic helicity sign of a large set of active regions (ARs) observed during Solar Cycle 23. Magnetic tongues appear during the emergence of twisted toroidal magnetic flux tubes that form ARs due to contribution of the azimuthal component of the magnetic field around the torus axis. The method to compute the helicity sign is based on the determination of the polarity inversion line (PIL) and its relative orientation respect to the direction of the AR main bipolar axis (the AR's tilt), as well as the analysis of its evolution during the AR emergence. We analyze a set of 150 bipolar ARs observed with SOHO/MDI between 1996 and 2010. The PIL method, as tested in previous works, needs ARs with simple bipolar structures and devoid of backgroud magnetic remnants in order to provide reliable computations. Therefore, the low number of sunspots registered along the mínimum between Cycles 23 and 24 is a favourable period to find simple isolated ARs. We determine a series of statistical properties of the studied ARs, such as the latitudinal and hemispherical dependence of the magnetic helicity sign, the AR tilt, the total unsigned magnetic flux, and the presence of asymmetries between the main polarities. Title: Electric currents in solar active regions Authors: Dalmasse, Kévin; Pariat, Etienne; Kliem, Bernhard; Aulanier, Guillaume; Demoulin, Pascal; Torok, Tibor Bibcode: 2014cosp...40E.613D Altcode: There is a recurring question in solar physics about whether or not photospheric vertical electric currents are neutralized in solar active regions, i.e. if the total electric current integrated over a single photospheric magnetic polarity of an active region vanishes. Different arguments have been proposed in favor of, or against, the neutralization of electric currents, but both theory and observations are still not fully conclusive. The answer to this question has implications for eruption models. Indeed, if currents are neutralized in active regions, then any eruption model based on non-neutralized electric currents, such as the torus instability, would need to be further analyzed. We addressed the question of electric currents neutralization in active regions using 3D zero-beta, line-tied, slow driving motions of an initially potential magnetic field. We compared our results to a recent study of electric currents build-up in a MHD numerical simulation of the emergence of a current-neutralized twisted flux tube. Our parametric analyses show that, as for the emergence, photospheric motions are associated with the formation of both direct and return currents. It further shows that both processes can lead to the formation of strong net currents in the solar corona, and that the non-neutralization of electric currents is related to the presence of magnetic shear at the polarity inversion line. We will discuss the implications of our results for the observations and for the different solar eruption models. Title: Evolution of interplanetary coronal mass ejections and magnetic clouds in the heliosphere Authors: Démoulin, Pascal Bibcode: 2014IAUS..300..245D Altcode: Interplanetary Coronal Mass Ejections (ICMEs), and more specifically Magnetic Clouds (MCs), are detected with in situ plasma and magnetic measurements. They are the continuation of the CMEs observed with imagers closer to the Sun. A review of their properties is presented with a focus on their magnetic configuration and its evolution. Many recent observations, both in situ and with imagers, point to a key role of flux ropes, a conclusion which is also supported by present coronal eruptive models. Then, is a flux rope generically present in an ICME? How to quantify its 3D physical properties when it is detected locally as a MC? Is it a simple flux rope? How does it evolve in the solar wind? This paper reviews our present answers and limited understanding to these questions. Title: Photospheric Injection of Magnetic Helicity: Connectivity-Based Flux Density Method Authors: Dalmasse, K.; Pariat, E.; Démoulin, P.; Aulanier, G. Bibcode: 2014SoPh..289..107D Altcode: 2013arXiv1307.2829D Magnetic helicity quantifies the degree to which the magnetic field in a volume is globally sheared and/or twisted. This quantity is believed to play a key role in solar activity due to its conservation property. Helicity is continuously injected into the corona during the evolution of active regions (ARs). To better understand and quantify the role of magnetic helicity in solar activity, the distribution of magnetic helicity flux in ARs needs to be studied. The helicity distribution can be computed from the temporal evolution of photospheric magnetograms of ARs such as the ones provided by SDO/HMI and Hinode/SOT. Most recent analyses of photospheric helicity flux derived a proxy to the helicity-flux density based on the relative rotation rate of photospheric magnetic footpoints. Although this proxy allows a good estimate of the photospheric helicity flux, it is still not a true helicity flux density because it does not take into account the connectivity of the magnetic field lines. For the first time, we implement a helicity density that takes this connectivity into account. To use it for future observational studies, we tested the method and its precision on several types of models involving different patterns of helicity injection. We also tested it on more complex configurations - from magnetohydrodynamics (MHD) simulations - containing quasi-separatrix layers. We demonstrate that this connectivity-based proxy is best-suited to map the true distribution of photospheric helicity injection. Title: Active region upflow plasma: its relation to small activity and the solar wind Authors: Mandrini, Cristina H.; Culhane, J. Leonard; Cristiani, Germán; Vásquez, Alberto; Van Driel-Gesztelyi, Lidia; Baker, Deborah; Pick, Monique; Demoulin, Pascal; Nuevo, Federico Bibcode: 2014cosp...40E1979M Altcode: Recent studies show that active region (AR) upflowing plasma, observed by the Hinode EUV Imaging Spectrometer (EIS), can gain access to open field lines and be released into the solar wind via magnetic interchange reconnection occurring below the source surface at magnetic null-points in pseudo-streamer configurations. When only one simple bipolar AR is present on the Sun and it is fully covered by the separatrix of a streamer, like AR 10978 on December 2007, it seems unlikely that the upflowing AR plasma could find its way into the slow solar wind. However, signatures of plasma with AR composition at 1 AU that appears to originate from the West of AR 10978 were recently found by Culhane and coworkers. We present a detailed topology analysis of AR 10978 based on a linear force-free magnetic field model at the AR scale, combined with a global PFSS model. This allows us, on one hand, to explain the variations observed in the upflows to the West of the AR as the result of magnetic reconnection at quasi-separatrix layers (QSLs). While at a global scale, we show that reconnection, occurring in at least two main steps, first at QSLs and later at a high-altitude coronal null-point, allows the AR plasma to get around the topological obstacle of the streamer separatrix and be released into the solar wind. Title: Magnetic reconnection driven by filament eruption in the 7 June 2011 event Authors: van Driel-Gesztelyi, L.; Baker, D.; Török, T.; Pariat, E.; Green, L. M.; Williams, D. R.; Carlyle, J.; Valori, G.; Démoulin, P.; Matthews, S. A.; Kliem, B.; Malherbe, J. -M. Bibcode: 2014IAUS..300..502V Altcode: During an unusually massive filament eruption on 7 June 2011, SDO/AIA imaged for the first time significant EUV emission around a magnetic reconnection region in the solar corona. The reconnection occurred between magnetic fields of the laterally expanding CME and a neighbouring active region. A pre-existing quasi-separatrix layer was activated in the process. This scenario is supported by data-constrained numerical simulations of the eruption. Observations show that dense cool filament plasma was re-directed and heated in situ, producing coronal-temperature emission around the reconnection region. These results provide the first direct observational evidence, supported by MHD simulations and magnetic modelling, that a large-scale re-configuration of the coronal magnetic field takes place during solar eruptions via the process of magnetic reconnection. Title: Recurrent filament eruptions and associated CMEs Authors: Schmieder, Brigitte; Cremades, Hebe; Mandrini, Cristina; Démoulin, Pascal; Guo, Yang Bibcode: 2014IAUS..300..489S Altcode: We investigate the violent events in the cluster of two active regions (ARs), NOAA numbers 11121 and 11123, observed on 11 November 2010 by the Solar Dynamics Observatory (SDO). Within one day the magnetic field intensity increased by 70% with the emergence of new groups of bipoles in AR 11123, where three filaments are seen along the complex inversion line. The destabilization of the filaments led to flares and CMEs. The CMEs around 08:24 UT and 17:00 UT are directly related to the partial eruption of one filament in the new AR, as shown by a topology computation and analysis. The other CMEs on this day are due to either other ARs or to the destabilization of the global magnetic configuration of the two ARs. This conclusion can be only reached by using the three eyes of SOHO, STEREO and SDO. Title: Plasma Composition in a Sigmoidal Anemone Active Region Authors: Baker, D.; Brooks, D. H.; Démoulin, P.; van Driel-Gesztelyi, L.; Green, L. M.; Steed, K.; Carlyle, J. Bibcode: 2013ApJ...778...69B Altcode: 2013arXiv1310.0999B Using spectra obtained by the EUV Imaging Spectrometer (EIS) instrument onboard Hinode, we present a detailed spatially resolved abundance map of an active region (AR)-coronal hole (CH) complex that covers an area of 359'' × 485''. The abundance map provides first ionization potential (FIP) bias levels in various coronal structures within the large EIS field of view. Overall, FIP bias in the small, relatively young AR is 2-3. This modest FIP bias is a consequence of the age of the AR, its weak heating, and its partial reconnection with the surrounding CH. Plasma with a coronal composition is concentrated at AR loop footpoints, close to where fractionation is believed to take place in the chromosphere. In the AR, we found a moderate positive correlation of FIP bias with nonthermal velocity and magnetic flux density, both of which are also strongest at the AR loop footpoints. Pathways of slightly enhanced FIP bias are traced along some of the loops connecting opposite polarities within the AR. We interpret the traces of enhanced FIP bias along these loops to be the beginning of fractionated plasma mixing in the loops. Low FIP bias in a sigmoidal channel above the AR's main polarity inversion line, where ongoing flux cancellation is taking place, provides new evidence of a bald patch magnetic topology of a sigmoid/flux rope configuration. Title: Global axis shape of magnetic clouds deduced from the distribution of their local axis orientation Authors: Janvier, M.; Démoulin, P.; Dasso, S. Bibcode: 2013A&A...556A..50J Altcode: 2013arXiv1305.4039J Context. Coronal mass ejections (CMEs) are routinely tracked with imagers in the interplanetary space, while magnetic clouds (MCs) properties are measured locally by spacecraft. However, both imager and in situ data do not provide any direct estimation of the general flux rope properties.
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. Bibcode: 2013A&A...555A..77J Altcode: 2013arXiv1305.4053J Context. A standard model for eruptive flares aims at describing observational 3D features of the reconnecting coronal magnetic field. Extensions to the 2D model require the physical understanding of 3D reconnection processes at the origin of the magnetic configuration evolution. However, the properties of 3D reconnection without null point and separatrices still need to be analyzed.
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. Bibcode: 2013A&A...555A..19G Altcode: 2013arXiv1305.0902G Context. Jets of plasma are frequently observed in the solar corona. A self-similar recurrent behavior is observed in a fraction of them.
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 http://www.aanda.org Title: First observational application of a connectivity-based helicity flux density Authors: Dalmasse, K.; Pariat, E.; Valori, G.; Démoulin, P.; Green, L. M. Bibcode: 2013A&A...555L...6D Altcode: 2013arXiv1307.2838D Context. Measuring the magnetic helicity distribution in the solar corona can help in understanding the trigger of solar eruptive events because magnetic helicity is believed to play a key role in solar activity due to its conservation property.
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. Bibcode: 2013AdSpR..51.1967S Altcode: 2012arXiv1212.4014S Solar filament eruptions play a crucial role in triggering coronal mass ejections (CMEs). More than 80% of eruptions lead to a CME. This correlation has been studied extensively during the past solar cycles and the last long solar minimum. The statistics made on events occurring during the rising phase of the new solar cycle 24 is in agreement with this finding. Both filaments and CMEs have been related to twisted magnetic fields. Therefore, nearly all the MHD CME models include a twisted flux tube, called a flux rope. Either the flux rope is present long before the eruption, or it is built up by reconnection of a sheared arcade from the beginning of the eruption. Title: Study of magnetic flux emergence and related activity in active region NOAA 10314 Authors: Poisson, Mariano; López Fuentes, Marcelo; Mandrini, Cristina H.; Démoulin, Pascal; Pariat, Etienne Bibcode: 2013AdSpR..51.1834P Altcode: We study the extremely complex active region (AR) NOAA 10314, that was observed from March 13-19, 2003. This AR was the source of several energetic events, among them two major (X class) flares, along a few days. We follow the evolution of this AR since the very first stages of its emergence. From the photospheric evolution of the magnetic polarities observed with SOHO/MDI we infer the morphology of the flux tube that originates the AR. Using a computation technique that combines Local Correlation Tracking with magnetic induction constrains, we compute the rate of magnetic helicity injection at the photosphere during the observed evolution. From our results we conclude that the AR originated by the emergence of a severely deformed magnetic flux tube having a dominantly positive magnetic helicity. Title: Statistical analysis of magnetic cloud erosion by magnetic reconnection Authors: Ruffenach, A.; Lavraud, B.; Farrugia, C. J.; Démoulin, P.; Dasso, S.; Sauvaud, J.; Kajdic, P.; Rouillard, A. P.; Lynnyk, A.; Foullon, C.; Owens, M. J.; Savani, N. P.; Luhmann, J. G. Bibcode: 2013AGUSMSH33A..03R Altcode: Magnetic clouds (MCs), described as large-scale toroidal magnetic structures, interact with the surrounding interplanetary medium during propagation. It has been suggested in particular that magnetic reconnection may peel off their outer magnetic structure. Recently, Ruffenach et al. (2012) confirmed the occurrence of MC erosion thanks to a multi-spacecraft study combining a set of key signatures expected from this process. The aim of the present study is to extend previous works on the topic to all MCs of solar cycle 23 in order to quantify this phenomenon. This statistical analysis, primarily carried out with WIND and complemented with recent STEREO data, focuses on three signatures. First, based on careful determination of the MCs main axes, we estimate the amount of magnetic flux eroded for each event by analysing the azimuthal flux imbalance during the spacecraft sampling of the flux rope. We also search for magnetic reconnection signatures at the front boundary of the MCs. Finally, we investigate the characteristics of suprathermal electrons in the back region of the MCs. Those electrons are considered to signal potential large-scale topological changes expected from the erosion process. Title: Accuracy of magnetic energy computations Authors: Valori, G.; Démoulin, P.; Pariat, E.; Masson, S. Bibcode: 2013A&A...553A..38V Altcode: 2013arXiv1303.6773V Context. For magnetically driven events, the magnetic energy of the system is the prime energy reservoir that fuels the dynamical evolution. In the solar context, the free energy (i.e., the energy in excess of the potential field energy) is one of the main indicators used in space weather forecasts to predict the eruptivity of active regions. A trustworthy estimation of the magnetic energy is therefore needed in three-dimensional (3D) models of the solar atmosphere, e.g., in coronal fields reconstructions or numerical simulations.
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 http://www.aanda.org Title: The 3D Geometry of Active Region Upflows Deduced from Their Limb-to-Limb Evolution Authors: Démoulin, P.; Baker, D.; Mandrini, C. H.; van Driel-Gesztelyi, L. Bibcode: 2013SoPh..283..341D Altcode: 2012arXiv1211.5962D We analyze the evolution of coronal plasma upflows from the edges of AR 10978, which has the best limb-to-limb data coverage with Hinode's EUV Imaging Spectrometer (EIS). We find that the observed evolution is largely due to the solar rotation progressively changing the viewpoint of nearly stationary flows. From the systematic changes in the upflow regions as a function of distance from disc center, we deduce their 3D geometrical properties as inclination and angular spread in three coronal lines (Si VII, Fe XII, and Fe XV). In agreement with magnetic extrapolations, we find that the flows are thin, fan-like structures rooted in quasi separatrix layers (QSLs). The fans are tilted away from the AR center. The highest plasma velocities in these three spectral lines have similar magnitudes and their heights increase with temperature. The spatial location and extent of the upflow regions in the Si VII, Fe XII, and Fe XV lines are different owing to i) temperature stratification and ii) line of sight integration of the spectral profiles with significantly different backgrounds. We conclude that we sample the same flows at different temperatures. Further, we find that the evolution of line widths during the disc passage is compatible with a broad range of velocities in the flows. Everything considered, our results are compatible with the AR upflows originating from reconnections along QSLs between over-pressure AR loops and neighboring under-pressure loops. The flows are driven along magnetic field lines by a pressure gradient in a stratified atmosphere. Our interpretation of the above results is that, at any given time, we observe the superposition of flows created by successive reconnections, leading to a broad velocity distribution. Title: Does spacecraft trajectory strongly affect detection of magnetic clouds? Authors: Démoulin, P.; Dasso, S.; Janvier, M. Bibcode: 2013A&A...550A...3D Altcode: 2012arXiv1211.5343D Context. Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs). One property of MCs is the presence of a magnetic flux rope. Is the difference between ICMEs with and without MCs intrinsic or rather due to an observational bias?
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 & 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 > 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. Bibcode: 2013A&A...549A..66A Altcode: 2012arXiv1212.2086A Context. Solar flares strongly affect the Sun's atmosphere as well as the Earth's environment. Quantifying the maximum possible energy of solar flares of the present-day Sun, if any, is thus a key question in heliophysics.
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. Bibcode: 2012AGUFMSH31A2203R Altcode: Magnetic clouds (MCs), described as large-scale toroidal magnetic structures, interact with the surrounding interplanetary medium during propagation. It has been suggested in particular that magnetic reconnection may peel off their outer magnetic structure. Recently, Ruffenach et al. (2012) confirmed the occurrence of MC erosion thanks to a multi-spacecraft study combining a set of key signatures expected from this process. The aim of the present study is to extend previous works on the topic to all MCs of solar cycle 23 in order to quantify this phenomenon. This statistical analysis, primarily carried out with WIND and complemented with recent STEREO data, focuses on three signatures. First, based on careful determination of the MCs main axes, we estimate the amount of magnetic flux eroded for each event by analysing the azimuthal flux imbalance during the spacecraft sampling of the flux rope. We also search for magnetic reconnection signatures at the front boundary of the MCs. Finally, we investigate the characteristics of suprathermal electrons in the back region of the MCs. Those electrons are considered to signal potential large-scale topological changes expected from the erosion process. Title: Magnetic Topology of Active Regions and Coronal Holes: Implications for Coronal Outflows and the Solar Wind Authors: van Driel-Gesztelyi, L.; Culhane, J. L.; Baker, D.; Démoulin, P.; Mandrini, C. H.; DeRosa, M. L.; Rouillard, A. P.; Opitz, A.; Stenborg, G.; Vourlidas, A.; Brooks, D. H. Bibcode: 2012SoPh..281..237V Altcode: 2012SoPh..tmp..228V During 2 - 18 January 2008 a pair of low-latitude opposite-polarity coronal holes (CHs) were observed on the Sun with two active regions (ARs) and the heliospheric plasma sheet located between them. We use the Hinode/EUV Imaging Spectrometer (EIS) to locate AR-related outflows and measure their velocities. Solar-Terrestrial Relations Observatory (STEREO) imaging is also employed, as are the Advanced Composition Explorer (ACE) in-situ observations, to assess the resulting impacts on the solar wind (SW) properties. Magnetic-field extrapolations of the two ARs confirm that AR plasma outflows observed with EIS are co-spatial with quasi-separatrix layer locations, including the separatrix of a null point. Global potential-field source-surface modeling indicates that field lines in the vicinity of the null point extend up to the source surface, enabling a part of the EIS plasma upflows access to the SW. We find that similar upflow properties are also observed within closed-field regions that do not reach the source surface. We conclude that some of plasma upflows observed with EIS remain confined along closed coronal loops, but that a fraction of the plasma may be released into the slow SW. This suggests that ARs bordering coronal holes can contribute to the slow SW. Analyzing the in-situ data, we propose that the type of slow SW present depends on whether the AR is fully or partially enclosed by an overlying streamer. Title: Multispacecraft observation of magnetic cloud erosion by magnetic reconnection during propagation Authors: Ruffenach, A.; Lavraud, B.; Owens, M. J.; Sauvaud, J. -A.; Savani, N. P.; Rouillard, A. P.; Démoulin, P.; Foullon, C.; Opitz, A.; Fedorov, A.; Jacquey, C. J.; Génot, V.; Louarn, P.; Luhmann, J. G.; Russell, C. T.; Farrugia, C. J.; Galvin, A. B. Bibcode: 2012JGRA..117.9101R Altcode: 2012JGRA..11709101R During propagation, Magnetic Clouds (MC) interact with their environment and, in particular, may reconnect with the solar wind around it, eroding away part of its initial magnetic flux. Here we quantitatively analyze such an interaction using combined, multipoint observations of the same MC flux rope by STEREO A, B, ACE, WIND and THEMIS on November 19-20, 2007. Observation of azimuthal magnetic flux imbalance inside a MC flux rope has been argued to stem from erosion due to magnetic reconnection at its front boundary. The present study adds to such analysis a large set of signatures expected from this erosion process. (1) Comparison of azimuthal flux imbalance for the same MC at widely separated points precludes the crossing of the MC leg as a source of bias in flux imbalance estimates. (2) The use of different methods, associated errors and parametric analyses show that only an unexpectedly large error in MC axis orientation could explain the azimuthal flux imbalance. (3) Reconnection signatures are observed at the MC front at all spacecraft, consistent with an ongoing erosion process. (4) Signatures in suprathermal electrons suggest that the trailing part of the MC has a different large-scale magnetic topology, as expected. The azimuthal magnetic flux erosion estimated at ACE and STEREO A corresponds respectively to 44% and 49% of the inferred initial azimuthal magnetic flux before MC erosion upon propagation. The corresponding average reconnection rate during transit is estimated to be in the range 0.12-0.22 mV/m, suggesting most of the erosion occurs in the inner parts of the heliosphere. Future studies ought to quantify the influence of such an erosion process on geo-effectiveness. Title: Identifying the Main Driver of Active Region Outflows Authors: Baker, D.; van Driel-Gesztelyi, L.; Mandrini, C. H.; Démoulin, P.; Murray, M. J. Bibcode: 2012ASPC..454..425B Altcode: Hinode's EUV Imaging Spectrometer (EIS) has discovered ubiquitous outflows of a few to 50 km s-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. Bibcode: 2012ASPC..454..281W Altcode: The purpose of this investigation is to determine whether there is a difference between the evolution of an active region with additional new flux emergence if the new flux has either the same or the opposite sign of magnetic helicity from the active region. Of these two scenarios, the one that produces the most energetics is still a topic for debate. We present a study of two active regions following the emergence of a bipole, one with the same and one with the opposite sign of helicity from the active region. We discover that while there is less flaring in the mixed helicity active region the EUV flux normalised to the magnetic field is three times higher than that of the same helicity active region. We propose that reconnection is more likely to occur between opposite helicity structures and thus, the energy can never build up to the levels required for flaring. Title: Erratum: "Initiation and Development of the White-light and Radio Coronal Mass Ejection on 2001 April 15" (2012, ApJ, 750, 147) Authors: Démoulin, P.; Vourlidas, A.; Pick, M.; Bouteille, A. Bibcode: 2012ApJ...754..156D Altcode: No abstract at ADS Title: Reconstruction of 3D Coronal Magnetic Structures from THEMIS/MTR and Hinode/SOT Vector Maps Authors: Schmieder, B.; Guo, Y.; Aulanier, G.; Démoulin, P.; Török, T.; Bommier, V.; Wiegelmann, T.; Gosain, S. Bibcode: 2012ASPC..454..363S Altcode: Coordinated campaigns using THEMIS, Hinode, and other instruments have allowed us to study the magnetic fields of faculae, filaments, and active regions. In a first case, we modelled the 3D magnetic field in a flaring active region with a nonlinear force-free field extrapolation, using magnetic vectors observed by THEMIS/MTR as boundary condition. In order to construct a consistent bottom boundary for the model, we first removed the 180 degree ambiguity of the transverse fields and minimized the force and torque in the observed vector fields. We found a twisted magnetic flux rope, well aligned with the polarity inversion line and a part of an Hα filament, and located where a large flare is initiated about two hours later. In a second case, Hinode/SOT allowed us to detect fine flux concentrations in faculae, while MTR provided us with magnetic information at different levels in the atmosphere. The polarimetry analysis of the MTR and SOT data gave consistent results, using both UNNOFIT and MELANIE inversion codes. Title: Expansion of magnetic clouds in the outer heliosphere Authors: Gulisano, A. M.; Démoulin, P.; Dasso, S.; Rodriguez, L. Bibcode: 2012A&A...543A.107G Altcode: 2012arXiv1206.1532G Context. A large amount of magnetized plasma is frequently ejected from the Sun as coronal mass ejections (CMEs). Some of these ejections are detected in the solar wind as magnetic clouds (MCs) that have flux rope signatures.
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. Bibcode: 2012IAUS..286..139D Altcode: Magnetic clouds (MCs) are objects of extreme importance in the heliosphere. They have a major role on releasing magnetic helicity from the Sun (with crucial consequences on the solar dynamo), they are the hugest transient object in the interplanetary medium, and the main actors for the Sun-Earth coupling. The comparison between models and observations is beginning to clarify several open questions on MCs, such as their internal magnetic configuration and their interaction with the ambient solar wind. Due to the decay of the solar wind pressure with the distance to the Sun, MCs are typically in expansion. However, their detailed and local expansion properties depend on their environment plasma properties. On the other hand, while it is well known that the solar cycle determines several properties of the heliosphere, the effects of the cycle on MC properties are not so well understood. In this work we review two major properties of MCs: (i) their expansion, and (ii) the magnetic flux and helicity that they transport through the interplanetary medium. We find that the amount of magnetic flux and helicity released via MCs during the last solar minimum (years 2007-2009) was significantly lower than in the previous one (years 1995-1997). Moreover, both MC size and mean velocity are in phase with the solar cycle while the expansion rate is weakly variable and has no relationship with the cycle. Title: Evolution of a very complex active region during the decay phase of Cycle 23 Authors: Poisson, Mariano; Fuentes, Marcelo López; Mandrini, Cristina H.; Démoulin, Pascal; Pariat, Etienne Bibcode: 2012IAUS..286..246P Altcode: We study the emergence and evolution of AR NOAA 10314, observed on the solar disk during March 13-19, 2003. This extremely complex AR is of particular interest due to its unusual magnetic flux distribution and the clear rotation of the polarities of a δ-spot within the AR. Using SOHO/MDI magnetograms we follow the evolution of the photospheric magnetic flux to infer the morphology of the structure that originates the AR. We determine the tilt angle variation for the δ-spot and find a counter-clockwise rotation corresponding to a positive writhed flux tube. We compute the magnetic helicity injection and the total accumulated helicity in the AR and find a correlation with the observed rotation. Title: Magnetic topology, coronal outflows, and the solar wind Authors: Mandrini, Cristina H.; Culhane, J. Leonard; Vourlidas, Angelos; Demoulin, Pascal; Stenborg, Guillermo; Opitz, Andrea; Rouillard, Alexis; Van Driel-Gesztelyi, Lidia; Baker, Deborah; DeRosa, Marc; Brooks, David Bibcode: 2012cosp...39.1173M Altcode: 2012cosp.meet.1173M During 2-18 January 2008 a pair of low-latitude opposite polarity coronal holes were observed on the Sun flanked by two ARs with the heliospheric plasma sheet between them. Hinode/EUV Imaging Telescope (EIS) is used to locate AR-related outflows and measure their velocities. The Advanced Composition Explorer (ACE) in-situ observations are employed to assess the resulting impacts on the interplanetary solar wind (SW). Magnetic field extrapolations of the two ARs confirm that AR plasma outflows observed with EIS are co-spatial with quasi-separatrix layer locations, including the separatrix of a null point. Global potential field source-surface modeling indicates that field lines in the vicinity of the null point extend up to the source-surface, enabling a part of the EIS plasma upflows access to the SW. Similar upflow magnitude is also observed within closed field regions. Though part of the plasma upflows observed with EIS remain confined along closed coronal loops, a subset of them are indeed able to make their imprint in the slow SW, making ARs bordering coronal holes a slow SW contributor. Title: Photospheric injection of magnetic helicity: implementation of a new density estimate Authors: Dalmasse, Kévin; Pariat, Etienne; Demoulin, Pascal Bibcode: 2012cosp...39..393D Altcode: 2012cosp.meet..393D Magnetic helicity quantifies how globally sheared and/or twisted is the magnetic field, and thus, is a tracer of the non--potentiality of the magnetic field in a volume. In the conditions of the solar corona, magnetic helicity is a conserved quantity, and thus, imposes a high constraint on the evolution of the magnetic field. Helicity is continuously injected into the corona during the evolution of active regions (ARs), and CMEs are possibly the manifestation of the ejection of helicity excess. To better understand and quantify the role of magnetic helicity in solar activity, the distribution of magnetic helicity flux in ARs needs to be studied. The helicity distribution can be computed from the temporal evolution of photospheric magnetograms of ARs such as the ones provided by SDO/HMI and Hinode/SOT. Most of previous analyses of photospheric helicity flux derive helicity flux density proxies such as the so-called G_{A}, and recently G_{θ}. The proxy G_{θ} had been developed in order to reduce the fake signals observed using G_{A}. Although G_{θ} allows a better estimate of the photospheric helicity flux, it is still not a true helicity flux density because it does not account for the connectivity of the magnetic field lines. For the first time, we implement the helicity density G_{Φ} which takes into account such connectivity. In order to use G_{Φ} for future observational studies, we test the method and its precision on several models involving different types of helicity injection (by rotation and relative motions of two opposite magnetic polarities). We show that G_{Φ} is a much better proxy to estimate the photospheric helicity flux than G_{A} and G_{θ}. We discuss how it could be implemented from the dataset provided by SDO/HMI. Title: Topology analysis of emerging bipole clusters producing violent solar events observed by SDO Authors: Schmieder, Brigitte; Demoulin, Pascal; Mandrini, Cristina H.; Guo, Yang Bibcode: 2012cosp...39.1724S Altcode: 2012cosp.meet.1724S During the rising phase of Solar Cycle 24, tremendous magnetic solar activity occurs on the Sun with fast and compact emergence of magnetic flux leading to burts of flares (C to M and even X class) . We have investigated the violent events occuring in the cluster of two active regions AR 11121 and AR11123 observed in November by SDO. In less than two days the magnetic field increases by a factor of 10 with the emergence of groups of bipoles. A topology analysis demonstrates the formation of multiple separatrices and quasi-separatrix layers explaining possible mechanisms for destabilization of the magnetic structures such as filaments and coronal loops. Title: Comparing Values of the Relative Magnetic Helicity in Finite Volumes Authors: Valori, G.; Démoulin, P.; Pariat, E. Bibcode: 2012SoPh..278..347V Altcode: 2012SoPh..tmp..271G Relative magnetic helicity, as a conserved quantity of ideal magnetohydrodynamics, has been highlighted as an important quantity to study in plasma physics. Due to its nonlocal nature, its estimation is not straightforward in both observational and numerical data. In this study we derive expressions for the practical computation of the gauge-independent relative magnetic helicity in three-dimensional finite domains. The derived expressions are easy to implement and rapid to compute. They are derived in Cartesian coordinates, but can be easily written in other coordinate systems. We apply our method to a numerical model of a force-free equilibrium containing a flux rope, and compare the results with those obtained employing known half-space equations. We find that our method requires a much smaller volume than half-space expressions to derive the full helicity content. We also prove that values of relative magnetic helicity of different magnetic fields can be compared with each other in the same sense as free-energy values can. Therefore, relative magnetic helicity can be meaningfully and directly compared between different datasets, such as those from different active regions, but also within the same dataset at different times. Typical applications of our formulae include the helicity computation in three-dimensional models of the solar atmosphere, e.g., coronal-field reconstructions by force-free extrapolation and discretized magnetic fields of numerical simulations. Title: Implications of Non-cylindrical Flux Ropes for Magnetic Cloud Reconstruction Techniques and the Interpretation of Double Flux Rope Events Authors: Owens, M. J.; Démoulin, P.; Savani, N. P.; Lavraud, B.; Ruffenach, A. Bibcode: 2012SoPh..278..435O Altcode: Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs) which exhibit signatures consistent with a magnetic flux rope structure. Techniques for reconstructing flux rope orientation from single-point in situ observations typically assume the flux rope is locally cylindrical, e.g., minimum variance analysis (MVA) and force-free flux rope (FFFR) fitting. In this study, we outline a non-cylindrical magnetic flux rope model, in which the flux rope radius and axial curvature can both vary along the length of the axis. This model is not necessarily intended to represent the global structure of MCs, but it can be used to quantify the error in MC reconstruction resulting from the cylindrical approximation. When the local flux rope axis is approximately perpendicular to the heliocentric radial direction, which is also the effective spacecraft trajectory through a magnetic cloud, the error in using cylindrical reconstruction methods is relatively small (≈ 10∘). 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. Bibcode: 2012ApJ...750..147D Altcode: The 2001 April 15 event was one of the largest of the last solar cycle. A former study established that this event was associated with a coronal mass ejection (CME) observed both at white light and radio frequencies. This radio CME is illuminated by synchrotron emission from relativistic electrons. In this paper, we investigate the relation of the radio CME to its extreme-ultraviolet (EUV) and white-light counterpart and reach four main conclusions. (1) The radio CME corresponds to the white-light flux rope cavity. (2) The presence of a reconnecting current sheet behind the erupting flux rope is framed, both from below and above, by bursty radio sources. This reconnection is the source of relativistic radiating electrons which are injected down along the reconnected coronal arches and up along the flux rope border forming the radio CME. (3) Radio imaging reveals an important lateral overexpansion in the low corona; this overexpansion is at the origin of compression regions where type II and III bursts are imaged. (4) Already in the initiation phase, radio images reveal large-scale interactions of the source active region (AR) with its surroundings, including another AR and open magnetic fields. Thus, these complementary radio, EUV, and white-light data validate the flux rope eruption model of CMEs. Title: Nonlinear Force-Free Extrapolation of Emerging Flux with a Global Twist and Serpentine Fine Structures Authors: Valori, G.; Green, L. M.; Démoulin, P.; Vargas Domínguez, S.; van Driel-Gesztelyi, L.; Wallace, A.; Baker, D.; Fuhrmann, M. Bibcode: 2012SoPh..278...73V Altcode: We study the flux emergence process in NOAA active region 11024, between 29 June and 7 July 2009, by means of multi-wavelength observations and nonlinear force-free extrapolation. The main aim is to extend previous investigations by combining, as much as possible, high spatial resolution observations to test our present understanding of small-scale (undulatory) flux emergence, whilst putting these small-scale events in the context of the global evolution of the active region. The combination of these techniques allows us to follow the whole process, from the first appearance of the bipolar axial field on the east limb, until the buoyancy instability could set in and raise the main body of the twisted flux tube through the photosphere, forming magnetic tongues and signatures of serpentine field, until the simplification of the magnetic structure into a main bipole by the time the active region reaches the west limb. At the crucial time of the main emergence phase high spatial resolution spectropolarimetric measurements of the photospheric field are employed to reconstruct the three-dimensional structure of the nonlinear force-free coronal field, which is then used to test the current understanding of flux emergence processes. In particular, knowledge of the coronal connectivity confirms the identity of the magnetic tongues as seen in their photospheric signatures, and it exemplifies how the twisted flux, which is emerging on small scales in the form of a sea-serpent, is subsequently rearranged by reconnection into the large-scale field of the active region. In this way, the multi-wavelength observations combined with a nonlinear force-free extrapolation provide a coherent picture of the emergence process of small-scale magnetic bipoles, which subsequently reconnect to form a large-scale structure in the corona. Title: Estimation of the squashing degree within a three-dimensional domain Authors: Pariat, E.; Démoulin, P. Bibcode: 2012A&A...541A..78P Altcode: Context. The study of the magnetic topology of magnetic fields aims at determining the key sites for the development of magnetic reconnection. Quasi-separatrix layers (QSLs), regions of strong connectivity gradients, are topological structures where intense-electric currents preferentially build-up, and where, later on, magnetic reconnection occurs.
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. Bibcode: 2012EGUGA..14.7923L Altcode: Water vapour is a crucial climate variable involved in many processes which widely determine the energy budget of our planet. In particular, water vapour is the dominant greenhouse gas in the Earth's atmosphere and its radiative forcing is maximum in the middle and upper troposphere. Because of the extremely high variability of water vapour concentration in time and space, it is challenging for the available relevant measurement techniques to provide a consistent data set useful for trend analyses and climate studies. Schneider et al. (2006a) showed that ground-based Fourier Transform Infrared (FTIR) spectroscopy, performed from mountain observatories, allows for the detection of H2O variabilities up to the tropopause. Furthermore, the FTIR measurements allow the retrieval of HDO amounts and therefore the monitoring of HDO/H2O ratio profiles whose variations act as markers for the source and history of the atmospheric water vapour. In the framework of the MUSICA European project (Multi-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water, http://www.imk-asf.kit.edu/english/musica.php), a new approach has been developed and optimized by M. Schneider and F. Hase, using the PROFFIT algorithm, to consistently retrieve tropospheric water vapour profiles from high-resolution ground-based infrared solar spectra and so taking benefit from available long-term data sets of ground-based observations. The retrieval of the water isotopologues is performed on a logarithmic scale from 14 micro-windows located in the 2600-3100 cm-1 region. Other important features of this new retrieval strategy are: a speed dependant Voigt line shape model, a joint temperature profile retrieval and an interspecies constraint for the HDO/H2O profiles. In this contribution, we will combine the quality of the MUSICA strategy and of our observations, which are recorded on a regular basis with FTIR spectrometers, under clear-sky conditions, at the NDACC site (Network for the Detection of Atmospheric Composition Change, http://www.ndacc.org) of the Jungfraujoch International Scientific Station (Swiss Alps, 46.5° N, 8.0° E, 3580m asl). Information content analysis of the retrieved H2O products allows us to produce a long-term trend from 1996 to 2011 for different tropospheric levels. We will compare the annual cycle of tropospheric HDO/H2O ratio profiles with those already produced at other sites (Schneider et al., 2010). We will also focus on the diurnal variability of water vapour to determine a time limit in the inter-comparison of different water vapour measurement techniques. Acknowledgments The University of Liège involvement has primarily been supported by the PRODEX program funded by the Belgian Federal Science Policy Office, Brussels and by the Swiss GAW-CH program. The FRS-FNRS and the Fédération Wallonie-Bruxelles are further acknowledged for observational activities support. We thank the International Foundation High Altitude Research Stations Jungfraujoch and Gornergrat (HFSJG, Bern) for supporting the facilities needed to perform the observations. MUSICA is funded by the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013) / ERC Grant agreement n° 256961. Title: The interplanetary magnetic structure that guides solar relativistic particles Authors: Masson, S.; Démoulin, P.; Dasso, S.; Klein, K. -L. Bibcode: 2012A&A...538A..32M Altcode: 2011arXiv1110.6811M Context. Relating in-situ measurements of relativistic solar particles to their parent activity in the corona requires understanding the magnetic structures that guide them from their acceleration site to the Earth. Relativistic particle events are observed at times of high solar activity, when transient magnetic structures such as interplanetary coronal mass ejections (ICMEs) often shape the interplanetary magnetic field (IMF). They may introduce interplanetary paths that are longer than nominal, and magnetic connections rooted far from the nominal Parker spiral.
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. Title: Evolution of Hard X-Ray Sources and Ultraviolet Solar Flare Ribbons for a Confined Eruption of a Magnetic Flux Rope Authors: Guo, Y.; Ding, M. D.; Schmieder, B.; Démoulin, P.; Li, H. Bibcode: 2012ApJ...746...17G Altcode: 2011arXiv1111.1790G We study the magnetic field structures of hard X-ray (HXR) sources and flare ribbons of the M1.1 flare in active region NOAA 10767 on 2005 May 27. We have found in a nonlinear force-free field extrapolation over the same polarity inversion line, a small pre-eruptive magnetic flux rope located next to sheared magnetic arcades. RHESSI and the Transition Region and Coronal Explorer (TRACE) observed this confined flare in the X-ray bands and ultraviolet (UV) 1600 Å bands, respectively. In this event magnetic reconnection occurred at several locations. It first started at the location of the pre-eruptive flux rope. Then, the observations indicate that magnetic reconnection occurred between the pre-eruptive magnetic flux rope and the sheared magnetic arcades more than 10 minutes before the flare peak. This implies the formation of the larger flux rope, as observed with TRACE. Next, HXR sources appeared at the footpoints of this larger flux rope at the peak of the flare. The associated high-energy particles may have been accelerated below the flux rope in or around a reconnection region. Still, the close spatial association between the HXR sources and the flux rope footpoints favors an acceleration within the flux rope. Finally, a topological analysis of a large solar region, including active regions NOAA 10766 and 10767, shows the existence of large-scale Quasi-Separatrix Layers (QSLs) before the eruption of the flux rope. No enhanced emission was found at these QSLs during the flare, but the UV flare ribbons stopped at the border of the closest large-scale QSL. Title: Magnetic tongues properties in solar active regions Authors: Poisson, M.; López Fuentes, M.; Mandrini, C. H.; Démoulin, P. Bibcode: 2012BAAA...55..147P Altcode: We study the emergence of solar active regions (ARs) to determine how their magnetic helicity properties affect the evolution of the photospheric flux observed in longitudinal magnetograms. We characterize the so called ``magnetic tongues'', which appear due to the line of sight projection of the azimuthal component of the magnetic field in twisted emerging flux-tubes forming ARs. We determine and study the evolution of a series of parameters, such as: the tilt angle, the polarity inversion line (PIL) orientation, the magnetic flux, the size and shape of the polarities and of their tongues for 25 ARs observed between 2004 and 2010. We model the emergence of a toroidal flux-tube with different amounts of twist and we test different methods to determine the PIL. Finally, from the obtained PIL evolution we are able to infer the sign of the flux-tube twist by comparing the results with our model predictions. Title: Dynamical evolution of a magnetic cloud from the Sun to 5.4 AU Authors: Nakwacki, M. S.; Dasso, S.; Démoulin, P.; Mandrini, C. H.; Gulisano, A. M. Bibcode: 2011A&A...535A..52N Altcode: 2011arXiv1108.0951N Context. Significant quantities of magnetized plasma are transported from the Sun to the interstellar medium via interplanetary coronal mass ejections (ICMEs). Magnetic clouds (MCs) are a particular subset of ICMEs, forming large-scale magnetic flux ropes. Their evolution in the solar wind is complex and mainly determined by their own magnetic forces and the interaction with the surrounding solar wind.
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. Bibcode: 2011IAUS..273..328G Altcode: A nonlinear force-free magnetic field extrapolation of vector magnetogram data obtained by THEMIS/MTR on 2005 May 27 suggests the simultaneous existence of different magnetic configurations within one active region filament: one part of the filament is supported by field line dips within a flux rope, while the other part is located in dips within an arcade structure. Although the axial field chirality (dextral) and the magnetic helicity (negative) are the same along the whole filament, the chiralities of the filament barbs at different sections are opposite, i.e., right-bearing in the flux rope part and left-bearing in the arcade part. This argues against past suggestions that different barb chiralities imply different signs of helicity of the underlying magnetic field. This new finding about the chirality of filaments will be useful to associate eruptive filaments and magnetic cloud using the helicity parameter in the Space Weather Science. Title: Solar activity due to magnetic complexity of active regions Authors: Schmieder, Brigitte; Mandrini, Cristina; Chandra, Ramesh; Démoulin, Pascal; Török, Tibor; Pariat, Etienne; Uddin, Wahab Bibcode: 2011IAUS..273..164S Altcode: Active regions (ARs), involved in the Halloween events during October-November 2003, were the source of unusual activity during the following solar rotation. The flares on 18-20 November 2003 that occur in the AR NOAA10501 were accompanied by coronal mass ejections associated to some particularly geoeffective magnetic clouds.

Our analysis of the magnetic flux and helicity injection revealed that a new emerging bipole and consequent shearing motions continuously energized the region during its disk passage. The stored energy was eventually released through the interaction of the various systems of magnetic loops by several magnetic reconnection events. Active events on November 18 (filament eruptions and CMEs) were originated by shearing motions along a section of the filament channel that injected magnetic helicity with sign opposite to that of the AR. Two homologous flares, that occurred on November 20, were apparently triggered by different mechanisms as inferred from the flare ribbons evolution (filament eruption and CMEs). We studied in detail the behaviour of two North-South oriented filaments on November 20 2003. They merged and split following a process suggestive of `sling-shot' reconnection between two coronal flux ropes. We successfully tested this scenario in a 3D MHD simulation that is presented in this paper. Title: Twist and writhe of δ-island active regions Authors: López Fuentes, M. C.; Mandrini, C. H.; Démoulin, P. Bibcode: 2011IAUS..273..153L Altcode: We study the magnetic helicity properties of a set of peculiar active regions (ARs) including δ-islands and other high-tilt bipolar configurations. These ARs are usually identified as the most active in terms of flare and CME production. Due to their observed structure, they have been associated with the emergence of magnetic flux tubes that develop a kink instability. Our main goal is to determine the chirality of the twist and writhe components of the AR magnetic helicity in order to set constrains on the possible mechanisms producing the flux tube deformations. We determine the magnetic twist comparing observations of the AR coronal structure with force-free models of the magnetic field. We infer the flux-tube writhe from the rotation of the main magnetic bipole during the observed evolution. From the relation between the obtained twist and writhe signs we conclude that the development of the kink instability cannot be the single mechanism producing deformed flux-tubes. Title: On Asymmetry of Magnetic Helicity in Emerging Active Regions: High Resolution Observations Authors: Alexander, David; Tian, Lirong; Demoulin, Pascal; Zhu, Chunming Bibcode: 2011shin.confE..11A Altcode: We employ the DAVE (differential affine velocity estimator, Schuck 2005; 2006) tracking technique on a time series of MDI/1m high spatial resolution lineof- sight magnetograms to measure the photospheric flow velocity for three newly emerging bipolar active regions. We separately calculate the magnetic helicity injection rate of the leading and following polarities to confirm or refute the magnetic helicity asymmetry, found by Tian & Alexander (2009) using MDI/96m low spatial resolution magnetograms. Our results demonstrate that the magnetic helicity asymmetry is robust being present in the three active regions studied, two of which have an observed balance of the magnetic flux. The magnetic helicity injection rate measured is found to depend little on the window size selected, but does depend on the time interval used between the two successive magnetograms tracked. It is found that the measurement of the magnetic helicity injection rate performs well for a window size between 12-10 and 18-15 pixels, and at a time interval ∼t=10 minutes. Moreover, the short-lived magnetic structures, 10-60 minutes, are found to contribute 30-50% of the magnetic helicity injection rate. Comparing with the results calculated by MDI/96m data, we find that the MDI/96m data, in general, can outline the main trend of the magnetic properties, but they significantly underestimate the magnetic flux in strong field region and are not appropriate for quantitative tracking studies, so provide a poor estimate of the amount of magnetic helicity injected into the corona. Title: Interplanetary magnetic structure guiding relativistic particles Authors: Masson, Sophie; Démoulin, P.; Dasso, S.; Klein, K. -L. Bibcode: 2011shin.confE..77M Altcode: The origin and the propagation of relativistic solar particles (0.5 to few GeV) in the interplanetary medium remains a debated topic. These relativistic particles, detected at the Earth by neutron monitors have been previously accelerated close to the Sun and are guided by the interplanetary magnetic field (IMF) lines, connecting the acceleration site and the Earth. Usually, the nominal Parker spiral is considered for ensuring the magnetic connection to the Earth. However, in most GLEs the IMF is highly disturbed, and the active regions associated to the GLEs are not always located close to the solar footprint of the nominal Parker spiral. A possible explanation is that relativistic particles are propagating in transient magnetic structures, such as Interplanetary Coronal Mass Ejections (ICMEs).

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. Title: Actors of the main activity in large complex centres during the 23 solar cycle maximum Authors: Schmieder, B.; Démoulin, P.; Pariat, E.; Török, T.; Molodij, G.; Mandrini, C. H.; Dasso, S.; Chandra, R.; Uddin, W.; Kumar, P.; Manoharan, P. K.; Venkatakrishnan, P.; Srivastava, N. Bibcode: 2011AdSpR..47.2081S Altcode: During the maximum of Solar Cycle 23, large active regions had a long life, spanning several solar rotations, and produced large numbers of X-class flares and CMEs, some of them associated to magnetic clouds (MCs). This is the case for the Halloween active regions in 2003. The most geoeffective MC of the cycle (Dst = -457) had its source during the disk passage of one of these active regions (NOAA 10501) on 18 November 2003. Such an activity was presumably due to continuous emerging magnetic flux that was observed during this passage. Moreover, the region exhibited a complex topology with multiple domains of different magnetic helicities. The complexity was observed to reach such unprecedented levels that a detailed multi-wavelength analysis is necessary to precisely identify the solar sources of CMEs and MCs. Magnetic clouds are identified using in situ measurements and interplanetary scintillation (IPS) data. Results from these two different sets of data are also compared. Title: Twisted Flux Tube Emergence Evidenced in Longitudinal Magnetograms: Magnetic Tongues Authors: Luoni, M. L.; Démoulin, P.; Mandrini, C. H.; van Driel-Gesztelyi, L. Bibcode: 2011SoPh..270...45L Altcode: 2011SoPh..tmp...66L Bipolar active regions (ARs) are thought to be formed by twisted flux tubes, as the presence of such twist is theoretically required for a cohesive rise through the whole convective zone. We use longitudinal magnetograms to demonstrate that a clear signature of a global magnetic twist is present, particularly, during the emergence phase when the AR is forming in a much weaker pre-existing magnetic field environment. The twist is characterised by the presence of elongated polarities, called "magnetic tongues", which originate from the azimuthal magnetic field component. The tongues first extend in size before retracting when the maximum magnetic flux is reached. This implies an apparent rotation of the magnetic bipole. Using a simple half-torus model of an emerging twisted flux tube having a uniform twist profile, we derive how the direction of the polarity inversion line and the elongation of the tongues depend on the global twist in the flux rope. Using a sample of 40 ARs, we verify that the helicity sign, determined from the magnetic polarity distribution pattern, is consistent with the sign derived from the photospheric helicity flux computed from magnetogram time series, as well as from other proxies such as sheared coronal loops, sigmoids, flare ribbons and/or the associated magnetic cloud observed in situ at 1 AU. The evolution of the tongues observed in emerging ARs is also closely similar to the evolution found in recent MHD numerical simulations. We also found that the elongation of the tongue formed by the leading magnetic polarity is significantly larger than that of the following polarity. This newly discovered asymmetry is consistent with an asymmetric Ω-loop emergence, trailing the solar rotation, which was proposed earlier to explain other asymmetries in bipolar ARs. Title: Pulsed Flows Along a Cusp Structure Observed with SDO/AIA Authors: Thompson, Barbara; Démoulin, P.; Mandrini, C.; Mays, M.; Ofman, L.; Van Driel-Gesztelyi, L.; Viall, N. Bibcode: 2011SPD....42.2117T Altcode: 2011BAAS..43S.2117T We present observations of a cusp-shaped structure that formed after a flare and coronal mass ejection on 14 February 2011. Throughout the evolution of the cusp structure, blob features up to a few Mm in size were observed flowing along the legs and stalk of the cusp at projected speeds ranging from 50 to 150 km/sec. Around two dozen blob features, on order of 1 - 3 minutes apart, were tracked in multiple AIA EUV wavelengths. The blobs flowed outward (away from the Sun) along the cusp stalk, and most of the observed speeds were either constant or decelerating. We attempt to reconstruct the 3-D magnetic field of the evolving structure, discuss the possible drivers of the flows (including pulsed reconnection and tearing mode instability), and compare the observations to studies of pulsed reconnection and blob flows in the solar wind and the Earth's magnetosphere. Title: Homologous Flares and Magnetic Field Topology in Active Region NOAA 10501 on 20 November 2003 Authors: Chandra, R.; Schmieder, B.; Mandrini, C. H.; Démoulin, P.; Pariat, E.; Török, T.; Uddin, W. Bibcode: 2011SoPh..269...83C Altcode: 2010arXiv1011.1187C; 2010SoPh..tmp..249C We present and interpret observations of two morphologically homologous flares that occurred in active region (AR) NOAA 10501 on 20 November 2003. Both flares displayed four homologous Hα ribbons and were both accompanied by coronal mass ejections (CMEs). The central flare ribbons were located at the site of an emerging bipole in the centre of the active region. The negative polarity of this bipole fragmented in two main pieces, one rotating around the positive polarity by ≈ 110° within 32 hours. We model the coronal magnetic field and compute its topology, using as boundary condition the magnetogram closest in time to each flare. In particular, we calculate the location of quasi-separatrix layers (QSLs) in order to understand the connectivity between the flare ribbons. Though several polarities were present in AR 10501, the global magnetic field topology corresponds to a quadrupolar magnetic field distribution without magnetic null points. For both flares, the photospheric traces of QSLs are similar and match well the locations of the four Hα ribbons. This globally unchanged topology and the continuous shearing by the rotating bipole are two key factors responsible for the flare homology. However, our analyses also indicate that different magnetic connectivity domains of the quadrupolar configuration become unstable during each flare, so that magnetic reconnection proceeds differently in both events. Title: Initiation and Early Development of the 2008 April 26 Coronal Mass Ejection Authors: Huang, J.; Démoulin, P.; Pick, M.; Auchère, F.; Yan, Y. H.; Bouteille, A. Bibcode: 2011ApJ...729..107H Altcode: We present a detailed study of a coronal mass ejection (CME) with high temporal cadence observations in radio and extreme-ultraviolet (EUV). The radio observations combine imaging of the low corona with radio spectra in the outer corona and interplanetary space. The EUV observations combine the three points of view of the STEREO and SOHO spacecraft. The beginning of the CME initiation phase is characterized by emissions that are signatures of the reconnection of the outer part of the erupting configuration with surrounding magnetic fields. Later on, a main source of emission is located in the core of the active region. It is an indirect signature of the magnetic reconnection occurring behind the erupting flux rope. Energetic particles are also injected in the flux rope and the corresponding radio sources are detected. Other radio sources, located in front of the EUV bright front, trace the interaction of the flux rope with the surrounding fields. Hence, the observed radio sources enable us to detect the main physical steps of the CME launch. We find that imaging radio emissions in the metric range permits us to trace the extent and orientation of the flux rope which is later detected in interplanetary space. Moreover, combining the radio images at various frequencies with fast EUV imaging permits us to characterize in space and time the processes involved in the CME launch. Title: Filament Interaction Modeled by Flux Rope Reconnection Authors: Török, T.; Chandra, R.; Pariat, E.; Démoulin, P.; Schmieder, B.; Aulanier, G.; Linton, M. G.; Mandrini, C. H. Bibcode: 2011ApJ...728...65T Altcode: Hα observations of solar active region NOAA 10501 on 2003 November 20 revealed a very uncommon dynamic process: during the development of a nearby flare, two adjacent elongated filaments approached each other, merged at their middle sections, and separated again, thereby forming stable configurations with new footpoint connections. The observed dynamic pattern is indicative of "slingshot" reconnection between two magnetic flux ropes. We test this scenario by means of a three-dimensional zero β magnetohydrodynamic simulation, using a modified version of the coronal flux rope model by Titov and Démoulin as the initial condition for the magnetic field. To this end, a configuration is constructed that contains two flux ropes which are oriented side-by-side and are embedded in an ambient potential field. The choice of the magnetic orientation of the flux ropes and of the topology of the potential field is guided by the observations. Quasi-static boundary flows are then imposed to bring the middle sections of the flux ropes into contact. After sufficient driving, the ropes reconnect and two new flux ropes are formed, which now connect the former adjacent flux rope footpoints of opposite polarity. The corresponding evolution of filament material is modeled by calculating the positions of field line dips at all times. The dips follow the morphological evolution of the flux ropes, in qualitative agreement with the observed filaments. Title: On Asymmetry of Magnetic Helicity in Emerging Active Regions: High-resolution Observations Authors: Tian, Lirong; Démoulin, Pascal; Alexander, David; Zhu, Chunming Bibcode: 2011ApJ...727...28T Altcode: 2011arXiv1101.1068T We employ the DAVE (differential affine velocity estimator) tracking technique on a time series of Michelson Doppler Imager (MDI)/1 minute high spatial resolution line-of-sight magnetograms to measure the photospheric flow velocity for three newly emerging bipolar active regions (ARs). We separately calculate the magnetic helicity injection rate of the leading and following polarities to confirm or refute the magnetic helicity asymmetry, found by Tian & Alexander using MDI/96 minute low spatial resolution magnetograms. Our results demonstrate that the magnetic helicity asymmetry is robust, being present in the three ARs studied, two of which have an observed balance of the magnetic flux. The magnetic helicity injection rate measured is found to depend little on the window size selected, but does depend on the time interval used between the two successive magnetograms being tracked. It is found that the measurement of the magnetic helicity injection rate performs well for a window size between 12 × 10 and 18 × 15 pixels and at a time interval Δt = 10 minutes. Moreover, the short-lived magnetic structures, 10-60 minutes, are found to contribute 30%-50% of the magnetic helicity injection rate. Comparing with the results calculated by MDI/96 minute data, we find that the MDI/96 minute data, in general, can outline the main trend of the magnetic properties, but they significantly underestimate the magnetic flux in strong field regions and are not appropriate for quantitative tracking studies, so provide a poor estimate of the amount of magnetic helicity injected into the corona. Title: Investigating the observational signatures of magnetic cloud substructure Authors: Steed, K.; Owen, C. J.; Démoulin, P.; Dasso, S. Bibcode: 2011JGRA..116.1106S Altcode: Magnetic clouds (MCs) represent a subset of interplanetary coronal mass ejections (ICMEs) that exhibit a magnetic flux rope structure. They are primarily identified by smooth, large-scale rotations of the magnetic field. However, both small- and large-scale fluctuations of the magnetic field are observed within some magnetic clouds. We analyzed the magnetic field in the frames of the flux ropes, approximated using a minimum variance analysis (MVA), and have identified a small number of MCs within which multiple reversals of the gradient of the azimuthal magnetic field are observed. We herein use the term “substructure” to refer to regions that exhibit this signature. We examine, in detail, one such MC observed on 13 April 2006 by the ACE and WIND spacecraft and show that substructure has distinct signatures in both the magnetic field and plasma observations. We identify two thin current sheets within the substructure and find that they bound the region in which the observations deviate most significantly from those typically expected in MCs. The majority of these clouds are followed by fast solar wind streams, and a comparison of the properties of this magnetic cloud with five similar events reveals that they have lower nondimensional expansion rates than nonovertaken magnetic clouds. We discuss and evaluate several possible explanations for this type of substructure, including the presence of multiple flux ropes and warping of the MC structure, but we conclude that none of these scenarios is able to fully explain all of the aspects of the substructure observations. Title: Study of solar flares and filament interaction in NOAA 10501 on 20 November, 2003 Authors: Chandra, R.; Schmieder, B.; Mandrini, C. H.; Démoulin, P.; Pariat, E.; Török, T.; Aulanier, G.; Uddin, W.; Linton, M. G. Bibcode: 2011ASInC...2..323C Altcode: We analyze the observations of two flares from NOAA AR 10501 on 20 November, 2003. The flares are homologous, exhibit four ribbons and are located in a quadrupolar magnetic configuration. The evolution of the ribbons suggests that the first eruption is triggered by "tether cutting" (with subsequent quadrupolar reconnection as in the "magnetic breakout" model), whereas the second one is consistent with the "magnetic breakout" model. Another interesting feature of our observations is the interaction of two filaments elongated in the north-south direction. The filaments merge at their central parts and afterwards change their orientation to the east-west direction. This merging and splitting is closely related to the evolution found in an MHD simulation as a result of reconnection between two flux ropes. Title: Evolution of geoeffective ICMEs in the inner heliosphere (Invited) Authors: Dasso, S.; Demoulin, P.; Gulisano, A. M.; Nakwacki, M. Bibcode: 2010AGUFMSH43C..05D Altcode: Over recent years, the new generation of space observations using multispacecraft fleets combined with high performance MHD numerical simulations and with new theoretical interpretations, have led to a very fruitful advance on our knowledge about the evolution of geoeffective transient structures of solar origin, from their birth in the low corona to their arrival at Earth. Interplanetary Coronal Mass Ejections (ICMEs) are the most geoeffective transients in the solar wind (SW), and the comparison between models and observations is one of the keys to clarify their dynamical evolution, mainly given by interaction with the environment. In this presentation we will examine some important physical processes, which can take place during the interaction ICME-SW and ICME-ICME, as drag, deviation from radial propagation, distortion of their inner configuration, and compression or expansion with the consequent intensification or weakening of the internal magnetic field. All these processes are crucial to determine the geoeffectiveness of an ICME reaching Earth. Title: Expansion rate of Magnetic Clouds beyond Earth Authors: Gulisano, A. M.; Dasso, S.; Demoulin, P. Bibcode: 2010AGUFMSH43A1813G Altcode: Magnetic Clouds (MCs) are interplanetary manifestations of transient structures erupted from the Sun. They are formed by strong helical magnetic field lines, and their configuration evolve accordingly to their interaction with the surrounding plasma. Due to the decay of the solar wind pressure for increasing heliodistance, and because their magnetic configuration remains as an entity during their evolution, MCs are objects in global expansion. When the MC is not perturbed by fast streams or other interplanetary transients, its expansion rate is expected to be in agreement with the rate of decay of total solar wind pressure, as it was recently confirmed by observations at the ecliptic plane in the inner heliosphere and near Earth. In this work we present results of the local expansion of MCs observed at heliodistances between one and five AUs. In particular, we compute the dimensionless expansion rate (ζ [Démoulin et al., Solar Physics, 2008]) using the MC bulk velocity profile in-situ observed by Ulysses. We analyze the dependence of ζ with heliodistance, MC size and other MC properties. As it was done previously for the inner heliosphere, we find now that when the MC is not perturbed by the environment (and thus it shows a linear bulk velocity profile) ζ is in a very good agreement with the expected global expansion. Title: Tracking ICMEs from combining modeling, remote-sensing, and in-situ observations (Invited) Authors: Dasso, S.; Demoulin, P. Bibcode: 2010AGUFMSH52B..04D Altcode: Remote-sensing and in-situ techniques can be used to model and track the evolution of a Coronal Mass Ejection (CME) from its solar eruption to its interplanetary manifestation (ICME), including the travel through the low corona and the solar wind (SW). The synergy from combining these different observational techniques have produced very important progresses in our understanding of these astrophysical objects, with important consequences on Sun-Earth connection and space weather. In particular, major advances have been obtained on identifying different substructures inside ICMEs, some times forming multiple flux ropes. Recent results obtained from these combined techniques will be given in this presentation, with special focus on new insights about magnetic properties and expansion of ICMEs, and physical processes that can take place during the interaction ICME-SW and ICME-ICME. Title: Criteria for Flux Rope Eruption: Non-equilibrium Versus Torus Instability Authors: Démoulin, P.; Aulanier, G. Bibcode: 2010ApJ...718.1388D Altcode: 2010arXiv1006.1785D The coronal magnetic configuration of an active region typically evolves quietly for a few days before becoming suddenly eruptive and launching a coronal mass ejection (CME). The precise origin of the eruption is still under debate. The loss of equilibrium, or an ideal magnetohydrodynamic (MHD) instability such as torus instability are among the several mechanisms that have proposed to be responsible for the sudden eruptions. Distinct approaches have also been formulated for limited cases having circular or translation symmetry. We revisit the previous theoretical approaches setting them in the same analytical framework. The coronal field results from the contribution of a non-neutralized current channel added to a background magnetic field, which in our model is the potential field generated by two photospheric flux concentrations. The evolution on short Alfvénic timescale is governed by ideal MHD. We first show analytically that the loss of equilibrium and the stability analysis are two different views of the same physical mechanism. Second, we identify that the same physics is involved in the instabilities of circular and straight current channels. Indeed, they are just two particular limiting cases of more general current paths. A global instability of the magnetic configuration is present when the current channel is located at a coronal height, h, large enough so that the decay index of the potential field, ∂ln |B p|/∂ln h, is larger than a critical value. At the limit of very thin current channels, previous analysis has found critical decay indices of 1.5 and 1 for circular and straight current channels, respectively. However, with current channels being deformable and as thick as that expected in the corona, we show that this critical index has similar values for circular and straight current channels, and is typically in the range [1.1,1.3]. Title: 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. Bibcode: 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. Title: Coexisting Flux Rope and Dipped Arcade Sections Along One Solar Filament Authors: Guo, Y.; Schmieder, B.; Démoulin, P.; Wiegelmann, T.; Aulanier, G.; Török, T.; Bommier, V. Bibcode: 2010ApJ...714..343G Altcode: We compute the three-dimensional magnetic field of an active region in order to study the magnetic configuration of active region filaments. The nonlinear force-free field model is adopted to compute the magnetic field above the photosphere, where the vector magnetic field was observed by THEMIS/MTR on 2005 May 27. We propose a new method to remove the 180° ambiguity of the transverse field. Next, we analyze the implications of the preprocessing of the data by minimizing the total force and torque in the observed vector fields. This step provides a consistent bottom boundary condition for the nonlinear force-free field model. Then, using the optimization method to compute the coronal field, we find a magnetic flux rope along the polarity inversion line. The magnetic flux rope aligns well with part of an Hα filament, while the total distribution of the magnetic dips coincides with the whole Hα filament. This implies that the magnetic field structure in one section of the filament is a flux rope, while the other is a sheared arcade. The arcade induced a left-bearing filament in the magnetic field of negative helicity, which is opposite to the chirality of barbs that a flux rope would induce in a magnetic field of the same helicity sign. The field strength in the center of the flux rope is about 700 G, and the twist of the field lines is ~1.4 turns. Title: Evolution of magnetic clouds in the inner heliosphere Authors: Gulisano, Adriana Maria; Démoulin, Pascal; Dasso, Sergio; Ruiz, Maria Emilia; Marsch, Eckart Bibcode: 2010AIPC.1216..391G Altcode: Magnetic clouds (MCs) are objects in expansion during their travel through the heliosphere. In situ observations indicate that their front travel faster than their back, showing a clear empirical signature of expansion. With the aim of quantifying the expansion rate of MCs in the inner heliosphere (0.3 to 1 AU), we present here a statistical study of events observed by the spacecraft Helios 1 and 2, during their complete period of operations. From the analysis of the profile of the MC magnetic field components in its local frame, which is obtained from a rotation of the observed magnetic field vectors to a system of reference oriented as the main axis of the flux rope, we revise a list of events identified in previous works and redefine improved MC boundaries/orientation for each event. We then split the sample into two subsets according to the characteristics of their velocity profiles, (a) those MCs with a significantly perturbed velocity profile due to the interaction with their surrounding solar wind (i.e. overtaken by streams) and (b) those that are not perturbed. We compute the dimensionless local expansion rate (ζ) for MCs defined by several works [e.g. Démoulin et al., Solar Phys, 250, 347-374 (2008)]. We find significantly different distribution of values for ζ when perturbed and non perturbed events are considered. Non perturbed MCs expand at rates ζ consistent with the expected value from the global pressure decay in the surrounding solar wind for increasing helio-distances, while perturbed ones may present strong departures from that global rule. We interpret these departures of ζ for perturbed MCs as a consequence of interaction with streams on their expansion. Title: Interaction of ICMEs with the Solar Wind Authors: Démoulin, Pascal Bibcode: 2010AIPC.1216..329D Altcode: Interplanetary Coronal Mass Ejections (ICMEs) are formed of plasma and magnetic field launched from the Sun into the Solar Wind (SW). These coherent magnetic structures, frequently formed by a flux rope, interact strongly with the SW. This interaction is reviewed by comparing the results obtained from in situ observations and numerical simulations. Like fast ships in the ocean, fast ICMEs drive an extended shock in front. ICMEs expand in all directions while traveling away from the Sun, a sheath of SW plasma and magnetic field accumulates in front of the ICME, which partially reconnects with the ICME magnetic field. Furthermore, not only do ICMEs have a profound impact on the heliosphere, but the type of SW encountered by an ICME has an important impact on its evolution (e.g. increase of mass, global deceleration, lost of magnetic flux and helicity, distortion of the configuration). Title: Why proton temperature and velocity are correlated in the SW and not in ICMEs? Authors: Démoulin, Pascal Bibcode: 2010AIPC.1216..231D Altcode: The in situ correlation of the proton temperature with the bulk plasma velocity of the solar wind (SW) is a firm result confirmed by several spacecraft, while in interplanetary coronal mass ejections (ICMEs) the proton temperature is both cooler and not correlated with the velocity. For some specific heating mechanism, the internal energy equation alone could provide a temperature increasing with velocity, but the increase remains much weaker than observed in the SW. In fact, it is shown here that the observed correlation is generically obtained from a global energy conservation in thermally driven winds. It results from the conversion of thermal to kinetic energy close to the Sun. The absence (or even anti-) correlation observed in situ between electron temperature and SW velocity, together with the correlation found for proton temperature, show that protons have a dominant role in the SW acceleration. In contrast, in ICMEs the plasma is contained by the magnetic field since ICMEs have both a closed configuration and a low plasma β. It implies no significant correlation between temperature and velocity, as observed. In conclusion, a different dominating term in the impulsion equation is the main origin of the different relation observed between the proton temperature and the bulk velocity in SW and ICMEs. Title: Study of helicity properties of peculiar active regions Authors: López Fuentes, M. C.; Mandrini, C. H.; Démoulin, P. Bibcode: 2010IAUS..264..102L Altcode: 2010IAUS..264..102F Peculiar solar active regions (ARs), such as δ-islands and other high tilt bipoles, are commonly associated with the emergence of severely deformed magnetic flux tubes. Therefore, the study of these ARs provides valuable information on the origin and evolution of magnetic structures in the solar interior. Here, we infer the magnetic helicity properties of the flux tubes associated to a set of peculiar ARs by studying the evolution of photospheric magnetograms (SOHO/MDI) and coronal observations (SOHO/EIT and TRACE) in combination with force-free models of the magnetic field. We discuss how our results relate to different models of the evolution of emerging magnetic flux tubes. Title: Formation of Torus-Unstable Flux Ropes and Electric Currents in Erupting Sigmoids Authors: Aulanier, G.; Török, T.; Démoulin, P.; DeLuca, E. E. Bibcode: 2010ApJ...708..314A Altcode: We analyze the physical mechanisms that form a three-dimensional coronal flux rope and later cause its eruption. This is achieved by a zero-β magnetohydrodynamic (MHD) simulation of an initially potential, asymmetric bipolar field, which evolves by means of simultaneous slow magnetic field diffusion and sub-Alfvénic, line-tied shearing motions in the photosphere. As in similar models, flux-cancellation-driven photospheric reconnection in a bald-patch (BP) separatrix transforms the sheared arcades into a slowly rising and stable flux rope. A bifurcation from a BP to a quasi-separatrix layer (QSL) topology occurs later on in the evolution, while the flux rope keeps growing and slowly rising, now due to shear-driven coronal slip-running reconnection, which is of tether-cutting type and takes place in the QSL. As the flux rope reaches the altitude at which the decay index -∂ln B/∂ln z of the potential field exceeds ~3/2, it rapidly accelerates upward, while the overlying arcade eventually develops an inverse tear-drop shape, as observed in coronal mass ejections (CMEs). This transition to eruption is in accordance with the onset criterion of the torus instability. Thus, we find that photospheric flux-cancellation and tether-cutting coronal reconnection do not trigger CMEs in bipolar magnetic fields, but are key pre-eruptive mechanisms for flux ropes to build up and to rise to the critical height above the photosphere at which the torus instability causes the eruption. In order to interpret recent Hinode X-Ray Telescope observations of an erupting sigmoid, we produce simplified synthetic soft X-ray images from the distribution of the electric currents in the simulation. We find that a bright sigmoidal envelope is formed by pairs of J-shaped field lines in the pre-eruptive stage. These field lines form through the BP reconnection and merge later on into S-shaped loops through the tether-cutting reconnection. During the eruption, the central part of the sigmoid brightens due to the formation of a vertical current layer in the wake of the erupting flux rope. Slip-running reconnection in this layer yields the formation of flare loops. A rapid decrease of currents due to field line expansion, together with the increase of narrow currents in the reconnecting QSL, yields the sigmoid hooks to thin in the early stages of the eruption. Finally, a slightly rotating erupting loop-like feature (ELLF) detaches from the center of the sigmoid. Most of this ELLF is not associated with the erupting flux rope, but with a current shell that develops within expanding field lines above the rope. Only the short, curved end of the ELLF corresponds to a part of the flux rope. We argue that the features found in the simulation are generic for the formation and eruption of soft X-ray sigmoids. Title: The interplanetary magnetic field associated with the propagation of solar relativistic particles Authors: Masson, Sophie; Dasso, Sergio; Demoulin, Pascal Bibcode: 2010cosp...38.3009M Altcode: 2010cosp.meet.3009M The origin and the propagation of relativistic solar particles (450 MeV-few GeV) in the inter-planetary medium remains a complex topic. These particles, detected at the Earth by neutron monitors (called Ground level enhancement, GLE), have been previously accelerated close to the Sun. Before being detected at the Earth, these relativistic particles have to travel along an interplanetary magnetic field (IMF) connecting the acceleration site and the Earth. Generally, the nominal Parker spiral (SP), is considered for ensuring the magnetic connection to the Earth. However, in most GLEs the IMF is highly disturbed, and the active regions (ARs) associated to the GLEs are not always located close to the footprint of the nominal Parker spiral. If it is not the nominal Parker spiral, which IMF connects the acceleration site and the Earth during the GLEs? A possible explanation of relativistic particles propagation under these circumstances are transient magnetic structures, travelling in the IMF as Interplanetary coronal mass ejections (ICMEs). In order to check this interpretation, we studied in detail the interplanetary medium in which 10 GLEs of the last solar cycle propagate. Using the magnetic field and the plasma parameter measurements (ACE/MAG and ACE/SWEPAM), we found widely different IMF configurations. Those included obvious cases of propagation in an ICME, as well as some cases consistent with a Parker Spiral. But, we also found cases correponding to the propagation of relativistic particles in a highly disturbed Parker like IMF. In an independant approach we applied the velocity dispersion method (VDA) to energetic protons measured by SoHO/ERNE and relativistic particles measured by the neutron monitor network. We determined the path length travelled by energetic particles. These lengths are fully consistent with the IMF shape determined previously. Thus, the length associated to particles propagating along the nominal Parker spiral is of the order of 1-1.2 AU, contrary to the length associated with a distrubed interplanetary magnetic filed which is of order of 1.3-1.8 AU. For particles in an ICME, the velocity dispersion analysis gives a length approching 2 AU. This is an important element when one want use the timing of particle arrival at Earth to identify type of solar activity that leads to the acceleration of these particles. Title: Magnetic Flux Rope Eruption: Non Equilibrium versus Torus Instability Authors: Demoulin, Pascal; Aulanier, Guillaume; Toeroek, Tibor; Deluca, Edward Bibcode: 2010cosp...38.1855D Altcode: 2010cosp.meet.1855D The coronal magnetic configuration of an active region typically evolves quietly during few days before becoming suddenly eruptive and launching a CME. The precise origin of the eruption is still debated. Among other mechanisms, it has been long proposed that a loss of equilibrium, or an ideal MHD instability such as the torus instability, could be responsible for the sudden eruptivity. We first revisit both approaches with simple analytical models as well as with a 3D MHD simulation of an initially potential bipolar field, which evolves by means of simultaneous slow magnetic field diffusion and shearing motions in the photosphere. Reconnection of sheared arcade leads to the formation of a twisted flux rope, which corresponds to an electric current channel. We find that the electric current distribution and the field-line organization present in the MHD simulation provide an explanation for the recent X-rays Hinode observations of erupting sigmoidal regions. Next, we show analytically that the loss of equilibrium and the torus instability are two different views of the same physical mechanism. We compare the instability thresholds in the limit of straight and circular current channels, finding that they are closely comparable for thick current channels (as present in the MHD simulation and as expected in the corona) while these thresholds are well distinct at the limit of very thin current channels (as typically found in previous studies). Finally, including photospheric line tying of the current channel in the analytical models permits to have a closer comparison between instability thresholds found analytically and by the MHD simulation. Title: Magnetic reconnection along QSLs -a major driver of active region outflows Authors: Baker, Deborah; van Driel-Gesztelyi, Lidia; Mandrini, Cristina H.; Demoulin, Pascal Bibcode: 2010cosp...38.2926B Altcode: 2010cosp.meet.2926B The relationship between quasi-separatrix layers (QSLs), or in the limit of infinitely thin QSLs, separatrices, and various activity phenomena has been explored in many different solar magnetic configurations across all scales in recent years. In the absence of magnetic nulls, fast reconnec-tion along QSLs, which are specific locations in the magnetic topology where field lines display strong gradients of magnetic connectivity, was identified as the main physical process at the origin of flares. Recently, it was shown that fast (tens of km/s) persistent hot plasma upflows in active regions (ARs) can also be linked to locations of QSLs. It is likely that these upflows that occur at the edges of ARs over unipolar magnetic field concentrations are accelerated by magnetic reconnection along QSLs. We will show multi-temperature spectral scan observations from Hinode's EIS combined with magnetic modeling of QSLs in two ARs observed on 20-21 February 2007 and 11 January 2008. The latter AR is observed and modeled when it is in the vicinity of the solar central meridian where there are no projection effects, thereby eliminating ambiguity linking the origin of multi-temperature observations of AR upflows to QSLs. We use the Potential Source Surface Model to look for open field lines in the vicinity of upflows and QSL locations in order to demonstrate whether these upflows become outflows and can contribute to the solar wind. Title: Global and local expansion of magnetic clouds in the inner heliosphere Authors: Gulisano, A. M.; Démoulin, P.; Dasso, S.; Ruiz, M. E.; Marsch, E. Bibcode: 2010A&A...509A..39G Altcode: 2012arXiv1206.1112G Context. Observations of magnetic clouds (MCs) are consistent with the presence of flux ropes detected in the solar wind (SW) a few days after their expulsion from the Sun as coronal mass ejections (CMEs).
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 Bibcode: 2010cosp...38.1886M Altcode: 2010cosp.meet.1886M On 18 and 20 November 2003 active region (AR) 10501 produced a series of M flares all of them associated with coronal mass ejections (CMEs). The particularity of this AR is that while observational tracers of the magnetic helicity sign indicate that the large scale field in the region had a negative magnetic helicity sign, the MC associated to the most intense flare/CME on November 18 showed the opposite sign. Furthermore, the filaments observed on November 20 present morphological characteristics that correspond to a negative magnetic helicity sign, the rotation of the polarities of an emerging bipole indicate negative magnetic helicity sign injection; however, the flare ribbons observed after two homologous events can be connected either by field lines computed using a positive or a negative helicity sign magnetic field. We combine Hα, EUV, hard X-rays, and magnetic field data analysis with magnetic field modelling, and magnetic helicity injection computations to understand the origin of the helicity sign discrepancies discussed above. On November 20 magnetic field modeling and topology computations (in particular, the location of quasi-separatrix layers in relation to flare ribbons and evolution) give us clues about the CME initiation process. Title: Actors of the main activity of large complex centres during the 23 Solar Cycle maximum Authors: Schmieder, Brigitte; Chandra, Ramesh; Demoulin, Pascal; Mandrini, Cristina H.; Venkatakrishnan, P.; Manoharan, P. K.; Uddin, Wahab; Pariat, Etienne; Toeroek, Tibor; Molodij, Guillaume; Kumar, P. Bibcode: 2010cosp...38.1861S Altcode: 2010cosp.meet.1861S During the maximum of the last Solar Cycle solar cycle 23, large active regions had a long life spanning several solar rotations and produced a large number of X-ray class flares, CMEs and Magnetic clouds (MC). This was the case for the Halloween active regions in 2003. The most geoeffective magnetic cloud of the cycle (Dst=-457) has its source in one passage of the active region (NOAA 10501) on November 18, 2003. Such an activity is presumably due to continuous emerging magnetic flux that was observed during this passage. Moreover, the region exhibited a complex topology with multiple domains of distinct magnetic helicities. The complexity is observed to reach such unprecedented levels that a detailed multi wavelength analysis is necessary to precisely identify the sources of CMEs and MCs. Title: Analysis of Magnetic Clouds Evolution from 0.3 to 5 Astronomical Units Authors: Dasso, Sergio; Gulisano, Adriana Maria; Demoulin, Pascal; Marsch, Eckart Bibcode: 2010cosp...38.1922D Altcode: 2010cosp.meet.1922D Magnetic clouds (MCs) are transient structures in the solar wind, formed by large scale magnetic flux ropes as deduced from in situ observations of magnetic field. Moreover, in situ observations of the plasma velocity frequently show a clear evidence of an expansion in the radial direction from the Sun, unlike in the solar wind. This expansion has important consequences on the MC evolution, such as on the rates of decrease of mass density or magnetic field intensity. The aim of this work is to show properties of the evolution of MCs in the inner and outer heliosphere from 0.3 to 5 AUs. We present here an analysis of MCs observed by the Helios and Ulysses spacecraft, using in situ magnetic field and bulk plasma measurements. We analyze the dependence of several properties of MCs with the distance to the Sun, and in particular we analyze the dimensionless local expansion rate (ζ) [e.g. Démoulin et al., 2008]. We explore the dependence of the expansion speed on the MC size, the translation velocity, and the heliocentric distance, finding that there is a subset of MCs with almost the same non-dimensional expansion rate (ζ). The time velocity profile observed in this subset of MCs is almost linear, then we call them non perturbed MCs. These MCs expand at rates ζ consistent with the expected value from the global pressure decay in the surrounding solar wind for increasing helio-distances, while perturbed ones may present strong departures from that global rule. We interpret these departures of ζ for perturbed MCs as a consequence of the interaction of MCs with fast streams on their expansion. Title: Magnetic Reconnection along Quasi-separatrix Layers as a Driver of Ubiquitous Active Region Outflows Authors: Baker, D.; van Driel-Gesztelyi, L.; Mandrini, C. H.; Démoulin, P.; Murray, M. J. Bibcode: 2009ApJ...705..926B Altcode: 2009arXiv0909.4738B Hinode's EUV Imaging Spectrometer (EIS) has discovered ubiquitous outflows of a few to 50 km s-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. Bibcode: 2009A&A...507..969D Altcode: Context: Magnetic clouds (MCs) are formed by magnetic flux ropes that are ejected from the Sun as coronal mass ejections. These structures generally have low plasma beta and travel through the interplanetary medium interacting with the surrounding solar wind. Thus, the dynamical evolution of the internal magnetic structure of a MC is a consequence of both the conditions of its environment and of its own dynamical laws, which are mainly dominated by magnetic forces.
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. Bibcode: 2009AnGeo..27.3883B Altcode: 2009arXiv0909.5624B Combining STEREO, ACE and Hinode observations has presented an opportunity to follow a filament eruption and coronal mass ejection (CME) on 17 October 2007 from an active region (AR) inside a coronal hole (CH) into the heliosphere. This particular combination of "open" and closed magnetic topologies provides an ideal scenario for interchange reconnection to take place. With Hinode and STEREO data we were able to identify the emergence time and type of structure seen in the in-situ data four days later. On the 21st, ACE observed in-situ the passage of an ICME with "open" magnetic topology. The magnetic field configuration of the source, a mature AR located inside an equatorial CH, has important implications for the solar and interplanetary signatures of the eruption. We interpret the formation of an "anemone" structure of the erupting AR and the passage in-situ of the ICME being disconnected at one leg, as manifested by uni-directional suprathermal electron flux in the ICME, to be a direct result of interchange reconnection between closed loops of the CME originating from the AR and "open" field lines of the surrounding CH. Title: Why Do Temperature and Velocity Have Different Relationships in the Solar Wind and in Interplanetary Coronal Mass Ejections? Authors: Démoulin, P. Bibcode: 2009SoPh..257..169D Altcode: In-situ observations of the solar wind (SW) show temperature increasing with the wind speed, whereas such a dependence is not observed in interplanetary coronal mass ejections (ICMEs). The aim of this paper is to understand the main origin of this correlation in the SW and its absence in ICMEs. For that purpose both the internal-energy and momentum equations are solved analytically with various approximations. The internal-energy equation does not provide a strong link between temperature and velocity, but the momentum equation does. Indeed, the observed correlation in the open magnetic-field configuration of the SW is the result of its acceleration and heating close to the Sun. In contrast, the magnetic configuration of ICMEs is closed, and moreover the momentum equation is dominated by magnetic forces. This implies no significant correlation between temperature and velocity, as observed. Title: Causes and consequences of magnetic cloud expansion Authors: Démoulin, P.; Dasso, S. Bibcode: 2009A&A...498..551D Altcode: Context: A magnetic cloud (MC) is a magnetic flux rope in the solar wind (SW), which, at 1 AU, is observed ~2-5 days after its expulsion from the Sun. The associated solar eruption is observed as a coronal mass ejection (CME).
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 Bibcode: 2009EP&S...61..565S Altcode: 2009EP&S...61L.565S Solar two ribbon flares are commonly explained by magnetic field reconnections in the low corona. During the reconnection energetic particles (electrons and protons) are accelerated from the reconnection site. These particles are following the magnetic field lines down to the chromosphere. As the plasma density is higher in these lower layers, there are collisions and emission of radiation. Thus bright ribbons are observed at both ends of flare loops. These ribbons are typically observed in Hα and in EUV with SoHO and TRACE. As the time is going, these ribbons are expanding away of each other. In most studied models, the reconnection site is a separator line, where two magnetic separatrices intersect. They define four distinct connectivity domains, across which the magnetic connectivity changes discontinuously. In this paper, we present a generalization of this model to 3D complex magnetic topologies where there are no null points, but quasi-separatrices layers instead. In that case, while the ribbons spread away during reconnection, we show that magnetic field lines can quickly slip along them. We propose that this new phenomenon could explain fast extension of Hα and TRACE 1600 Å ribbons, fast moving HXR footpoints along the ribbons as observed by RHESSI, and that it is observed in soft X rays with Hinode/XRT. Title: Modelling and observations of photospheric magnetic helicity Authors: Démoulin, P.; Pariat, E. Bibcode: 2009AdSpR..43.1013D Altcode: Mounting observational evidence of the emergence of twisted magnetic flux tubes through the photosphere have now been published. Such flux tubes, formed by the solar dynamo and transported through the convection zone, eventually reach the solar atmosphere. Their accumulation in the solar corona leads to flares and coronal mass ejections. Since reconnections occur during the evolution of the flux tubes, the concepts of twist and magnetic stress become inappropriate. Magnetic helicity, as a well preserved quantity, in particular in plasma with high magnetic Reynolds number, is a more suitable physical quantity to use, even if reconnection is involved.

Only recently, it has been realized that the flux of magnetic helicity can be derived from magnetogram time series. This paper reviews the advances made in measuring the helicity injection rate at the photospheric level, mostly in active regions. It relates the observations to our present theoretical understanding of the emergence process. Most of the helicity injection is found during magnetic flux emergence, whereas the effect of differential rotation is small, and the long-term evolution of active regions is still puzzling. The photospheric maps of the injection of magnetic helicity provide new spatial information about the basic properties of the link between the solar activity and its sub-photospheric roots. Finally, the newest techniques to measure photospheric flows are reviewed. Title: The link between CME-associated dimmings and interplanetary magnetic clouds Authors: Mandrini, Cristina H.; Nakwacki, María S.; Attrill, Gemma; van Driel-Gesztelyi, Lidia; Dasso, Sergio; Démoulin, Pascal Bibcode: 2009IAUS..257..265M Altcode: Coronal dimmings often develop in the vicinity of erupting magnetic configurations. It has been suggested that they mark the location of the footpoints of ejected flux ropes and, thus, their magnetic flux can be used as a proxy for the ejected flux. If so, this quantity can be compared to the flux in the associated interplanetary magnetic cloud (MC) to find clues about the origin of the ejected flux rope. In the context of this interpretation, we present several events for which we have done a comparative solar-interplanetary analysis. We combine SOHO/Extreme Ultraviolet Imaging Telescope (EIT) data and Michelson Doppler Imager (MDI) magnetic maps to identify and measure the flux in the dimmed regions. We model the associated MCs and compute their magnetic flux using in situ observations. We find that the magnetic fluxes in the dimmings and MCs are compatible in some events; though this is not the case for large-scale and intense eruptions that occur in regions that are not isolated from others. We conclude that, in these particular cases, a fraction of the dimmed regions can be formed by reconnection between the erupting field and the surrounding magnetic structures, via a stepping process that can also explain other CME associated events. Title: Linking two consecutive nonmerging magnetic clouds with their solar sources Authors: Dasso, S.; Mandrini, C. H.; Schmieder, B.; Cremades, H.; Cid, C.; Cerrato, Y.; Saiz, E.; Démoulin, P.; Zhukov, A. N.; Rodriguez, L.; Aran, A.; Menvielle, M.; Poedts, S. Bibcode: 2009JGRA..114.2109D Altcode: 2009JGRA..11402109D; 2012arXiv1212.5546D On 15 May 2005, a huge interplanetary coronal mass ejection (ICME) was observed near Earth. It triggered one of the most intense geomagnetic storms of solar cycle 23 (Dst 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. Bibcode: 2008AGUFMSH23B1638S Altcode: Using ACE in situ data we identify and describe an interplanetary magnetic cloud (MC) observed near Earth on 13 April 2006. We also use multi-instrument and multi-wavelength observations from SOHO, TRACE and ground-based solar observatories to determine the solar source of this magnetic cloud. A launch window for the MC between 9 and 11 April 2006 was estimated from the propagation time of the ejecta observed near Earth. A number of large active regions were present on the Sun during this period, which were initially considered to be the most likely candidate source regions of the MC. However, it was determined that the solar source of the MC was a small, spotless active region observed in the Northern Hemisphere. Following an eruption from this region on 11 April 2006, the ACE spacecraft detected, 59 h later, the passage of the MC, preceded by the arrival of a weak, forward fast shock. The link between the eruption in this active region and the interplanetary MC is supported by several pieces of evidence, including the location of the solar source near to the disk centre and to the east of the central meridian (in agreement with the spacecraft trajectory through the western leg of the magnetic cloud), the propagation time of the ejecta, the agreement between the amount of flux in the magnetic cloud and in the active region, and the agreement between the signs of helicity of the magnetic cloud and the active region (which differs from the sign of helicity of each of the other active regions on the Sun at this time). In addition, the active region is located on the boundary of a coronal hole, and a high speed solar wind stream originating from this region is observed near Earth shortly after the passage of the magnetic cloud. This event highlights the complexities associated with locating the solar source of an ICME observed near Earth, and serves to emphasise that it is the combination of a number of physical characteristics and signatures that is important for successfully tying together the Earth-end and the Sun-end of an event. Further investigation of this MC has revealed some sub-structure towards its centre, observed as a small scale reversal of the azimuthal magnetic field of the MC, similar to that reported by Dasso et al., 2007. We explore several possible explanations for this signature, including the occurrence of multiple flux ropes and/or warping of the magnetic cloud. We also consider whether magnetic reconnection plays a role in creating the geometry that would explain these observations. Title: The Recovery of CME-Related Dimmings and the ICME's Enduring Magnetic Connection to the Sun Authors: Attrill, G. D. R.; van Driel-Gesztelyi, L.; Démoulin, P.; Zhukov, A. N.; Steed, K.; Harra, L. K.; Mandrini, C. H.; Linker, J. Bibcode: 2008SoPh..252..349A Altcode: 2008SoPh..tmp..158A It is generally accepted that transient coronal holes (TCHs, dimmings) correspond to the magnetic footpoints of CMEs that remain rooted in the Sun as the CME expands out into the interplanetary space. However, the observation that the average intensity of the 12 May 1997 dimmings recover to their pre-eruption intensity in SOHO/EIT data within 48 hours, whilst suprathermal unidirectional electron heat fluxes are observed at 1 AU in the related ICME more than 70 hours after the eruption, leads us to question why and how the dimmings disappear whilst the magnetic connectivity is maintained. We also examine two other CME-related dimming events: 13 May 2005 and 6 July 2006. We study the morphology of the dimmings and how they recover. We find that, far from exhibiting a uniform intensity, dimmings observed in SOHO/EIT data have a deep central core and a more shallow extended dimming area. The dimmings recover not only by shrinking of their outer boundaries but also by internal brightenings. We quantitatively demonstrate that the model developed by Fisk and Schwadron (Astrophys. J.560, 425, 2001) of interchange reconnections between "open" magnetic field and small coronal loops is a strong candidate for the mechanism facilitating the recovery of the dimmings. This process disperses the concentration of "open" magnetic field (forming the dimming) out into the surrounding quiet Sun, thus recovering the intensity of the dimmings whilst still maintaining the magnetic connectivity to the Sun. Title: A review of the quantitative links between CMEs and magnetic clouds Authors: Démoulin, P. Bibcode: 2008AnGeo..26.3113D Altcode: Magnetic clouds (MCs), and more generally, interplanetary coronal mass ejections (ICMEs), are believed to be the interplanetary counterparts of CMEs. The link has usually been shown by taking into account the CME launch position on the Sun, the expected time delay and by comparing the orientation of the coronal and interplanetary magnetic field. Making such a link more quantitative is challenging since it requires a relation between very different kinds of magnetic field measurements: (i) photospheric magnetic maps, which are observed from a distant vantage point (remote sensing) and (ii) in-situ measurements of MCs, which provide precise, directly measured, magnetic field data merely from one-dimensional linear samples. The association between events in these different domains can be made using adequate coronal and MC models. Then, global quantities like magnetic fluxes and helicity can be derived and compared. This review paper describes all the general trends found in the above association criteria. A special focus is given for the cases which do not follow the earlier derived mean laws since interesting physics is usually involved. Title: Why are CMEs large-scale coronal events: nature or nurture? Authors: van Driel-Gesztelyi, L.; Attrill, G. D. R.; Démoulin, P.; Mandrini, C. H.; Harra, L. K. Bibcode: 2008AnGeo..26.3077V Altcode: The apparent contradiction between small-scale source regions of, and large-scale coronal response to, coronal mass ejections (CMEs) has been a long-standing puzzle. For some, CMEs are considered to be inherently large-scale events eruptions in which a number of flux systems participate in an unspecified manner, while others consider magnetic reconnection in special global topologies to be responsible for the large-scale response of the lower corona to CME events. Some of these ideas may indeed be correct in specific cases. However, what is the key element which makes CMEs large-scale? Observations show that the extent of the coronal disturbance matches the angular width of the CME an important clue, which does not feature strongly in any of the above suggestions. We review observational evidence for the large-scale nature of CME source regions and find them lacking. Then we compare different ideas regarding how CMEs evolve to become large-scale. The large-scale magnetic topology plays an important role in this process. There is amounting evidence, however, that the key process is magnetic reconnection between the CME and other magnetic structures. We outline a CME evolution model, which is able to account for all the key observational signatures of large-scale CMEs and presents a clear picture how large portions of the Sun become constituents of the CME. In this model reconnection is driven by the expansion of the CME core resulting from an over-pressure relative to the pressure in the CME's surroundings. This implies that the extent of the lower coronal signatures match the final angular width of the CME. Title: Locating the solar source of 13 April 2006 magnetic cloud Authors: Steed, K.; Owen, C. J.; Harra, L. K.; Green, L. M.; Dasso, S.; Walsh, A. P.; Démoulin, P.; van Driel-Gesztelyi, L. Bibcode: 2008AnGeo..26.3159S Altcode: Using Advanced Composition Explorer (ACE) in situ data we identify and describe an interplanetary magnetic cloud (MC) observed near Earth on 13 April 2006. We also use multi-instrument and multi-wavelength observations from the Solar and Heliospheric Observatory (SOHO), the Transition Region and Coronal Explorer (TRACE) and ground-based solar observatories to determine the solar source of this magnetic cloud. A launch window for the MC between 9 and 11 April 2006 was estimated from the propagation time of the ejecta observed near Earth. A number of large active regions (ARs) were present on the Sun during this period, which were initially considered to be the most likely candidate source regions of the MC. However, it was determined that the solar source of the MC was a small, spotless active region observed in the Northern Hemisphere. Following an eruption from this region on 11 April 2006, the ACE spacecraft detected, 59 h later, the passage of the MC, preceded by the arrival of a weak, forward fast shock. The link between the eruption in this active region and the interplanetary MC is supported by several pieces of evidence, including the location of the solar source near to the disk centre and to the east of the central meridian (in agreement with the spacecraft trajectory through the western leg of the magnetic cloud), the propagation time of the ejecta, the agreement between the amount of flux in the magnetic cloud and in the active region, and the agreement between the signs of helicity of the magnetic cloud and the active region (which differs from the sign of helicity of each of the other active regions on the Sun at this time). In addition, the active region is located on the boundary of a coronal hole, and a high speed solar wind stream originating from this region is observed near Earth shortly after the passage of the magnetic cloud. Title: Multi-scale reconnections in a complex CME Authors: van Driel-Gesztelyi, L.; Goff, C. P.; Démoulin, P.; Culhane, J. L.; Matthews, S. A.; Harra, L. K.; Mandrini, C. H.; Klein, K. -L.; Kurokawa, H. Bibcode: 2008AdSpR..42..858V Altcode: A series of three flares of GOES class M, M and C, and a CME were observed on 20 January 2004 occurring in close succession in NOAA 10540. Types II, III, and N radio bursts were associated. We use the combined observations from TRACE, EIT, Hα images from Kwasan Observatory, MDI magnetograms, GOES, and radio observations from Culgoora and Wind/ WAVES to understand the complex development of this event. We reach three main conclusions. First, we link the first two impulsive flares to tether-cutting reconnections and the launch of the CME. This complex observation shows that impulsive quadrupolar flares can be eruptive. Second, we relate the last of the flares, an LDE, to the relaxation phase following forced reconnections between the erupting flux rope and neighbouring magnetic field lines, when reconnection reverses and restores some of the pre-eruption magnetic connectivities. Finally, we show that reconnection with the magnetic structure of a previous CME launched about 8 h earlier injects electrons into open field lines having a local dip and apex (located at about six solar radii height). This is observed as an N-burst at decametre radio wavelengths. The dipped shape of these field lines is due to large-scale magnetic reconnection between expanding magnetic loops and open field lines of a neighbouring streamer. This particular situation explains why this is the first N-burst ever observed at long radio wavelengths. Title: Twist, Writhe and Rotation of Magnetic Flux Ropes in Filament Eruptions and Coronal Mass Ejections Authors: Török, T.; Berger, M. A.; Kliem, B.; Démoulin, P.; Linton, M.; van Driel-Gesztelyi, L. Bibcode: 2008ESPM...12.3.54T Altcode: We present the first quantitative analysis of the conversion of twist into writhe in the course of ideal MHD instabilities in erupting coronal magnetic flux ropes. For our analysis, we consider numerical simulations of two instabilities which have been suggested as trigger and initial driving mechanisms in filament eruptions and coronal mass ejections, namely the helical kink instability and the torus instability. We use two different coronal flux rope models as initial conditions in the simulations, namely the cylindrical Gold-Hoyle equilibrium and the toroidal Titov-Demoulin equilibrium.

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. Bibcode: 2008SoPh..250..347D Altcode: 2008SoPh..tmp..121D In situ data provide only a one-dimensional sample of the plasma velocity along the spacecraft trajectory crossing an interplanetary coronal mass ejection (ICME). Then, to understand the dynamics of ICMEs it is necessary to consider some models to describe it. We derive a series of equations in a hierarchical order, from more general to more specific cases, to provide a general theoretical basis for the interpretation of in situ observations, extending and generalizing previous studies. The main hypothesis is a self-similar expansion, but with the freedom of possible different expansion rates in three orthogonal directions. The most detailed application of the equations is though for a subset of ICMEs, magnetic clouds (MCs), where a magnetic flux rope can be identified. The main conclusions are the following ones. First, we obtain theoretical expressions showing that the observed velocity gradient within an ICME is not a direct characteristic of its expansion, but that it depends also on other physical quantities such as its global velocity and acceleration. The derived equations quantify these dependencies for the three components of the velocity. Second, using three different types of data we show that the global acceleration of ICMEs has, at most, a small contribution to the in situ measurements of the velocity. This eliminates practically one contribution to the observed velocity gradient within ICMEs. Third, we provide a method to quantify the expansion rate from velocity data. We apply it to a set of 26 MCs observed by Wind or ACE spacecrafts. They are typical MCs, and their main physical parameters cover the typical range observed in MCs in previous statistical studies. Though the velocity difference between their front and back includes a broad range of values, we find a narrow range for the determined dimensionless expansion rate. This implies that MCs are expanding at a comparable rate, independently of their size or field strength, despite very different magnitudes in their velocity profiles. Furthermore, the equations derived provide a base to further analyze the dynamics of MCs/ICMEs. Title: Analysis of large scale MHD quantities in expanding magnetic clouds Authors: Nakwacki, María Soledad; Dasso, Sergio; Mandrini, Cristina Hemilse; Démoulin, Pascal Bibcode: 2008JASTP..70.1318N Altcode: Magnetic clouds (MCs) transport the magnetic flux and helicity released by the Sun. They are generally modeled as a static flux rope traveling in the solar wind, though they can present signatures of expansion. We analyze three expanding MCs using a self-similar free radial expansion model with a cylindrical linear force-free field (i.e., Lundquist solution) as the initial condition. We derive expressions for the magnetic fluxes, the magnetic helicity and the magnetic energy per unit length along the flux tube. We find that these quantities do not differ more than 25% when using the static or expansion model. Title: Non-Linear Force-Free Field Modeling of a Solar Active Region Around the Time of a Major Flare and Coronal Mass Ejection Authors: De Rosa, M. L.; Schrijver, C. J.; Metcalf, T. R.; Barnes, G.; Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann, T.; Wheatland, M.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann, M.; Kusano, K.; Régnier, S.; Thalmann, J. Bibcode: 2008AGUSMSP31A..06D Altcode: Solar flares and coronal mass ejections are associated with rapid changes in coronal magnetic field connectivity and are powered by the partial dissipation of electrical currents that run through the solar corona. A critical unanswered question is whether the currents involved are induced by the advection along the photosphere of pre-existing atmospheric magnetic flux, or whether these currents are associated with newly emergent flux. We address this problem by applying nonlinear force-free field (NLFFF) modeling to the highest resolution and quality vector-magnetographic data observed by the recently launched Hinode satellite on NOAA Active Region 10930 around the time of a powerful X3.4 flare in December 2006. We compute 14 NLFFF models using 4 different codes having a variety of boundary conditions. We find that the model fields differ markedly in geometry, energy content, and force-freeness. We do find agreement of the best-fit model field with the observed coronal configuration, and argue (1) that strong electrical currents emerge together with magnetic flux preceding the flare, (2) that these currents are carried in an ensemble of thin strands, (3) that the global pattern of these currents and of field lines are compatible with a large-scale twisted flux rope topology, and (4) that the ~1032~erg change in energy associated with the coronal electrical currents suffices to power the flare and its associated coronal mass ejection. We discuss the relative merits of these models in a general critique of our present abilities to model the coronal magnetic field based on surface vector field measurements. Title: Nonlinear Force-free Field Modeling of a Solar Active Region around the Time of a Major Flare and Coronal Mass Ejection Authors: Schrijver, C. J.; DeRosa, M. L.; Metcalf, T.; Barnes, G.; Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann, T.; Wheatland, M. S.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann, M.; Kusano, K.; Régnier, S.; Thalmann, J. K. Bibcode: 2008ApJ...675.1637S Altcode: 2007arXiv0712.0023S Solar flares and coronal mass ejections are associated with rapid changes in field connectivity and are powered by the partial dissipation of electrical currents in the solar atmosphere. A critical unanswered question is whether the currents involved are induced by the motion of preexisting atmospheric magnetic flux subject to surface plasma flows or whether these currents are associated with the emergence of flux from within the solar convective zone. We address this problem by applying state-of-the-art nonlinear force-free field (NLFFF) modeling to the highest resolution and quality vector-magnetographic data observed by the recently launched Hinode satellite on NOAA AR 10930 around the time of a powerful X3.4 flare. We compute 14 NLFFF models with four different codes and a variety of boundary conditions. We find that the model fields differ markedly in geometry, energy content, and force-freeness. We discuss the relative merits of these models in a general critique of present abilities to model the coronal magnetic field based on surface vector field measurements. For our application in particular, we find a fair agreement of the best-fit model field with the observed coronal configuration, and argue (1) that strong electrical currents emerge together with magnetic flux preceding the flare, (2) that these currents are carried in an ensemble of thin strands, (3) that the global pattern of these currents and of field lines are compatible with a large-scale twisted flux rope topology, and (4) that the ~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 Bibcode: 2008cosp...37.1900M Altcode: 2008cosp.meet.1900M Coronal dimmings are often present on both sides of erupting magnetic configurations. It has been suggested that dimmings mark the location of the footpoints of ejected flux ropes and, thus, their magnetic flux can be used as a proxy for the flux involved in the ejection. If so, this quantity can be compared to the flux in the associated interplanetary magnetic cloud to find clues about the origin of the ejected flux rope. In the context of this physical interpretation, we analyse several events, flares and coronal mass ejections (CMEs), for which we can find their interplanetary counterpart. We combine SOHO/Extreme Ultraviolet Imaging Telescope data and Michelson Doppler Imager magnetic maps to identify and measure the flux in the dimming regions. We model the associated clouds and compute their magnetic flux using in situ observations. We find that the magnetic fluxes of the dimmings and magnetic clouds are compatible in some cases; though this is not the case for large-scale events and eruptions that occur in regions that are not isolated from other flux concentrations. We conclude that the interpretation of dimmings requires a deeper analysis of the global magnetic field configuration, since at least a fraction of the dimmed regions could be formed by reconnection between the erupting field and the surrounding magnetic structures. Title: Interaction between emerging flux and coronal hole - observations and simulations Authors: van Driel-Gesztelyi, Lidia; Baker, Deborah; Murray, Michelle; Demoulin, Pascal; Attrill, Gemma; Matthews, Sarah A.; Mandrini, Cristina H.; Toeroek, Tibor Bibcode: 2008cosp...37.3288V Altcode: 2008cosp.meet.3288V Flux emergence in the vicinity of or inside a coronal hole (CH) is expected to induce magnetic reconnection between the closed emerging and open CH magnetic field lines, resulting in an evolution of the CH as formerly closed field lines become topologically open, while at the same time, open field lines close down. Through two case studies we show observational signatures of this (interchange) reconnection process and discuss its implications. First, using SOHO EIT and MDI data, we study a small active region (AR10869) emerging in the close vicinity of a low-latitude coronal hole in April 2006. The interfacing magnetic polarities between the AR and the CH were opposite, favourable for magnetic reconnection. We indeed observe the coupled formation of bright closed loops between the CH and the AR and coronal dimming on the far side of the AR, which we interpret as evidence of interchange reconnection. This process effectively modifies the CH boundary (making it retreat), while simultaneously displacing open field lines to the far side of the AR. In order to study this process in detail, we perform 2.5D MHD simulations, which qualitatively reproduce important aspects of the observations. We expect to find upflows of plasma at the location where previously closed field lines are opening up as well as on the reconnecting side, but since we had no spectroscopic data for this event, we can not verify this. Therefore we analyze Hinode/EIS line-of-sight velocity maps of another low-latitude CH with a small AR in its midst observed on 18 Oct. 2007. We find that while closed loops of the bipole are dominated by downflows in the Fe XII, Fe XIII and Fe XV lines, the strongest coronal plasma upflows are indeed located around and particularly at the "far side" of the bipolar AR, i.e. having the same polarity as the dominant polarity of the CH. The emerging biplole and the series of interchange reconnections it induces create a significant additional plasma upflow in the CH, thus we identify this outflow must contribute to the acceleration of the fast solar wind. Title: Magnetic Clouds: Global and local expansion Authors: Gulisano, Adriana; Demoulin, Pascal; Soledad Nakwacki, Ms Maria; Dasso, Sergio; Emilia Ruiz, Maria Bibcode: 2008cosp...37.1113G Altcode: 2008cosp.meet.1113G Magnetic clouds (MCs) are magnetized objects forming flux ropes, which are expelled from the Sun and travel through the heliosphere, transporting important amounts of energy, mass, magnetic flux, and magnetic helicity from the Sun to the interplanetary medium. To know the detailed dynamical evolution of MCs is very useful to improve the knowledge of solar processes, for instance from linking a transient solar source with its interplanetary manifestation. During its travel, and mainly due to the decrease of the total (magnetic plus thermal) pressure in the surrounding solar wind, MCs are objects in expansion. However, the detailed magnetic structure and the dynamical evolution of MCs is still not fully known. Even the identification of their boundaries is an open question in some cases. In a previous work we have shown that from onepoint observations of the bulk velocity profile, it is possible to infer the 'local' expansion rate for a given MC, i.e., the expansion rate while the MC is observed by the spacecraft. By the another hand, and from the comparison of sizes for different MCs observed at different heliodistances, it is possible to quantify an 'average' expansion law (i.e., a global expansion). In this work, in order to study the variability of the 'local' expansion with respect to the 'average' expansion of MCs during their travel, we present results and a comparison between both approaches. We make a detailed study of one-point observations (magnetic and bulk velocity) using a set of MCs and we get the 'local' expansion rate for each studied event. We compare the obtained 'local' expansion rates with the 'average' expansion law, and also with the expansion rates for the stationary solar wind. Title: Modelling and observations of photospheric helicity Authors: Demoulin, Pascal Bibcode: 2008cosp...37..694D Altcode: 2008cosp.meet..694D There is mounting observational evidence of the emergence of twisted magnetic flux tubes through the photosphere. Such flux tubes are formed by the solar dynamo, then transported through the convection zone and eventually reach the solar atmosphere. Their accumulation in the solar corona leads to flares and coronal mass ejections. Since a series of reconnections occur during the evolution of the flux tubes, the notions of twist and magnetic stress become inappropriate. However, since magnetic helicity is a well preserved quantity, even in the presence of reconnection, it is a suitable physical quantity to use. Until recently, the main difficulty was that its observational estimations involved the determination of the vector potential of the magnetic field, a quantity which cannot be deduced from observations. Only relatively recently it has been realized that the magnetic helicity flux can be derived from magnetogram time series. In addition, only the vertical component of the magnetic field and the photospheric flux-tube motions are needed to obtain a good estimation of the total helicity flux. The photospheric maps for the injection of magnetic helicity provide a new spatial information about the basic properties of the link between the solar activity and its sub-photospheric roots. Title: Are Constant Loop Widths an Artifact of the Background and the Spatial Resolution? Authors: López Fuentes, M. C.; Démoulin, P.; Klimchuk, J. A. Bibcode: 2008ApJ...673..586L Altcode: 2007arXiv0704.0637L We study the effect of the coronal background in the determination of the diameter of EUV loops, and we analyze the suitability of the procedure followed in a previous paper for characterizing their expansion properties. For the analysis we create different synthetic loops, and we place them on real backgrounds from data obtained with the Transition Region and Coronal Explorer (TRACE). We apply to these loops the same procedure followed in our previous works, and we compare the results with real loop observations. We demonstrate that the procedure allows us to distinguish constant width loops from loops that expand appreciably with height, as predicted by simple force-free field models. This holds even for loops near the resolution limit. The procedure can easily determine when loops are below the resolution limit and therefore not reliably measured. We find that small-scale variations in the measured loop width are likely due to imperfections in the background subtraction. The greatest errors occur in especially narrow loops and in places where the background is especially bright relative to the loop. We stress, however, that these effects do not impact the ability to measure large-scale variations. The result that observed loops do not expand systematically with height is robust. Title: Acceleration and expansion of interplanetary coronal mass ejections Authors: Soledad Nakwacki, Maria; Demoulin, Pascal; Dasso, Sergio; Mandrini, Cristina H. Bibcode: 2008cosp...37.2171S Altcode: 2008cosp.meet.2171S Coronal mass ejections (CMEs) are solar eruptions that release huge amounts of magnetized plasma into the interplanetary medium. When a CME is observed in the interplanetary space, it is called an ICME (interplanetary coronal mass ejection). These heliospheric counterparts can be identified from the surrounding solar wind because of their particular characteristics. In their travel from the Sun, ICMEs expand and accelerate. However, from single spacecraft observations, expansion and acceleration cannot be distinguished from each other. In this work, we take a new approach to study the acceleration and expansion of ICMEs, which is based on the assumption of a self-similar expansion with a different rate in each direction. To decouple the effects of expansion and acceleration, we use multi-spacecraft observations. Title: Breaking or maintaining magnetic connection of CMEs to the Sun - solar vs. interplanetary signatures tested Authors: van Driel-Gesztelyi, Lidia; Attrill, Gemma; Demoulin, Pascal; Mandrini, Cristina H.; Harra, Louise K. Bibcode: 2008cosp...37.3287V Altcode: 2008cosp.meet.3287V Though their relationship is complex, the presence of suprathermal unior bi-directional electron streams in ICMEs are treated as signatures of magnetic field lines with one or both ends being connected to the Sun, respectively, while their absence is interpreted as disconnection. However, do we have any reliable signature in the solar corona distinguishing between maintained connection and disconnection? We test two solar signatures against interplanetary suprathermal electron signatures in order to establish their relevance. We test the hypothesis that the recovery of Transient Coronal Holes (TCHs, dimming regions corresponding to the footpoints of CMEs) is a signature of magnetic disconnection from the Sun. Through three case studies we quantitatively demonstrate that magnetic reconnections between field lines of the expanded CME magnetic field and small coronal loops can act to disperse the concentration of CME footpoints (forming the dimming region) out into the surrounding quiet Sun, thus recovering the intensity of the dimming region whilst still maintaining the magnetic connectivity to the Sun. This analysis provides evidence that the recovery of coronal dimming regions can, in fact, be simply reconciled with maintained magnetic connectivity to the Sun. However, disconnection can occur when open field lines are involved in reconnection with CMEs. We show through two well-observed case studies that magnetic reconnection between the expanding CME and a nearby coronal hole (CH) is indeed able to disconnect one leg of the expanding CME magnetic structure, as indicated by uni-directional electron streams in their respective ICMEs. Therefore we suggest that brightenings (signatures of reconnection) appearing along a coronal hole boundary in the wake of a CME can be treated as a signature of (at least partial) disconnection of one of the CME legs from the Sun. Title: Coronal ``wave'': A signature of the mechanism making CMEs large-scale in the low corona? Authors: Attrill, G. D. R.; Harra, L. K.; van Driel-Gesztelyi, L.; Démoulin, P.; Wülser, J. -P. Bibcode: 2007AN....328..760A Altcode: We analyse one of the first coronal waves observed by STEREO/EUVI associated with a source region just behind the limb, NOAA 10940. We apply the coronal ``wave'' model proposed by Attrill et al. (2007) to explain the evolution of the observed bright fronts, thereby arguing that the bright fronts and dimmings are due to magnetic reconnections between the expanding CME core and surrounding magnetic structures. We offer a discussion showing that this model provides a mechanism via which CMEs, expanding from a small source region can naturally become large-scale in the low corona. Title: Progressive Transformation of a Flux Rope to an ICME. Comparative Analysis Using the Direct and Fitted Expansion Methods Authors: Dasso, S.; Nakwacki, M. S.; Démoulin, P.; Mandrini, C. H. Bibcode: 2007SoPh..244..115D Altcode: 2007arXiv0706.2889D The solar wind conditions at one astronomical unit (AU) can be strongly disturbed by interplanetary coronal mass ejections (ICMEs). A subset, called magnetic clouds (MCs), is formed by twisted flux ropes that transport an important amount of magnetic flux and helicity, which is released in CMEs. At 1 AU from the Sun, the magnetic structure of MCs is generally modeled by neglecting their expansion during the spacecraft crossing. However, in some cases, MCs present a significant expansion. We present here an analysis of the huge and significantly expanding MC observed by the Wind spacecraft during 9 - 10 November 2004. This MC was embedded in an ICME. After determining an approximate orientation for the flux rope using the minimum variance method, we obtain a precise orientation of the cloud axis by relating its front and rear magnetic discontinuities using a direct method. This method takes into account the conservation of the azimuthal magnetic flux between the inbound and outbound branches and is valid for a finite impact parameter (i.e., not necessarily a small distance between the spacecraft trajectory and the cloud axis). The MC is also studied using dynamic models with isotropic expansion. We have found (6.2±1.5)×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'' (ApJ, 656, L105 [2007]) Authors: Vourlidas, Angelos; Pick, Monique; Hoang, Sang; Démoulin, Pascal Bibcode: 2007ApJ...665L.179V Altcode: In our recent Letter (A. Vourlidas et al. [ApJ, 656, L105 [2007]], 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, & J.-L. Bougeret (ApJ, 656, L105 [2007]) 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, & J.-L. Bougeret (ApJ, 656, L105 [2007]). Title: Are CME-Related Dimmings Always a Simple Signature of Interplanetary Magnetic Cloud Footpoints? Authors: Mandrini, C. H.; Nakwacki, M. S.; Attrill, G.; van Driel-Gesztelyi, L.; Démoulin, P.; Dasso, S.; Elliott, H. Bibcode: 2007SoPh..244...25M Altcode: Coronal dimmings are often present on both sides of erupting magnetic configurations. It has been suggested that dimmings mark the location of the footpoints of ejected flux ropes and, thus, their magnetic flux can be used as a proxy for the flux involved in the ejection. If so, this quantity can be compared to the flux in the associated interplanetary magnetic cloud to find clues about the origin of the ejected flux rope. In the context of this physical interpretation, we analyze the event, flare, and coronal mass ejection (CME) that occurred in active region 10486 on 28 October 2003. The CME on this day is associated with large-scale dimmings, located on either side of the main flaring region. We combine SOHO/Extreme Ultraviolet Imaging Telescope data and Michelson Doppler Imager magnetic maps to identify and measure the flux in the dimming regions. We model the associated cloud and compute its magnetic flux using in situ observations from the Magnetometer Instrument and the Solar Wind Electron Proton Alpha Monitor aboard the Advance Composition Explorer. We find that the magnetic fluxes of the dimmings and magnetic cloud are incompatible, in contrast to what has been found in previous studies. We conclude that, in certain cases, especially in large-scale events and eruptions that occur in regions that are not isolated from other flux concentrations, the interpretation of dimmings requires a deeper analysis of the global magnetic configuration, since at least a fraction of the dimmed regions is formed by reconnection between the erupting field and the surrounding magnetic structures. Title: Coronal "wave": Magnetic Footprint Of A Cme? Authors: Attrill, Gemma; Harra, L. K.; van Driel-Gesztelyi, L.; Demoulin, P.; Wuelser, J. Bibcode: 2007AAS...210.2921A Altcode: 2007BAAS...39..141A We propose a new mechanism for the generation of "EUV coronal waves". This work is based on new analysis of data from SOHO/EIT, SOHO/MDI & 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 & the coronal waves display rotations in opposite senses. We observe deep dimmings near the flare site & 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 & 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 & quiet-Sun magnetic loops generate the observed bright diffuse front. The dual brightenings & 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 & 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 & the "open" magnetic field of a low-latitude coronal hole. We use both the SOHO/EIT & STEREO/EUVI events to demonstrate that through successive reconnections, this new model provides a natural mechanism via which CMEs can become large-scale in the lower corona. Title: Slip running reconnection in the Sun's atmosphere observed by RHESSI, SOHO, TRACE and Hinode Authors: Schmieder, B.; Aulanier, G.; Démoulin, P.; Pariat, E.; Golub, L. Bibcode: 2007AGUSMSH22A..01S Altcode: Solar double ribbon flares are commonly explained by magnetic field reconnections in the high corona. The bright ribbons, typically observed in Halpha, in EUV with SoHO, TRACE correspond to the ends of the reconnected loops. In most studied cases, the reconnection site is an X-point, where two magnetic separatrices intersect. In this presentation, we show a generalization of this model to 3D complex magnetic topologies where there are no null points, but quasi-separatrices layers instead. In that case, while the ribbons spread away during reconnection, we show that magnetic field lines can quickly slip along them. We propose that this new phenomenon could explain also fast moving HXR footpoints as observed by RHESSI, and that it may be observed in soft X rays with XRT. Title: Coronal Loops Really Do Have Constant Cross Sections! Authors: Klimchuk, James A.; Lopez Fuentes, M.; Demoulin, P. Bibcode: 2007AAS...210.9111K Altcode: 2007BAAS...39..205K The observation that coronal loops do not expand systematically with height has been one of the more intriguing puzzles in solar physics. Simple force-free magnetic field models based on extrapolated magnetograms predict a much larger expansion than is observed. It has been suggested that the cross section uniformity is an artifact of inadequate spatial resolution, complex background emission, or both. For example, loops that are everywhere thinner than the instrument point spread function (PSF) would be seen to have a nearly constant thickness even if they actually expand. We have argued previously that actual loops are wide enough to rule out this possibility. Our present work also rules out the background emission as a possible explanation. We have simulated TRACE observations in the following manner. We constructed synthetic loops with both uniform and expanding cross sections, convolved them with the PSF, and placed them on actual TRACE images. We then measured the widths of the loops using the same technique used in our earlier studies of real observations. We find that expanding loops can be readily distinguished from loops with a constant cross section. Thus, the enigma remains! We tentatively suggest that constant cross sections are a consequence of the complex internal structure of loops (e.g., loops as bundles of tangled elemental strands). We are confident that this can explain the observed symmetry of loops, but whether it can also explain the lack of systematic expansion with height is not at all clear. Title: A Multiple Flare Scenario where the Classic Long-Duration Flare Was Not the Source of a CME Authors: Goff, C. P.; van Driel-Gesztelyi, L.; Démoulin, P.; Culhane, J. L.; Matthews, S. A.; Harra, L. K.; Mandrini, C. H.; Klein, K. L.; Kurokawa, H. Bibcode: 2007SoPh..240..283G Altcode: A series of flares (GOES class M, M and C) and a CME were observed in close succession on 20 January 2004 in NOAA 10540. Radio observations, which took the form of types II, III and N bursts, were associated with these events. We use the combined observations from TRACE, EIT, Hα images from Kwasan, MDI magnetograms and GOES to understand the complex development of this event. Contrary to a standard interpretation, we conclude that the first two impulsive flares are part of the CME launch process while the following long-duration event flare represents simply the recovery phase. Observations show that the flare ribbons not only separate but also shift along the magnetic inversion line so that magnetic reconnection progresses stepwise to neighboring flux tubes. We conclude that "tether cutting" reconnection in the sheared arcade progressively transforms it to a twisted flux tube, which becomes unstable, leading to a CME. We interpret the third flare, a long-duration event, as a combination of the classical two-ribbon flare with the relaxation process following forced reconnection between the expanding CME structure and neighboring magnetic fields. Title: Decametric N Burst: A Consequence of the Interaction of Two Coronal Mass Ejections Authors: Démoulin, P.; Klein, K. -L.; Goff, C. P.; van Driel-Gesztelyi, L.; Culhane, J. L.; Mandrini, C. H.; Matthews, S. A.; Harra, L. K. Bibcode: 2007SoPh..240..301D Altcode: Radio emissions of electron beams in the solar corona and interplanetary space are tracers of the underlying magnetic configuration and of its evolution. We analyse radio observations from the Culgoora and WIND/WAVES spectrographs, in combination with SOHO/LASCO and SOHO/MDI data, to understand the origin of a type N burst originating from NOAA AR 10540 on January 20, 2004, and its relationship with type II and type III emissions. All bursts are related to the flares and the CME analysed in a previous paper (Goff et al., 2007). A very unusual feature of this event was a decametric type N burst, where a type III-like burst, drifting towards low frequencies (negative drift), changes drift first to positive, then again to negative. At metre wavelengths, i.e., heliocentric distances ≲1.5R⊙, 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 Bibcode: 2007ApJ...656L.105V Altcode: We report the discovery of a new radio feature associated with coronal mass ejection (CME) events. The feature is a low-frequency (<1 MHz), relatively wide (~300 kHz) continuum that appears just after the main phase of the eruptive event, lasts for several hours, and exhibits a slow negative frequency drift. So far, we have identified this radio signature in a handful of CME events and suspect it might be a common occurrence. The radio continuum starts almost simultaneously with the commonly observed decimetric type IV stationary continuum (also called flare continuum), but the two seem unrelated. The emission mechanism, whether plasma emission or gyroresonance, is unclear at the moment. On the basis of our preliminary analysis, we interpret this radio continuum as the lateral interaction of the CME with magnetic structures. Another possibility is that this continuum traces the reconfiguration of large-scale loop systems, such as streamers. In other words, it could be the large-scale counterpart of the post-CME arcades seen over active region neutral lines after big CME events. This Letter aims to bring attention to this feature and attract more research into its nature. Title: Coronal ``Wave'': Magnetic Footprint of a Coronal Mass Ejection? Authors: Attrill, Gemma D. R.; Harra, Louise K.; van Driel-Gesztelyi, Lidia; Démoulin, Pascal Bibcode: 2007ApJ...656L.101A Altcode: We investigate the properties of two ``classical'' EUV Imaging Telescope (EIT) coronal waves. The two source regions of the associated coronal mass ejections (CMEs) possess opposite helicities, and the coronal waves display rotations in opposite senses. We observe deep core dimmings near the flare site and also widespread diffuse dimming, accompanying the expansion of the EIT wave. We also report a new property of these EIT waves, namely, that they display dual brightenings: persistent ones at the outermost edge of the core dimming regions and simultaneously diffuse brightenings constituting the leading edge of the coronal wave, surrounding the expanding diffuse dimmings. We show that such behavior is consistent with a diffuse EIT wave being the magnetic footprint of a CME. We propose a new mechanism where driven magnetic reconnections between the skirt of the expanding CME magnetic field and quiet-Sun magnetic loops generate the observed bright diffuse front. The dual brightenings and the widespread diffuse dimming are identified as innate characteristics of this process. Title: Estimation of the bias of the Minimum Variance technique in the determination of magnetic clouds global quantities and orientation Authors: Gulisano, A. M.; Dasso, S.; Mandrini, C. H.; Démoulin, P. Bibcode: 2007AdSpR..40.1881G Altcode: Magnetic clouds (MCs) are highly magnetized plasma structures that have a low proton temperature and a magnetic field vector that rotates when seen by a heliospheric observer. More than 25 years of observations of magnetic and plasma properties of MCs at 1 AU have provided significant knowledge of their magnetic structure. However, because in situ observations only give information along the trajectory of the spacecraft, their real 3D magnetic configuration remains still partially unknown. We generate a set of synthetic clouds, exploring the space of parameters that represents the possible orientations and minimum distances of the satellite trajectory to the cloud axis, p. The synthetic clouds have a local cylindrical symmetry and a linear force-free magnetic configuration. From the analysis of synthetic clouds, we quantify the errors introduced in the determination of the orientation/size (and, consequently, of the global magnetohydrodynamic quantities) by the Minimum Variance method when p is not zero. Title: From The Photosphere to the Interplanetary Medium: The Magnetic Helicity Sign from Observations Authors: Luoni, M. L.; Mandrini, C. H.; Dasso, S.; Démoulin, P.; Van Driel-Gesztelyi, L. Bibcode: 2007BAAA...50...43L Altcode: The helicity sign of the solar magnetic field exhibits a hemispheric preference. On a certain statistical base, it is negative (positive) in the northern (southern) hemisphere. In this work we study a set of active regions, observed from 1997 to 2001, for which we can determine the magnetic helicity sign from the evolution of their polarities during flux emergence. We confirm this sign analyzing the coronal field of the studied regions. Then, we combine this analysis with ``in situ'' observations of the magnetic clouds associated with the coronal mass ejections that occurred in those regions. Finally, we find that the helicity sign predicted by the distribution of the photospheric flux agrees with the one observed at coronal and interplanetary level. Title: What is the role of magnetic null points in large flares? Authors: Schmieder, B.; Mandrini, C. H.; Démoulin, P.; Aulanier, G.; Li, H.; Berlicki, A. Bibcode: 2007AdSpR..39.1840S Altcode: We have performed the analysis of the magnetic topology of active region NOAA 10486 before two large flares occurring on October 26 and 28, 2003. The 3D extrapolation of the photospheric magnetic field shows the existence of magnetic null points when using two different methods. We use TRACE 1600 Å and 195 Å brightenings as tracers of the energy release due to magnetic reconnections. We conclude on the three following points: The small events observed before the flares are related to low lying null points. They are long lasting and associated with low energy release. They are not triggering the large flares.

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. Bibcode: 2007MmSAI..78..136D Altcode: Magnetic energy and helicity fluxes can now be derived from measurements of the photospheric magnetic and velocity fields. We show that only photospheric flux-tube motions are needed to estimate the full fluxes. The derived maps of flux densities permit to localize where energy and helicity input occurs in active regions (ARs). The precision of the energy flux density is dominantly limited by the precision obtained on the transverse component of the magnetic field. On the contrary, the helicity flux density requires only the measurement of the vertical component of the magnetic field. Previously, the magnetic helicity maps were strongly affected by a false definition of the helicity flux density involving the magnetic vector potential. Applied to observations, this approach introduces important fake polarities. We define a better helicity flux density; it reduces the fake polarities by more than an order of magnitude. The spatial distribution of helicity injected into the studied ARs is much more coherent than previously thought, and presents a dominant sign in each AR. Finally, the correct helicity flux density could be derived from magnetograms if coronal connectivities are known. Title: The magnetic field topology associated with two M flares Authors: Luoni, M. L.; Mandrini, C. H.; Cristiani, G. D.; Démoulin, P. Bibcode: 2007AdSpR..39.1382L Altcode: 2007arXiv0706.0242L On 27 October, 2003, two GOES M-class flares occurred in an interval of 3 h in active region NOAA 10486. The two flares were confined and their associated brightenings appeared at the same location, displaying a very similar shape both at the chromospheric and coronal levels. We focus on the analysis of magnetic field (SOHO/MDI), chromospheric (HASTA, Kanzelhöhe Solar Observatory, TRACE) and coronal (TRACE) observations. By combining our data analysis with a model of the coronal magnetic field, we compute the magnetic field topology associated with the two M flares. We find that both events can be explained in terms of a localized magnetic reconnection process occurring at a coronal magnetic null point. This null point is also present at the same location one day later, on 28 October, 2003. Magnetic energy release at this null point was proposed as the origin of a localized event that occurred independently with a large X17 flare on 28 October, 2003 [Mandrini, C.H., Démoulin, P., Schmieder, B., Deluca, E., Pariat, E., Uddin, W. Companion event and precursor of the X17 flare on 28 October, 2003. Solar Physics, 238, 293-312, 2006], at 11:01 UT. The three events, those on 27 October and the one on 28 October, are homologous. Our results show that coronal null points can be stable topological structures where energy release via magnetic reconnection can happen, as proposed by classical magnetic reconnection models. Title: How to improve the maps of magnetic helicity injection in active regions? Authors: Pariat, Etienne; Démoulin, Pascal; Nindos, Alexander Bibcode: 2007AdSpR..39.1706P Altcode: Magnetic helicity, a topological quantity which measures the twist, the writhe and the shear of a magnetic field, has recently appeared as a key quantity to understand some mechanisms of the solar activity such as Coronal Mass Ejections and flare onset. It is thus becoming of major importance to be able to compute magnetic helicity in active regions. Computing photospheric maps of the injection of magnetic helicity provides new spatial information that helps us to understand basic properties of solar activity, such as where and how magnetic helicity is injected. Several helicity flux density maps have been published for different active regions. Unfortunately, the classical helicity flux density is not a correct physical quantity and it does induce spurious signals (fake polarities) which mask the real injection of helicity. To map the real helicity injection, the knowledge of the complete connectivity of the field lines is fundamental. Even without the connectivity, improved helicity flux density maps can be derived. They have fake polarities which are lower by more than a factor 10 than the previous incorrect maps. Rather than a mixture of negative and positive injection patterns, they show almost unipolar injection on the active region scale. This leads to a completely new way of understanding the dynamics of active regions, in the frame of magnetic helicity studies. Title: Recent theoretical and observational developments in magnetic helicity studies Authors: Démoulin, P. Bibcode: 2007AdSpR..39.1674D Altcode: Magnetic helicity quantifies how the magnetic field is sheared and twisted compared to its lowest energy state (potential field). Such stressed magnetic fields are usually observed in association with flares, eruptive filaments, and coronal mass ejections (CMEs). Magnetic helicity plays a key role in magnetohydrodynamics because it is almost preserved on a timescale less than the global diffusion time scale. Its conservation defines a constraint to the magnetic field evolution. Only relatively recently, scientists have realized that magnetic helicity can be computed from observations, and methods have been derived to bridge the gap between theory and observations. At the photospheric level, the rate (or flux) of magnetic helicity can be computed from the evolution of longitudinal magnetograms. The coronal helicity is estimated from magnetic extrapolation, while the helicity ejected in magnetic clouds (interplanetary counter-part of CMEs) is derived through modelling of in situ magnetic field measurements. Using its conserved property, a quantitative link between phenomena observed in the corona and then in the interplanetary medium has been achieved. Title: Where will efficient energy release occur in 3-D magnetic configurations? Authors: Démoulin, P. Bibcode: 2007AdSpR..39.1367D Altcode: The energy needed to power flares is thought to be stored in the coronal magnetic field. However, the energy release is efficient only at very small scales. Magnetic configurations with a complex topology, i.e. with separatrices, are the most obvious configurations where current sheets can form, and then, reconnection can efficiently occur. This has been confirmed for several flares computing the coronal field and comparing the locations of the flare loops and ribbons to the deduced 3-D magnetic topology. However, this view is too restrictive taking into account the variety of observed solar flaring configurations. Indeed, "Quasi-Separatrix Layers" (QSLs), which are regions where there is a drastic change in field-line linkage, generalize the definition of separatrices. They let us understand where reconnection occurs in a broader variety of flares than separatrices do. The strongest electric field and current are generated at, or close to where the QSLs are thinnest. This defines the region where particle acceleration can efficiently occur. A new feature of 3-D reconnection is the natural presence of fast field-line slippage along the QSLs, a process called "slip-running reconnection". This is a plausible origin for the motions of the X-ray sources along flare ribbons. Title: Companion Event and Precursor of the X17 Flare on 28 October 2003 Authors: Mandrini, C. H.; Demoulin, P.; Schmieder, B.; Deluca, E. E.; Pariat, E.; Uddin, W. Bibcode: 2006SoPh..238..293M Altcode: 2006SoPh..tmp...79M A major two-ribbon X17 flare occurred on 28 October 2003, starting at 11:01 UT in active region NOAA 10486. This flare was accompanied by the eruption of a filament and by one of the fastest halo coronal mass ejections registered during the October-November 2003 strong activity period. We focus on the analysis of magnetic field (SOHO/MDI), chromospheric (NainiTal observatory and TRACE), and coronal (TRACE) data obtained before and during the 28 October event. By combining our data analysis with a model of the coronal magnetic field, we concentrate on the study of two events starting before the main flare. One of these events, evident in TRACE images around one hour prior to the main flare, involves a localized magnetic reconnection process associated with the presence of a coronal magnetic null point. This event extends as long as the major flare and we conclude that it is independent from it. A second event, visible in Hα and TRACE images, simultaneous with the previous one, involves a large-scale quadrupolar reconnection process that contributes to decrease the magnetic field tension in the overlaying field configuration; this allows the filament to erupt in a way similar to that proposed by the breakout model, but with magnetic reconnection occurring at Quasi-Separatrix Layers (QSLs) rather than at a magnetic null point. Title: Slip-Running Reconnection in Quasi-Separatrix Layers Authors: Aulanier, G.; Pariat, E.; Démoulin, P.; Devore, C. R. Bibcode: 2006SoPh..238..347A Altcode: 2006SoPh..tmp...62A; 2006SoPh..tmp...81A Using time dependent MHD simulations, we study the nature of three-dimensional magnetic reconnection in thin quasi-separatrix layers (QSLs), in the absence of null points. This process is believed to take place in the solar atmosphere, in many solar flares and possibly in coronal heating. We consider magnetic field configurations which have previously been weakly stressed by asymmetric line-tied twisting motions and whose potential fields already possessed thin QSLs. When the line-tied driving is suppressed, magnetic reconnection is solely due to the self-pinching and dissipation of narrow current layers previously formed along the QSLs. A generic property of this reconnection process is the continuous slippage of magnetic field lines along each other, while they pass through the current layers. This is contrary to standard null point reconnection, in which field lines clearly reconnect by pair and abruptly exchange their connectivities. For sufficiently thin QSLs and high resistivities, the field line footpoints slip-run at super-Alfvénic speeds along the intersection of the QSLs with the line-tied boundary, even though the plasma velocity and resistivity are there fixed to zero. The slip-running velocities of a given footpoint have a well-defined maximum when the field line crosses the thinnest regions of the QSLs. QSLs can then physically behave as true separatrices on MHD time scales, since magnetic field lines can change their connections on time scales far shorter than the travel-time of Alfvén waves along them. Since particles accelerated in the diffusive regions travel along the field much faster than the Alfvén speed, slip-running reconnection may also naturally account for the fast motion of hard X-ray sources along chromospheric ribbons, as observed during solar flares. Title: Build-up of a CME and its Interaction with Large-Scale Magnetic Structures Authors: van Driel-Gesztelyi, L.; Goff, C. P.; Demoulin, P.; Culhane, J. L.; Klein, K. L.; Mandrini, C. H.; Matthews, S. A.; Harra, K. L.; Kurokawa, H. Bibcode: 2006IAUJD...3E..86V Altcode: Introduction: A series of flares (GOES class M, M and C) and a CME were observed on 20-JAN-2004 occurring in close succession in NOAA 10540. Types II, III and a N radio bursts were associated. We investigate the link between the flares (two impulsive flares followed by an LDE) and the CME as well as the origin of the rare decametric N-burst. Methods: We use the combined observations from TRACE, SOHO/EIT, H-alpha images from Kwasan Observatory, SOHO/MDI magnetograms, GOES and radio observations from Culgoora and Wind/WAVES as well as magnetic modelling to understand the complex development of this event. Results: We link the first two impulsive flares to tether-cutting reconnections and the launch of the CME, while the last of the flares, an LDE, to the relaxation phase following forced reconnections between the erupting flux rope and neighbouring magnetic field lines. We show that reconnection with the magnetic structure of a previous CME, launched about 8 hours earlier, injects electrons into open field lines having a local dip and apex of about 6 solar radii height. The dipped shape of these field lines was due to large-scale magnetic reconnection between expanding magnetic loops and open field lines of a neighbouring streamer. This particular situation explains the observed decametric N burst. Discussion: This complex observation shows that impulsive quadrupolar flares can be eruptive, while an LDE may remain a confined event. We find that reconnection forced by the expanding CME structure is followed by a relaxation phase, when reconnection reverses and restores some of the pre-eruption magnetic connectivities. The observed decametric N-burst was caused by the interaction of two CMEs and reconnection of their expanding magnetic field with neighbouring streamer field lines - a very particular interplay, which explains why N-bursts are so rare. Title: A new model-independent method to compute magnetic helicity in magnetic clouds Authors: Dasso, S.; Mandrini, C. H.; Démoulin, P.; Luoni, M. L. Bibcode: 2006A&A...455..349D Altcode: Context: .Magnetic clouds are transient magnetic structures expulsed from the Sun that travel toward the external heliosphere carrying a significant amount of magnetic flux and helicity.
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.
Title: Linking solar to interplanetary events: A new direct method to quantify global MHD magnitudes in magnetic clouds Authors: Dasso, S.; Mandrini, C. H.; Demoulin, P. Bibcode: 2006IAUJD...3E..26D Altcode: Magnetic Clouds (MCs) carry a significant amount of magnetic flux (MF) and helicity (MH) away from the solar corona as they travel to the outer heliosphere. From a theoretical point of view, MH is a conserved magnitude in the solar corona and heliosphere; thus, it is expected that MH be preserved in MCs during their evolution through the interplanetary medium. In this sense, MH plays a key role to link the magnetic properties of MCs with their solar active region (AR) sources, helping us to improve the knowledge of the ejection mechanisms in the corona. We present here a new method to compute MH in clouds, which provides values for the helicity per unit length along the flux tube axis using the observed interplanetary magnetic field, without assuming a given model to describe the twist of magnetic field lines inside the MC. This method let us also determine the cloud boundaries with more precision, which improves the estimation of MH. We apply this method to two MCs, one of the biggest and one of the smallest ever observed, and compare our results with the helicity ejected from their respective solar sources. Title: Magnetic Sources of Flares and CMEs from Multi-Wavelength Flare Studies Authors: Schmieder, B.; Mandrini, C.; Berlicki, A.; Démoulin, P.; Li, H. Bibcode: 2006ESASP.617E.145S Altcode: 2006soho...17E.145S No abstract at ADS Title: Global Magnitudes in Expanding Magnetic Clouds Authors: Nakwacki, M. S.; Dasso, S.; Mandrini, C. H.; Demoulin, P. Bibcode: 2006RMxAC..26..155N Altcode: Magnetic clouds (MCs) are the interplanetary counterpart of coronal mass ejections (CMEs). They transport the magnetic flux and helicity released in CMEs by the Sun. At 1 AU from the Sun, an MC is generally modeled as a static flux rope and its magnetic helicity content can be quantified (Dasso et al., JGR 108, 1362, 2003). However, an MC can be also modeled as an expanding structure when its velocity profile shows evidence of a significant expansion. Here we present a quantification of the global magnitudes for the expanding MC observed by the spacecraft Wind between August 09 (10:48UT) and August 10 (15:48UT), 1999. We use magnetic (Magnetic Field Instrument, MFI) and plasma (Solar Wind Experiment, SWE) data. We analyze here two cylindrical models: (1) a static model that considers the cloud magnetic structure as a linear force free field (i.e., the Lundquist's solution), and (2) a radial expanding selfsimilar model (Farrugia et al., JGR 98, 7621, 1993). In both cases, we derive expressions for magnetic fluxes, helicity, and energy. We apply the minimun variance method to find the cloud orientation and compute the cloud radius for the static model (R_s). For the dynamic model, we fit the initial radius for the expanding model (R_0) and the age of the cloud (T_0) from the observed velocity profile. We also fit the free parameters of each magnetic model using the magnetic observations, and find that the dynamical model better represents the data, since it fits the assymetry caused by the expansion in the cloud. Finally, for both models, we quantify the magnetic fluxes, helicity and energy, as done in Nakwacki et al. (Proc. Solar Wind 11 - SOHO 16, ESA SP-592, 629, 2005). We find a change in the computed helicity and fluxes of less than 30% (comparing static and dynamic models). Considering the range of time in which Wind observes the cloud, and the dynamic model, we find a magnetic energy decay of less than ≈ 12% and a radial expansion of 17%. Title: Multi-Wavelength Analysis of an M6.7 Flare from AR 10486 Authors: Luoni, M. L.; Raulin, J. -P.; Mandrini, C. H.; Bandeira, W.; Demoulin, P.; Kaufmann, P.; Luthi, T.; Giménez de Castro, G. G. Bibcode: 2006RMxAC..26R.154L Altcode: The most intense flares of Solar Physics history were registered during October - November 2003. Here we analyze the M6.7 flare (12:27 UT) on October 27, 2003, that occurred in the complex active region (AR) 10486 (NOAA number). We use data in different wavelengths provided by instruments observing from the photosphere to the corona. Using the Michelson Doppler Imager (SoHO/MDI) magnetogram at 12:47:03 UT as boundary condition, we compute the coronal magnetic field under the linear force-free field assumption. We compare the computed magnetic field lines with the Extreme ultraviolet Imaging Telescope (SoHO/EIT) loops to determine the free parameters of our model. From the model we find that a magnetic null point is present in the corona. We propose that magnetic reconnection at this null point is responsible for the M6.7 flare. Concerning radio wavelengths, we analyze the Solar Submillimeter Telescope (SST) data. At 12:31 UT, a short impulsive phase (∼ 1 minute) is detected followed by a gradual (∼ 1 hour) emission associated with H α radiation observed by the H-Alpha Solar Telescope for Argentina (HASTA). The radio spectrum during the impulsive peak suggests the presence of energetic electrons radiating through the synchrotron process. During the extended phase the radio spectrum is flat up to very high frequencies, indicating that the emission is due to the thermal radiation of a cool and dense plasma. The radio analysis is complemented with patrol data from the Bern Polarimeters and Kosma and Bemrak observations. Title: Why Are Coronal Loops So Symmetric? Authors: Klimchuk, James A.; Lopez Fuentes, M. C.; Demoulin, P. Bibcode: 2006SPD....37.1706K Altcode: 2006BAAS...38..246K Coronal loops are observed to be very symmetric in the sense that the two legs have a comparable thickness. Magnetic flux tubes in magnetic field extrapolation models are typically much less symmetric. We have quantified these differences using 171 A images from TRACE and magnetograms from MDI/SOHO. For a sample of 20 different loops, we found the linear force-free field that best matches the observed loop. We then measured the plane-of-the-sky widths of the loops and corresponding flux tubes and computed footpoint-to-footpoint expansion factors (i.e., asymmetry ratios). The mean expansion factor of the flux tubes is 2.62, whereas the mean expansion factor of the loops is only 1.35. Note that these expansion factors are different from the footpoint-to-midpoint expansion factors that we have presented previously.Evidence suggests that the coronal magnetic field is comprised elemental flux strands that are tangled by turbulent convection. These strands are so small that many tens of them are contained within a single TRACE loop. We suggest that this fine structure is a critical missing ingredient of the extrapolation models and that a combination of footpoint shuffling and coronal reconnection can explain the observed loop symmetry. This has important implications for coronal heating.Research supported by NASA and the Office of Naval Research. Title: A new concept for magnetic reconnection : slip-running reconnection Authors: Pariat, E.; Aulanier, G.; Démoulin, P. Bibcode: 2006sf2a.conf..559P Altcode: In magnetohydrodynamics (MHD), most models of magnetic reconnection suppose that this mechanism takes places when the magnetic field configuration contains separatrices. Separatrices are surfaces through which the magnetic field connectivity is discontinuous. But such topological structures are not always present when solar flares takes place. Quasi-separatrix layers (QSLs), which are regions of strong variations of magnetic connectivity, are a generalisation of separatrices. Using a 3D MHD simulation of several solar-like magnetic configurations containing QSLs, we investigated the link between the build-up of current layers and the location of QSLs. Thin current sheets are naturally formed along QSLs whatever the line-tied boundary driven motions are. When the line-tied driving is suppressed, magnetic reconnection is solely due to the self-pinching and dissipation of narrow current layers. In this reconnection process, field line continuously slip along each other while they pass through the current layers. This slip-running reconnection may naturally account for the fast motion of hard X-ray sources along chromospheric ribbons, as observed during solar flares. Title: What is the spatial distribution of magnetic helicity injected in a solar active region? Authors: Pariat, E.; Nindos, A.; Démoulin, P.; Berger, M. A. Bibcode: 2006A&A...452..623P Altcode: Context: .Magnetic helicity is suspected to play a key role in solar phenomena such as flares and coronal mass ejections. Several investigations have recently computed the photospheric flux of magnetic helicity in active regions. The derived spatial maps of the helicity flux density, called G_A, have an intrinsic mixed-sign patchy distribution.
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. Title: Magnetic Sources of flares and CMEs in October 2003 Authors: Schmieder, B.; Démoulin, P.; Berlicki, A.; Mandrini, C.; Hui, Li Bibcode: 2006sf2a.conf..565S Altcode: We present the data analysis of an observing campaign on October 2003 with the objective of understanding the onset of Coronal Mass Ejections (CME) and solar flares. The magnetic field was observed with THEMIS and MDI, the chromosphere with the MSDP operating on THEMIS, the EUV images with SOHO/EIT and TRACE, the X-rays with RHESSI. Two examples of flares will be presented: the 28 Oct 2003 X17 flare and the 20 October 2003 M1.9 flare. The magnetic field analysis of the active regions is done using a linear-force-free field code. The X17 flare is at the origin of a halo CME while the M1.9 flare has no corresponding CME. Before the X17 flare there was a pre-flare event which allowed to change the connectivities in a first phase and to destabilize the stressed field in a second phase producing the X17 flare. A compact twisted emerging flux was responsible of the M1.9 flare, which remains a compact flare due to very tied overlaying loops. These two examples illustrate the major role of the magnetic configuration involved on the flare physical characteristics. Title: The Magnetic Structure of Coronal Loops Observed by TRACE Authors: López Fuentes, M. C.; Klimchuk, J. A.; Démoulin, P. Bibcode: 2006ApJ...639..459L Altcode: 2006ApJ...639..459F; 2005astro.ph..7462L Previous studies have found that coronal loops have a nearly uniform thickness, which seems to disagree with the characteristic expansion of active region magnetic fields. This is one of the most intriguing enigmas in solar physics. We here report on the first comprehensive one-to-one comparison of observed loops with corresponding magnetic flux tubes obtained from cotemporal magnetic field extrapolation models. We use EUV images from TRACE, magnetograms from the MDI instrument on SOHO, and linear force-free field extrapolations satisfying b.nabla XB=αB, with α equal to a constant. For each loop, we find the particular value of α that best matches the observed loop axis and then construct flux tubes using different assumed cross sections at one footpoint (circle and ellipses with different orientations). We find that the flux tubes expand with height by typically twice as much as the corresponding loops. We also find that many flux tubes are much wider at one footpoint than the other, whereas the corresponding loops are far more symmetric. It is clear that the actual coronal magnetic field is more complex than the models we have considered. We suggest that the observed symmetry of loops is related to the tangling of elemental magnetic flux strands produced by photospheric convection. Title: The magnetic field topology associated to an M6.7 flare Authors: Luoni, M.; Mandrini, C.; Cristiani, G.; Démoulin, P. Bibcode: 2006cosp...36.1657L Altcode: 2006cosp.meet.1657L We study an M6 7 solar flare that occurred on October 27 2003 12 27 UT We use data in different wavelenghts magnetograms from the Michelson Doppler Imager SoHO MDI images from the H alpha Solar Telescope for Argentina HASTA and Extreme Ultraviolet Imaging Telescope SoHO EIT We analyze the magnetic field evolution and compute the coronal field to identify the energy release site From this study we find evidence of a magnetic null point in the corona We relate the chromospheric and EUV brightenings to the magnetic field topology in its neighborhood A null point at about the same location is also found in the magnetogram closest in time to the X17 flare observed on October 28 2003 The shape of bright loops observed by the Transition Region and Coronal Explorer TRACE in 195 AA during a secondary confined event accompayning the X-ray flare agrees with those of EIT during the M6 7 flare We especulate that this null point is a stable topological structure where reconnection occurred giving raise to two sympathetic events Title: Magnetic structure and observed width of coronal loops Authors: Lopez-Fuentes, M. C.; Klimchuk, J. A.; Demoulin, P. Bibcode: 2006cosp...36.2575L Altcode: 2006cosp.meet.2575L Previous studies have found that coronal loops have a nearly uniform thickness which seems to disagree with the characteristic expansion of active region magnetic fields This is one of the most intriguing enigmas in solar physics We here report on the first comprehensive one-to-one comparison of observed loops with corresponding magnetic flux tubes obtained from cotemporal magnetic field extrapolation models We use EUV images from TRACE magnetograms from the MDI instrument on SOHO and linear force-free field extrapolations For each loop we find the particular value of the force-free parameter alpha that best matches the observed loop axis and then construct flux tubes using different assumed cross sections at one footpoint circle and ellipses with different orientations We find that the flux tubes expand with height by typically twice as much as the corresponding loops We also find that many flux tubes are much wider at one footpoint than the other whereas the corresponding loops are far more symmetric It is clear that the actual coronal magnetic field is more complex than the models we have considered We suggest that the observed symmetry of loops is related to the tangling of elemental magnetic flux strands produced by photospheric convection Title: Basic Properties of Mutual Magnetic Helicity Authors: Demoulin, P.; Pariat, E.; Berger, M. A. Bibcode: 2006SoPh..233....3D Altcode: We derive the magnetic helicity for configurations formed by flux tubes contained fully or only partially in the spatial domain considered (called closed and open configurations, respectively). In both cases, magnetic helicity is computed as the sum of mutual helicity over all possible pairs of magnetic flux tubes weighted by their magnetic fluxes. We emphasize that these mutual helicities have properties which are not those of mutual inductances in classical circuit theory. For closed configurations, the mutual helicity of two closed flux tubes is their relative winding around each other (known as the Gauss linkage number). For open configurations, the magnetic helicity is derived directly from the geometry of the interlaced flux tubes so it can be computed without reference to a ground state (such as a potential field). We derive the explicit expression in the case of a planar and spherical boundary. The magnetic helicity has two parts. The first one is given only by the relative positions of the flux tubes on the boundary. It is the only part if all flux tubes are arch-shaped. The second part counts the integer number of turns each pair of flux tubes wind about each other. This provides a general method to compute the magnetic helicity with discrete or continuous distributions of magnetic field. The method sets closed and open configurations on an equal level within the same theoretical framework. Title: Extending the concept of separatrices to QSLs for magnetic reconnection Authors: Démoulin, P. Bibcode: 2006AdSpR..37.1269D Altcode: Magnetic reconnection is usually thought to be linked to the presence of magnetic null points and to be accompanied by the transport of magnetic field lines across separatrices, the set of field lines where the field-line linkage is discontinuous. However, this view is too restrictive taking into account the variety of observed solar flaring configurations. Indeed “quasi-separatrix layers” (QSLs), which are regions where there is a drastic change in field-line linkage, generalize the definition of separatrices. Magnetic reconnection is expected to occur preferentially at QSLs in 3-D magnetic configurations. This paper surveys the evolution of the QSL concept from the beginning to its recent status. The theory was successfully tested with multi-wavelength observations of solar flares. This validates the reconnection scenario as the main physical process at the origin of flares. The confrontation of observations with the state-of-the-art theory gives us also hints how to further develop our understanding of 3-D magnetic reconnection. Title: Multi-scale reconnections in a complex CME Authors: van Driel-Gesztelyi, L.; Goff, C.; Demoulin, P.; Culhane, J. L.; Matthews, S. A.; Harra, L. K.; Mandrini, C. H.; Klein, K. L.; Kurokawa, H. Bibcode: 2006cosp...36.2371V Altcode: 2006cosp.meet.2371V A series of flares GOES class M M and C and a CME were observed on 20-JAN-2004 occurring in close succession in NOAA 10540 Types II III and an N radio bursts were associated We use the combined observations from TRACE EIT H-alpha images from Kwasan Observatory MDI magnetograms GOES and radio observations from Culgoora and Wind WAVES to understand the complex development of this event We link the first two impulsive flares to tether-cutting reconnections and the launch of the CME while the last of the flares an LDE to the relaxation phase following forced reconnections between the erupting flux rope and neighbouring magnetic field lines We show that reconnection with the magnetic structure of a previous CME launched about 8 hours earlier injects electrons into open field lines having a local dip and apex of about 6 solar radii height The dipped shape of these field lines was due to large-scale magnetic reconnection between expanding magnetic loops and open field lines of a neighbouring streamer This particular situation explains the observed decametric N burst and why N-bursts are so rare Title: Magnetic reconfiguration before the X 17 Solar flare of October 28 2003 Authors: Schmieder, B.; Mandrini, C. H.; Démoulin, P.; Pariat, E.; Berlicki, A.; Deluca, E. Bibcode: 2006AdSpR..37.1313S Altcode: An active region (AR) NOAA 10486, which produced a large number of X-ray flares during October November 2003, was observed during a multi-wavelength campaign with ground based and space instruments. We focus our analysis on the observations of October 28, 2003. The magnetic field was observed with THEMIS (Na D1) and MDI (Ni I), the chromosphere with THEMIS (Ca II 8542 Å) and with the Meudon heliograph in Hα, the EUV images with SOHO/EIT and TRACE. Two pre-events started just before the major X 17 flare. One was related to localized flux emergence and lasted until the decay phase of the X flare; while the second one involved a large scale quadrupolar reconnection, that we infer by modeling the AR magnetic field. Extended dimming areas across the equator (EIT), large arcades of post-flare loops (TRACE 195 Å) and a halo CME (LASCO) were observed consequently after the flare. We perform an extrapolation of the magnetic field above the photosphere using a linear force-free-field approximation that allows us to find the connectivity among the four polarities that would be involved in the quadrupolar reconnection event. The X 17 flare is plausibly due to the destabilisation of a twisted flux tube, the bottom part of this magnetic structure can be visualized by the presence of a filament. The destabilization is caused by converging and shearing photospheric motions towards the main magnetic inversion line. The large scale quadrupolar reconnection related to the second pre-event would favour the opening of the field above the twisted flux tube and, consequently, the coronal mass ejection. Title: Magnetic clouds: An statistical study of their global magnetohydrodynamic magnitudes Authors: Gulisano, A. M.; Dasso, S.; Mandrini, C. H.; Demoulin, P. Bibcode: 2006cosp...36.2971G Altcode: 2006cosp.meet.2971G Magnetic clouds MCs are highly magnetized plasma structures that have a low proton temperature and a magnetic field vector that rotates when seen by a heliospheric observer More than 20 years of observations of magnetic and plasma properties of MCs at 1 AU have provided significant knowledge on their magnetic structure However because in situ observations only give information along the one-dimensional trajectory of the spacecraft its real 3D magnetic configuration remains still unknown We study a set of 20 magnetic clouds observed by the Wind spacecraft at 1 AU during a solar minimum We explore different models force free and non-force free fields and two different methods one is a simultaneous fitting that let us take the minimum distance from the cloud axis to the spacecraft the impact parameter p different from zero to reconstruct the magnetic structure of clouds from in situ observations Thus for each cloud and for each model method we determine the cloud axis orientation p and the two physical free parameters of each model the twist and the magnetic field intensity both at the cloud axis Then for every cloud we analyze the variation of the computed amounts of magnetic flux and helicity using the different approaches We generate a set of synthetic clouds by changing the space of parameter that represents the possible orientations and p values for real clouds and then we model them using our code to check the validity of our numerical tools Finally from the analysis of the synthetic clouds we Title: On the origin of the 28 October 2003 X17 event and its companion event Authors: Mandrini, C. H.; Demoulin, P.; Schmieder, B.; de Luca, E. E.; Pariat, E.; Uddin, W. Bibcode: 2006BAAA...49..109M Altcode: An X17 flare started at 11:01 UT on 28 October, 2003, in active region (AR) NOAA 10486. This event was accompanied by a filament eruption and one of the fastest coronal mass ejections (CMEs) observed during the extreme activity period of October-November 2003. Combining chromospheric, coronal and magnetic field data with modeling, we concentrate in the study of two events that started before the X17 flare. One of them, which appears in UV images one hour before the major event, is associated with localized magnetic reconnection occurring at a magnetic mull point. T his event lasts as long as the X17 flare and our analysis indicates that it is independent of it. The other one, visible in Hα and UV images and simultaneous with the previous one, is related to a large scale quadrupolar reconnection process. This process is similar to the one proposed by the breakout model for the initiation of CMEs, but it takes place at quasiseparatrices and not in null points. These results will be published in Solar Physics. Title: Recent theoretical and observational developments in magnetic helicity studies Authors: Demoulin, P. Bibcode: 2006cosp...36..117D Altcode: 2006cosp.meet..117D Magnetic helicity quantifies how the magnetic field is sheared and twisted compared to its lowest energy state potential field Such stressed magnetic fields are usually observed in association with flares eruptive filaments and coronal mass ejections CMEs Magnetic helicity plays a key role in magnetohydrodynamics because it is almost preserved on a timescale less than the global diffusion time scale Its conservation defines a constraint to the magnetic field evolution Only relatively recently it has been realized that magnetic helicity can be computed from observations and methods have been derived to bridge the gap between theory and observations At the photospheric level the flux of magnetic helicity can be computed from the evolution of longitudinal magnetograms The coronal helicity is estimated from magnetic extrapolation while the helicity ejected in magnetic clouds interplanetary counter-part of CMEs is derived through modelling the in-situ magnetic field measurements Using its conserved property a quantitative link between phenomena observed in the corona and then in the inter-planetary medium has been achieved Title: A new method to determine the boundary of magnetic clouds Authors: Dasso, S.; Démoulin, P.; Mandrini, C. H.; Luoni, M. L. Bibcode: 2006cosp...36.2390D Altcode: 2006cosp.meet.2390D Magnetic clouds MCs are transient structures formed by magnetic flux ropes with low proton temperature and strongly enhanced magnetic field intensity with respect to ambient values The identification of the MC boundaries is an open question for some clouds mainly because different proxies can provide different positions In this paper we analyze the magnetic cloud observed by the spacecraft Wind on October 18-20 1995 a cloud previously studied by several authors The front of this cloud seems to be relatively well determined from plasma and magnetic data However different authors set the rear boundary at different times We present a new method that determines the centre and the rear boundary of a flux rope when the front boundary is well known It is based on the azimuthal magnetic flux conservation We deduce that the leading flux of the analyzed magnetic cloud had reconnected with the overtaken solar-wind magnetic field Then we estimate the magnetic flux associated with the full cloud before it reconnects with the solar wind Finally we evaluate the sensitivity of our results using different models methods and magnetic-cloud boundaries applied to the same magnetic cloud data Title: Where will efficient energy release occur in 3D magnetic configurations? Authors: Demoulin, P. Bibcode: 2006cosp...36..118D Altcode: 2006cosp.meet..118D The energy needed to power flares is thought to be stored in the coronal magnetic field However the energy release which results in thermal energy brightenings is efficient only at very small scales Magnetic configurations with a complex topology i e with separatrices are the most obvious configurations where current layers then reconnection can efficiently occur This has been confirmed for several flares by computing the coronal field and by comparing the locations of the flare loops and ribbons to the deduced 3D magnetic topology However this view is too restrictive taking into account the variety of observed solar flaring configurations Indeed Quasi-Separatrix Layers QSLs which are regions where there is a drastic change in field-line linkage generalize the definition of separatrices They permit us to understand where reconnection occurs in a broader variety of flares than separatrices do The location where the QSL are the thinnest called Hyperbolic Flux Tube HFT is the location for the strongest electric field and current being generated This is a good candidate for the region where particle acceleration can occur efficiently Title: How to derive the real pattern of magnetic helicity injection in an active region? Authors: Pariat, E.; Nindos, A.; Démoulin, P.; Berger, M. Bibcode: 2006cosp...36..851P Altcode: 2006cosp.meet..851P Magnetic helicity a topological quantity which measures the twist the writhe and the shear of a magnetic field has recently appeared as a key quantity to understand some mechanisms of the solar activity such as Coronal Mass Ejections and flare onset It is thus becoming of major importance to be able to compute magnetic helicity in active regions Looking at the pattern of the photospheric injection of magnetic helicity may provide new useful pieces of information to understand the basic properties of solar activity If several helicity flux density maps were published no one yet wondered if helicity flux density is a correct physical quantity Unfortunately the classical helicity flux density do induce spurious signal fake polarities which mask the real injection of helicity To map the real helicity injection the knowledge of the complete connectivity of the field lines is fundamental Even without the connectivity improved helicity flux density maps can be derived which present strong differences with the previous incorrect maps This leads to a complete new way of understanding the dynamics of the active region in the frame of the magnetic helicity study Title: The role of null points in large flares Authors: Schmieder, B.; Mandrini, C.; Démoulin, P.; Aulanier, G.; Li, H. Bibcode: 2006cosp...36..156S Altcode: 2006cosp.meet..156S We have performed the analysis of the magnetic topology of the active region NOAA 10486 before two large flares occurring on October 26 and 28 2003 The 3D extrapolation of photospheric magnetic field show the existence of magnetic null points We used TRACE 1600 A brightenings as tracers of the energy release during magnetic reconnections We conclude on the three following points 1 The observed small pre-events observed before the flares were related to low lying null points They were long lasting and associated with low energy release They were not triggering of the large flares 2 On October 26 a high altitude null point was detected We looked at the TRACE 1600 A images for bright patches corresponding to a possible coronal reconnection at the null point However no bright patch was observed before the main flare 3 On October 28 a breakout of the large scale overlaying magnetic field lines occurred but without the presence of a null point in the corona So the existence of a null point in the corona is not a sufficient and or necessary condition for getting large flares Title: Tracing magnetic helicity from the solar corona to the interplanetary space Authors: Luoni, M. L.; Mandrini, C. H.; Dasso, Sergio; van Driel-Gesztelyi, L.; Démoulin, P. Bibcode: 2005JASTP..67.1734L Altcode: 2005JATP...67.1734L On October 14, 1995, a C1.6 long duration event (LDE) started in active region (AR) NOAA 7912 at approximately 5:00 UT and lasted for about 15 h. On October 18, 1995, the Solar Wind Experiment and the Magnetic Field Instrument (MFI) on board the Wind spacecraft registered a magnetic cloud (MC) at 1 AU, which was followed by a strong geomagnetic storm. We identify the solar source of this phenomenon as AR 7912. We use magnetograms obtained by the Imaging Vector Magnetograph at Mees Solar Observatory, as boundary conditions to the linear force-free model of the coronal field, and, we determine the model in which the field lines best fit the loops observed by the Soft X-ray Telescope on board Yohkoh. The computations are done before and after the ejection accompanying the LDE. We deduce the loss of magnetic helicity from AR 7912. We also estimate the magnetic helicity of the MC from in situ observations and force-free models. We find the same sign of magnetic helicity in the MC and in its solar source. Furthermore, the helicity values turn out to be quite similar considering the large errors that could be present. Our results are a first step towards a quantitative confirmation of the link between solar and interplanetary phenomena through the study of magnetic helicity. Title: a Series of Compact Flares with AN Associated CME Authors: Goff, C. P.; van Driel-Geszrelyi, L.; Culhane, J. L.; Matthews, S. A.; Harra, L. K.; Démoulin, P.; Mandrini, C. H.; Kurokawa, H. Bibcode: 2005ESASP.600E.157G Altcode: 2005ESPM...11..157G; 2005dysu.confE.157G No abstract at ADS Title: Magnetic clouds: A statistical study of magnetic helicity Authors: Gulisano, A. M.; Dasso, S.; Mandrini, C. H.; Démoulin, P. Bibcode: 2005JASTP..67.1761G Altcode: 2005JATP...67.1761G We select a set of 20 magnetic clouds (MCs) observed by the spacecraft Wind and reconstruct their local magnetic structure from in situ observations under different models. In particular, we quantify their relative magnetic helicity per unit length (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. Bibcode: 2005A&A...444..961A Altcode: In 3D magnetic field configurations, quasi-separatrix layers (QSLs) are defined as volumes in which field lines locally display strong gradients of connectivity. Considering QSLs both as the preferential locations for current sheet development and magnetic reconnection, in general, and as a natural model for solar flares and coronal heating, in particular, has been strongly debated issues over the past decade. In this paper, we perform zero-β resistive MHD simulations of the development of electric currents in smooth magnetic configurations which are, strictly speaking, bipolar though they are formed by four flux concentrations, and whose potential fields contain QSLs. The configurations are driven by smooth and large-scale sub-Alfvénic footpoint motions. Extended electric currents form naturally in the configurations, which evolve through a sequence of quasi non-linear force-free equilibria. Narrow current layers also develop. They spontaneously form at small scales all around the QSLs, whatever the footpoint motions are. For long enough motions, the strongest currents develop where the QSLs are the thinnest, namely at the Hyperbolic Flux Tube (HFT), which generalizes the concept of separator. These currents progressively take the shape of an elongated sheet, whose formation is associated with a gradual steepening of the magnetic field gradients over tens of Alfvén times, due to the different motions applied to the field lines which pass on each side of the HFT. Our model then self-consistently accounts for the long-duration energy storage prior to a flare, followed by a switch-on of reconnection when the currents reach the dissipative scale at the HFT. In configurations whose potential fields contain broader QSLs, when the magnetic field gradients reach the dissipative scale, the currents at the HFT reach higher magnitudes. This implies that major solar flares which are not related to an early large-scale ideal instability, must occur in regions whose corresponding potential fields have broader QSLs. Our results lead us to conjecture that physically, current layers must always form on the scale of the QSLs. This implies that electric currents around QSLs may be gradually amplified in time only if the QSLs are broader than the dissipative length-scale. We also discuss the potential role of QSLs in coronal heating in bipolar configurations made of a continuous distribution of flux concentrations. Title: Quantitative Link Between Solar Ejecta and Interplanetary Magnetic Clouds: Magnetic Helicity Authors: Mandrini, C. H.; Dasso, S.; Luoni, M. L.; Pohjolainen, S.; Démoulin, P.; van Driel-Gesztelyi, L. Bibcode: 2005ESASP.596E..29M Altcode: 2005ccmf.confE..29M No abstract at ADS Title: Erratum: Photospheric flux density of magnetic helicity Authors: Pariat, E.; Démoulin, P.; Berger, M. A. Bibcode: 2005A&A...442.1105P Altcode: No abstract at ADS Title: Magnetic Topologies: where Will Reconnection Occur ? Authors: Démoulin, P. Bibcode: 2005ESASP.596E..22D Altcode: 2005ccmf.confE..22D No abstract at ADS Title: Helicity Analysis for Expanding Magnetic Clouds: A Case Study Authors: Nakwacki, M. S.; Dasso, S.; Mandrini, C. H.; Démoulin, P. Bibcode: 2005ESASP.592..629N Altcode: 2005soho...16E.123N; 2005ESASP.592E.123N No abstract at ADS Title: Large Scale Properties of Magnetic Clouds: Different Approaches to Estimate their Orientation and Impact Parameter Authors: Gulisano, A. M.; Dasso, S.; Mandrini, C. H.; Démoulin, P. Bibcode: 2005ESASP.592..621G Altcode: 2005ESASP.592E.121G; 2005soho...16E.121G No abstract at ADS Title: Photospheric flux density of magnetic helicity Authors: Pariat, E.; Démoulin, P.; Berger, M. A. Bibcode: 2005A&A...439.1191P Altcode: Several recent studies have developed the measurement of magnetic helicity flux from the time evolution of photospheric magnetograms. The total flux is computed by summing the flux density over the analyzed region. All previous analyses used the density 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 Bibcode: 2005ESASP.592..605D Altcode: 2005soho...16E.117D; 2005ESASP.592E.117D No abstract at ADS Title: Flows in the solar atmosphere due to the eruptions on the 15th July, 2002 Authors: Harra, L. K.; Démoulin, P.; Mandrini, C. H.; Matthews, S. A.; van Driel-Gesztelyi, L.; Culhane, J. L.; Fletcher, L. Bibcode: 2005A&A...438.1099H Altcode: Which kind of flows are present during flares? Are they compatible with the present understanding of energy release and which model best describes the observations? We analyze successive flare events in order to answer these questions. The flares were observed in the magnetically complex NOAA active region (AR) 10030 on 15 July 2002. One of them is of GOES X-class. The description of these flares and how they relate to the break-out model is presented in Gary & 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 Bibcode: 2005ApJ...628L.163W Altcode: 2005astro.ph..7661W We present rapid-cadence Transition Region and Coronal Explorer (TRACE) observations that show evidence of a filament eruption from NOAA active region 10696, accompanied by an X2.5 flare, on 2004 November 10. The eruptive filament, which manifests as a fast coronal mass ejection some minutes later, rises as a kinking structure with an apparently exponential growth of height within TRACE's field of view. We compare the characteristics of this filament eruption with MHD numerical simulations of a kink-unstable magnetic flux rope, finding excellent qualitative agreement. We suggest that while tether weakening by breakout-like quadrupolar reconnection may be the release mechanism for the previously confined flux rope, the driver of the expansion is most likely the MHD helical kink instability. Title: Radio and X-Ray Signatures of Magnetic Reconnection behind an Ejected Flux Rope Authors: Pick, M.; Démoulin, P.; Krucker, S.; Malandraki, O.; Maia, D. Bibcode: 2005ApJ...625.1019P Altcode: We present a detailed study of a complex solar event observed on 2002 June 2. Joint imaging EUV, X-ray, and multiwavelength radio observations allow us to trace the development of the magnetic structure involved in this solar event up to a radial distance of the order of 2 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. Bibcode: 2005A&A...434..725M Altcode: Using multi-instrument and multi-wavelength observations (SOHO/MDI and EIT, TRACE and Yohkoh/SXT), as well as computing the coronal magnetic field of a tiny bipole combined with modelling of Wind in situ data, we provide evidences for the smallest event ever observed which links a sigmoid eruption to an interplanetary magnetic cloud (MC). The tiny bipole, which was observed very close to the solar disc centre, had a factor one hundred less flux than a classical active region (AR). In the corona it had a sigmoidal structure, observed mainly in EUV, and we found a very high level of non-potentiality in the modelled magnetic field, 10 times higher than we have ever found in any AR. From May 11, 1998, and until its disappearance, the sigmoid underwent three intense impulsive events. The largest of these events had extended EUV dimmings and a cusp. The Wind spacecraft detected 4.5 days later one of the smallest MC ever identified (about a factor one hundred times less magnetic flux in the axial component than that of an average MC). The link between this last eruption and the interplanetary magnetic cloud is supported by several pieces of evidence: good timing, same coronal loop and MC orientation, same magnetic field direction and magnetic helicity sign in the coronal loops and in the MC. We further quantify this link by estimating the magnetic flux (measured in the dimming regions and in the MC) and the magnetic helicity (pre- to post-event change in the solar corona and helicity content of the MC). Within the uncertainties, both magnetic fluxes and helicities are in reasonable agreement, which brings further evidences of their link. These observations show that the ejections of tiny magnetic flux ropes are indeed possible and put new constraints on CME models. Title: Equilibrium and observational properties of line-tied twisted flux tubes Authors: Aulanier, G.; Démoulin, P.; Grappin, R. Bibcode: 2005A&A...430.1067A Altcode: We describe a new explicit three-dimensional magnetohydrodymanic code, which solves the standard zero-β MHD equations in Cartesian geometry, with line-tied conditions at the lower boundary and open conditions at the other ones. Using this code in the frame of solar active regions, we simulate the evolution of an initially potential and concentrated bipolar magnetic field, subject to various sub-Alfvénic photospheric twisting motions which preserve the initial photospheric vertical magnetic field. Both continuously driven and relaxation runs are performed. Within the numerical domain, a steep equilibrium curve is found for the altitude of the apex of the field line rooted in the vortex centers as a function of the twist. Its steepness strongly depends on the degree of twist in outer field lines rooted in weak field regions. This curve fits the analytical expression for the asymptotic behaviour of force-free fields of spherical axisymmetric dipoles subject to azimuthal shearing motions, as well as the curve derived for other line-tied twisted flux tubes reported in previous works. This suggests that it is a generic property of line-tied sheared/twisted arcades. However, contrary to other studies we never find a transition toward a non-equilibrium within the numerical domain, even for twists corresponding to steep regions of the equilibrium curve. The calculated configurations are analyzed in the frame of solar observations. We discuss which specific conditions are required for the steepness of the generic equilibrium curve to result in dynamics which are typical of both fast and slow CMEs observed below 3 R_⊙. We provide natural interpretations for the existence of asymmetric and multiple concentrations of electric currents in homogeneoulsy twisted sunspots, due to the twisting of both short and long field lines. X-ray sigmoids are reproduced by integrating the Joule heating term along the line-of-sight. These sigmoids have inverse-S shapes associated with negative force-free parameters α, which is consistent with observed rules in the northern solar hemisphere. We show that our sigmoids are not formed in the main twisted flux tube, but rather in an ensemble of low-lying sheared and weakly twisted field lines, which individually never trace the whole sigmoid, and which barely show their distorded shapes when viewed in projection. We find that, for a given bipolar configuration and a given twist, neither the α nor the altitude of the lines whose envelope is a sigmoid depends on the vortex size. Title: Analysis of 20 magnetic clouds at 1 AU during a solar minimum Authors: Gulisano, A. M.; Dasso, S.; Mandrini, C. H.; Démoulin, P. Bibcode: 2005BAAA...48...79G Altcode: We study 20 magnetic clouds, observed in situ by the spacecraft Wind, at the Lagrangian point L1, from 22 August, 1995, to 7 November, 1997. In previous works, assuming a cylindrical symmetry for the local magnetic configuration and a satellite trajectory crossing the axis of the cloud, we obtained their orientations using a minimum variance analysis. In this work we compute the orientations and magnetic configurations using a non-linear simultaneous fit of the geometric and physical parameters for a linear force-free model, including the possibility of a not null impact parameter. We quantify global magnitudes such as the relative magnetic helicity per unit length and compare the values found with both methods (minimum variance and the simultaneous fit). FULL TEXT IN SPANISH Title: Magnetic topology analysis of an M6.7 solar flare Authors: Luoni, M. L.; Mandrini, C. H.; Démoulin, P. Bibcode: 2005BAAA...48...84L Altcode: We study an M6.7 solar flare that occurred on October 27, 2003 (12:27 UT). We use data in different wavelenghts: magnetograms from the Michelson Doppler Imager (SoHO/MDI), images from the Halpha Solar Telescope for Argentina (HASTA) and Extreme Ultraviolet Imaging Telescope (SoHO/EIT).We analyze the magnetic field evolution and compute the coronal field to identify the energy release site. From this study, we find evidence of a magnetic null point in the corona. We relate the chromospheric and EUV brightenings to the magnetic field topology in its neighborhood. FULL TEXT IN SPANISH Title: A Direct Method to Estimate Magnetic Helicity in Magnetic Clouds Authors: Dasso, S.; Mandrini, C. H.; Gulisano, A. M.; Démoulin, P. Bibcode: 2005IAUS..226..403D Altcode: Magnetic clouds are extended and magnetized plasma structures that travel from the Sun toward the outer heliosphere, carrying an important amount of magnetic helicity. The magnetic helicity quantifies several aspects of a given magnetic structure, such as the twist, kink, and the number of knots between magnetic field lines, the linking between magnetic flux tubes, etc. Since the helicity is practically conserved in the solar atmosphere and the heliosphere, it is a useful quantity to compare the physical properties of magnetic clouds to those of their solar source regions. In this work we describe a method that, assuming a cylindrical geometry for the magnetic cloud structures, allows us to calculate their helicity (per unit length) content directly from the observed magnetic field values. We apply the method to a set of 20 magnetic clouds observed by the WIND spacecraft. To test its reliability we compare our results with the helicity computed using a linear force-free field model under cylindrical geometry (i.e. Lundquist's solution). Title: The smallest source region of an interplanetary magnetic cloud: A mini-sigmoid Authors: Mandrini, C. H.; Pohjolainen, S.; Dasso, S.; Green, L. M.; Démoulin, P.; van Driel-Gesztelyi, L.; Foley, C.; Copperwheat, C. Bibcode: 2005AdSpR..36.1579M Altcode: We provide evidence for the smallest sigmoid eruption - CME - interplanetary magnetic cloud event ever observed by combining multi-wavelength remote sensing and in situ observations, as well as computing the coronal and interplanetary magnetic fields. The tiny bipole had 100 times less flux than an average active region (AR). It had a sigmoidal structure in the corona and we detected a very high level of twist in its magnetic field. On 11 May 1998, at about 8 UT, the sigmoid underwent eruption evidenced by expanding elongated EUV loops, dimmings and formation of a cusp. The Wind spacecraft, 4.5 days later, detected one of the smallest magnetic clouds (MC) ever identified (100 times less magnetic flux than an average MC). The link between the EUV bright point eruption and the interplanetary MC is supported by several pieces of evidence: timing, same coronal loop and MC orientation relative to the ecliptic, same magnetic field direction and magnetic helicity sign in the coronal loops and in the MC, comparable magnetic flux measured in the dimming regions and in the interplanetary MC and, most importantly, the pre- to post-event change of magnetic helicity in the solar corona is found to be comparable to the helicity content of the cloud. Title: Linking Coronal to Interplanetary Magnetic Helicity Authors: Luoni, M. L.; Dasso, S.; Mandrini, C. H.; Van Driel-Gesztelyi, L.; Démoulin, P. Bibcode: 2005ASSL..320..243L Altcode: 2005smp..conf..243L No abstract at ADS Title: Large scale MHD properties of interplanetary magnetic clouds Authors: Dasso, S.; Mandrini, C. H.; Démoulin, P.; Luoni, M. L.; Gulisano, A. M. Bibcode: 2005AdSpR..35..711D Altcode: Magnetic Clouds (MCs) are the interplanetary manifestation of Coronal Mass Ejections. These huge astrophysical objects travel from the Sun toward the external heliosphere and can reach the Earth environment. Depending on their magnetic field orientation, they can trigger intense geomagnetic storms. The details of the magnetic configuration of clouds and the typical values of their magnetohydrodynamic magnitudes are not yet well known. One of the most important magnetohydrodynamic quantities in MCs is the magnetic helicity. The helicity quantifies several aspects of a given magnetic structure, such as the twist, kink, number of knots between magnetic field lines, linking between magnetic flux tubes, etc. The helicity is approximately conserved in the solar atmosphere and the heliosphere, and it is very useful to link solar phenomena with their interplanetary counterpart. Since a magnetic cloud carries an important amount of helicity when it is ejected from the solar corona, estimations of the helicity content in clouds can help us to understand its evolution and its coronal origin. In situ observations of magnetic clouds at one astronomical unit are in agreement with a local helical magnetic structure. However, since spacecrafts only register data along a unique direction, several aspects of the global configuration of clouds cannot be observed. In this paper, we review the general properties of magnetic clouds and different models for their magnetic structure at one astronomical unit. We describe the corresponding techniques to analyze in situ measurements. We also quantify their magnetic helicity and compare it with the release of helicity in their solar source for some of the analyzed cases. Title: Study of an expanding magnetic cloud Authors: Nakwacki, M. S.; Dasso, S.; Mandrini, C. H.; Démoulin, P. Bibcode: 2005BAAA...48...93N Altcode: Magnetic Clouds (MCs) transport into the interplanetary medium the magnetic flux and helicity released in coronal mass ejections by the Sun. At 1 AU from the Sun, MCs are generally modelled as static flux ropes. However, the velocity profile of some MCs presents signatures of expansion. We analise here the magnetic structure of an expanding magnetic cloud observed by Wind spacecraft. We consider a dynamical model, based on a self-similar behaviour for the cloud radial velocity. We assume a free expansion for the cloud, and a cylindrical linear force free field (i.e., the Lundquist's field) as the initial condition for its magnetic configuration. We derive theoretical expressions for the magnetic flux across a surface perpendicular to the cloud axis, for the magnetic helicity and magnetic energy per unit length along the tube using the self-similar model. Finally, we compute these magntitudes with the fitted parameters. FULL TEXT IN SPANISH Title: Solar and Interplanetary Magnetic Helicity Balance of Active Regions Authors: Mandrini, Cristina H.; Démoulin, Pascal; van Driel-Gesztelyi, Lidia; Dasso, Sergio; Green, Lucinda M.; López Fuentes, Marcelo Bibcode: 2005HiA....13..122M Altcode: No abstract at ADS Title: Model-independent large-scale magnetohydrodynamic quantities in magnetic clouds Authors: Dasso, S.; Gulisano, A. M.; Mandrini, C. H.; Démoulin, P. Bibcode: 2005AdSpR..35.2172D Altcode: Magnetic clouds are the interplanetary manifestation of coronal mass ejections, which are transient expulsions of major quantities of magnetized plasma, from the Sun toward the heliosphere. The magnetic flux and helicity are two key physical magnitudes to track solar structures from the photosphere-corona to the interplanetary medium. To determine the content of flux and helicity in magnetic clouds, we have to know their 3D structure. However, since spacecrafts register data along a unique direction, several aspects of their global configuration cannot be observed. We present a method to estimate the magnetic flux and the magnetic helicity per unit length in magnetic clouds, directly from in situ magnetic observations, assuming only a cylindrical symmetry for the magnetic field configuration in the observed cross-section of the cloud. We select a set of 20 magnetic clouds observed by the spacecraft Wind and estimate their magnetic flux and their helicity per unit length. We compare the results obtained from our direct method with those obtained under the assumption of a helical linear force-free field. This direct method improves previous estimations of helicity in clouds. Title: Observational Consequences of a Magnetic Flux Rope Emerging into the Corona Authors: Gibson, S. E.; Fan, Y.; Mandrini, C.; Fisher, G.; Demoulin, P. Bibcode: 2004ApJ...617..600G Altcode: We show that a numerical simulation of a magnetic flux rope emerging into a coronal magnetic field predicts solar structures and dynamics consistent with observations. We first consider the structure, evolution, and relative location and orientation of S-shaped, or sigmoid, active regions and filaments. The basic assumptions are that (1) X-ray sigmoids appear at the regions of the flux rope known as ``bald-patch-associated separatrix surfaces (BPSSs), where, under dynamic forcing, current sheets can form, leading to reconnection and localized heating, and that (2) filaments are regions of enhanced density contained within dips in the magnetic flux rope. We demonstrate that the shapes and relative orientations and locations of the BPSS and dipped field are consistent with observations of X-ray sigmoids and their associated filaments. Moreover, we show that current layers indeed form along the sigmoidal BPSS as the flux rope is driven by the kink instability. Finally, we consider how apparent horizontal motions of magnetic elements at the photosphere caused by the emerging flux rope might be interpreted. In particular, we show that local correlation tracking analysis of a time series of magnetograms for our simulation leads to an underestimate of the amount of magnetic helicity transported into the corona by the flux rope, largely because of undetectable twisting motions along the magnetic flux surfaces. Observations of rotating sunspots may provide better information about such rotational motions, and we show that if we consider the separated flux rope legs as proxies for fully formed sunspots, the amount of rotation that would be observed before the region becomes kink unstable would be in the range 40°-200° per leg/sunspot, consistent with observations. Title: Comparisons Between SCIAMACHY Scientific Products and Ground-Based FTIR Data for Total Columns of CO, CH4 and N2O. Authors: de Mazière, M.; Barret, B.; Blumenstock, T.; Buchwitz, M.; de Beek, R.; Demoulin, P.; Fast, H.; Gloudemans, A.; Griesfeller, A.; Griffith, D.; Ionov, D.; Janssens, K.; Jones, N.; Mahieu, E.; Mellqvist, J.; Mittermeier, R. L.; Notholt, J.; Rinsland, C.; Schrijver, H.; Schultz, A.; Smale, D.; Strandberg, A.; Strong, K.; Sussmann, R.; Warneke, T.; Wood, S. Bibcode: 2004ESASP.562E..12D Altcode: 2004acve.conf...12D Total column amounts of CO, CH4 and N2O retrieved from SCIAMACHY nadir observations in its near-infrared channels have been compared to data from a ground-based network of Fourier-transform infrared (FTIR) spectrometers as well as to data obtained with an FTIR instrument during a ship cruise in January-February 2003, along the African West Coast. The SCIAMACHY data considered here have been produced by two different scientific retrieval algorithms, wfm-doas (version 4.0) and IMLM (version 5.1), and cover different time periods, making the number of reliable coincidences that satisfy the temporal and spatial collocation criteria rather limited and different for both. Also the quality of the SCIAMACHY Level 1 data, and thus of the Level 2 data for the different time periods is very different. Still the comparisons demonstrate the capability of SCIAMACHY, using one of both algorithms, to deliver geophysically valuable products for the target species under consideration, on a global scale Title: Geophysical Validation of SCIAMACHY NO2 Vertical Columns: Overview of Early 2004 Results Authors: Lambert, J. -C.; Blumenstock, T.; Boersma, F.; Bracher, A.; de Mazière, M.; Demoulin, P.; de Smedt, I.; Eskes, H.; Gil, M.; Goutail, F.; Granville, J.; Hendrick, F.; Ionov, D. V.; Johnston, P. V.; Kostadinov, I.; Kreher, K.; Kyr, E.; Martin, R.; Meier, A.; Navarro-Comas, M.; Petritoli, A.; Pommereau, J. -P.; Richter, A.; Roscoe, H. K.; Sioris, C.; Sussmann, R.; van Roozendael, M.; Wagner, T.; Wood, S.; Yela, M. Bibcode: 2004ESASP.562E...6L Altcode: 2004acve.conf....6L Following the recommendations drawn after the Commissioning Phase of the ENVISAT satellite in 2002, SCIAMACHY near real time data processors were upgraded to version 5.01 in early 2004. Before public release of the new SCIAMACHY nitrogen dioxide (NO2) vertical column data product, several validation teams investigated its improvement and assessed its geophysical consistency by means of correlative studies involving NDSC-affiliated groundbased networks of DOAS UV-visible and FTIR spectrometers and the ERS-2 GOME satellite. In parallel, preliminary SCIAMACHY NO2 column data products generated by research processors under development at scientific institutes were also tested, using the same correlative data and validation procedures. Digesting the results obtained by a list of validation teams and SCIAMACHY data processing teams, this overview paper draws a preliminary quality assessment of the SCIAMACHY NO2 column data sets available in spring 2004. Title: First Ground-Based Validation of SCIAMACHY V5.01 Ozone Column Authors: Lambert, J. -C.; Allaart, M.; Andersen, S. B.; Blumenstock, T.; Bodeker, G.; Brinksma, E.; Cambridge, C.; de Mazière, M.; Demoulin, P.; Gerard, P.; Gil, M.; Goutail, F.; Granville, J.; Ionov, D. V.; Kyrö, E.; Navarro-Comas, M.; Piters, A.; Pommereau, J. -P.; Richter, A.; Roscoe, H. K.; Schets, H.; Shanklin, J. D.; Suortti, T.; Sussmann, R.; van Roozendael, M.; Varotsos, C.; Wagner, T.; Wood, S.; Yela, M. Bibcode: 2004ESASP.562E...3L Altcode: 2004acve.conf....3L In early 2004, the near real-time data processor of ENVISAT SCIAMACHY (SCI_NL) was upgraded to version 5.01. Based on the correlative measurements acquired and collected during the commissioning phase of the satellite in 2002, a preliminary validation was organised to verify the improvement and assess the geophysical consistency of the new SCIAMACHY o z o n e vertical column data product. The present overview summarises the results obtained by a list of v a l i d a t i o n teams and involving ground-based data acquired from pole to pole by complementary groundbased sensors. The studies conclude to an improvement compared to previous versions 3.5x. They also confirm the presence of expected errors (e.g. dependence on solar elevation and on ozone column) inherited from the G O M E Data Processor GDP 2.4, on which the SCIAMACHY processor SCI_NL is based Title: Solar Origin of Interplanetary Impulsive Electron Events Authors: Pick, M.; Maia, D. J.; Malandraki, O.; Krucker, S.; Demoulin, P. Bibcode: 2004AGUSMSH22A..03P Altcode: Many solar impulsive electron events have been traditionally associated with type III radio emissions. Several recent studies however showed that, in the majority of the events, the solar release of electrons at high energies can present delays of up-to-half an hour with respect of the onset of type III bursts. We have revisited the origin of a large number of events using multiwave-length observations. For each event, we investigated the coronal restructuring using EUV, white-light, radio imaging and spectral observations in a wide frequency range that allows us to follow the evolution of the corona from a few tenths above the solar limb up to a few solar radii. Radio observations revealed direct energetic electron signatures, close in time with the electron release. The release time for the delayed events always coincides with the onset or major changes in the complex of radio emissions. This close association indicates that the coronal processes involved in the radio emissions are at the origin of the electron acceleration. We illustrate our results by presenting, more particularly, one recent event for which the observations were also coupled with imaging spectroscopy measurements obtained by the RHESSI mission (from 3 keV to 17 MeV). RHESSI observed a hard X-ray emission, which lasted for more than fifteen minutes. This emission was closely associated in time and space with the radio emission imaged by the Nançay Radioheliograph. The results suggest that, for this event, both electrons detected in the corona and those injected in the interplanetary medium are due to a similar process involving coronal magnetic field interactions. Their respective sites of acceleration/injection are however distinct in space and time. The energetic electrons detected in the interplanetary medium are not released during the X-ray burst. Title: Magnetic Helicity Budget of Solar-Active Regions from the Photosphere to Magnetic Clouds Authors: Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.; van Driel-Gesztelyi, L.; van Driel-Gesztelyi, L.; van Driel-Gesztelyi, L. L. M.; López Fuentes, M. C. Bibcode: 2004Ap&SS.290..319M Altcode: We have analyzed the long-term evolution of two active regions (ARs) from their emergence through their decay using observations from several instruments on board SoHO (MDI, EIT and LASCO) and Yohkoh/SXT. We have computed the evolution of the relative coronal magnetic helicity combining data from MDI and SXT with a linear force-free model of the coronal magnetic field. Next, we have computed the injection of helicity by surface differential rotation using MDI magnetic maps. To estimate the depletion of helicity we have counted all the CMEs of which these ARs have been the source, and we have evaluated their magnetic helicity assuming a one to one correspondence with magnetic clouds with an average helicity contain. When these three values (variation of coronal magnetic helicity, injection by differential rotation and ejection via CMEs) are compared, we find that surface differential rotation is a minor contributor to the helicity budget since CMEs carry away at least 10 times more helicity than the one differential rotation can provide. Therefore, the magnetic helicity flux needed in the global balance should come from localized photospheric motions that, at least partially, reflect the emergence of twisted flux tubes. We estimate that the total helicity carried away in CMEs can be provided by the end-to-end helicity of the flux tubes forming these ARs. Therefore, we conclude that most of the helicity ejected in CMEs is generated below the photosphere and emerges with the magnetic flux. Title: The long-term evolution of active regions, multi-wavelength flux and heating studies: observations and theory Authors: Démoulin, P. Bibcode: 2004IAUS..223...13D Altcode: 2005IAUS..223...13D Analyzing the long-term evolution of active regions (ARs) permits to quantify the link between their atmospheric emission (from optical to X-rays) and the magnetic field. Multi-wavelength studies provide the full story, and not just a snapshot, of the phenomena and they allow us analyze how the atmosphere changes as the field strength decreases (with the dispersion of the AR). Title: An Observational Test for Coronal Heating Models Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Mandrini, C. H.; Harra, L. K.; Klimchuk, J. A. Bibcode: 2004IAUS..219..473V Altcode: 2003IAUS..219E..97V We correlate the evolution of the mean X-ray flux emission measure and temperature (Yohkoh SXT & BCS) with the magnetic flux density (SOHO/MDI) in active region NOAA 7978 from its birth throughout its decay for five solar rotations. We show that these plasma parameters together with other quantities deduced from them such as the density and the pressure follow power-law relationships with the mean magnetic flux density (bar{B}). We derive the dependence of the mean coronal heating rate on the magnetic flux density. We use the obtained scaling laws of coronal loops in thermal equilibrium to derive observational estimates of the scaling of the coronal heating with bar{B}. These results are used to test the validity of coronal heating models. We find that models invoking stochastic buildup of energy current layers and MHD turbulence are in best agreement with the observations. This narrows down the range of possible models retained by previous results obtained for individual coronal loops as well as for the global coronal emission of the Sun and cool stars. Title: Magnetohydrodinamic properties of solar origin magnetic clouds: an statistical study Authors: Gulisano, A. M.; Dasso, S.; Mandrini, C. H.; Démoulin, P. Bibcode: 2004BAAA...47...28G Altcode: Magnetic Clouds (MCs) are the interplanetary manifestation of transient expulsions of solar mass, the so-called coronal mass ejections. Despite several statistical works that have been done studying diverse properties of MCs, systematic studies of their magnetohydrodynamic (MHD) global magnitudes, such as their magnetic helicity (MH) and energy, have not yet been undertaken. In this work we present a study of 20 MCs observed by the spacecraft Wind and quantify their MHD properties. The study is performed exploring 4 helical models with substantial differences in the magnetic field twist distribution. We find that the values of the MH content are almost independent from the analyzed models, in the sense that their dispersion when considering different models for a given event is smaller than the dispersion when considering different events. Title: Emerging Flux and the Heating of Coronal Loops Authors: Schmieder, B.; Rust, D. M.; Georgoulis, M. K.; Démoulin, P.; Bernasconi, P. N. Bibcode: 2004ApJ...601..530S Altcode: We use data collected by a multiwavelength campaign of observations to describe how the fragmented, asymmetric emergence of magnetic flux in NOAA active region 8844 triggers the dynamics in the active-region atmosphere. Observations of various instruments on board Yohkoh, SOHO, and TRACE complement high-resolution observations of the balloon-borne Flare Genesis Experiment obtained on 2000 January 25. We find that coronal loops appeared and evolved rapidly ~6+/-2 hr after the first detection of emerging magnetic flux. In the low chromosphere, flux emergence resulted in intense Ellerman bomb activity. Besides the chromosphere, we find that Ellerman bombs may also heat the transition region, which showed ``moss'' ~100% brighter in areas with Ellerman bombs as compared to areas without Ellerman bombs. In the corona, we find a spatiotemporal anticorrelation between the soft X-ray (SXT) and the extreme ultraviolet (TRACE) loops. First, SXT loops preceded the appearance of the TRACE loops by 30-40 minutes. Second, the TRACE and SXT loops had different shapes and different footpoints. Third, the SXT loops were longer and higher than the TRACE loops. We conclude that the TRACE and the SXT loops were formed independently. TRACE loops were mainly heated at their footpoints, while SXT loops brightened in response to coronal magnetic reconnection. In summary, we observed a variety of coupled activity, from the photosphere to the active-region corona. Links between different aspects of this activity lead to a unified picture of the evolution and the energy release in the active region. Title: Multi-wavelength flare study and magnetic configuration Authors: Schmieder, Brigitte; Berlicki, A.; Vilmer, N.; Aulanier, G.; Démoulin, P.; Mein, P.; Mandrini, C.; Deluca, E. Bibcode: 2004IAUS..223..397S Altcode: 2005IAUS..223..397S Recent results of two observation campaigns (October 2002 and October 2003) are presented with the objective of understanding the onset of flares and CMEs. The magnetic field was observed with THEMIS and MDI, the chromosphere with the MSDP operating on the German telescope VTT and on THEMIS, the EUV images with SOHO/CDS and TRACE, the X-ray with RHESSI. We show how important is the magnetic configuration of the active region to produce CMEs using two examples: the October 28 2003 X 17 flare and the October 22 2002 M 1.1 flare. The X 17 flare gave a halo CME while the M 1.1 flare has no corresponding CME. The magnetic topology analysis of the active regions is processed with a linear-force-free field configuration. Title: Linking coronal observations of a `mini´active region with its interplanetary manifestation Authors: Dasso, S.; Mandrini, C. H.; Pohjolainen, S.; Green, L. M.; Démoulin, P.; van Driel-Gesztelyi, L.; Foley, C.; Copperwheat, C. Bibcode: 2004BAAA...47...18D Altcode: We analyze the smallest 'sigmoidal eruption - CME - interplanetary magnetic cloud' event even observed before. We find: (a) the same magnetic helicity sign and (b) similar magnetic flux values in the coronal source region and associated cloud, and (c) that the magnetic helicity changes, before and after the ejection, in approximately the same amount as the helicity content in the interplanetary cloud. These results stress the importance of complementary solar and interplanetary studies, to achieve a better understanding of the origin of eruptive phenomena. Title: Emerging Flux and the Heating of Coronal Loops Authors: Schmieder, B.; Démoulin, P.; Rust, D. M.; Georgoulis, M. K.; Bernasconi, P. N. Bibcode: 2004IAUS..219..483S Altcode: 2003IAUS..219E..18S We suggest that coronal loop heating is caused by dissipation of magnetic energy as new magnetic flux emerges from the photosphere. Based on data from a multi wavelength campaign of observations during the flight of the Flare Genesis Experiment we describe how emergence of flux from the photosphere appears directly to heat the corona to 2-3 MK. Following intense heating the loops cool and become visible through the filters of the TRACE (Transition Region and Coronal Explorer)instrument at one million degrees. We determine the relaxation time of the cooling and compare it withtheoretical heating functions. The proposed mechanism is well accepted in flare loops but we suggest that the mechanism is generally valid and helps to explain the visibility of active region loops in transition region lines. Title: Can we determine the magnetic helicity sign of the solar active regions? Authors: Luoni, M. L.; Mandrini, C. H.; Démoulin, P.; van Diel-Gesztelyi, L.; Kövári, Zs. Bibcode: 2004BAAA...47...14L Altcode: To improve space weather prediction it is important to know the characteristics of the solar active event responsable for the observed disturbances in the interplanetary (IP)medium. The comparison of the magnetic helicity sign of the active region (AR) and the interplanetary magnetic cloud, observed after a coronal mass ejection (CME), is a useful tool to link solar and interplanetary events. However, the determination of the coronal helicity sign requires the analysis of loop observations which is not promptly available (and, sometimes, non-conclusive), vector magnetograms that are not obtained in a routine way, and/or coronal magnetic field modeling. In this preliminary work, we show that it is possible to determine the magnetic helicity sign of an AR using only observations of the photospheric line of sight component of the magnetic field (Bl) during its emergence and early life-time stages. Title: The smallest source region of an interplanetary magnetic cloud: a mini-sigmoid Authors: Mandrini, C.; Pohjolainen, S.; Dasso, S.; Green, L.; Demoulin, P.; van Driel-Gesztelyi, L.; Copperwheat, C.; Foley, C. Bibcode: 2004cosp...35..290M Altcode: 2004cosp.meet..290M Using multi-instrument and multi-wavelength observations (SOHO/MDI and EIT, TRACE and Yohkoh/SXT), as well as computing the coronal magnetic field of a tiny bipole combined with modelling of WIND in situ data, we provide evidence for the smallest sigmoid eruption - CME - interplanetary magnetic cloud event ever observed. The tiny bipole, which was observed very close to the solar disc centre, had 100 times less flux than an average active region (AR). In the corona it had a sigmoidal structure and we detected a very high level of twist. On 11 May 1998, at about 8 UT, the sigmoid underwent eruption evidenced by expanding elongated EUV loops, dimmings and formation of a cusp. The WIND spacecraft detected 4.5 days later one of the smallest magnetic clouds (MC) ever identified (100 times less flux and radius than an average MC). The link between the sigmoidal EUV bright point eruption and the interplanetary magnetic cloud is supported by several pieces of evidence: good timing, same coronal loop and MC orientation relative to the ecliptic, same magnetic field direction and magnetic helicity sign in the coronal loops and in the MC, comparable magnetic flux measured in the dimming regions and in the interplanetary MC and, most importantly, the pre- to post-event change of magnetic helicity in the solar corona is found to be similar to the helicity content of the cloud, when assuming a length compatible with the fact that the cloud can be detached from the Sun one day after its ejection. These observations are a challenge to present theoretical CME models, and show us the need of missions such us Solar B and Stereo to contribute to our understanding of the broad spectrum covered by solar eruptive phenomena. Title: How small can an interplanetary magnetic cloud source-region be? Authors: Mandrini, C.; Pohjolainen, S.; Dasso, S.; Green, L.; Demoulin, P.; van Driel-Gesztelyi, L.; Copperwheat, C.; Foley, C. Bibcode: 2004cosp...35..282M Altcode: 2004cosp.meet..282M Using multi-instrument and multi-wavelength observations (SOHO/MDI and EIT, TRACE and Yohkoh/SXT), as well as computing the coronal magnetic field of a tiny bipole combined with modelling of WIND in situ data, we provide evidence for the smallest sigmoid eruption - CME - interplanetary magnetic cloud event ever observed. The tiny bipole, which was observed very close to the solar disc centre, had 100 times less flux than an average active region (AR). In the corona it had a sigmoidal structure and we detected a very high level of twist. On 11 May 1998, at about 8 UT, the sigmoid underwent eruption evidenced by expanding elongated EUV loops, dimmings and formation of a cusp. The WIND spacecraft detected 4.5 days later one of the smallest magnetic clouds (MC) ever identified (100 times less flux and radius than an average MC). The link between the sigmoidal EUV bright point eruption and the interplanetary magnetic cloud is supported by several pieces of evidence: good timing, same coronal loop and MC orientation relative to the ecliptic, same magnetic field direction and magnetic helicity sign in the coronal loops and in the MC, comparable magnetic flux measured in the dimming regions and in the interplanetary MC and, most importantly, the pre- to post-event change of magnetic helicity in the solar corona is found to be similar to the helicity content of the cloud, when assuming a length compatible with the fact that thecloud can be dettached from the Sun one day after its ejection. These observations are a challenge to present theoretical CME models, and show us the need of missions such us Solar B and Stereo to contribute to our understandig of the broad spectrum covered by solar eruptive phenomena. Title: Extending the concept of separatrices to QSLs for magnetic reconnection Authors: Demoulin, P. Bibcode: 2004cosp...35.1084D Altcode: 2004cosp.meet.1084D Magnetic reconnection is usually thought to be linked to the presence of magnetic null points and to be accompanied by the transport of magnetic field lines across separatrices, the set of field lines where the mapping of field lines is discontinuous. However, this view is too restrictive taking into account the variety of observed solar flaring configurations. Indeed ``quasi-separatrix layers" (QSLs), which are regions where there is drastic change in field-line linkage generalize the definition of separatrices. The use of this broader concept allows us to localize these thin regions where magnetic reconnection can preferentially occur in three-dimensional magnetic configurations. I will survey the evolution of the QSL concept from the beginning to the recent developments. The application to solar observations requires first the computation of the coronal magnetic field from photospheric data. Then, the determination of the QSLs allows us to understand the observed location of flare kernels and loops and so to validate the reconnection scenario as the main physical process at the origin of flares. On the theoretical side, locating the QSLs let us predict where strong current layers will form as a consequence of boundary evolution. Numerical simulations broadly confirm this, with direct implications for coronal heating. This QSL approach is also compatible with an MHD turbulence scenario for coronal heating as numerical simulations show the development of MHD turbulence when reconnection starts in QSLs. Title: Direct observation of large scale magnetohydrodynamic quantities in magnetic clouds Authors: Dasso, S.; Gulisano, A.; Mandrini, C. H.; Démoulin, P. Bibcode: 2004cosp...35..530D Altcode: 2004cosp.meet..530D Magnetic Clouds (MCs) are the interplanetary manifestation of Coronal Mass Ejections (CMEs). Despite these astrophysical objects have been observed for more than 20 years, several details of their magnetic configuration at 1AU, as consequence of their dynamical evolution through the inner heliosphere, are not well known. The magnetic flux (F) and helicity (MH) are very important magnetohydrodynamic (MHD) quantities characterizing the magnetic configuration in these objects, and there are very few studies quantifying their typical values. MH measures several aspects of a given magnetic structure, and it is practically conserved in the solar atmosphere and the heliosphere. MCs travel from the Sun toward the external heliosphere carrying an important amount of MH. In situ observations of MCs at 1 AU agree with a local helical magnetic structure. However, since spacecrafts only register data along a unique direction, several aspects of the global configuration are not observed. We select a set of MCs observed by the spacecraft Wind and we analyze them, obtaining values for F and MH directly from the observations. We apply first the Minimum Variance method to obtain the components of the magnetic field in the coordinates of the cloud, then we apply a method to calculate the MH and the F from these components, assuming only a cylindrical symmetry for the magnetic field configuration in the cloud. We compare the results obtained from our direct method with that obtained under the assumption of a helical linear force-free field (i.e., the Lundquist's solution). Our direct method is useful to compare the MH content in a given MC, with the MH variation in the solar corona before and after the associated CME. Title: 3D MHD models for XUV sigmoids Authors: Aulanier, G.; Démoulin, P.; Grappin, R.; Marqué, C. Bibcode: 2004cosp...35.3011A Altcode: 2004cosp.meet.3011A Solar sigmoids observed in XUV wavelengths have recently been identified as good probes of current-carrying magnetic fields which can precede the launch of a CME. However, the amplitude and the distribution of these pre-eruptive currents are yet very poorly known, since several 3D magnetostatic models are able to produce S-shaped field lines projected onto the photospheric plane, most of them implying that more or less twisted field lines trace the whole sigmoid. We will show two new families of magnetic models for XUV sigmoids: a generic model based on MHD calculations of line-tied twisted flux tubes, and a model for one observed sigmoid based on linear force-free field extrapolations. Both models predict that XUV sigmoids do not trace the central twisted flux tube, also that no single field line can ever trace the whole sigmoid, and finally that sigmoids may only show an ensemble of low-lying sheared field lines of various lengths, with several interruptions of connectivities all along the sigmoid depending on the shear distribution and on the local complexity of the photospheric field. So, these new models predict that sigmoids may not have a magnetic topology as simple as what is predicted by classic models, and that the derivation of the degree of twist from the shape of the sigmoid may not be directly doable, so that it may require the use of models. The 3D characteristic of these new XUV sigmoid models, combined with their synthetic transverse photospheric fields, provide new predictions and tools which will be very well suited for the analyzis of the upcoming STEREO and SOLAR-B combined observations of these structures. Title: Magnetic configuration reorganisation before the X 17 flare of October28 2003 Authors: Schmieder, B.; Mandrini, C.; Demoulin, P.; Mein, P. Bibcode: 2004cosp...35.1528S Altcode: 2004cosp.meet.1528S The active region NOAA 0486 was observed during a multi-wavelength campaign with ground based and space instruments. We analyse the magnetic configuration of the region during a pre-event, which reorganizes the magnetic connectivities of the field lines before the occurence of a X17 flare of October 28 2003. The magnetic field was observed with THEMIS and MDI, the chromosphere with the MSDP operating on on THEMIS and with the Meudon heliograph, the EUV images with SOHO/CDS and TRACE. The X17 flare gave a halo CME while the M1.9 flare has no corresponding CME. The magnetic field analysis of the active regions is performed by using a linear-force-free field code. The pre-flare event before the X17 flare change the connectivities in a first phase and allows the stressed field to relax in a second phase producing the X17 flare. Title: Observational consequences of a magnetic flux rope topology Authors: Gibson, S.; Barnes, G.; Demoulin, P.; Fan, Y.; Fisher, G.; Leka, K.; Longcope, D.; Mandrini, C.; Metcalf, T. Bibcode: 2003AGUFMSH42B0516G Altcode: We consider the implications of a magnetic flux rope topology for the interpretation of observations of sigmoidal active regions. A region of tangential magnetic discontinuities can be identified using techniques that determine a bald patch (BP) and corresponding separatrices or a quasi-separatrix layer (QSL) -- for a flux rope this region can be S-shaped, or sigmoidal. If such a region is physically driven, current sheets can form yielding conditions appropriate for reconnective heating. Using a numerical simulation of an emerging flux rope driven by the kink instability, Fan and Gibson (ApJL, 2003) showed that current sheets indeed formed a sigmoidal surface. In this poster we will demonstrate that the current sheets formed on the BP and BP separatrices. Moreover, we will use the results of the numerical simulation as proxies for observations: specifically the simulated field at the photosphere as proxy for the magnetic boundary condition, the sigmoidal current sheets as proxy for the X-ray active region emission, and the location of dipped magnetic field lines as proxy for a filament. We will then consider to what extent such observations might be used to understand and constrain the basic properties of the coronal field. Title: Magnetic helicity analysis of an interplanetary twisted flux tube Authors: Dasso, S.; Mandrini, C. H.; DéMoulin, P.; Farrugia, C. J. Bibcode: 2003JGRA..108.1362D Altcode: We compute the magnetic flux and helicity of an interplanetary flux tube observed by the spacecraft Wind on 24-25 October 1995. We investigate how model-dependent are the results by determining the flux-tube orientation using two different methods (minimum variance and a simultaneous fit), and three different models: a linear force-free field, a uniformly twisted field, and a nonforce-free field with constant current. We have fitted the set of free parameters for the six cases and have found that the two force-free models fit the data with very similar quality for both methods. Then, both the comparable computed parameters and global quantities, magnetic flux and helicity per unit length, agree to within 10% for the two force-free models. These results imply that the magnetic flux and helicity of the tube are well-determined quantities, nearly independent of the model used, provided that the fit to the data is good enough. Title: The Magnetic Helicity of an Interplanetary Hot Flux Rope Authors: Dasso, S.; Mandrini, C. H.; Démoulin, P. Bibcode: 2003AIPC..679..786D Altcode: In the last years, interest in the study of the relationship between the magnetic helicity of solar active regions and the one contained in the interplanetary structures has grown. This has lead us to compute the helicity content of an interplanetary hot tube observed by Wind on October 24-25, 1995, applying three different approaches in cylindrical geometry: a linear force-free field, a constant twist angle, and a non force-free model with constant current. We have fitted the set of free parameters for each of the three models, finding that the determined magnetic helicity values are very similar when using the same orientation for the flux tube. From our point of view, these results imply that, whatever be the model used, magnetic helicity is a well-determined quantity and, thus, it is worth using it to understand the link between solar and interplanetary phenomena. Title: Magnetic Energy and Helicity Fluxes at the Photospheric Level Authors: Démoulin, P.; Berger, M. A. Bibcode: 2003SoPh..215..203D Altcode: The source of coronal magnetic energy and helicity lies below the surface of the Sun, probably in the convective zone dynamo. Measurements of magnetic and velocity fields can capture the fluxes of both magnetic energy and helicity crossing the photosphere. We point out the ambiguities which can occur when observations are used to compute these fluxes. In particular, we show that these fluxes should be computed only from the horizontal motions deduced by tracking the photospheric cut of magnetic flux tubes. These horizontal motions include the effect of both the emergence and the shearing motions whatever the magnetic configuration complexity is. We finally analyze the observational difficulties involved in deriving such fluxes, in particular the limitations of the correlation tracking methods. Title: How are Emerging Flux, Flares and CMEs Related to Magnetic Polarity Imbalance in Midi Data? Authors: Green, L. M.; Démoulin, P.; Mandrini, C. H.; Van Driel-Gesztelyi, L. Bibcode: 2003SoPh..215..307G Altcode: 2003astro.ph..4092G In order to understand whether major flares or coronal mass ejections (CMEs) can be related to changes in the longitudinal photospheric magnetic field, we study 4 young active regions during seven days of their disk passage. This time period precludes any biases which may be introduced in studies that look at the field evolution during the short-term flare or CME period only. Data from the Michelson Doppler Imager (MDI) with a time cadence of 96 min are used. Corrections are made to the data to account for area foreshortening and angle between line of sight and field direction, and also the underestimation of the flux densities. We make a systematic study of the evolution of the longitudinal magnetic field, and analyze flare and CME occurrence in the magnetic evolution. We find that the majority of CMEs and flares occur during or after new flux emergence. The flux in all four active regions is observed to have deviations from polarity balance both on the long term (solar rotation) and on the short term (few hours). The long-term imbalance is not due to linkage outside the active region; it is primarily related to the east-west distance from central meridian, with the sign of polarity closer to the limb dominating. The sequence of short-term imbalances are not closely linked to CMEs and flares and no permanent imbalance remains after them. We propose that both kinds of imbalance are due to the presence of a horizontal field component (parallel to the photospheric surface) in the emerging flux. Title: Hyperbolic Flux Tubes in Flaring Magnetic Configurations Authors: Titov, Vyacheslav S.; Démoulin, Pascal; Hornig, Gunnar Bibcode: 2003ANS...324...17T Altcode: 2003ANS...324..B16T No abstract at ADS Title: Amplitude and orientation of prominence magnetic fields from constant-alpha magnetohydrostatic models Authors: Aulanier, G.; Démoulin, P. Bibcode: 2003A&A...402..769A Altcode: We analyze outputs from three-dimensional models for three observed filaments, which belong to the quiescent, intermediate and plage class respectively. Each model was calculated from a constant-alpha magnetohydrostatic extrapolation, assuming that the prominence material is located in magnetic dips, so that the field is nearly horizontal throughout the prominence body and feet. We calculate the spatial distribution of the magnetic field amplitude B and orientation theta with respect to the filament axis, neither of which were imposed a priori in the models. In accordance with past magnetic field measurements within prominence bodies, we also obtain nearly homogeneous magnetic fields, respectively of about B ~ 3, 14 and 40 G for the quiescent, intermediate and plage prominence, with a systematic weak vertical field gradient of partial B / partial z ~ 0.1-1.5 x 10-4 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 < +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. Bibcode: 2003ApJ...586..579V Altcode: We analyze the evolution of the fluxes observed in X-rays and correlate them with the magnetic flux density in active region (AR) NOAA 7978 from its birth throughout its decay, for five solar rotations. We use Solar and Heliospheric Observatory Michelson Doppler Imager (MDI) data, together with Yohkoh Soft X-Ray Telescope (SXT) and Yohkoh Bragg Crystal Spectrometer (BCS) data, to determine the global evolution of the temperature and the emission measure of the coronal plasma at times when no significant brightenings were observed. We show that the mean X-ray flux and derived parameters, temperature and emission measure (together with other quantities deduced from them, such as the density and the pressure), of the plasma in the AR follow power-law relationships with the mean magnetic flux density (B). The exponents (b) of these power-law functions (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. Bibcode: 2003ApJ...586..592D Altcode: We derive the dependence of the mean coronal heating rate on the magnetic flux density. Our results are based on a previous study of the plasma parameters and the magnetic flux density (B) in the active region NOAA 7978 from its birth to its decay, throughout five solar rotations using the Solar and Heliospheric Observatory Michelson Doppler Imager, Yohkoh Soft X-Ray Telescope (SXT), and Yohkoh Bragg Crystal Spectrometer (BCS). We use the scaling laws of coronal loops in thermal equilibrium to derive four observational estimates of the scaling of the coronal heating with B (two from SXT and two from BCS observations). These results are used to test the validity of coronal heating models. We find that models based on the dissipation of stressed, current-carrying magnetic fields are in better agreement with the observations than models that attribute coronal heating to the dissipation of MHD waves injected at the base of the corona. This confirms, with smaller error bars, previous results obtained for individual coronal loops, as well as for the global coronal emission of the Sun and cool stars. Taking into account that the photospheric field is concentrated in thin magnetic flux tubes, both SXT and BCS data are in best agreement with models invoking a stochastic buildup of energy, current layers, and MHD turbulence. Title: The large scale magnetic helicity content of the interplanetary magnetic cloud of October 18-19, 1995 Authors: Dasso, S.; Mandrini, C. H.; Démoulin, P.; Luoni, M. L. Bibcode: 2003BAAA...46....3D Altcode: Magnetic helicity (MH) quantifies various aspects of a given magnetic structure, such as the twist, kink, and the number of knotts between magnetic field lines, the linking between magnetic flux tubes, the shear in layers of magnetic flux, etc. MH is practically conserved in the solar atmosphere and in the heliosphere. The relation between the MH generated in the Sun and that ejected into the interplanetary medium is not yet well known. Interplanetary magnetic clouds (MCs) are huge objects that travel from the Sun toward the external heliosphere carrying an important amount of MH. Despite being expanding systems, in situ observations of their magnetic field have been frequently modelled using several different magnetohydrostatic solutions. At present, it is not at all evident which model gives the best representation of their magnetic structure. Interest has grown on both the solar physics and the interplanetary communities to study the relation between the helicity generated in the Sun and ejected into the interplanetary medium. However, detailed studies of the magnetic helicity in MCs do not yet exist. In this work we analyse the helicity content of the magnetic cloud observed by the spacecraft Wind on October 18-19, 1995; we use three different models with cylindrical symmetry (two of them are force free and the third one has constant current). We compute the free parameters for each of the three models from observations and, from the fitted values, we compute the MH and compare the results. These multi-approaches allow us to quantify the range of MH contained in the MC. We found that even if the distribution of the twist inside the MC is very different in every model, the MH is practically independent of the model. We also conclude that, due to the sensitivity of the helicity content with the radius of the cloud, it is essential to use an appropriate method in order to determine, without ambiguity, the orientation of the flux tube. Title: How to test coronal heating models? Authors: Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.; Klimchuk, J. A.; Harra, L. K. Bibcode: 2003BAAA...46....5M Altcode: We have tested coronal heating models following two different approaches. In the first case, we compared the dependence of the coronal heating rate predicted by theoretical models with the observed one, deriving the scalings of parameters, such as: the density, temperature and intensity of the coronal magnetic field, with the length of magnetic field lines. To do so, we combined density and temperature measurements for 47 coronal loops with magnetic field models for 14 active regions. In the second case, we analyzed the long term evolution of an active region observed during seven rotations on the solar disk and we determined the dependence of the observed heating rate with the magnetic field density (bar{B}), after finding the scalings of plasma parameters with bar{B}. In both cases, we found that models based on the dissipation of stressed, current-carrying magnetic fields (called direct current models) are in better agreement with observations than models that attribute coronal heating to the dissipation of MHD waves injected at the base of the corona (called alternate current models). Taking into account that the photospheric field is concentrated in thin magnetic flux tubes, observations are in best agreement with models invoking a stochastic buildup of energy, current layers and MHD turbulence, within direct current models. Title: Validation of Envisat Level-2 Products Related to Lower Atmosphere O3 and NOY Chemistry by a FTIR Quasi-Global Network (AOID126) Authors: De Maziere, M.; Coosemans, T.; Barret, B.; Blumenstock, T.; Griesfeller, A.; Demoulin, P.; Fast, H.; Griffith, D.; Jones, N.; Mahieu, E.; Mellqvist, J.; Mittermeier, R. L.; Notholt, J.; Rinsland, C.; Schulz, A.; Smale, D.; Strandberg, A.; Sussmann, R.; Wood, S.; Buchwitz, M. Bibcode: 2003ESASP.531E..40D Altcode: No abstract at ADS Title: Active region helicity evolution and related coronal mass ejection activity Authors: Green, L. M.; López Fuentes, M. C.; Mandrini, C. H.; van Driel-Gesztelyi, L.; Démoulin, P. Bibcode: 2003AdSpR..32.1959G Altcode: The computation of magnetic helicity has become increasingly important in the studies of solar activity. Observations of helical structures in the solar atmosphere, and their subsequent ejection into the interplanetary medium, have resulted in considerable interest to find the link between the amount of helicity in the coronal magnetic field and the origin of coronal mass ejections (CMEs), which provide a natural method to remove helicity from the corona. Recent works have endeavored to find the source of helicity to explain the observed CME activity in specific cases. The main candidates being differential rotation, shear motions or a transfer of helicity from below the photosphere into the corona. We study an active region for several rotations during 1997 and 1998 to investigate the relative importance of these mechanisms. We find that photospheric differential rotation cannot provide the required magnetic helicity to the corona and the ejected CMEs. Localized photospheric motions can provide a larger helicity flux, though still not sufficient. Title: Magnetic twist and writhe of active regions. On the origin of deformed flux tubes Authors: López Fuentes, M. C.; Démoulin, P.; Mandrini, C. H.; Pevtsov, A. A.; van Driel-Gesztelyi, L. Bibcode: 2003A&A...397..305L Altcode: 2014arXiv1411.5626L We study the long term evolution of a set of 22 bipolar active regions (ARs) in which the main photospheric polarities are seen to rotate one around the other during several solar rotations. We first show that differential rotation is not at the origin of this large change in the tilt angle. A possible origin of this distortion is the nonlinear development of a kink-instability at the base of the convective zone; this would imply the formation of a non-planar flux tube which, while emerging across the photosphere, would show a rotation of its photospheric polarities as observed. A characteristic of the flux tubes deformed by this mechanism is that their magnetic twist and writhe should have the same sign. From the observed evolution of the tilt of the bipoles, we derive the sign of the writhe of the flux tube forming each AR; while we compute the sign of the twist from transverse field measurements. Comparing the handedness of the magnetic twist and writhe, we find that the presence of kink-unstable flux tubes is coherent with no more than 35% of the 20 cases for which the sign of the twist can be unambiguously determined. Since at most only a fraction of the tilt evolution can be explained by this process, we discuss the role that other mechanisms may play in the inferred deformation. We find that 36% of the 22 cases may result from the action of the Coriolis force as the flux tube travels through the convection zone. Furthermore, because several bipoles overpass in their rotation the mean toroidal (East-West) direction or rotate away from it, we propose that a possible explanation for the deformation of all these flux tubes may lie in the interaction with large-scale vortical motions of the plasma in the convection zone, including also photospheric or shallow sub-photospheric large scale flows. Title: Observations of magnetic helicity Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Mandrini, C. H. Bibcode: 2003AdSpR..32.1855V Altcode: The first observational signature of magnetic helicity in the solar atmosphere (sunspot whirls) was discovered 77 years ago. Since then, the existence of a cycle-invariant hemispheric helicity pattern has been firmly established through current helicity and morphological studies. During the last years, attempts were made to estimate/ measure magnetic helicity from solar and interplanetary observations. Magnetic helicity (unlike current helicity) is one of the few global quantities that is conserved even in resistive magnetohydrodynamics (MHD) on a timescale less than the global diffusion timescale, thus magnetic helicity studies make it possible to trace helicity as it emerges from the sub-photospheric layers to the corona and then is ejected via coronal mass ejections (CMEs) into the interplanetary space reaching the Earth in a magnetic cloud. We give an overview of observational studies on the relative importance of different sources of magnetic helicity, i.e. whether photospheric plasma motions (photospheric differential rotation and localized shearing motions) or the twist of the emerging flux tubes created under the photosphere (presumably by the radial shear in the differential rotation in the tachocline) is the dominant helicity source. We examine the sources of errors present in these early results and try to judge how realistic they are. Title: Why to determine the magnetic helicity in corona and interplanetary medium? Authors: Luoni, M. L.; Dasso, S.; Mandrini, C. H.; van Driel-Gesztelyi, L.; Démoulin, P. Bibcode: 2003BAAA...46....8L Altcode: Magnetic clouds are huge objects that travel in the interplanetary medium, transporting magnetic helicity (MH) produced by the Sun. Since the dissipation time of MH is much larger than the typical time associated with the dynamical processes in the solar corona and the heliosphere, MH is the natural magnetohydrodinamic (MHD) magnitude to compare interplanetary manifestations with the associated solar processes. In this work we study an active region that produced a coronal mass ejection (CME). We model the coronal magnetic field using a linear force free approach, and we calculate the magnetic flux and the variation of MH, before and after the ejection of the CME. We model also the magnetic field configuration of the associated interplanetary cloud, using several cylindrical models, and estimate the flux and the content of MH. Finally, we compare the coronal and the interplanetary values for the flux and the MH, and we find a very good agreement. The coronal flux is 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. Bibcode: 2002ESASP.505..121M Altcode: 2002solm.conf..121M; 2002IAUCo.188..121M We study the long term evolution of a set of bipolar active regions (ARs) in which the main photospheric polarities are seen to rotate one around the other during several solar rotations. After showing that differential rotation cannot produce this large change in the tilt angle, we interpret this peculiar evolution as being the result of the emergence of magnetic flux tubes that are distorted with respect to the classical Ω-loop shape. A possible origin of this distortion is the nonlinear development of a kink-instability. Flux tubes deformed by this mechanism must have the same sign of twist and writhe. From the observed evolution of the tilt of the bipoles, we derive the sign of the writhe of the tube forming each AR; while we compute the sign of the twist from transverse field measurements. Comparing the handedness of the magnetic twist and writhe, we find that the presence of kink-unstable flux tubes is coherent with no more than 32% of the studied cases; so, a small fraction of these peculiar ARs can be explained by this process. Then we discuss the role that other mechanisms may play inducing the inferred deformation, such as the Coriolis force or external rotational motions of the plasma as the tube ascends in the convection zone. Title: The Structure and Evolution of a Sigmoidal Active Region Authors: Gibson, S. E.; Fletcher, L.; Del Zanna, G.; Pike, C. D.; Mason, H. E.; Mandrini, C. H.; Démoulin, P.; Gilbert, H.; Burkepile, J.; Holzer, T.; Alexander, D.; Liu, Y.; Nitta, N.; Qiu, J.; Schmieder, B.; Thompson, B. J. Bibcode: 2002ApJ...574.1021G Altcode: Solar coronal sigmoidal active regions have been shown to be precursors to some coronal mass ejections. Sigmoids, or S-shaped structures, may be indicators of twisted or helical magnetic structures, having an increased likelihood of eruption. We present here an analysis of a sigmoidal region's three-dimensional structure and how it evolves in relation to its eruptive dynamics. We use data taken during a recent study of a sigmoidal active region passing across the solar disk (an element of the third Whole Sun Month campaign). While S-shaped structures are generally observed in soft X-ray (SXR) emission, the observations that we present demonstrate their visibility at a range of wavelengths including those showing an associated sigmoidal filament. We examine the relationship between the S-shaped structures seen in SXR and those seen in cooler lines in order to probe the sigmoidal region's three-dimensional density and temperature structure. We also consider magnetic field observations and extrapolations in relation to these coronal structures. We present an interpretation of the disk passage of the sigmoidal region, in terms of a twisted magnetic flux rope that emerges into and equilibrates with overlying coronal magnetic field structures, which explains many of the key observed aspects of the region's structure and evolution. In particular, the evolving flux rope interpretation provides insight into why and how the region moves between active and quiescent phases, how the region's sigmoidicity is maintained during its evolution, and under what circumstances sigmoidal structures are apparent at a range of wavelengths. Title: The role of magnetic bald patches in surges and arch filament systems Authors: Mandrini, C. H.; Démoulin, P.; Schmieder, B.; Deng, Y. Y.; Rudawy, P. Bibcode: 2002A&A...391..317M Altcode: The short-lived active region (AR) NOAA 7968 was thoroughly observed all along its disk transit (June 3 to 10, 1996) from space and from the ground. During the early stage of its evolution, flux emerged in between the two main polarities and arch filament systems (AFS) were observed to be linked to this emergence. New bipoles and a related surge were observed on June 9. We have modeled the magnetic configuration of AR 7968 using a magnetohydrostatic approach and we have analyzed its topology on June 6 and June 9 in detail. We have found that some of the AFS and the surge were associated with field lines having dips tangent to the photosphere (the so called ``bald patches'', BPs). Two interacting BP separatrices, defining a separator, have been identified in the configuration where these very different events occurred. The observed evolution of the AFS and the surge is consistent with the expected results of magnetic reconnection occuring in this magnetic topology, which is specific to 3D configurations. Previously BPs have been found to be related to filament feet, small flares and transition region brightenings. Our results are evidence of the importance of BPs in a much wider range of phenomena, and show that current layers can be formed and efficiently dissipated in the chromosphere. Title: Theory of magnetic connectivity in the solar corona Authors: Titov, Vyacheslav S.; Hornig, Gunnar; Démoulin, Pascal Bibcode: 2002JGRA..107.1164T Altcode: Although the analysis of observational data indicates that quasi-separatrix layers (QSLs) of magnetic configurations have to play an important role in solar flares, the corresponding theory is only at an initial stage so far. In particular, there is still a need of a proper definition of QSLs based on a comprehensive mathematical description of magnetic connectivity. Such a definition is given here by analyzing the mapping produced by the field lines which connect photospheric areas of positive and negative magnetic polarities. It is shown that magnetic configurations may have regions, where cross sections of magnetic flux tubes are strongly squashed by this mapping. These are the geometrical features that can be identified as the QSLs. The theory is applied to quadrupole configuration to demonstrate that it may contain two QSLs combined in a special structure called hyperbolic flux tube (HFT). Both theoretical and observational arguments indicate that the HFT is a preferred site for magnetic reconnection processes in solar flares. Title: The Magnetic Helicity Budget of a cme-Prolific Active Region Authors: Green, L. M.; López fuentes, M. C.; Mandrini, C. H.; Démoulin, P.; Van Driel-Gesztelyi, L.; Culhane, J. L. Bibcode: 2002SoPh..208...43G Altcode: Coronal mass ejections (CMEs) are thought to be the way by which the solar corona expels accumulated magnetic helicity which is injected into the corona via several methods. DeVore (2000) suggests that a significant quantity is injected by the action of differential rotation, however Démoulin et al. (2002b), based on the study of a simple bipolar active region, show that this may not be the case. This paper studies the magnetic helicity evolution in an active region (NOAA 8100) in which the main photospheric polarities rotate around each other during five Carrington rotations. As a result of this changing orientation of the bipole, the helicity injection by differential rotation is not a monotonic function of time. Instead, it experiences a maximum and even a change of sign. In this particular active region, both differential rotation and localized shearing motions are actually depleting the coronal helicity instead of building it. During this period of five solar rotations, a high number of CMEs (35 observed, 65 estimated) erupted from the active region and the helicity carried away has been calculated, assuming that each can be modeled by a twisted flux rope. It is found that the helicity injected by differential rotation (≈−7×1042 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. Bibcode: 2002SoPh..207...87D Altcode: Photospheric shearing motions are one of the possible ways to inject magnetic helicity into the corona. We explore their efficiency as a function of their particular properties and those of the magnetic field configuration. Based on the work of M. A. Berger, we separate the helicity injection into two terms: twist and writhe. For shearing motions concentrated between the centers of two magnetic polarities the helicity injected by twist and writhe add up, while for spatially more extended shearing motions, such as differential rotation, twist and writhe helicity have opposite signs and partially cancel. This implies that the amount of injected helicity can change in sign with time even if the shear velocity is time independent. We confirm the amount of helicity injected by differential rotation in a bipole in the two particular cases studied by DeVore (2000), and further explore the parameter space on which this injection depends. For a given latitude, tilt and magnetic flux, the generation of helicity is slightly more efficient in young active regions than in decayed ones (up to a factor 2). The helicity injection is mostly affected by the tilt of the AR with respect to the solar equator. The total helicity injected by shearing motions, with both spatial and temporal coherence, is at most equivalent to that of a twisted flux tube having the same magnetic flux and a number of turns of 0.3. In the solar case, where the motions have not such global coherence, the injection of helicity is expected to be much smaller, while for differential rotation this maximum value reduces to 0.2 turns. We conclude that shearing motions are a relatively inefficient way to bring magnetic helicity into the corona (compared to the helicity carried by a significantly twisted flux tube). Title: Long-term helicity evolution in NOAA active region 8100 Authors: Green, L. M.; López Fuentes, M. C.; Mandrini, C. H.; van Driel-Gesztelyi, L.; Démoulin, P. Bibcode: 2002ESASP.477...43G Altcode: 2002scsw.conf...43G Magnetic helicity is the topological parameter used to describe the structure in the magnetic field and has become increasingly important in coronal studies. Helicity is well preserved in the corona even under non-ideal MHD conditions (see Biskamp 1993), and the Sun can avoid endless accumulation of helicity by ejecting it via the launch of coronal mass ejections (eg. Rust 1994; Low 1996; Devore 2000). Computations are made for NOAA active region 8100 to determine the coronal helicity and helicity injected into the region by differential rotation. These values are then compared to the total amount of helicity lost via coronal mass ejections to test whether differential rotation can inject a significant amount of helicity into the corona. It is found that differential rotation cannot inject a significant amount of helicity to be a viable source for the coronal mass ejection activity. Instead, helicity is likely to be brought into the corona by the emergence of twisted and distorted flux tubes. Title: The distribution of peculiar active regions along two solar cycles Authors: Mandrini, C. H.; López Fuentes, M. C.; Démoulin, P.; van Driel-Gesztelyi, L. Bibcode: 2002ESASP.477...27M Altcode: 2002scsw.conf...27M We perform a statistical study of the spatial and temporal distribution of "peculiar" active regions (ARs) along solar cycles 21 and 22. ARs usually appear in the photosphere in the form of bipolar concentrations of magnetic flux, by "peculiar" we mean regions in which the the main polarities rotate one around the other along several solar rotations. Our results show that these regions are spatially distributed as usual ARs when no selection on their magnetic flux is applied. When classified according to their flux, the latitudinal distribution of ARs above 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. Bibcode: 2002A&A...382..650D Altcode: An isolated active region (AR) was observed on the Sun during seven rotations, starting from its birth in July 1996 to its full dispersion in December 1996. We analyse the long-term budget of the AR relative magnetic helicity. Firstly, we calculate the helicity injected by differential rotation at the photospheric level using MDI/SoHO magnetograms. Secondly, we compute the coronal magnetic field and its helicity selecting the model which best fits the soft X-ray loops observed with SXT/Yohkoh. Finally, we identify all the coronal mass ejections (CMEs) that originated from the AR during its lifetime using LASCO and EIT/SoHO. Assuming a one to one correspondence between CMEs and magnetic clouds, we estimate the magnetic helicity which could be shed via CMEs. We find that differential rotation can neither provide the required magnetic helicity to the coronal field (at least a factor 2.5 to 4 larger), nor to the field ejected to the interplanetary space (a factor 4 to 20 larger), even in the case of this AR for which the total helicity injected by differential rotation is close to the maximum possible value. However, the total helicity ejected is equivalent to that of a twisted flux tube having the same magnetic flux as the studied AR and a number of turns in the interval [0.5,2.0]. We suggest that the main source of helicity is the inherent twist of the magnetic flux tube forming the active region. This magnetic helicity is transferred to the corona either by the continuous emergence of the flux tube for several solar rotations (i.e. on a time scale much longer than the classical emergence phase), or by torsional Alfvén waves. Title: Properties of bipolar active regions through two and a half solar cycles Authors: Villar, P. I.; López Fuentes, M. C.; Mandrini, C. H.; Démoulin, P. Bibcode: 2002BAAA...45...22V Altcode: Hale's Law (Hale & 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 & 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 & McClymont for the tilt angle, latitude and magnetic flux. Consequently, we found that the tilt angle holds a linear dependence with the sin(λ) and the value of α is 0.22. Our results constrain the validity of theoretical and numerical models of the solar dynamo and flux tube emergence. Title: Relation between the coronal magnetic helicity to the helicity in interplanetary magnetic clouds Authors: Luoni, M. L.; Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.; López Fuentes, M. C. Bibcode: 2002BAAA...45...20L Altcode: On October 18, 1995, the Solar Wind Experiment and the Magnetic Field Instrument on board the WIND spacecraft registered a magnetic cloud at 1 AU, which was followed by a strong geomagnetic storm. The solar source of this phenomenon was located in active region (AR) NOAA 7912. On October 14, 1995, a C1.6 long duration event (LDE) started at approximately 5:00 UT and lasted for around 15 hours. In this work, we compute the variation of the coronal magnetic helicity using a linear force-free model of the field. We use magnetograms obtained at Kitt Peak National Solar Observatory as boundary conditions to extrapolate the photospheric magnetic field to the corona. The magnetic helicity is calculated at three different times, changing the parameters of the magnetic field model to fit the loops observed in soft X-rays by the Soft X-ray Telescope on board of Yohkoh (SXT/Yohkoh). The computations are done before the LDE, during its maximun and its decay phase. The variation of the coronal magnetic helicity is compared to the helicity of the interplanetary magnetic cloud observed by WIND. These values turn out to be quite similar, considering the errors involved. Our results confirm quantitatively the link between solar and interplanetary phenomena. Title: Active region helicity evolution and related coronal mass ejection activity. Authors: Green, L.; Mandrini, C.; van Driel-Gesztelyi, L.; Demoulin, P. Bibcode: 2002cosp...34E1213G Altcode: 2002cosp.meetE1213G The computation of magnetic helicity has become increasingly important in the studies of solar activity. Observations of helical structures in the solar atmosphere, and their subsequent ejection into the interplanetary medium, have resulted in considerable interest to find the link between the amount of helicity in the coronal magnetic field and the origin of coronal mass ejections (CMEs). This is reinforced by theory which shows magnetic helicity to be a well preserved quantity (Berger, 1984), and so with a continued injection into the corona an endless accumulation will occur. CMEs therefore provide a natural method to remove helicity from the corona. Recent works (DeVore, 2000, Chae, 2001, Chae et al., 2001, Demoulin et al., 2002, Green et al., 2002) have endeavoured to find the source of helicity in the corona to explain the observed CME activity in specific cases. The main candidates being differential rotation, shear motions or a transfer of helicity from below the photosphere into the corona. In order to establish a confident relation between CMEs and helicity, these works needs to be expanded to include CME source regions with different characteristics. A study of a very different active region will be presented and the relationship between helicity content and CME activity will be discussed in the framework of the previous studies. Title: Energetics of the 18 May 1994 brightening event Authors: Tang, Y. H.; Li, Y. N.; Fang, C.; Schmieder, B.; Aulanier, G.; Demoulin, P. Bibcode: 2002AdSpR..30..557T Altcode: By using YOHKOH soft X-ray images, vector magnetograms and Hα filtergrams, the energetics of the brightening event of May 18, 1994 has been studied. It occurred in a nearly potential magnetic configuration as shown by the comparison between the magnetic extrapolation(linear force free field) and the large scale soft X-ray loops. This event is related to the emergence of a new magnetic flux. The brightening points of Hα and soft X-ray are located at computed separatrices associated with field lines which are tangent to the photosphere. This brightening may be a signature of reconnection taking place between the pre-existing non-potential loops and the new emerging small loops. The magnetic energy provided by reconnection is likely to be stored in the non-potential loops and shearing emerging flux. A phenomenological model is offered. Title: Helicity Loading and Dissipation: The Helicity Budget of AR 7978 from the Cradle to the Grave Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Mandrini, C. H.; Plunkett, S.; Thompson, B.; Kövári, Zs.; Aulanier, G.; Young, A.; López Fuentes, M.; Poedts, S. Bibcode: 2002mwoc.conf..143V Altcode: An isolated active region was observed on the Sun during seven rotations, starting in July 1996. I will present a study of its magnetic field, concentrating on its helicity budget. The photospheric field is extrapolated into the corona in a linear force-free approach, using SOHO/MDI magnetograms and Yohkoh/SXT images, allowing us to compute, in a crude way, the relative coronal magnetic helicity of the active region. Using the observed magnetic field distribution (SOHO/MDI magnetograms) we also calculate the helicity injected by the differential rotation during seven solar rotations. Finally, using SOHO/LASCO and EIT as well as Yohkoh/SXT observations, we identify all the 26 CMEs which originated from this active region during its lifetime and using average values of the field and radius of magnetic clouds, we estimate the helicity which should be shed via CMEs. We compare these three values to evaluate the importance of the differential rotation relative to twisted flux emergence as a source of magnetic helicity. We find that the differential rotation can neither provide enough helicity to account for the diagnosed coronal heicity values, nor for the helicity carried away by CMEs. We suggest that the main source of the magnetic helicity must be the inherent twist of the magnetic flux tube forming the active region. This magnetic helicity is transferred to the corona either by a slow continuous emergence of the flux tube or by torsional Alfven waves, during several solar rotations. Title: Surges y Arch Filament Systems: Una topología inusual Authors: Mandrini, C. H.; Démoulin, P.; Schmieder, B.; Deng, Y. Y.; Rudawy, P. Bibcode: 2002BAAA...45...17M Altcode: Active region (AR) NOAA 7968 was observed during its solar disk transit by several instruments on ground and on board satellites (Yohkoh and SOHO). During its emergence Arch Filament Systems (AFS) linking the polarities of the main bipole were observed. During its decay a surge (a chromospheric confined mass ejection) occurred to the South of the positive polarity of this bipole. We model the AR magnetic field in the magnetohydrostatic approach and compute its topology. We find that the evolution of both events, AFS and surge, agrees with magnetic field reconnection occurring in field lines that are tangentially touching the photosphere. These lines define the so called ``bald patches'' (BPs). In previous studies these topological structures have been found to be related to small flares and transition region brightenings. Our results point out the importance of BPs in a wider phenomenological context and show that current sheets can develop and efficiently dissipate in the chromosphere. Title: Inferring the Writhe of Emerging Flux Tubes from the Evolution of the Orientation of Bipole Axes Authors: López Fuentes, M. C.; Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.; Pevtsov, A. Bibcode: 2002RMxAC..14..108L Altcode: No abstract at ADS Title: High Resolution Observations of Reconnected Magnetic Loops Authors: Luoni, M. L.; Mandrini, C. H.; Karim, Y.; Schieder, B.; Démoulin, P. Bibcode: 2002RMxAC..14Q.107L Altcode: No abstract at ADS Title: Magnetic helicity in interplanetary structures of solar origin Authors: Dasso, S.; Mandrini, C. H.; Démoulin, P. Bibcode: 2002BAAA...45...15D Altcode: Interplanetary manifestations of transient coronal mass ejections (so called ICMEs) form helical structures of magnetic flux that travel through the solar wind from the Sun toward the outer heliosphere. The global magnetic helicity (MH) contained in these huge structures, whose typical length when pass near Earth is of the order of an astronomical unit, plays a very important role in the understanding of the solar-terrestrial relationship. Moreover, the study of MH is crucial in order to link solar active regions with their corresponding interplanetary flux tubes. MH is one of the few global quantities conserved even under non-ideal MHD. In spite of its importance do not yet exist exhaustive studies that estimate the content of MH in ICMEs. In spite of ICMEs are structures out of equilibrium, generally ICMEs are modeled using three different MHD models with cylindrical geometry: linear force-free field, constant twist angle, and non force-free model with constant current. In this work, we derive analytically the expressions to calculate the MH for every of the three models mentioned before, and also present numerical results for a hot flux tube observed by the spacecraft Wind on October 24-25, 1995. We have fitted the set of free parameters for every model, finding that the derived MHs are very similar. Thus, our results support that the MH in ICMEs is a well-determined quantity what do not depend of the assumed model, being very valuable in order to get insight of the link between solar and interplanetary phenomena. Title: Peculiar Active Regions during the Last Two Solar Cycles Authors: López Fuentes, M. C.; Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L. Bibcode: 2002RMxAC..14R.107L Altcode: No abstract at ADS Title: Relationships between CME's and prominences Authors: Schmieder, B.; van Driel-Gesztelyi, L.; Aulanier, G.; Démoulin, P.; Thompson, B.; De Forest, C.; Wiik, J. E.; Saint Cyr, C.; Vial, J. C. Bibcode: 2002AdSpR..29.1451S Altcode: We have studied the erupting prominences which were associated with coronal mass ejections during a series of campaigns involving both spacecraft and ground-based observatories. The evolution of the physical conditions within the prominences was established from Hα and magnetic field observations. Particular attention ahs been paid to the presence of mixed amgnetic polarity in the filament channel, the evolution of the shear of the large-scale magnetic field, and the existence of multiple magnetic inversion lines. We conclude that reconnection of large-scale coronal magnetic fields is responsible for both the CME and filament eruption. Title: A Relationship Between Transition Region Brightenings, Abundances, and Magnetic Topology Authors: Fletcher, Lyndsay; López Fuentes, Marcelo C.; Mandrini, Cristina H.; Schmieder, Brigitte; Démoulin, Pascal; Mason, Helen E.; Young, Peter R.; Nitta, Nariaki Bibcode: 2001SoPh..203..255F Altcode: We present multi-instrument observations of active region (AR) 8048, made between 3 June and 5 June 1997, as part of the SOHO Joint Observing Program 33. This AR has a sigmoid-like global shape and undergoes transient brightenings in both soft X-rays and transition region (TR) lines. We compute a magneto-hydrostatic model of the AR magnetic field, using as boundary condition the photospheric observations of SOHO/MDI. The computed large-scale magnetic field lines show that the large-scale sigmoid is formed by two sets of coronal loops. Shorter loops, associated with the core of the SXT emission, coincide with the loops observed in the hotter CDS lines. These loops reveal a gradient of temperature, from 2 MK at the top to 1 MK at the ends. The field lines most closely matching these hot loops extend along the quasi-separatrix layers (QSLs) of the computed coronal field. The TR brightenings observed with SOHO/CDS can also be associated with the magnetic field topology, both QSL intersections with the photosphere, and places where separatrices issuing from bald patches (sites where field lines coming from the corona are tangent to the photosphere) intersect the photosphere. There are, furthermore, suggestions that the element abundances measured in the TR may depend on the type of topological structure present. Typically, the TR brightenings associated with QSLs have coronal abundances, while those associated with BP separatrices have abundances closer to photospheric values. We suggest that this difference is due to the location and manner in which magnetic reconnection occurs in two different topological structures. Title: Measurement of coronal magnetic twists during loop emergence of NOAA 8069 Authors: Portier-Fozzani, F.; Aschwanden, M.; Démoulin, P.; Neupert, W.; EIT Team; Delaboudinière, J. -P. Bibcode: 2001SoPh..203..289P Altcode: Emerging coronal loops were studied with extreme ultraviolet observations performed by SOHO/EIT on 5 and 6 August 1997 for NOAA 8069. Physical parameters (size and twist) were determined by a new stereoscopic method. The flux tubes were measured twisted when first observed by EIT. After emerging, they de-twisted as they expanded, which corresponds to a minimization of the energy. Different scenarios which take into account the conservation of the magnetic helicity are discussed in relation with structure and temperature variations. Title: Long-Term Evolution of Active Regions Authors: López Fuentes, M.; Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L. Bibcode: 2001ASPC..248..131L Altcode: 2001mfah.conf..131L No abstract at ADS Title: CDS UV Brightenings Explained by Quasi-separatrices and Bald Patches in an S-shape active region Authors: Schmieder, B.; Démoulin, P.; Fletcher, L.; López Fuentes, M. C.; Mandrini, C. H.; Mason, H. E.; Young, P. R.; Nitta, N. Bibcode: 2001IAUS..203..314S Altcode: We present multi-instrument observations of AR 8048, made between June 3 and June5 1997 as part of SoHO JOP033. This active region has a sigmoid-like global shape and undergoes transient erupting phenomena which releases the stored energy. Using a force free field approach, we defined coronal magnetic field lines which fit with the observations. The large-scale magnetic field lines confirms the sigmoid characteristics of the active region. The study in 3D of the configuration explained where and how the energy is released at different places. The Ne VI brightenings correspond to the location of tangent to the photosphere field lines, named "bald patch", they are localized in the low transition region and represent feet of field lines. The Si XII brightenings at coronal temperature are at the top of coronal loops joining quasi-separatrices. Title: An Observational Test for Solar Atmospheric Heating Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Ireland, J.; Thompson, B.; Fludra, A.; Oláh, K.; Kövári, Zs.; Harra, L. K.; Mandrini, C. H.; Bocchialini, K.; Orlando, S. Bibcode: 2001IAUS..203..514V Altcode: We study the evolution of the emissivity and heating correlated with magnetic observables of an active region from its birth throughout its decay during seven solar rotations (July-Dec. 1996). Taking one "snapshot" per g:wq: Command not found. time of flares, we analyse multi-wavelength and multi-instrument data obtained from SOHO (MDI, EIT, CDS and SUMER), Yohkoh (SXT), GOES, SOLSTICE and 10.7 cm radio data from DRAO, Canada. We utilise our results to test the validity of coronal heating models. We find that models which are based on the dissipation of stressed, current-carrying magnetic fields are in better agreement with the observations than the models which attribute coronal heating to the dissipation of MHD waves. Title: Magnetic Evolution of a Long-Lived Active Region: The Sources of Magnetic Helicity Authors: Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.; Aulanier, G.; Thompson, B.; Plunkett, S.; Kövári, Zs. Bibcode: 2001ASPC..248..139M Altcode: 2001mfah.conf..139M No abstract at ADS Title: Emergence of a U-loop - sub-photospheric link between solar active regions Authors: van Driel-Gesztelyi, L.; Malherbe, J. -M.; Démoulin, P. Bibcode: 2000A&A...364..845V Altcode: Using SOHO/MDI magnetic maps we present the first direct observational evidence for the emergence of a U-loop in the solar photosphere. We show that two active regions (ARs), i.e. two adjacent Omega -loops, which were emerging at the same time at the same solar latitude, about 150000 km distance in longitude from each other, emerged from at least partially the same toroidal flux strand, and we bring five independent arguments to prove this assertion. The opposite polarity legs of the two Omega -loops were connected below the photosphere by a U-shaped loop. Following the emergence of the Omega -loops, the U-loop started emerging, manifested by the fast proper motion of the leading spots of the eastern (smaller) active region, which, after forming an elongated channel, collided with the following spots of the westerly AR and started cancelling with them. The full cancellation could not be followed because the ARs rotated out of sight. The total magnetic flux of the two ARs was unequal, the flux in the smaller AR was a quarter of that of the larger one. We propose scenarios for the formation of such a U-loop and discuss the implications of the confirmed existence of U-loops for the solution of such puzzles as the in-situ disappearance of magnetic flux from active regions, active nests and the formation of inter-AR filaments. Title: Magnetic reconnection: a common origin for flares and AR interconnecting arcs Authors: Bagalá, L. G.; Mandrini, C. H.; Rovira, M. G.; Démoulin, P. Bibcode: 2000A&A...363..779B Altcode: We present a study of active region (AR) 7031, where several flares occurred throughout the last week of January, 1992. We analyze in detail the three largest flares, both in Hα and soft X-rays. During its transit across the disk this region interacted with another one (AR 7038), as indicated by the recurrent brightening in soft X-rays of an interconnecting loop, accompanied by sympathetic flaring. Using a linear force free extrapolation of the photospheric magnetic field, we compute the locations of Quasi-Separatrix Layers (QSLs), which are the likely places where the magnetic field can reconnect. We find that flare brightenings can be linked by field lines having footpoints at the QSLs. Furthermore, field lines connecting AR 7031 and AR 7038 belong to the QSLs computed when magnetograms from both ARs are combined. We conclude that both soft X-ray flare loops and interconnecting loops result from magnetic reconnection at the QSLs. Which of the many QSLs found in the computations are the site of magnetic reconnection depends on the magnetic field evolution. In the studied ARs we can identify three different drivers for energy release: flux emergence, photospheric displacements of the polarities and nearby magnetic reconnection. This last process leads to sympathetic flaring and to the brightness enhancement of the interconnecting arc. Title: Initiation of CMEs: the role of magnetic twist Authors: van Driel-Gesztelyi, L.; Manoharan, P. K.; Démoulin, P.; Aulanier, G.; Mandrini, C. H.; Lopez-Fuentes, M.; Schmieder, B.; Orlando, S.; Thompson, B.; Plunkett, S. Bibcode: 2000JASTP..62.1437V Altcode: 2000JATP...62.1437V Recent multiwavelength observations, modelling results and theoretical developments indicate the importance of twisted magnetic configurations in solar active regions (ARs) in the initiation of coronal mass ejections (CMEs). Through multiwavelength analysis of a few representative events we make an attempt to provide constraints for CME models. The two events presented here in detail start with the expansion of sigmoids (S- or inverse S-shaped loops) observed in soft X-rays. Both events (on 25 October /1994 and 14 October /1995) occurred before the launch of the SOHO spacecraft, but indirect evidences (i.e. signatures of an outward propagation traced up to /~20 solar radii and an associated magnetic cloud) suggest that both of them were related to CMEs. We show evidence that sigmoids are the coronal manifestations of twisted magnetic flux tubes, which start expanding presumably due to a loss of equilibrium. It is noteworthy that the analysed CMEs occurred in a complex (not simply bipolar) magnetic environment and in all cases we found evidences of the interaction (magnetic reconnection) with the surrounding fields. We propose a scenario for sigmoid expansion related CME events and suggest that twisted magnetic configurations are good candidates for being source regions of CMEs. Title: The Counterkink Rotation of a Non-Hale Active Region Authors: López Fuentes, M. C.; Demoulin, P.; Mandrini, C. H.; van Driel-Gesztelyi, L. Bibcode: 2000ApJ...544..540L Altcode: 2014arXiv1412.1456L We describe the long-term evolution of a bipolar non-Hale active region that was observed from 1995 October to 1996 January. During these four solar rotations the sunspots and subsequent flux concentrations, during the decay phase of the region, were observed to move in such a way that by December their orientation conformed to the Hale-Nicholson polarity law. The sigmoidal shape of the observed soft X-ray coronal loops allows us to determine the sense of the twist in the magnetic configuration. This sense is confirmed by extrapolating the observed photospheric magnetic field, using a linear force-free approach, and comparing the shape of computed field lines with the observed coronal loops. This sense of twist agrees with that of the dominant helicity in the solar hemisphere where the region lies, as well as with the evolution observed in the longitudinal magnetogram during the first rotation. At first sight the relative motions of the spots may be misinterpreted as the rising of an Ω loop deformed by a kink instability, but we deduce from the sense of their relative displacements a handedness for the flux-tube axis (writhe) that is opposite to that of the twist in the coronal loops and, therefore, to what is expected for a kink-unstable flux tube. After excluding the kink instability, we interpret our observations in terms of a magnetic flux tube deformed by external motions while rising through the convective zone. We compare our results with those of other related studies, and we discuss, in particular, whether the kink instability is relevant to explain the peculiar evolution of some active regions. Title: Hα and Soft X-Ray Brightening Events Caused by Emerging Flux Authors: Tang, Y. H.; Li, Y. N.; Fang, C.; Aulanier, G.; Schmieder, B.; Demoulin, P.; Sakurai, T. Bibcode: 2000ApJ...534..482T Altcode: By using Yohkoh soft X-ray images, vector magnetograms, and Hα filtergrams, the brightening event that occurred on 1994 May 18 has been studied in detail. It occurred in a nearly potential large-scale magnetic configuration as shown by the comparison between the magnetic extrapolation (linear force-free field) and the large-scale soft X-ray loops. This event is related to the emergence of a new magnetic flux of about 3×1020 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. Bibcode: 2000SoPh..193..227B Altcode: As it crossed the solar disk in May and June 1998, AR 8227 was tracked by TRACE, Yohkoh, SOHO, and many ground-based observatories. We have studied how the evolution of the magnetic field resulted in changes in activity in the corona. In particular, we examine how the evolving field may have led to the acceleration of electrons which emit noise storms observed by the Nançay Radio Heliograph between 30 May and 1 June 1998, in the absence of any flare. The magnetic changes were related to moving magnetic features (MMFs) in the vicinity of the leading spot and are related to the decay of this spot. Within the limits of the instrumental capabilities, the location in time and space of the radio emissions followed the changes observed in the photospheric magnetograms. We have extrapolated the photospheric magnetic field with a linear force-free approximation and find that the active region magnetic field was very close to being potential. These computations show a complex magnetic topology associated to the MMFs. The observed photospheric evolution is expected to drive magnetic reconnection in such complex magnetic topology. We therefore propose that the MMFs are at the origin of the observed metric noise-storms. Title: Magnetic Field and Plasma Scaling Laws: Their Implications for Coronal Heating Models Authors: Mandrini, C. H.; Démoulin, P.; Klimchuk, J. A. Bibcode: 2000ApJ...530..999M Altcode: In order to test different models of coronal heating, we have investigated how the magnetic field strength of coronal flux tubes depends on the end-to-end length of the tube. Using photospheric magnetograms from both observed and idealized active regions, we computed potential, linear force-free, and magnetostatic extrapolation models. For each model, we then determined the average coronal field strength, <B>, in approximately 1000 individual flux tubes with regularly spaced footpoints. Scatter plots of <B> 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<=C3<=-1, and 40<=S<=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, <B2>, exhibits a similar behavior, with only C3 being significantly different. For flux tubes of intermediate length, 50<=L<=300 Mm, corresponding to the soft X-ray loops in a study by Klimchuk & Porter (1995), we find a universal scaling law of the form ~Lδ, where δ=-0.88+/-0.3. By combining this with the Klimchuk & 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. Bibcode: 2000AdSpR..25.1829T Altcode: By using Yohkoh soft X-ray images, vector magnetograms and Hα filtergrams, a brightening event that occurred on May 18, 1994 has been studied in detail. It occurred in a nearly potential large-scale magnetic configuration as shown by the comparisons between the magnetic extrapolations (linear force-free field) and the large-scale soft X-ray loops. This brightening event observed in Hα line and soft X-ray seems to be related to new emerging magnetic flux with an amount of photospheric magnetic flux of about 3× 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. Bibcode: 2000AdSpR..26..485A Altcode: The 3-D magnetic configuration of a filament and of a low energy flare is reconstructed, using linear mag- netohydrostatic (lmhs) extrapolations. In both cases, we find observational signatures of energy release at the locations of computed ``bald patches'' separatrices, characterised by field lines which are tangent to the photosphere.The filament was observed on Sept. 25, 1996, in Hα with the MSDP on the German VTT, Tenerife, as well as in Si IV with SOHO/SUMER. It is modeled as a twisted flux-tube deformed by the magnetic polarities observed with SOHO/MDI. The shape and location of the computed dipped field lines are in good agreement with the shape of the filament and its feet observed in Hα. Some ``bald patches'' (BPs) are present where the distribution of dips reaches the photosphere. We show that some of the large scale field lines rooted in BPs can be related to bright fine structures in Si IV. We propose that the plasma there is heated by ohmic dissipation from the currents expected to be present along the BP separatrices.The flare was observed on May 18, 1994, in soft X-rays with Yohkoh/SXT, and in Hα at Mitaka (Japan). The magnetic field is directly extrapolated from a photospheric magnetogram from Kitt Peak Observatory. The intersections with the photosphere of the computed separatrices match well the bright Hα ribbons. The later are associated to three BPs, with overlaying dipped field lines. We show that enhanced densities are present in these dips, which can be correlated with dark Hα fibrils.Both cases show the importance of dipped field lines and BPs in the solar atmosphere. Energy release via ohmic dissipation as well as reconnection along BP separatrices is proposed to provide heating observed as UV brightenings in filament channels and even as small flares Title: Structuring of the Solar Plasma by the Magnetic Field Authors: Demoulin, Pascal; Klein, Karl-Ludwig Bibcode: 2000LNP...553...99D Altcode: 2000tech.conf...99D This paper presents a simplified overview of the role of the magnetic field in the solar atmosphere. The magnetic field emanating from the solar interior governs energy transport and plasma motions in the outer solar atmosphere. Thereby it creates structure, such as coronal holes, loops and prominences, and the dynamical phenomena known as coronal mass ejections and flares. The magnetic field is also thought to be at the origin of the coronal heating, so of the corona itself. An overview of atmospheric structure is presented, followed by illustrations on present ideas on the interaction between plasma and magnetic field. The physical conditions in the corona are briefly compared to those in the magnetosphere. The emphasis is then put on the energetic processes from the largest ones (coronal mass ejections) over flares and X-ray bright points to coronal heating. In all cases magnetic reconnection is likely to play a key role. Solar prominences are then described because their observations provide important information on the surrounding coronal magnetic field. Finally the implications of processes in the convection zone on the physics of the corona and of the interplanetary medium are illustrated for the case of formation, storage and ejection of twisted magnetic flux tubes. Title: What Can we Learn Studying Long-Term Magnetic Evolution of Solar Active Regions? Authors: van Driel-Gesztelyi, L.; Kovari, Zs.; Lopez-Fuentes, M.; Mandrini, C. H.; Demoulin, P. Bibcode: 2000ESASP.463..451V Altcode: 2000sctc.proc..451V No abstract at ADS Title: Test on the parameter dependence of coronal heating models Authors: Démoulin, P.; Mandrini, C. H.; Klimchuk, J. A. Bibcode: 2000ssls.work...85D Altcode: The motivation of this work has been to provide observational constraints on coronal heating models by testing their predictions for the heating rate as a function of several physical parameters. In Mandrini et al. (1999), we have investigated how the magnetic field strength, , of coronal flux tubes depends on the end-to-end length, L, of the tube. For flux tubes of intermediate length, 50 ≤ L ≤ 300 Mm, corresponding to the soft X-ray loops in a study by Klimchuk & Porter (1995), we find a universal scaling law of the form ∝Lδ, where δ= -0.88±0.3. By combining this with the Klimchuk & 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. Bibcode: 1999ESASP.448..915P Altcode: 1999ESPM....9..915P; 1999mfsp.conf..915P No abstract at ADS Title: Interpretation of the Activity due to Flux Emergence in an AR Authors: Mandrini, C. H.; Démoulin, P.; Schmieder, B.; Deng, Y. Y.; Rudawy, P. Bibcode: 1999ESASP.448..617M Altcode: 1999ESPM....9..617M; 1999mfsp.conf..617M No abstract at ADS Title: Basic topology of twisted magnetic configurations in solar flares Authors: Titov, V. S.; Démoulin, P. Bibcode: 1999A&A...351..707T Altcode: It is accepted now that flare-like phenomena are the result of reconnection of topologically complex magnetic fields. Observations show that such fields are often characterized by a twisted structure. This is modeled here using a force-free flux tube whose arc-like body is embedded into an external potential magnetic field. We study how the topological structure of this configuration evolves when the flux tube emerges quasi-statically from below the photosphere to a certain height in the corona, where the tube becomes unstable and its eruption has to occur. During this evolution below the flux tube there appears a separator field line, along which two separatrix surfaces intersect. This separator is of generalized type because there are no magnetic nulls in the configuration. Both the separator and the separatrices are topological features, where the connectivity of magnetic field lines suffers a jump. We propose that the eruption of the flux tube has to stimulate the formation of strong current layers, in which the free magnetic energy of configuration is released in the form of a flare. The model predicts the formation of hot loops of two kinds during the reconnection phase: the long loops which make nearly one turn around the twisted flux tube, and short sheared loops below. The proposed model provides important clues to the mechanism of solar flares in twisted configurations. Title: Long-Term Evolution Of Emissivity And Heating In A Solar Active Region Authors: van Driel-Gesztelyi, L.; Thompson, B.; Démoulin, P.; Orlando, S.; Bocchialini, K.; Oláh, K.; Kövári, Z.; Deforest, C.; Khan, J.; Fludra, A.; Mandrini, C. Bibcode: 1999ESASP.446..663V Altcode: 1999soho....8..663V We study the evolution of the heating and emissivity of an active region from its birth throughout its decay during six solar rotations (July-Nov. 1996). We analyse multi-wavelength and multi-instrument data obtained from SOHO (EIT, SUMER, CDS, MDI), Yohkoh (SXT), GOES and 10.7cm radio data from DRAO, Canada. We take one "snapshot" per rotation at the time of the central meridian passage (CMP) of the AR, outside of time of flares, which appears to be representative enough to allow us to make some general conclusions about the long-term evolution. Deriving physical parameters like intensity (flux), temperature and emission measure of the entire AR vs. time, we formulate mathematically the change in radiation emitted by the decaying AR at several wavelengths. Combining the emissivity data with the evolution of magnetic flux density as the flux is being dispersed by small- and larger-scale convective motions, we make an attempt to understand the physics behind the emission and heating. We also analyse the effects of flaring on the heating of the AR, and study whether and how the flare properties evolve during the life of the active region. Title: The Role of "Magnetic Dips" and "Bald Patches" for a Filament Observed by SOHO and GBO Authors: Aulanier, G.; Schmieder, B.; Kucera, T.; van Driel-Gesztelyi, L.; Démoulin, P.; Mein, N.; Vial, J. -C.; Mein, P. Bibcode: 1999ASPC..184..291A Altcode: The studied filament was observed on Sept. 25, 1996, in Hα with the MSDP on the German VTT, Tenerife, as well as in Si IV with SOHO/SUMER. The 3-D magnetic configuration of the filament channel is reconstructed, using linear magnetohydrostatic (lmhs) extrapolations from a SOHO/MDI magnetogram, which is modified by a background magnetic component constraining a twisted flux-tube. This flux-tube is deformed by the magnetic polarities observed with SOHO/MDI. The shape and location of the computed "dipped field lines" are in good agreement with the shape of the filament and its feet observed in Hα. Some "bald patches" (BPs) are present where the distribution of dips reaches the photosphere. We find observational signatures in Si IV brightenings of energy release at the locations of computed "bald patch separatrices", defined by field lines which are tangent to the photosphere. We propose that the plasma is there heated by ohmic dissipation from the expected currents in the BP separatrices. The results show the importance of "dipped field lines" and "bald patches" in filament channels. Title: Magnetic Field Evolution and Topology of an AR Authors: Mandrini, C. H.; Deng, Y. Y.; Schmieder, B.; Démoulin, P.; Rudawy, P.; Nitta, N.; Newmark, J.; de Forest, C. Bibcode: 1999ASPC..184..276M Altcode: Active region 7968 was observed during runs of a coordinated SOHO, Yohkoh and ground-based observatory program (Joint Observing Program, JOP, 17). The region appeared and decayed in a seven day period (June 3 to 10, 1996). In this time, mainly during June 6, it presented a very dynamical behaviour. Flux emerged in between the two main polarities and Arch Filament Systems (AFS) were observed to be linked to this emergence. We analyze the evolution of some over dark arches observed during flux emergence, forming two systems of AFS. Modelling the magnetic field, we find that these systems were associated to field lines having dips tangent to the photosphere (the so called "bald patches", BPs). We discuss their evolution in terms of emergence of the dipped portion of the lines or of magnetic field reconnection. Title: Long-Term Magnetic Evolution of an AR and its CME Activity Authors: van Driel-Gesztelyi, L.; Mandrini, C. H.; Thompson, B.; Plunkett, S.; Aulanier, G.; Démoulin, P.; Schmieder, B.; de Forest, C. Bibcode: 1999ASPC..184..302V Altcode: Using SOHO/MDI full-disc magnetic maps, we follow the magnetic evolution of a solar active region for several months in the period of July-November 1996. We extrapolate the photospheric magnetic fields in the linear force-free approximation and match the modelled field lines with the soft X-ray loops observed with the Yohkoh/SXT in order to diagnose the coronal magnetic shear. We find that while the turbulent motions diffuse the flux, the differential rotation, and possibly twisted flux emergence, increase the magnetic shear. Flares are observed during the first three rotations, while CME events (observed by SOHO/EIT and LASCO) originate from this AR from its emergence throughout its decay. Several early CMEs, while none of the late CMEs, are related to flare events above the GOES B1 level. We find that the late CMEs occur when the magnetic shear, after accumulating for four rotations, reaches a high level and saturates. We propose that CME activity serves as a valve through which the AR could get rid of excess shear and helicity. Title: The Magnetic Topology of a Twisted Force-Free Configuration in an Active Region Authors: Titov, V. S.; Démoulin, P. Bibcode: 1999ASPC..184...76T Altcode: It is widely accepted now that flare-like phenomena in active regions are due to magnetic reconnection process in configurations having a topological complexity. Observations demonstrate that such configurations are often characterized by a twisted structure. It is modeled here by a force-free flux tube, whose curved arc-like body is in equilibrium with an external potential magnetic field. We study how the topological structure of this configuration evolves with emerging of the flux tube from below the photosphere until it achieves a nonequilibrium point, where the eruption of the flux tube must occur. At some moment of the emergence process there appears a generalized separator field line, which is determined without null points and along which two separatrix surfaces intersect. Both the separator and these surfaces are topological features, where the magnetic connectivity suffers a jump, which may cause the formation of strong current sheets there. The obtained results give a good insight into the mechanism of solar flares with a twisted magnetic field structure. Title: The evolution from birth to decay of a short-lived active region Authors: Deng, Yuan Yong; Schmieder, Brigitte; Mandrini, Cristina H.; Khan, Josef I.; Démoulin, Pascal; Rudawy, Pawel Bibcode: 1999A&A...349..927D Altcode: In the following paper we present results of the analysis of NOAA active region 7968, which was the target of a coordinated observing campaign involving the instruments aboard the Solar and Heliospheric Observatory (SOHO), Yohkoh, and ground-based observatories (Bialków, Pic du Midi, and Huairou). This active region was relatively short-lived, and thus provides a rare example of a region observed continuously from its birth to its decay phase. We have extrapolated the SOHO Michelson Doppler Imager (MDI) longitudinal magnetograms, and have compared the results of the modeled field with loops observed over a wide range of temperatures ( ~ 10(5) -3x10(6) K). We find that, throughout the interval of disk passage, the global magnetic structure of the active region corresponds to a nearly potential-field configuration. Magnetic field shear is only seen in isolated patches along the polarity inversion line and is associated with the emergence of parasitic polarity regions. Several small GOES (B-class) X-ray flares and surge-like ejections were observed during the lifetime of the active region. We interpret both the heating of the active region loops and the flaring in terms of magnetic reconnection. In our scenario, the flares are assumed to be due to reconnection between the pre-existing field and newly emerging twisted flux tubes (as indicated by observed changes in the transverse field and inferred twisting motions of the plasma); while the heating of the plasma in quasi-static active region loops is assumed to be due to a relaxation process of the magnetic configuration. These loops appear anchored at places where the photospheric field is highly fragmented, creating a very complex connectivity pattern. This fact, together with the continual photospheric motions, provides the favorable conditions for current sheet formation and release of magnetic energy. Title: Some Advances in 3D-Magnetic Field Topology: an Observed Case of a "Bald Patch" Flare Authors: Démoulin, P.; Aulanier, G.; Schmieder, B. Bibcode: 1999ASPC..184...65D Altcode: The aim of this work is to bring observational evidences of the possible role of the "bald patch" topology in flaring events. A bald patch (or BP) is present along the photospheric inversion line where the field lines are curved-up, so when magnetic dips are present. The set of field lines associated to the BP define a separatrix where a current sheet may form. We find such configuration in AR 7722 where, on May 18, 1994, a sub-flare was observed in X-rays by Yohkoh/SXT and in Hα at NAOJ. Using the magnetohydrostatic equations derived by Low (1992), we model the magnetic field configuration by extrapolation of the Kitt Peak photospheric field, taking into account the effects of pressure and gravity. Hα flare kernels are shown to be located at the lower parts of the computed separatrices associated to bald patches (BPs). This is an evidence that BPs can be involved in flares, and that current sheets can be dissipated in low levels of the solar atmosphere. Title: Quasi-Separatrix Layers in a Reduced Magnetohydrodynamic Model of a Coronal Loop Authors: Milano, Leonardo J.; Dmitruk, Pablo; Mandrini, Cristina H.; Gómez, Daniel O.; Démoulin, Pascal Bibcode: 1999ApJ...521..889M Altcode: We run a pseudospectral magnetohydrodynamic code to simulate reconnection between two flux tubes inside a solar coronal loop. We apply a stationary velocity field at one of the footpoints consisting of two vortices in such a way as to induce the development of a current layer and force the field lines to reconnect. During the process we find a remarkable coincidence between the location of the current layer and the location of quasi-separatrix layers, which are thin magnetic volumes where the field line connectivity changes abruptly. This result lends support to a scenario in which quasi-separatrix layers are the most likely locations for impulsive energy release in the solar corona. Another important result of this simulation is the observed transient of strong magnetohydrodynamic turbulence characterized by a k-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 Bibcode: 1999PPMtO..18..131L Altcode: By using Yohkoh soft X-ray images, vector magnetograms and Hα filtergrams, a brightening event of Hα and soft X-ray of 18 May, 1994 has been studied in detail. It is shown that the event is obviously caused by new emerging flux. The brightening points of Hα and soft X-ray are located at computed separatrices associated to field lines which are tangent to the photosphere. This brightening event may be a signature of reconnection taking place between the pre-existing loops and the new emerging small loops in the lower solar atmosphere. Title: Magnetic Field Scaling Laws and Their Implications for Coronal Heating Authors: Klimchuk, J. A.; Demoulin, P.; Mandrini, C. H. Bibcode: 1999AAS...194.2304K Altcode: 1999BAAS...31..861K Ever since it was realized, some 60 years ago, that the solar corona is two orders of magnitude hotter than the underlying photosphere, scientists have puzzled over the reason for these extreme conditions. A number of plausible ideas have been proposed, including the dissipation of MHD waves (AC models) and the dissipation of stressed, current-carrying magnetic fields (DC models), but it has proved difficult to establish which, if any, is correct. One approach to answering this fundamental question is to determine scaling laws relating the heating rate to observable physical parameters. Klimchuk & 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 <= c <= -1, depending on the complexity of the region. More importantly, for the range of loop lengths studied by Klimchuk & Porter, 50 < L < 300 Mm, there is a universal scaling law of the form B ~ L(delta ,) where delta = -0.98 +/- 0.3. The details of these results will be presented, and their implications for theories of coronal heating will be discussed. It will be shown that DC models are in better agreement with the observations than are AC models. This work was supported in part by NASA grant W-19,200. Title: New 3-D magnetic model for prominences based on dipped field lines and compared with observations Authors: Aulanier, G.; Demoulin, P. Bibcode: 1999AAS...194.3103A Altcode: 1999BAAS...31R.868A Despite of the large number of 2D and 3D models for the magnetic fields in prominences, none has been succesfully directly compared with observational data untill recently, even if many of them still satisfied some well established observational results. This has led to a never ending controversy between theorists and observers, about the relevance of dipped field lines for mass support against gravity in these objects. Here we present a new 3D magnetohydrostatic model based on dipped field lines. The main body of the filament is formed by a twisted flux rope in a bipolar region, and we show how small parasitic polarities near the neutral line lead to a local perturbation of the magnetic fields in the corona, leading to the formation of lateral dips, which appear aside from the flux rope. We show that these are formed by local expansions of the fluxe rope, as well as by the bending of some surrounding sheared field lines, toward the photospheric parasitic polarities. We suggest that these lateral dips can form lateral feet of filaments. Moreover the global magnetic configuration shows in a natural fashion a very large number of typical observational aspects of prominences. Using a magnetogram obtained by SOHO/MDI on 09/25/96 as boundary conditions, we extrapolate the magnetic field under the assumptions of the model. Comparing the 3D distribution of dips with the morphology of the filament observed in Hα on the German VTT (Tenerife) at the same time, we show a good correlation between the dips and the filament body, as well as with its lateral feet. All these results suggest that the model is well adapted for the description of the magnetic field in filaments and their close environement. Furthermore its direct comparison with observations provide evidence in favor of dipped field lines in prominences. Title: 3-D magnetic configurations supporting prominences. III. Evolution of fine structures observed in a filament channel Authors: Aulanier, G.; Démoulin, P.; Mein, N.; van Driel-Gesztelyi, L.; Mein, P.; Schmieder, B. Bibcode: 1999A&A...342..867A Altcode: On September 25() th 1996, a quiescent filament located near the center disc (S2, E5) was observed on the German VTT (Tenerife) with the MSDP instrument, in the Hα line center and wings. SOHO/MDI line-of-sight magnetograms were co-aligned with the MSDP images, showing the position and evolution of the lateral feet of the filament in the vicinity of the parasitic magnetic polarities observed in the filament channel. Using the assumptions developed in the previous papers of this series related to the reconstruction of the 3-D magnetic configuration of filaments, we perform ``linear magnetohydrostatic'' extrapolations (taking into account the effects of plasma pressure and gravity) on the SOHO/MDI magnetograms. The main hypothesis is the presence of a twisted flux-tube located above the photospheric inversion line. Assuming that the parameters of the model do not need to be significantly modified during the evolution of the configuration for a duration of 1 day, we have shown that the 3-D distribution of dipped field lines is well correlated with Hα dark absorbing features in the filament channel: the filament itself, its lateral feet and some of the surrounding dark fibrils. In this way we confirm what was suggested in our earlier papers, i.e. that the feet are composed of the dipped portions of some field lines, which form a continuous pattern from the corona to the photosphere. We propose the same explanation for the magnetic configuration of some of the dark Hα fibrils in the channel. We show that the plasma effects are not responsible for the existence of most of the magnetic dips, however their inclusion helps to get a better correspondence between the model and the observations. We find that the average Hα Doppler velocities associated with the filament and with the chromospheric fibrils is of the order of a few hundred m s(-1) (though it can go locally up to 3 km s(-1) in the filament). These upward velocities are consistent with a quasi-static evolution of the magnetic configuration and with the support of dense plasma in magnetic dips. Title: Results on 3-D solar magnetic field, observations and models Authors: Démoulin, P. Bibcode: 1999JASTP..61..101D Altcode: 1999JATP...61..101D This review presents some of the new developments in the understanding of coronal magnetic fields in flares and coronal mass ejections. The modelling of the coronal magnetic field based on observed photospheric field permits to understand the location of energy release. Various flare observations are consistent with a model where magnetic reconnection occurs between two magnetic fields of different connectivity. Because magnetic helicity is almost conserved, the stored energy cannot be fully released in confined flares. The corona gets rid of the helicity injected by the convection zone only by ejecting part of the magnetic field. A severe physical constraint (open-field limit) on these ejections has been firmly established for force-free fields. It is, however, possible to open partially the field or to eject a twisted flux-tube keeping the energy of the field behind the open-field limit. New results show that in simply connected fields this happen after a finite time without loss of equilibrium, while in more complex topology a loss of equilibrium can still be present. Title: Bright Points and Subflares in Ultraviolet Lines and X-Rays Authors: Rovira, M.; Schmieder, B.; Démoulin, P.; Simnett, G. M.; Hagyard, M. J.; Reichmann, E.; Tandberg-Hanssen, E. Bibcode: 1999ApJ...510..474R Altcode: We have analyzed an active region which was observed in Hα (Multichannel Subtractive Double Pass Spectrograph), in UV lines (SMM/UVSP), and in X-rays (SMM/HXIS). In this active region there were only a few subflares and many small bright points visible in UV and in X-rays. Using an extrapolation based on the Fourier transform, we have computed magnetic field lines connecting different photospheric magnetic polarities from ground-based magnetograms. Along the magnetic inversion lines we find two different zones: (1) a high-shear region (>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. Bibcode: 1999BAAA...43...24L Altcode: We study the active region (AR) 8048 observed on June 1997 in several wavelenghts. The combined observations obtained using CDS (SOHO) and SXT (Yohkoh) show the heating of the coronal magnetic loops at different atmospheric altitudes. Extrapolating the magnetic field in the corona from longitudinal magnetograms from MDI (SOHO), we determine the location of Bald Patches in the surroundings of the leading spot. This magnetic feature, the emergence of parasitic magnetic polarities and the observed photospheric motions provide the conditions to explain the observed heating. Title: The NOAA AR 6718 magnetic field extrapolation with localized current filaments. Authors: Karlický, M.; Démoulin, P.; Aulanier, G.; van Driel-Gesztelyi, L.; Hénoux, J. C.; Jirička, K. Bibcode: 1999joso.proc...97K Altcode: The 3-D extrapolation of magnetic field lines of the July 11, 1991 Kitt Peak magnetogram shows a differential magnetic field shear in the NOAA 6718 active region. A new combined extrapolation technique, which includes localized current filaments is suggested and applied in modelling of this shear. First, the potential field extrapolation is made and then force-free current paths for several current filaments in specific positions are computed. It is shown that with the electric current increase the localized magnetic field shear is increasing. The total electric current in 16 current filaments is considered up to 1.2×1012A. Title: Magnetohydrostatic Model of a Bald-Patch Flare Authors: Aulanier, G.; Démoulin, P.; Schmieder, B.; Fang, C.; Tang, Y. H. Bibcode: 1998SoPh..183..369A Altcode: On 18 May, 1994, a subflare was observed in AR 7722 in X-rays by Yohkoh/SXT and in Hα at National Astronomical Observatory of Japan. The associated brightenings are due to small-scale magnetic energy release, triggered by parasitic fluxes emerging and moving at the edge of leading sunspots. Using the magnetohydrostatic equations derived by Low (1992), we model the magnetic field configuration by extrapolation of the Kitt Peak photospheric field, taking into account the effects of pressure and gravity. Hα flare kernels are shown to be located at computed separatrices associated with field lines which are tangent to the photosphere, namely 'bald patches' (BPs). This is evidence that BPs can be involved in flares, and that current sheets can be dissipated in low levels of the solar atmosphere. The presence of dense plasma which is supported against gravity in the magnetic dips above BPs is correlated to dark elongated features observed in Hα. Mass flows in these flat fibrils are discussed in the context of energy release in the BP separatrices. The effect of the plasma on the computed magnetic configuration is shown to be of secondary importance with respect to the topology of the field. Title: The Effect of Curvature on Flux-Rope Models of Coronal Mass Ejections Authors: Lin, J.; Forbes, T. G.; Isenberg, P. A.; Démoulin, P. Bibcode: 1998ApJ...504.1006L Altcode: The large-scale curvature of a flux rope can help propel it outward from the Sun. Here we extend previous two-dimensional flux-rope models of coronal mass ejections to include the curvature force. To obtain analytical results, we assume axial symmetry and model the flux rope as a torus that encircles the Sun. Initially, the flux rope is suspended in the corona by a balance between magnetic tension, compression, and curvature forces, but this balance is lost if the photospheric sources of the coronal field slowly decay with time. The evolution of the system shows catastrophic behavior as occurred in previous models, but, unlike the previous models, flux ropes with large radii are more likely to erupt than ones with small radii. The maximum total magnetic energy that can be stored before equilibrium is lost is 1.53 times the energy of the potential field, and this value is less than the limiting value of 1.662 for the fully opened field. As a consequence, the loss of ideal MHD equilibrium that occurs in the model cannot completely open the magnetic field. However, the loss of equilibrium does lead to the sudden formation of a current sheet, and if rapid reconnection occurs in this sheet, then the flux rope can escape from the Sun. We also find that the field can gradually become opened without suffering any loss of equilibrium if the photospheric field strength falls below a critical value. This behavior is analogous to the opening of a spherically symmetric arcade in response to a finite amount of shear. Title: 3-D magnetic configurations supporting prominences. II. The lateral feet as a perturbation of a twisted flux-tube Authors: Aulanier, G.; Demoulin, P.; van Driel-Gesztelyi, L.; Mein, P.; Deforest, C. Bibcode: 1998A&A...335..309A Altcode: In a previous paper we have shown that a twisted flux-tube is the most probable magnetic configuration supporting prominences. The model interprets many observations in a natural way (in particular the magnetic measurements in prominences and the chirality properties). Moreover, prominence feet appear as a direct consequence of the parasitic polarities present in the filament channel. Here we investigate further the link between feet and parasitic polarities by modelling explicitly these polarities. We show that the prominence lateral feet appear naturally, above secondary photospheric inversion lines and we describe the morphological change of feet as parasitic polarities evolve. This approach is applied to an observed filament in Hα with the MSDP on the German VTT (Tenerife) where SOHO/MDI magnetograms are available. We show that the shape of the prominence is defined by the distribution of the dips in the computed magnetic configuration. Then we analyse the topology of the magnetic field using the quasi-separatrix layers (QSLs) method. We describe the basic changes in the topology as the parasitic polarities evolve, in particular how the configuration pass from an OX to an OF topology. We find a correspondance between the computed QSLs and some of the chromospheric brightenings, observed around the feet of filaments in the y line (Ca II, 8542 Angstroms). It confirms the deduced magnetic configuration and shows that energy release is present at a low level in the complex topology of the filament configuration. Title: Interactions between nested sunspots. II. A confined X1 flare in a delta-type sunspot Authors: Gaizauskas, V.; Mandrini, C. H.; Demoulin, P.; Luoni, M. L.; Rovira, M. G. Bibcode: 1998A&A...332..353G Altcode: We study the flaring activity in a nest of sunspots in which two bipolar regions emerge inside a third one. These bipolar regions belong to a large complex of activity (McMath 15314) formed by five bipoles on its May 1978 rotation. The usual spreading action during the growth of the bipoles leads to the formation of a $Delta lta-configuration: the preceding and following spots of the two interior regions overlap (p-f collision) into a single penumbra. While Delta lta-configurations created in this way normally favor strong flaring activity, only very small flares occur during 5 days. Only when the following umbra in the Delta lta$-spot breaks into pieces, accompanied by rapid photospheric motions, do intense flares occur. The largest and best observed one in this sequence, a class 1B/X1 flare on 28 May 1978, is remarkable for the absence of ejecta and for the concentration of its emission in three widely spaced sites, a pattern which holds in general over two days for lesser flares. We take this pattern as evidence that the flare is confined to the low corona. We first compute the coronal magnetic field using subphotospheric sources to model the observed magnetic data and derive the location of separatrices. In this case the magnetic field topology is defined by the link between these discrete sources. The relevant generalization of separatrices in any kind of magnetic configuration are `quasi-separatrix layers' (QSLs). We calculate them using the previous model, but also for a model obtained with a more classical extrapolation technique based on the fast Fourier transform method. We show, with both approaches, that the plage brightenings during the quiescent phase of the region and the flare kernels are located at the intersection of separatrices and QSLs with the photosphere. Moreover, they are magnetically linked. Bright and dark `post'-flare loops which form in the maximum and gradual phases of the 1B/X1 flare also highlight the location of the separatrices and the QSLs. This confirms previous studies on the importance of the magnetic field topology for flares and, with this study, we further constrain the underlying physical mechanism. We draw some conclusions about the role of magnetic reconnection in the solar corona; depending on the photospheric conditions that we identify, reconnection can lead to steady heating or flaring. Title: Evolution of the Magnetic Field and Chromospheric Fine Structure in a Filament Channel Authors: van Driel-Gesztelyi, L.; Mein, P.; Mein, N.; Schmieder, B.; Malherbe, J. -M.; Aulanier, G.; Démoulin, P.; Deforest, C.; Staiger, J. Bibcode: 1998ASPC..155..321V Altcode: 1998sasp.conf..321V No abstract at ADS Title: Reorganization of solar magnetic field by a flare event Authors: Manoharan, P. K.; van Driel-Gesztelyi, L.; Pick, M.; Démoulin, P. Bibcode: 1998BASI...26..319M Altcode: No abstract at ADS Title: Non potentiality of coronal loops above active regions Authors: Aulanier, G.; Schmieder, B.; Démoulin, P.; van Driel-Gesztelyi, L.; Deforest, C. Bibcode: 1998ASPC..155..105A Altcode: 1998sasp.conf..105A No abstract at ADS Title: Filament Disparition Brusque and CME - September 25-26, 1996 Event Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Aulanier, G.; Demoulin, P.; Martens, P. C. H.; Zarro, D.; Deforest, C.; Thompson, B.; St. Cyr, C.; Kucera, T.; Burkepile, J. T.; White, O. R.; Hanaoka, Y.; Nitta, N. Bibcode: 1998ASPC..150..366V Altcode: 1998IAUCo.167..366V; 1998npsp.conf..366V No abstract at ADS Title: MHS model of an active region associated to a flare Authors: López Fuentes, M.; Mandrini, C. H.; Rovira, M. G.; Démoulin, P. Bibcode: 1998BAAA...42...34L Altcode: Using observations obtained by different instruments, we have analyzed the active region (AR) NOAA 7070 associated to an X3/B3 flare. The intense UV emission has been an outstanding characteristic of this event, 17 times larges than that of the whole solar disk. This is similar to the emission observed in stars in which flares are produced. We have modelled the atmospheric magnetic field, using a magnetohydrostatic approach using photospheric magnetograms as boundary conditions. The magnetic field presents a high shear close to the AR inversion line. This is seen not only in the transverse component of the photospheric, but also in the coronal loops observed in X-rays. The high shear of the coronal loops disappears after the flare, and they show a topology closer to that of a potential field. This is in agreement with what is expected when the field relaxes after the stored energy has been released. Using the magnetic virial theorem, and after the computed model, we estimate that the energy variation is enough to account for the observed flare. Title: 3-D magnetic configurations supporting prominences. I. The natural presence of lateral feet Authors: Aulanier, G.; Demoulin, P. Bibcode: 1998A&A...329.1125A Altcode: It is now commonly accepted that prominence plasma is supported in magnetic dips, in particular in twisted flux-tubes. But present two-dimensional models are unable to explain the observed presence and structure of prominences feet. This requires three-dimensional models. We modeled the field using linear force-free field equations. Combining a small number of harmonics, and using observational constraints, we have found the area in the parameter space where prominences are likely to be present. Then, adding 3-D harmonics, we show that feet appear periodically underneath the prominence body. For great helicity, the parameter space is mostly fulfilled by configurations which have feet alternating between both sides of the prominence axis, as observed. The theoretical photospheric field has a quasi-bipolar pattern and the prominence stands above a magnetic corridor containing only small parasitic polarities. The lateral feet are formed by dips in the vicinity of these small polarities. These configurations show in a natural fashion a number of well-established as well as more recent observational aspects of prominences, in particular the vector magnetic field measurements in prominences and the chirality patterns (the dextral/sinistral, right/left bearing, skew of the overlying coronal arcade and fibril organization in prominence channels). Title: Bright Points and Subflares in UV Lines and in X-Rays Authors: Rovira, M.; Schmieder, B.; Demoulin, P.; Simnett, G. M.; Hagyard, M. J.; Reichmann, E.; Tandberg-Hanssen, E. Bibcode: 1998msfc.rept.....R Altcode: We have analysed an active region which was observed in Hα (MSDP), UV lines (SMM/UVSP), and in X rays (SMM/HXIS). In this active region there were only a few subflares and many small bright points visible in UV and in X rays. Using an extrapolation based on the Fourier transform we have computed magnetic field lines connecting different photospheric magnetic polarities from ground-based magnetograms. Along the magnetic inversion lines we find 2 different zones: 1. a high shear region (less than 70 degrees) where subflares occur 2. a low shear region along the magnetic inversion line where UV bright points are observed. Title: 3-D Modelling of a Filament Observed in Hα and with SOHO Authors: Aulanier, G.; Schmieder, B.; Démoulin, P.; Mein, N.; van Driel-Gesztelyi, L.; Mein, P.; Vial, J. C.; Deforest, C. Bibcode: 1998ESASP.417..217A Altcode: 1998cesh.conf..217A No abstract at ADS Title: The Energetics of Flux-Rope Prominence Models in Axially Symmetric Systems Authors: Lin, J.; Forbes, T. G.; Isenberg, P. A.; Demoulin, P. Bibcode: 1998ASPC..150..350L Altcode: 1998npsp.conf..350L; 1998IAUCo.167..350L No abstract at ADS Title: 3-D Modelling of a Filament Observed in Hα and with SOHO/MDI Authors: Aulanier, G.; Démoulin, P.; van Driel-Gesztelyi, L.; Mein, P.; Deforest, C. Bibcode: 1998ASPC..155..326A Altcode: 1998sasp.conf..326A No abstract at ADS Title: Magnetic Fields in Filaments (Review) Authors: Demoulin, P. Bibcode: 1998ASPC..150...78D Altcode: 1998npsp.conf...78D; 1998IAUCo.167...78D No abstract at ADS Title: 3-D Twisted Flux-Tube in a Linear Force-Free Equilibrium Authors: Aulanier, G.; Demoulin, P. Bibcode: 1998ASPC..150...86A Altcode: 1998npsp.conf...86A; 1998IAUCo.167...86A No abstract at ADS Title: Quasi-separatrix layers in solar flares. II. Observed magnetic configurations. Authors: Demoulin, P.; Bagala, L. G.; Mandrini, C. H.; Henoux, J. C.; Rovira, M. G. Bibcode: 1997A&A...325..305D Altcode: We show that the location of Hα or OV flare brightenings is related to the properties of the field-line linkage of the underlying magnetic region. The coronal magnetic field is extrapolated from the observed photospheric field assuming a linear force-free field configuration in order to determine the regions of rapid change in field-line linkage, called "quasi-separatrix layers" or QSLs. They are open layers that behave physically like separatrices: breakdown of ideal magnetohydrodynamics and release of free magnetic-energy may occur at these locations when their thickness is small enough. A feature common to all the flaring regions studied is found to be the presence of QSLs where Hα flare kernels are observed. The brightenings are along restricted regions of very thin QSLs; an upper bound of their thickness is 1Mm but it is several order of magnitude smaller in most of the cases. These places coincide in general with zones where the longitudinal field component is greater than 100G. These results allow us to constrain present models of solar flares and localise where a break-down of ideal MHD can occur. The studied flares are found to be fed in general by only one electric current loop, but they imply the interaction of two magnetic bipoles. The extrapolated coronal field lines involved in the process have their photospheric footpoints located at both sides of QSLs, as expected in recent 3D magnetic reconnection models. Title: Magnetic reconnection driven by emergence of sheared magnetic field. Authors: Schmieder, B.; Aulanier, G.; Demoulin, P.; van Driel-Gesztelyi, L.; Roudier, T.; Nitta, N.; Cauzzi, G. Bibcode: 1997A&A...325.1213S Altcode: Recurrent subflares (Class C) were observed in the NOAA 7608 active region on 27 October 1993. From multi-wavelength observations (white-light, magnetic field, H-alpha, X-ray), obtained during a coordinated campaign between Pic du Midi and Yohkoh, it appears that these flares were double ribbon flares caused by new flux emergence. As the flare begins, the X-ray emission observed with Yohkoh/SXT is loop-shaped with the axis almost parallel to the magnetic inversion line, while during the flare development, X-ray loops appear at the location of the emerging flux. The extrapolation of the photospheric magnetic field in a linear force-free field configuration allows identification of the magnetic configuration given by the flares. The Hα flare ribbons are located at the intersections of the computed quasi-separatrice layers (QSLs) with the chromosphere. We show that the initial loop-shaped X-ray emission region is in fact formed by several smaller loops directed in a nearly orthogonal direction with their feet anchored close to or in the Hα ribbons. During the flare development there are X-ray loops which represent only one foot of open or largescale magnetic loops. For the studied flares the puzzling soft X-rays observations could only be understood with the help of Hα and magnetic data combined with a modeling of the coronal magnetic field. Further, from the deduced magnetic field topology, the width of the QSLs and our present knowledge of 3-D magnetic reconnection, we conclude that the flare was due to magnetic reconnection driven by emergence of sheared magnetic field impacting in the pre-existing coronal field. Title: The Importance of Photospheric Intense Flux Tubes for Coronal Heating Authors: Démoulin, P.; Priest, E. R. Bibcode: 1997SoPh..175..123D Altcode: Dissipation of magnetic energy in the corona requires the creation of very fine scale-lengths because of the high magnetic Reynolds number of the plasma. The formation of current sheets is a natural possible solution to this problem and it is now known that a magnetic field that is stressed by continous photospheric motions through a series of equilibria can easily form such sheets. Furthermore, in a large class of 3D magnetic fields without null points there are locations, called `quasi-separatrix layers' (QSLs), where the field-line linkage changes drastically. They are the relevant generalisation of normal separatrices to configurations without nulls: along them concentrated electric currents are formed by smooth boundary motions and 3D magnetic reconnection takes place when the layers are thin enough. With a homogenous normal magnetic field component at the boundaries, the existence of thin enough QSL to dissipate magnetic energy rapidly requires that the field is formed by flux tubes that are twisted by a few turns. However, the photospheric field is not homogeneous but is fragmented into a large number of thin flux tubes. We show that such thin tubes imply the presence of a large number of very thin QSLs in the corona. The main parameter on which their presence depends is the ratio between the magnetic flux located outside the flux tubes to the flux inside. The thickness of the QSLs is approximately given by the distance between neighbouring flux tubes multiplied by the ratio of fluxes to a power between two and three (depending on the density of flux tubes). Because most of the photospheric magnetic flux is confined in thin flux tubes, very thin QSLs are present in the corona with a thickness much smaller than the flux tube size. We suggest that a turbulent resistivity is triggered in a QSL, which then rapidly evolves into a dynamic current sheet that releases energy by fast reconnection at a rate that we estimate to be sufficient to heat the corona. We conclude that the fragmentation of the photospheric magnetic field stimulates the dissipation of magnetic energy in the corona. Title: Quelques données sur la comète Hale-Bopp. Authors: Demoulin, P. Bibcode: 1997Ciel...59..213D Altcode: No abstract at ADS Title: Evidence of Magnetic Reconnection from Hα, Soft X-Ray and Photospheric Magnetic Field Observations Authors: Mandrini, C. H.; DÉmoulin, P.; BagalÁ, L. G.; Van Driel-Gesztelyi, L.; HÉnoux, J. C.; Schmieder, B.; Rovira, M. G. Bibcode: 1997SoPh..174..229M Altcode: A conventional view of magnetic reconnection is mainly based on the 2-D picture of an X-type neutral point, or on the extension of it to 3-D, and it is thought to be accompanied by flux transport across separatrices (places where the field-line mapping is discontinuous). This view is too restrictive when we realize the variety of configurations that are seen flaring. We designed an algorithm, called Source Method (SM), to determine the magnetic topology of active regions (ARs). The observed photospheric field was extrapolated to the corona using subphotospheric sources and the topology was defined by the link between these sources. Hα flare brightenings were found to be located at the intersection with the chromosphere of the separatrices so defined. These results and the knowledge we gained on the properties of magnetic field-line linkage, led us to generalize the concept of separatrices to `quasi-separatrix layers' (QSLs) and to design a new method (`quasi-separatrix layers method', QSLM) to determine the magnetic topology of ARs. QSLs are regions where the magnetic field-line linkage changes drastically (discontinuously when they behave like separatrices) and the QSLM can be applied to ARs where the photospheric field has been extrapolated using any kind of technique. In this paper we apply the QSLM to observed flaring regions presenting very different configurations and also to a decaying AR where a minor phenomenon, like an X-ray bright point (XBP), is observed. We find that the locations of flare and XBP brightenings are related to the properties of the field-line linkage of the underlying magnetic region, as expected from recent developments of 3-D magnetic reconnection. The extrapolated coronal field lines representing the structures involved in the analyzed events have their photospheric footpoints located at both sides of QSLs. Our results strongly support the hypothesis that magnetic reconnection is at work in various coronal phenomena, ranging from the less energetic ones to large-scale eruptions. Title: Can we Extrapolate a Magnetic Field when its Topology is Complex? Authors: DÉmoulin, P.; HÉnoux, J. C.; Mandrini, C. H.; Priest, E. R. Bibcode: 1997SoPh..174...73D Altcode: In order to understand various solar phenomena controlled by the magnetic field, such as X-ray bright points, flares and prominence eruptions, the structure of the coronal magnetic field must be known. This requires a precise extrapolation of the photospheric magnetic field. Presently, only potential or linear force-free field approximations can be used easily. A more realistic modelling of the field is still an active research area because of well-known difficulties related to the nonlinear mixed elliptic-hyperbolic nature of the equations. An additional difficulty arises due to the complexity of the magnetic field structure which is caused by a discrete partition of the photospheric magnetic field. This complexity is not limited to magnetic regions having magnetic nulls (and so separatrices) but also occurs in those containing thin elongated volumes (called Quasi-Separatrix Layers) where the photospheric field-line linkage changes rapidly. There is a wide range for the thickness of such layers, which is determined by the character (bipolar or quadrupolar) of the magnetic region, by the sizes of the photospheric field concentrations and by the intensity of the electric currents. The aim of this paper is to analyse the recent nonlinear force-free field extrapolation techniques for complex coronal magnetic fields. Title: 3-D reconnection related to new emerging flux Authors: Schmeider, B.; Démoulin, P.; Aulanier, G.; Malherbe, J. M.; van Driel-Gesztelyi, L.; Mandrini, C. H.; Roudier, T.; Nitta, N.; Harra-Murnion, L. K. Bibcode: 1997AdSpR..19.1871S Altcode: We present evidences that emergence of new flux in the lower atmosphere leads to magnetic reconnection of field lines. In a first phase the phenomenon is observed in the chromosphere by the formation of dark filaments (arch filament system) which are overlaid by bright loops visible in soft X-rays. Different types of event appear according to the magnetic field configuration and the amount of energy involved. 3-D modelling of the photospheric magnetic field provides a new tool for understanding reconnection in real configurations. The observed chromospheric and coronal loops are good diagnostics for the modelling. We document our statement by examples obtained during coordinated campaigns with the Hα Multichannel Subtractive Double Pass spectrographs-MSDP (Pic du Midi and Tenerife) and the Yohkoh instruments. Title: Magnetic reconnection driven by an emerging flux. Authors: Aulanier, G.; Démoulin, P.; Schmieder, B.; Malherbe, J. M.; van Driel-Gesztelyi, L.; Roudier, T. Bibcode: 1997joso.proc...51A Altcode: No abstract at ADS Title: Fulguraciones Solares en Regiones Activas Interactuantes Authors: Bagalá, L. G.; Rovira, M. G.; Mandrini, C. H.; Démoulin, P. Bibcode: 1997BAAA...41...57B Altcode: We present a topological approach for the 30th January 1992 solar flares of AR 7031. We study Hα and soft X-ray emission for the most important flares, and compare these brightenings with the properties of the field-line linkage of the underlying magnetic region. The coronal magnetic field is computed from the observed photospheric field using a linear force-free extrapolation and the regions of drastic change in field-line linkage (called ``quasi-separatrix layers'' or QSLs) are determined by a computer algorithm. We find that a feature common to the two flares studied is the presence of QSLs where Hα flare kernels are observed. The extrapolated coronal field lines representing these structures have their photospheric footpoints located at both sides of QSLs, as expected if 3D magnetic reconnection were occurring at QSLs. These results allow us to constrain present models of solar flares. Title: Retrieval of ozone vertical column amounts from ground-based high resolution infrared solar spectra. Authors: Hamdouni, A.; Barbe, A.; Demoulin, P.; Zander, R. Bibcode: 1997JQSRT..57...11H Altcode: Good infrared spectral regions to retrieve accurately the vertical column amount of ozone from ground observations are proposed. Their selection was based on studies of the influence of spectroscopic (frequencies, halfwidths, intensities) as well as geophysical parameters (volume mixing ratios, temperature profiles) with a particular attention for temperature. The results, obtained in three different spectral regions, with a realistic T profile are very consistent. Title: Fulguraciones en una configuración tipo δ Authors: Luoni, M. L.; Mandrini, C. H.; Rovira, M. G.; Démoulin, P.; Gaizauskas, V. Bibcode: 1997BAAA...41...62L Altcode: Through the determination of the magnetic field topology, we focus this study on the flaring activity occurring in a nest of five bipoles. These bipoles belonged to a ``great complex of activity" (Mc Math 15314). We are interested in the largest and best observed flare on May 28, 1978, a class 1B/X1, occurring in a δ spot. The usual spreading action during the growth of the bipoles lead to the formation of a δ-configuration: the preceding and following spots of the two inner regions overlapped into a single penumbra. In this case, the spots approached continuously during five days. We first compute the coronal magnetic field using subphotospheric sources to model the longitudinal magnetograms and derive the location of separatrices, for May 27 and 28. Quasi-separatrix layers are a generalization of separatrices for any magnetic field configuration, these are thin volumes where the connectivity of field lines changes drastically. We calculate them using a model of the field obtained by extrapolation of the observations based on the fast Fourier transform method. With both approaches, we show that the plage brightenings, on the 27, and the flare kernels, on the 28, are located at the intersection of separatrices with the photosphere. This confirms the importance of the magnetic field topology for solar flares. Taking into account Hα observations and the magnetic field modelling, we conclude that energy is released in the solar corona, between the preceding and following spots, in the region of the separator. Bright and dark post-flare loops follow the location of separatrices and quasi-separatrix layers. This is consistent with magnetic reconnection models. Our results confirm the importance of the field topology for the comprehension of the active phenomena and allow us to characterize the energy release mechanism that is at their origin. Title: Reorganization of the solar corona following a C4.7 flare Authors: van Driel-Gesztelyi, L.; Manoharan, P. K.; Pick, M.; Démoulin, P. P. Bibcode: 1997AdSpR..19.1883V Altcode: Yohkoh X-ray images, multifrequency two-dimensional observations of the Nancay Radioheliograph, Kitt Peak and Mees magnetograms provide a unique set of data with which to study a C4.7 long-duration flare that was observed close to the equator (S07, W11) on 25 Oct. 1994 at 09:49 UT. Linear force-free field extrapolations indicate a very high degree of non-potentiality in the active region. The X-ray flare started with the expansion of spectacular twisted loops. Fifteen minutes after the flare onset sporadic radio (type III) bursts were observed spreading over an area of almost <FR SHAPE="SOL">1<DE>3</DE></FR> of the solar disc and two remote X-ray brightenings appeared over quiet regions of opposite magnetic polarity located in on opposite hemispheres of the Sun. In the close vicinity of these remote brightenings two coronal holes formed. The timing and location of these events combined with the overall magnetic configuration provide evidence for a large-scale magnetic reconnection occurring between the expanding twisted loops and the overlying huge loops which inter-connect quiet solar regions. Title: Quasi-Separatrix Layers and Their Relationship with Solar Flares Authors: Bagala, L. G.; Mandrini, C. H.; Rovira, M. G.; Demoulin, P.; Henoux, J. C. Bibcode: 1996RMxAC...4Q..90B Altcode: No abstract at ADS Title: Quasi-Separatrix Layers in Simple Magnetic Configurations Authors: Mandrini, C. H.; Demoulin, P.; Henoux, J. C.; Priest, E. Bibcode: 1996RMxAC...4Q.104M Altcode: No abstract at ADS Title: Evidence for Large-Scale Solar Magnetic Reconnection from Radio and X-Ray Measurements Authors: Manoharan, P. K.; van Driel-Gesztelyi, L.; Pick, M.; Demoulin, P. Bibcode: 1996ApJ...468L..73M Altcode: Utilizing Yohkoh Soft X-ray Telescope and Nancay radioheliograph data, we present, for the first time, observations of expanding twisted X-ray loops and a series of nonthermal radio bursts that follow the loop expansion in time and space up to ~12' distance. The loops were produced during a long-duration C4.7 flare close to disk center on 1994 October 25 at 1049 UT. The series of radio bursts were observed on the southern hemisphere above a weak positive-polarity region. The Kitt Peak magnetogram shows the existence of a weak negative-polarity region on the northern hemisphere at the same heliolongitude. Simultaneously with the nonthermal radio bursts, we observed the appearance of two remote X-ray brightenings and subsequent formation of two coronal holes above these weak (quiet) magnetic regions of opposite polarity, which strongly suggest the involvement of these remote regions in the event. During the 6 hr--long gradual phase of the flare, new X-ray loop connections developed among the active region and the remote quiet regions. A nonthermal radio continuum emission originating from the active region was also observed. We propose that the series of radio bursts, two remote X-ray brightenings, and new coronal loop connections were all signatures of a large-scale reconnection process between the expanding twisted flare loops and overlying transequatorial loops connecting quiet-Sun regions. The reconnection was only partial; the external part of the overlying large-scale fields were pushed out in the solar wind by the expanding twisted loops, leading to the formation of the coronal holes. The interaction between the active region and the large-scale fields seemed to be active during the entire gradual phase of the flare. This scenario may also explain the measurement of high-energy electrons in the interplanetary medium from 74 deg south heliolatitude as observed by Ulysses. Title: 3D Magnetic Reconnection at an X-Ray Bright Point Authors: Mandrini, C. H.; Démoulin, P.; Van Driel-Gesztelyi, L.; Schmieder, B.; Cauzzi, G.; Hofmann, A. Bibcode: 1996SoPh..168..115M Altcode: On May 1, 1993, a flaring X-ray bright point (XBP) was observed for about 16 hours in the old, disintegrating, bipolar active region (AR) NOAA 7493. During this period, a minor magnetic bipole (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. Bibcode: 1996ApJ...467..881S Altcode: The three-dimensional extrapolation of magnetic field lines from a magneto gram obtained at Kitt Peak allows us to understand the global structure of the NOAA active region 6718, as observed in X-rays with the Normal Incidence X-ray Telescope (NIXT) and in Hα with the Multichannel Subtractive Double Pass spectrograph (MSDP) in Meudon on 1991 July 11. This active region was in a quiet stage. Bright X-ray loops connect plages having field strengths of ∼300 G, while Hα fibriles connect penumbrae having strong spot fields to the surrounding network. Small, intense X-ray features in the moat region around a large spot, which could be called X-ray-bright points, are due mainly to the emergence of magnetic flux and merging of these fields with surrounding ones. A set of large-scale, sheared X-ray loops is observed in the central part of the active region. Based on the fit between the observed coronal structure and the field configurations (and assuming a linear force-free field), we propose a differential magnetic field shear model for this active region. The decreasing shear in outer portions of the active region may indicate a continual relaxation of the magnetic field to a lower energy state in the progressively older portions of the AR. Title: (Erratum) Stationary subalfvenic and low-β MHD flows in solar coronal loops and arcades. Authors: Surlantzis, G.; Demoulin, P.; Heyvaerts, J.; Sauty, C. Bibcode: 1996A&A...310..351S Altcode: Erratum to Astron. Astrophys. 284, 985-999 (1994) Title: Three-dimensional magnetic reconnection without null points 2. Application to twisted flux tubes Authors: Démoulin, P.; Priest, E. R.; Lonie, D. P. Bibcode: 1996JGR...101.7631D Altcode: Magnetic reconnection has traditionally been associated exclusively with the presence of magnetic null points or field lines tangential to a boundary. However, in many cases introducing a three-dimensional perturbation in a two-and-half-dimensional magnetic configuration implies the disappearance of separatrices. Faced with this structural instability of separatrices when going from two-and-half to three-dimensional configurations, several approaches have been investigated to replace the topological ideas familiar in two-dimensional, but no unanimity has yet emerged on the way reconnection should be defined. While it is true that the field line linkage is continuous in three-dimensional, we show here that extremely thin layers (called quasi-separatrix layers (QSLs)) are present. In these layers the gradient of the mapping of field lines from one part of a boundary to another is very much larger than normal (by many orders of magnitude). Even for highly conductive media these extremely thin layers behave physically like separatrices. Thus reconnection without null points can occur in QSLs with a breakdown of ideal MHD and a change in connectivity of plasma elements. We have analyzed several twisted flux tube configurations, going progressively from two-and-half to three-dimensional, showing that QSLs are structurally stable features (in contrast to separatrices). The relative thickness w of QSLs depends mainly on the maximum twist; typically, with two turns, w~10-6, 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. Bibcode: 1996A&A...308..643D Altcode: Magnetic reconnection is usually thought to be linked to the presence of magnetic null points and to be accompanied by the transport of magnetic field lines across separatrices, the set of field lines where the mapping of field lines is discontinuous. In view of the variety of observed flaring configurations, we show that this view is too restrictive. Instead, Priest and Demoulin (1995) have explored a way of generalising the concept of separatrices to magnetic configurations without field-line linkage discontinuities. They propose that magnetic reconnection may also occur in 3D in the absence of null points at "quasi-separatrix layers" (QSLs), which are regions where there is drastic change in field-line linkage. In previous studies we have shown that solar flare kernels are linked to the topology of the active-region magnetic field. The observed photospheric field was extrapolated to the corona using subphotospheric magnetic sources and the topology was defined by the magnetic linkage between these sources, the method being called SM (for Source Method). In this paper we define a new method, called QSLM (for Quasi-Separatrix Layers Method), which finds the location of QSLs above the photosphere. It is designed to be applied to any kind of magnetic field representation, while, in the present paper, we apply it only to simple theoretical magnetic configurations in order to compare it with the SM. It generalises the concept of separatrices to magnetic configurations without field-line linkage discontinuities. The QSLM determines elongated regions that are in general located along small portions of the separatrices defined by the SM, and in the limit of very concentrated photospheric fields both methods give the same result. In bipolar magnetic configurations two QSLs are found at both sides of the inversion line, while in quadrupolar configurations four appear. We find that there is a wide range for the thickness of the QSLs, which is determined by the character (bipolar or quadrupolar) of the magnetic region and by the sizes of the photospheric field concentrations. We then show that smooth photospheric motions induce concentrated currents at the locations defined by the QSLM. We prove this only for initially potential configurations but, due to the form of the equations, we conjecture that it is also valid for any kind of initial magnetic equilibrium. We conclude that, even in bipolar configurations, there are localized places where current build-up can be induced by photospheric motions, leading to ideal MHD breakdown with strong flows and magnetic energy release. Title: Las fulguraciones como manifestación de reconexión en el campo magnético solar Authors: Bagalá, L. G.; Mandrini, M. C.; Rovira, M. G.; Démoulin, P. Bibcode: 1996BAAA...40R...2B Altcode: Las fulguraciones solares son fenómenos transitorios de liberación de energía que se desarrollan en las estructuras magnéticas de las regiones activas del Sol. Las fulguraciones pueden llegar a liberar hasta 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. Bibcode: 1996ASPC..111..398M Altcode: 1997ASPC..111..398M Reports a unique set of observations, for a low heliolatitude flare, obtained with the Yohkoh satellite and the Nançay radioheliograph. This flare starts with the expansion of spectacularly twisted loops, followed by sporadic radio bursts (some of them are detected at high heliolatitude, ≡65°S), appearance of two remote X-ray brightenings and formation of two coronal holes on opposite hemispheres of the Sun. The timing and location of these events provide evidence for a large-scale magnetic reconnection between the expanding twisted flare loops and overlying huge loops inter-connecting quiet regions on the Sun. Title: Reconexión magnética en una región activa en decaimiento Authors: Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.; Schmieder, B.; Bagalá, L. G.; Rovira, M. G. Bibcode: 1996BAAA...40....5M Altcode: Se han obtenido observaciones desde Tierra (Hα y magnetogramas) coordinadas con el Soft X-ray Telescope (SXT), a bordo del satélite japonés Yohkoh, de una región activa bipolar en decaimiento. Estos datos constituyen la base para el estudio de un punto brillante en rayos X (PBX) y de la actividad relacionada con el mismo en distintas capas de la atmósfera solar. Las observaciones muestran que el PBX está relacionado con la aparición de un bipolo menor (~ 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 (>= 10^4 m) cuando el PBX desaparece de las imágenes del SXT. Estos resultados señalan que el abrillantamiento y las ``fulguraciones" de este PBX se deben al proceso de reconexión en 3D que tiene lugar en las CSs. Title: Dynamics of solar magnetic arches in the photosphere and the chromosphere. Authors: Mein, P.; Demoulin, P.; Mein, N.; Engvold, O.; Molowny-Horas, R.; Heinzel, P.; Gontikakis, C. Bibcode: 1996A&A...305..343M Altcode: Mass motions in chromospheric arch filaments have been observed with imaging spectroscopy (MSDP) at the VTT telescope of the Teide Observatory. Coordinated observations of time sequences of continuum images were carried out at the SVST telescope of the Observatorio del Roque de los Muchachos, which provided transverse velocities of photospheric tracers, by "local correlation tracking." Hα profiles along 3 arch filaments are analysed in terms of "differential cloud MODel", to discuss the Doppler velocities of chromospheric material. Models of ascending arches with downflows in both legs are investigated. The gas pressure is neglected, but the free-fall equations are integrated versus time (non-stationary case). We first assume circular lines of force with constant radius. We can account for chromospheric velocities, but we cannot fit the slow motion of footpoints derived from photospheric tracers. A better agreement is obtained by assuming lines of force with fixed footpoints and variable radius. Typical values are: half distance between footpoints of 10 to 15Mm, upward velocity at the top of loops of 4km/s after an integration time of 800s. The obtained values are consistent with the sizes and the lifetime of arch filaments. Title: Modelisation of magnetic field. Authors: Démoulin, P. Bibcode: 1996joso.proc..117D Altcode: Magnetic reconnection is usually thought to be linked to the presence of magnetic null points and to be accompanied by the transport of magnetic field lines across separatrices, the set of field lines where the mapping of field lines is discontinuous. In view of the variety of observed flaring configurations, the author shows that this view is too restrictive. He generalises the concept of separatrices to Quasi-Separatrix Layers and applies this method to X-bright points and eruption of twisted structures and reports the results. Title: 3D Magnetic Reconnection: Example of an X-Ray Bright Point Authors: Demoulin, P.; Mandrini, C. H.; van Driel-Gesztelyi, L.; Priest, E. R.; Henoux, J. C.; Schmieder, B. Bibcode: 1996ASPC..111...49D Altcode: 1997ASPC..111...49D In the classical view magnetic reconnection occurs at neutral points and implies transport of magnetic field-lines across separatrices. The authors show that reconnection may also occur in the absence of neutral points at so-called "quasi-separatrix layers" (QSLs), where there is a steep gradient in field-line linkage at the boundaries. Reconnection occurs in QSLs where the field-line velocity becomes larger than the allowed maximal plasma velocity or where the electric-current density becomes too great. The authors describe both a theoretical and an observed configuration. In the case of a simple sheared X-field they show that even a smooth continuous shear flow, imposed at the boundary, gives strong plasma jetting inside and parallel to the QSLs. Applying the QSL method to an X-ray bright point observed by Yohkoh, they find field lines in the extrapolated field which are on both sides of QSLs and which are in good agreement with loops observed in Hα and X-rays related to emerging flux. The evolution of the QSL width may explain the brightness evolution of the XBP. Title: Emerging Flux, Reconnection, and XBP Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Demoulin, P.; Mandrini, C.; Cauzzi, G.; Hofmann, A.; Nitta, N.; Kurokawa, H.; Mein, N.; Mein, P. Bibcode: 1996mpsa.conf..459V Altcode: 1996IAUCo.153..459V No abstract at ADS Title: Emerging flux seen by Yohkoh. Authors: van Driel-Gesztelyi, L.; Schmieder, B.; Mandrini, C.; Démoulin, P.; Cauzzi, G.; Hofmann, A.; Nitta, N.; Kurokawa, H.; Mein, N.; Mein, P. Bibcode: 1996joso.proc..124V Altcode: No abstract at ADS Title: Three-dimensional magnetic reconnection without null points. 1. Basic theory of magnetic flipping Authors: Priest, E. R.; Démoulin, P. Bibcode: 1995JGR...10023443P Altcode: In two or three dimensions, magnetic reconnection may occur at neutral points and is accompanied by the transport of magnetic field lines across separatrices, the field lines (or flux surfaces in three dimensions) at which the mapping of field lines is discontinuous. Here we show that reconnection may also occur in three dimensions in the absence of neutral points at so-called ``quasi-separatrix layers,'' where there is a steep gradient in field line linkage. Reconnection is a global property, and so, in order to determine where it can occur, the first step is to enclose the volume being considered by a boundary (such as a spherical surface). Then the mapping of field lines from one part of the boundary to another is determined, and quasi-separatrix layers may be identified as regions where the gradient of the mapping or its inverse is very much larger than normal. The most effective measure of the presence of such layers is the norm of the displacement gradient tensor; their qualitative location is robust and insensitive to the particular surface that is chosen. Reconnection itself occurs when there is a breakdown of ideal MHD and a change of connectivity of plasma elements, where the field line velocity becomes larger than the plasma velocity, so that the field lines slip through the plasma.

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. Bibcode: 1995A&A...303..927M Altcode: We present a detailed analysis of the magnetic topology of AR 6233 on two consecutive days (August 28 and 29, 1990) and compare the location of the magnetic separatrices and separators with off-band Hα observations and other flare manifestations, such as intense nonthermal electron precipitation and high coronal pressure sites, for two flares that occured on these days. Since for one of the days of our analysis we have two magnetograms covering fields of view with different scale lengths, we analyzed the dependence of the topology of the region of interest on the presence of external magnetic field concentrations. We have found that considering these concentrations does not modify the location of separatrices in the region. Because transverse magnetograms indicate that strong magnetic shear is present along the longitudinal inversion line where flare brightenings are located, the observed photospheric magnetic field is modeled in an approach in which a combination of sources with current-free and non current-free magnetic field is used. This model allows us to obtain a better fit between the observed and modeled transverse field, then we find a closer relationship between separatrices and flare features. The results of a current-free and of a linear force-free approach are also shown for comparison. As in other flaring regions studied previously, chromospheric flare brightenings are found on separatrices. The topological structure obtained for these flares is rather complex. We find that the connectivity of field lines may change drastically from one edge of a ribbon to the other. Electron precipitation and high coronal pressure sites, and some photospheric intense currents are also found in the immediate vicinity of separatrices. The early kernels of August 28 flare are found closer to the separatrices of the nonpotential field, while the later are closer to those of the potential field. All these results agree with the hypothesis that magnetic energy is stored in field-aligned currents and released due to magnetic field reconnection, with a noticeable relaxation of the field, either at the separator region or on separatrices. Title: A Topological Approach to Understand a Multiple-Loop Solar Flare Authors: Bagalá, L. G.; Mandrini, C. H.; Rovira, M. G.; Démoulin, P.; Hénoux, J. C. Bibcode: 1995SoPh..161..103B Altcode: We analyze the UV and X-ray data obtained by the SMM satellite for the flare starting at 02:36 UT on November 12, 1980 in AR 2779. From a detailed revision of the OV emission, we find that the observations are compatible with energy being released in a zone above the magnetic inversion line of the AR intermediate bipole. This energy is then transported mainly by conduction towards the two distant kernels located in the AR main bipole. One of these kernels is first identified in this paper. Accelerated particles contribute to the energy transport only during the impulsive phase. Title: Reduction, Analysis, and Properties of Electric Current Systems in Solar Active Regions Authors: Gary, G. Allen; Demoulin, Pascal Bibcode: 1995ApJ...445..982G Altcode: The specific attraction and, in large part, the significance of solar magnetograms lie in the fact that they give the most important data on the electric currents and the nonpotentiality of active regions. Using the vector magnetograms from the Marshall Space Flight Center (MSFC), we employ a unique technique in the area of data analysis for resolving the 180 deg ambiguity in order to calculate the spatial structure of the vertical electric current density. The 180 deg ambiguity is resolved by applying concepts from the nonlinear multivariable optimization theory. The technique is shown to be of particular importance in very nonpotential active regions. The characterization of the vertical electric current density for a set of vector magnetograms using this method then gives the spatial scale, locations, and magnitude of these current systems. The method, which employs an intermediate parametric function which covers the magnetogram and which defines the local `preferred' direction, minimizes a specific functional of the observed transverse magnetic field. The specific functional that is successful is the integral of the square of the vertical current density. We find that the vertical electric current densities have common characteristics for the extended bipolar (beta) (gamma) (delta)-regions studied. The largest current systems have 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. Bibcode: 1995SPD....26.1319G Altcode: 1995BAAS...27R.991G No abstract at ADS Title: Evolution of Active Regions Leading to Flares Authors: Schmieder, B.; Demoulin, P.; Henoux, J. -C.; Driel-Gesztelyi, L. V.; Mandrini, C.; Rovira, M. Bibcode: 1994kofu.symp..297S Altcode: We model observed longitudinal magnetic fields obtained in Potsdam, Meudon, MSFC Hunstville by a series of magnetic sources located below the photosphere. H_alpha flare kernels are found situated on intersecting separatrices (surfaces delimiting regions of different magnetic connectivities). We deduce that energy release occurs mainly at the separator by magnetic reconnection. Evidence for both neutralized and un-neutralized currents are observed in different flaring regions. Moreover we have found two photospheric currents of opposite sign, linked in the corona by field lines, at the border of flare kernels. Title: Are magnetic null points important in solar flares ? Authors: Demoulin, P.; Henoux, J. C.; Mandrini, C. H. Bibcode: 1994A&A...285.1023D Altcode: When they are present, null points (points where the 3 components of the magnetic field vanish) determine the topology of the magnetic field configuration. It has been suggested that the presence of nulls is related to flares, and that they settle the region where the energy is released by magnetic reconnection. Since solar flares are initially coronal events, nulls should be located above the photosphere. Therefore, we investigate the location of nulls in configurations formed by a parasitic and a main bipole (4 magnetic sources). For both potential and linear-force free field approaches, we have found that a null was present in the corona only when the two bipoles were nearly antiparallel. The flaring regions analysed here are those where the magnetic topology has been related to flare kernels in previous papers. These observations show that flares occur for any horizontal orientation of the parasitic bipole to the main one, having only in particular cases a null in the extrapolated field. When a null is present, it can be at any place along the separator and it is not necessarily related to the region where the energy is released. These results are found both in the subflares and the intense X-ray flares studied. Examples of observed configurations that can be analysed with 2D or 3D models are presented. We conclude that nulls above the photosphere are not needed for flaring but that the spatial properties of the coronal field still determines the location where reconnection takes place. Results are discuss in the context of present understanding of 3D reconnection. Title: Observational support of reconnection in solar flares Authors: Démoulin, P.; Hénoux, J. C.; Schmieder, B.; Mandrini, C. H.; Rovira, M. G.; Somov, B. Bibcode: 1994SSRv...68..129D Altcode: We present a detailed analysis of the magnetic topology of flaring active region. TheH 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. Bibcode: 1994A&A...284..985S Altcode: We present general two-dimensional solutions for low-β and subalfvenic stationary MHD flow. Our method of solution applies to any type of boundary conditions. It solves for the pertubation of the magnetic configuration brought about by flows and by the development of shock waves in it. Solutions in cartesian and cylindrical geometries are presented to model flows in coronal loops and counter-Evershed flows above spots. In symmetrical magnetic configurations, when the distribution of pressure at the foot points is symmetrical, the flow is necessarily subsonic. Otherwise it can become supersonic at the summit of the magnetic field line and then passes through a shock. Such shocks can be very inclined to the magnetic field and the shocked material may form a dense hot sheet around a cooler core, a situation which seems to be observed in cool loops. For asymmetrical magnetic configurations, the flow accelerates towards the low gas pressure foot point and could be subsonic or trans-sonic depending on the pressure difference between the foot points. Loops can have a significant density contrast against their environment only if their energy flux differs markedly from the background one. In asymmetrical loops one leg can be much less dense than the other and poorly visible. Near spots, the sign of the difference of pressure between the two foot points is such as to drive a reverse Evershed flow towards the spot. Additional effects would be needed to drive a direct Evershed flow. Title: Interpretation of multiwavelength observations of November 5, 1980 solar flares by the magnetic topology of AR 2766 Authors: Demoulin, P.; Mandrini, C. H.; Rovira, M. G.; Henoux, J. C.; Machado, M. E. Bibcode: 1994SoPh..150..221D Altcode: We present a detailed analysis of the magnetic topology of AR 2776 together with Hα UV, X-rays, and radio observations of the November 5, 1980 flares in order to understand the role of the active region large-scale topology on the flare process. As at present the coronal magnetic field is modeled by an ensemble of sub-photospheric sources whose positions and intensities are deduced from a least-square fit between the computed and observed longitudinal magnetic fields. Charges and dipole representations are shown to lead to similar modeling of the magnetic topology provided that the number of sources is great enough. However, for AR 2776, departure from a potential field has to be taken into account, therefore a linear force-free field extrapolation is used. Title: Relationship between magnetic field evolution and flaring sites in AR 6659 in June 1991 Authors: Schmieder, B.; Hagyard, M. J.; Guoxiang, Ai; Hongqi, Zhang; Kalman, B.; Gyori, L.; Rompolt, B.; Demoulin, P.; Machado, M. E. Bibcode: 1994SoPh..150..199S Altcode: During the international campaign of June 1991, the active region AR 6659 produced six very large, long-duration flares (X10/12) during its passage across the solar disk. We present the characteristics of four of them (June 4, 6, 9, 15). Precise measurements of the spot motions from Debrecen and Tokyo white-light pictures are used to understand the fragmentation of the main sunspot group with time. This fragmentation leads to a continuous restructuring of the magnetic field pattern while rapid changes are evidenced due to fast new flux emergence (magnetograms of MFSC, Huairou). The first process leads to a shearing of the field lines along which there is energy storage; the second one is the trigger which causes the release of energy by creating a complex topology. We conjecture that these two processes with different time scales are relevant to the production of flares. Title: Relationship between electric currents, photospheric motions, chromospheric activity, and magnetic field topology Authors: van Driel-Gesztelyi, L.; Hofmann, A.; Demoulin, P.; Schmieder, B.; Csepura, G. Bibcode: 1994SoPh..149..309V Altcode: Through coordinated observations made during the Max'91 campaign in June 1989 in Potsdam (magnetograms), Debrecen (white light and Hα), and Meudon (MSDP), we follow the evolution of the sunspot group in active region NOAA 5555 for 6 days. The topology of the coronal magnetic field is investigated by using a method based on the concept of separatrices - applied previously (Mandriniet al., 1991) to a magnetic region slightly distorted by field-aligned currents. The present active region differs by having significant magnetic shear. We find that the Hα flare kernels and the main photospheric electric current cells are located close to the intersection of the separatrices with the chromosphere, in a linear force-free field configuration adapted to the observed shear. Sunspot motions, strong currents, isolated polarities, or intersecting separatrices are not in themselves sufficient to produce a flare. A combination of them all is required. This supports the idea that flares are due to magnetic reconnection, when flux tubes with field-aligned currents move towards the separatrix locations. Title: Zones with quasi-discontinuous magnetic connections in the photosphere and solar flares Authors: Bagalá, L. G.; Mandrini, C. H.; Démoulin, P. Bibcode: 1994BAAA...39...46B Altcode: The topological structure of active regions is related with flare brightening. (Mandrini et a!, 1991, 1993; Démoulin et ai, 1992, 1993, 1994). In these works, we modeled the observed longitudinal magnetic field by means of a discrete number of sub-photospheric magnetic poles, and derived the magnetic topology taking into account the connections between these poles (source method, MF). We present here a new method (quasi-discontinuity method, MQD). It finds the regions above the photosphere where the connectivity of field lines changes drastically. Title: Electric Current Systems in Solar Active Regions Authors: Gary, G. Allen; Demoulin, Pascal Bibcode: 1994ASPC...68..171G Altcode: 1994sare.conf..171G No abstract at ADS Title: CFHT eclipse observation of the very fine-scale solar corona Authors: Koutchmy, S.; Belmahdi, M.; Coulter, R. L.; Demoulin, P.; Gaizauskas, V.; MacQueen, R. M.; Monnet, G.; Mouette, J.; Noens, J. C.; November, L. J. Bibcode: 1994A&A...281..249K Altcode: At the July 11, 1991 solar total eclipse, a modern large optical telescope, Canada-France-Hawaii telescope (CFHT), was used to probe the solar corona. The best possible pictures were obtained with the CFHT, using fast imaging techniques and post-facto image selection and processing. Several cameras were run during totality to acquire sub-arcsec spatial resolution white-light images, with both narrow-band and broad-band filters. The setup and the observing procedure are described. Preliminary results, together with an evaluation of the merits of the experiment, are given, as well as a sample of images. Fine-scale coronal features were observed for the first time in a time series, confirming the importance of plasmoid-like activity in the inner corona. The observation of the smallest coronal feature ever reported is analyzed, giving a typical cross-section of 0.4 +/- 0.1 arcsec. On a larger scale, dark loops around a foreground prominence are resolved for the first time, suggesting that sheet-like voids exist above a filament channel. Title: Magnetic topology of a complex active region Authors: Mandrini, C. H.; Rovira, M. G.; Démoulin, P.; de La Beaujarière, J. -F.; Hénoux, J. C. Bibcode: 1994BAAA...39...52M Altcode: We present a detailed analysis of the magnetic topology of AR 6233 on two consecutive days (August 28 and 29, 1990). We compare the location of the magnetic separatrices and separators with off-band Hα observations and other flare manifestations, such as intense non-thermal electron precipitation and high coronal pressure sites, for two flares that occurred on these days. Because transverse magnetograms indicate that strong magnetic shear is present along the longitudinal inversion line, where flare brightening are located, the observed photospheric magnetic field is modeled in an approach in which a combination of sources with current-free and non current-free magnetic held is used. This model allows us to obtain a better ht between the observed and modeled transverse held. Then, we find a closer relationship between separatrices and hare features. The results of a current-free and of a linear force-free approach are also discussed. As in other haring regions studied previously, chromospheric flare brightening are found on separatrices. The topological structure obtained for these flares is rather complex and cannot be explained by classical flare models. We find that the connectivity of field lines may change drastically from one edge of an Ha; ribbon to the other. Electron precipitation and high coronal pressure sites, and some photospheric intense currents are also found in the immediate vicinity of separatrices. The early kernels of August 28 flare are found closer to the separatrices of the non-potential held, while the later are closer to those of the potential held. All these results agree with the hypothesis that magnetic energy is stored in field-aligned currents and released due to magnetic held reconnection, with a noticeable relaxation of the held, either at the separator region or on separatrices. Title: Dynamics of solar magnetic arches in photosphere and chromosphere Authors: Mein, P.; Mein, N.; Démoulin, P.; Gontikakis, C.; Engvold, O.; Molowby, R. Bibcode: 1994smf..conf..366M Altcode: No abstract at ADS Title: Understanding Solar Active Phenomena: A Phenomenological Approach Authors: Machado, M. E.; Demoulin, P.; Gary, G. A.; Henoux, J. C.; Mandrini, C. H.; Rovira, M. G. Bibcode: 1994step.conf..125M Altcode: No abstract at ADS Title: The control of the corona by the convective zone magnetic fields Authors: Démoulin, P. Bibcode: 1994LNP...432..121D Altcode: 1994LNPM...11..121D A review is presented on the physics of the convective zone and the implications at the coronal level. Solar magnetic fields are created in the convective layer from the kinetic energy of the dense plasma. At the coronal level, the magnetic field controls the plasma and is forced to evolve according to the time-dependent boundary conditions given at the photospheric level by the convective zone. The coronal field cannot find a smooth equilibrium when its topology is complex and current sheets are formed. These are the preferred regions where reconnection can occur. Present development of 3D reconnection is reviewed, and we show how observed flare kernels are related to the magnetic field topology. Then we describe how our present theoretical understanding of flares can help us to understand both large and small scale coronal events. Title: Twisted Flux Tubes and Sunspot Motions in AR 5555 Authors: van Driel-Gesztelyi, L.; Démoulin, P.; Schmieder, B.; Hofmann, A.; Csepura, G. Bibcode: 1994emsp.conf..115V Altcode: No abstract at ADS Title: Magnetic reconnection as a mechanism for solar flares Authors: Bagala, L. G.; Rovira, M. G.; Mandrini, C. H.; Demoulin, P.; Henoux, J. C. Bibcode: 1994iaf..conf.....B Altcode: In this paper we summarize the results of our quantitative analysis of the 3D magnetic topology of several active regions (ARs). We show that the flare brightenings in different wavelengths (H-alpha, UV, X-rays) are located at the intersection of separatrices with the chromospheric plane. Flare kernels are magnetically connected by field lines passing close to the separator in different types of configurations. We also find that photospheric current concentrations are associated with flare brightenings and can be linked in the corona by field lines following separatrices, supporting the hypothesis that magnetic energy is stored in field-aligned currents. Since magnetic reconnection is expected to take place at the separator region or on separatrices, these results strongly suggest that this is the process driving energy release in solar flares. Title: Catastrophic Evolution of a Force-free Flux Rope: A Model for Eruptive Flares Authors: Isenberg, P. A.; Forbes, T. G.; Demoulin, P. Bibcode: 1993ApJ...417..368I Altcode: We present a self-consistent, two-dimensional, magnetohydrodynamic model of an eruptive flare based on an ideal-MHD coronal magnetic field configuration which is line-tied at the photosphere and contains a forcefree flux rope. If the flux rope is not too large, the gradual disappearance of the photospheric field causes the flux rope to lose equilibrium catastrophically and jump to a higher altitude, releasing magnetic energy in the process. During the jump, an extended current sheet forms below the flux rope, and subsequent reconnection of this current sheet allows the flux rope to escape into the outer corona. A critical flux-rope radius, which depends on the form of the photospheric field, divides configurations which undergo a catastrophic loss of equilibrium from those which do not. For a photospheric field equivalent to that produced by a submerged, two-dimensional magnetic quadrupole, the critical radius is 0.23 times the length scale of the photospheric field. This result shows that catastrophic eruptions can occur for flux ropes having plausible solar values. We identify the catastrophic loss of equilibrium with the impulsive phase of eruptive flares and the subsequent reconnection of the current sheet with the gradual phase. Title: Multiwavelength Observations and Magnetic Field Modelling of a Solar Flare Authors: Bagala, L. G.; Rovira, M. G.; Mandrini, C. H.; Demoulin, P.; Henoux, J. C. Bibcode: 1993RMxAA..26..135B Altcode: No abstract at ADS Title: Filament formation Authors: Démoulin, P. Bibcode: 1993AdSpR..13i..95D Altcode: 1993AdSpR..13...95D Prominences are thin structures consisting of cold plasma embedded in the hot corona. Because the plasma beta is low, the magnetic field plays a key role in all the processes involved. During their quiescent stage, magnetic measurements can be made inside them. These give local but also direct information on the neighbouring coronal field. Our understanding of the formation of prominences simultaneously improves our knowledge about the coronal magnetic field. Based on our present observational and theoretical understanding of prominences, this review will attempt to answer the following questions: What are the magnetic configurations favourable for the formation of prominences? What can we learn about the coronal magnetic field from the study of prominences? How can prominence plasma be formed? Title: Sites of flares and filaments in solar active regions Authors: Schmieder, B.; van-Driel, L.; Hofmann, A.; Démoulin, P.; Hénoux, J. C.; Hagyard, M. Bibcode: 1993AdSpR..13i.119S Altcode: 1993AdSpR..13..119S We applied a method developed to derive from magnetic field data the location of energy release in solar active regions. This method has been applied to two sets of data (June 13-15 1980 and June 23-25 1989) using magnetograms (Meudon, MSFC, Potsdam) and Hα data (Debrecen, MSDP Meudon). The Hα flares are located at intersections of the separatrices with the chromosphere in places where high density currents are observed. This supports the idea that the energy released in flares is due to magnetic reconnection at the location of a separator and subsequently transported to the chromosphere along field lines. It is found that strong magnetic shear is a necessary condition for filament formation. Magnetic shear merely determines the importance of the flare and is certainly not a necessary condition for flare activity. Title: Relationship between magnetic field evolution and flaring sites in AR 6659 on June 1991 Authors: Schmieder, B.; Démoulin, P.; Hagyard, M.; Machado, M. E.; Guo, Xiang Ai; Zhang, Hongqi; Fu, Qijun; Zhi, Kai Li; Luan, Ti; Kalman, B.; Györi, L. Bibcode: 1993AdSpR..13i.123S Altcode: 1993AdSpR..13..123S During the international campaign of June 1991, the active region AR 6659 produced 6 very large long duration flares at the same location during its passage across the solar disk. Vector magnetograms were obtained at Marshall (Huntsville) and Huairou Station (Beijing) with a time difference of 10 to 12 hours, thus giving a good survey of the magnetic field evolution with time. The flare of June 6/01:08 UT (X12 plus/4B) was observed in Shahe Station (Beijing) in white light, in Hα and in radio centimetric wavelengths. The evolution of the flare of June 9/01:43 UT (X10/3B) has been followed in Hα at the Yunnan Observatory (Kunming). An other one was well observed on June 15 at 08:20 UT in Wroclaw and in Debrecen. Some subflares were observed at Sac Peak on June 4, 5, 7 at Meudon on June 10, 14 and Debrecen on June 12 and 13.

In this short communication we concentrate on the relationship between magnetic field shear and flare sites. Title: Conditions for the appearance of "bald patches" at the solar surface Authors: Titov, V. S.; Priest, E. R.; Demoulin, P. Bibcode: 1993A&A...276..564T Altcode: A general criterion for the existence of sections of the photospheric polarity inversion line where the overlying magnetic field lines are parallel to the photosphere is presented. It is shown that such sections, called "bald patches", exist for a wide range of parameters in potential and constant-α force-free fields created by four concentrated sources of magnetic flux. Bald patches appear when the polarity inversion line is bent too much in an S-like manner. The appearance of bald patches may be important for the formation of prominences and possibly for solar flares. Title: Common Evolution of Adjacent Sunspot Groups Authors: van Driel-Gesztelyi, L.; Csepura, G.; Nagy, I.; Gerlei, O.; Schmieder, B.; Rayrole, J.; Demoulin, P. Bibcode: 1993SoPh..145...77V Altcode: The evolution of two adjacent bipolar sunspot groups is studied using Debrecen full-disc, white-light photoheliograms and Hα filtergrams as well as Meudon magnetograms. The proper motions of the principal preceding spots of both groups show quite similar patterns; the spots move along almost parallel tracks and change the direction of their motion on the same day at almost the same heliographic longitude. Also, three simultaneous emergences of magnetic flux were observed in both groups. These observations support the idea that these adjacent sunspot groups were magnetically linked below the photosphere. Matching the extrapolated magnetic field lines with the chromospheric fibril structure appears to be different in the two groups since they indicate quite different model solutions for each group, i.e., a near-potential magnetic field configuration in the older group (1) and a twisted force-free field configuration in the younger group (2). The latter configuration could be created by a considerable twist of the main bunch of flux tubes in Group 2, which is reflected in the relative sunspot motions. It is also showed how this twist contributed to the formation of a filament between the two groups. Title: Evidence for magnetic reconnection in large-scale magnetic structures in solar flares Authors: Mandrini, C. H.; Rovira, M. G.; Demoulin, P.; Henoux, J. C.; Machado, M. E.; Wilkinson, L. K. Bibcode: 1993A&A...272..609M Altcode: Modelling the observed vertical magnetic field of an active region (NOAA 2372) for two consecutive days, April 7 and 8, 1980, by the potential field of an ensemble of magnetic dipoles, we derived the location of the separatrices, surfaces that separate cells of different field line connectivities, and of the separator which is the intersection of the separatrices. The overall temporal evolution of the magnetic fields and the location of the off-band Hα kernels of flares, that occurred before the obtention of the magnetograms, support the hypothesis that the flares were due to magnetic reconnection taking place in the main separator of the active region. The triggering of reconnection in a second separator appearing on April 8 by reconnection in the main separator is strongly suggested by the observed magnetic connectivities and the kernels locations. The location of the emerging currents on the separatrices support the idea that flares are fed by the release of magnetic free energy. Title: A Model for an Inverse Polarity Prominence Supported in a Dip of a Quadrupolar Region Authors: Demoulin, P.; Priest, E. R. Bibcode: 1993SoPh..144..283D Altcode: We investigate the formation and support of solar prominences in a quadrupolar magnetic configuration. The prominence is modeled as a current sheet with mass in equilibrium in a two-dimensional field. The model possesses an important property which is now thought to be necessary, namely that the prominence forms within the dip, rather than the dip being created by the prominence. Title: Evidence for magnetic reconnection in solar flares Authors: Demoulin, P.; van Driel-Gesztelyi, L.; Schmieder, B.; Hemoux, J. C.; Csepura, G.; Hagyard, M. J. Bibcode: 1993A&A...271..292D Altcode: From a study of the magnetic field topology in an active region, evidence is derived that solar flares are produced by magnetic reconnection. We study a complex group with two active regions (AR 25 t 1 and AR 2512) for three consecutive days, June 13-15 1980. The observed longitudinal magnetic field is used to model the coronal magnetic field by the potential field created by a series of magnetic charges. This computed field matches satisfactorily the Ho fibrils and the observed transverse field direction. A set of flares occurs principally in the northern group (AR 2511). During these three days, two different magnetic configurations in succession are responsible for the occurrence of these flares: first the intrusion of a new opposite flux in the following polarity, secondly the emergence of new flux between the main polarities. In this last case flares occurred, although the emerging bipole is almost parallel to the main bipole. We show that even in this bipolar configuration a separator is present and that observed H flare ribbons are located near the intersection of the computed separatrices with the photosphere. This provides strong support to a model where reconnection releases the stored magnetic energy. The induced evolution of the magnetic field forces reconnection along others separators. They are connected by magnetic field lines to fainter kernels. Title: The solar corona's magnetism. Authors: Amari, T.; Démoulin, P. Bibcode: 1993Rech...24..258A Altcode: No abstract at ADS Title: Observational Evidence for Magnetic Reconnection in Solar Flares (Invited) Authors: Henoux, J. C.; Demoulin, P.; Mandrini, C. H.; Rovira, M. G. Bibcode: 1993ASPC...46..333H Altcode: 1993IAUCo.141..333H; 1993mvfs.conf..333H No abstract at ADS Title: Interpretación de las observaciones de fulguraciones solares en función de la topología de la región activa Authors: Rovira, M. G.; Mandrini, C. H.; Demoulin, P.; Henoux, J. C.; Machado, M. E. Bibcode: 1993BAAA...38..114R Altcode: Con el objeto de comprender el rol que juega la topología a gran escala durante las fulguraciones solares, realizamos un estudio detallado de la estructura topológica de la región activa (AR) 2776 y la comparamos con observaciones en Hα , UV, rayos X y radio de dos fulguraciones que tuvieron lugar el 5 de Noviembre de 1980. Como en casos anteriores el campo magnético coronal se modeló usando un conjunto de fuentes subfotosféricas, cuyas posiciones e intensidades se dedujeron a partir de un ajuste por cuadrados mínimos al campo longitudinal observado. En este caso, dado que el campo de AR 2776 no es potencial, se uso en el modelo una extrapolación libre de fuerzas lineal. La relación entre la posición de los cuatro abrillantamientos en Hα de distintas fulguraciones y la topología de regiones activas cuadrupolares ha sido estudiada anteriormente. En este caso la región es bipolar y las fulguraciones muestran una estructura de dos bandas. Estas se ubican sobre las separatrices cuando se tiene en cuenta el shear del campo, deducido de la dirección de las fibrillas observadas a nivel cromosférico. Este estudio esta de acuerdo con la hipótesis de que la energía magnética está almacenada en corrientes alineadas con el campo y que se libera por reconección del mismo, en la región del separador, antes de ser transportada a la cromosfera. También es posible que parte de la energía magnética se almacene y se libere sobre las separatrices. La ubicación de las corrientes fotosféricas, deducidas de los magnetogramas vectoriales, en la intersección de las separatrices con la fotosfera concuerda con este último punto. Title: Estabilidad de la estructura topológica de una región activa en presencia de fuentes de campo externas Authors: Mandrini, C. H.; Rovira, M. G.; Demoulin, P.; Henoux, J. C.; de La Beaujardiere, J. Bibcode: 1993BAAA...38..115M Altcode: A partir de las observaciones del campo magnético longitudinal de la región activa (AR) 6233, obtenidas en el Observatorio Mees (Universidad de Hawaii), derivamos su estructura topológica y estudiamos la evolución de la misma a lo largo de dos días. En el bipolo principal de esta región se desarrollaron numerosas fulguraciones y microfulguraciones en el período de estudio. Dado que en este caso contamos con magnetogramas que cubren distintas escalas espaciales, analizamos la influencia que las fuentes de campo externas a dicho bipolo tienen sobre la estructura topológica de la zona en donde se produjeron las fulguraciones. Esta se obtiene a partir de un modelo del campo de AR 6233 tanto en la aproximación potencial, como en la libre de fuerzas lineal. Nuestros resultados muestran que la estructura topológica básica de la región de interés permanece invariante en ambos casos. Esto justificaría el uso, debido a limitaciones instrumentales, de magnetogramas que cubren una porción limitada de la región activa al modelar el campo como se ha hecho en estudios anteriores. Title: MHD Equilibria in Uniform Gravity Authors: Surlantzis, G.; Démoulin, P.; Heyvaerts, J.; Sauty, C. Bibcode: 1993ASSL..183..629S Altcode: 1993pssc.symp..629S No abstract at ADS Title: Helical Structures around Quiescent Solar Prominences Computed from Observable Magnetic Fields Authors: Demoulin, P.; Raadu, M. A. Bibcode: 1992SoPh..142..291D Altcode: We analyse the magnetic support of solar prominences in two-dimensional linear force-free fields. A line current is added to model a helical configuration, well suited to trap dense plasma in its bottom part. The prominence is modeled as a vertical mass-loaded current sheet in equilibrium between gravity and magnetic forces. Title: Structural Characteristics of Eruptive Prominences Authors: Demoulin, P.; Vial, J. C. Bibcode: 1992SoPh..141..289D Altcode: Nowadays the primordial importance of the magnetic field for coronal plasma physics is well known. However, its determination is only made in cool regions, mainly the photosphere and prominences. The extrapolation to the corona gives some indications of the magnetic structure but is not presently sufficiently reliable. So it is important to consider all the other observable physical effects of the magnetic field. Title: Determination of force-free magnetic fields above the photosphere using three-component boundary conditions. II - Analysis and minimization of scale-related growing modes and of computational induced singularities Authors: Demoulin, P.; Cuperman, S.; Semel, M. Bibcode: 1992A&A...263..351D Altcode: The problem of the extrapolation of the observed three-component photospheric magnetic fields within is studied within the framework of the nonlinear force-free field model. The possible vertically growing modes and their relationship to the horizontal and vertical chosen scales is discussed, and the mathematical singularities arising along neutral field lines and leading to nondefinite alpha values are examined. A search is made for simple procedures aimed at minimizing these algorithm-dependent computational errors. Title: Book-Review - Dynamics of Quiescent Prominences Authors: Ruzdjak, V.; Tandberg-Hanssen, E.; Demoulin, P. Bibcode: 1992SSRv...61..427R Altcode: No abstract at ADS Title: Development of a Topological Model for Solar Flares Authors: Demoulin, P.; Henoux, J. C.; Mandrini, C. H. Bibcode: 1992SoPh..139..105D Altcode: The main theoretical studies of the process involved in solar flares have been made in the two-dimensional approximation. However, the preliminary studies made with three field components suggest that reconnection could take place in the separatrices, the separator (intersection of separatrices) being a privileged location for this process. As a consequence the sites of flare kernels must be located on the intersections of the separatrices with the photosphere. Therefore, in order to understand the role of interacting large-scale structures in solar flares, we have analysed the topology of three-dimensional potential and linear force-free fields. The magnetic field has been modelled by a distribution of charges or dipoles located below the photosphere. This modelling permits us to define the field connectivity by the charges or the dipoles at both ends of every field line. Title: The properties of sources and sinks of a linear force-free field Authors: Demoulin, P.; Priest, E. R. Bibcode: 1992A&A...258..535D Altcode: In a highly conducting plasma, the magnetic field topology determines where, for example, current sheets can form, which is of great importance as a potential coronal heating source. With the classical extrapolation of a continuous weak photospheric field, the determination of topology is in general a difficult challenge. Because of the concentration of the photospheric field at intense flux tubes in supergranulation boundaries a more realistic field representation may be a description in terms of magnetic singularities located just below the photosphere. In this paper we analyze in detail the generalization to linear force-free fields of the standard multipole expansion for singular potential fields. Solutions are presented in spherical coordinates with the constraint that all singularities are located in the half-space z is less than 0 below the solar photospheric plane (z = 0). A great variety of solutions is shown to exist depending on two continuous and one discrete parameter. The properties of monopole and dipole solutions in particular are discussed and it is shown that isolated magnetic charges exist only in the potential limit and not in a linear force-free field. Title: Linear force-free magnetic field around quiescent solar prominences computed from observable boundary conditions Authors: Demoulin, P.; Raadu, M. A.; Malherbe, J. M. Bibcode: 1992A&A...257..278D Altcode: The magnetic support of solar prominences in two-dimensional linear force-free fields is analyzed. The prominence was modeled as a vertical current sheet with mass in equilibrium between gravity and magnetic forces. A finite difference numerical technique was used which incorporates both vertical photospheric and horizontal prominence magnetic field observations as boundary conditions. The mixed-boundary value problem is described and the current singularity generally present is eliminated by a modification of the initial boundary condition. Using the linear force-free hypothesis the bipolar and quadripolar regions were found to be associated with normal and inverse prominence polarity respectively. An increase of magnetic shear decreases the mass supported for a given vertical dependence of the field component orthogonal to the prominence. Title: Weighted Current Sheets Supported in Normal and Inverse Configurations: A Model for Prominence Observations Authors: Demoulin, P.; Forbes, T. G. Bibcode: 1992ApJ...387..394D Altcode: A technique which incorporates both photospheric and prominence magnetic field observations is used to analyze the magnetic support of solar prominences in two dimensions. The prominence is modeled by a mass-loaded current sheet which is supported against gravity by magnetic fields from a bipolar source in the photosphere and a massless line current in the corona. It is found that prominence support can be achieved in three different kinds of configurations: an arcade topology with a normal polarity; a helical topology with a normal polarity; and a helical topology with an inverse polarity. In all cases the important parameter is the variation of the horizontal component of the prominence field with height. Adding a line current external to the prominence eliminates the nonsupport problem which plagues virtually all previous prominence models with inverse polarity. Title: Reconección magnética entre estructuras a gran escala durante fulguraciones solares Authors: Mandrini, C. H.; Rovira, M. G.; Demoulin, P.; Henoux, J. C.; Machado, M. E. Bibcode: 1992BAAA...37..112M Altcode: A partir del modelado del campo magnético de la región activa NOAA 2372 se determina la ubicación de sus distintas estructuras topológicas: separatrices y separador. Este análisis se hace en base a observaciones del campo magnético a lo largo de tres días. La evolución temporal del campo global y la ubicación de los abrillantamientos en H a de varias fulguraciones, en relación con la topología determinada, están de acuerdo con el hecho de que las fulguraciones son el resultado del proceso de reconección que tiene lugar en el separador principal de la región activa. Title: Fulguraciones solares y su relación con la topología del campo magnético Authors: Balgala, L. G.; Rovira, M. G.; Mandrini, C. H.; Demoulin, P. Bibcode: 1992BAAA...37..112B Altcode: En base a una distribución de dipolos magnéticos modelamos el campo de una región activa visible sobre el disco solar en noviembre de 1980. Comparamos la estructura topológica calculada a partir de este modelo, en su aproximación potencial, con la emisión en líneas cromosféricas y de la región de transición debidas a una figuración solar. Extendimos este análisis a las imágenes obtenidas por el Hard X-ray Imaging Spectrometer en el continuo de rayos X, entre 3,5 y 30 keV. Title: Interaction of Largescale Magnetic Structures in Solar Flares Authors: Mandrini, C. H.; Demoulin, P.; Henoux, J. C. Bibcode: 1992LNP...399...54M Altcode: 1992IAUCo.133...54M; 1992esf..coll...54M Modelling the observed vertical magnetic field of active region (AR) NOAA 2372 by the potential field of an ensemble of magnetic dipoles, we have derived the likely location of the separatrices, surfaces that separate cells of different field line connectivities, and of the separator which is the intersection of the separatrices. The connectivity of every magnetic field line, which is defined by the dipoles located at its ends, is computed by a code that, starting from any pixel in the photospheric plane, integrates numerically the differential equation defining a line of force towards both ends of this line until one dipole is reached. This code allows us to obtain the topology of the field in three dimensions. We have compared our results with observations of a 1B/M1 flare that developed in AR 2372 on April 6, 1980 at 20:53 UT (Lin and Gaizauskas, 1987), twenty minutes before obtaining the magnetogram. We found that four of the five off-band Ha kernels were located near or at the separatrices. These Ha kernels are connected by field lines that pass close to the separator. This indicates that the flare may have resulted from the interaction of large scale magnetic structures in the separator region. Moreover, Lin and Gaizauskas (1987) showed that the Ha flare kernels coincided with the peak values of the longitudinal electric current density. This finding and the fact that no strong current and no Ha kernel are observed at the intersection of the separator with the photosphere, lead to the conclusion that the magnetic energy released during the flare is mostly stored in an ensemble of currents flowing along lines of force. Some instability, presumably due to reconnection taking place in the separator, is likely to be the origin of the energy release and of the observed flare. Title: Evidence for the interaction of large scale magnetic structures in solar flares. Authors: Mandrini, C. H.; Demoulin, P.; Henoux, J. C.; Machado, M. E. Bibcode: 1991A&A...250..541M Altcode: By modeling the observed vertical magnetic field of an active region AR 2372 by the potential field of an ensemble of magnetic dipoles, the likely location of the separatrices, surfaces that separates cells of different field line connectivities, and of the separator which is the intersection of the separatrices, is derived. Four of the five off-band H-alpha kernels of a flare that occurred less than 20 minutes before obtaining the magnetogram are shown to have taken place near or at the separatrices. These H-alpha kernels are connected by field lines that pass near the separator. This indicates that the flare may have resulted from the interaction in the separator region of large scale magnetic structures. Title: Determination of absolute strengths of N2 quadrupole lines from high-resolution ground-based IR solar observations Authors: Demoulin, P.; Zander, R.; Farmer, C. B.; Rinsland, C. P. Bibcode: 1991JGR....9613003D Altcode: The strength of S-branch lines of the N2 (1-0) electric quadrupole vibration-rotation band are determined by an analysis of solar absorption spectra. The solar data were recorded with a Fourier transform spectrometer and are characterized by high resolution, and a high signal-to-noise ratio. By extrapolating equivalent width measurements of the lines from varying air masses to zero air mass, the line strengths are found for the transitions from S7 to S10. The results presented do not include half widths and are found to be accurate to within 5 percent, and following a redetermination the N2 transitions are accurate to within 0.0002/cm. Line-of-sight atmospheric air masses associated with remotely sensed IR spectroscopic observations can be determined directly by utilizing the highly accurate data. Title: Removal of singularities in the Cauchy problem for the extrapolation of solar force-free magnetic fields Authors: Cuperman, S.; Demoulin, P.; Semel, M. Bibcode: 1991A&A...245..285C Altcode: The singularities occurring in the Cauchy problem for the extrapolation of solar nonlinear force-free magnetic fields at positions of vanishing normal component, B(z), are removed. This is based on the observation that the constancy of the quantity alpha(r), characterizing the force-free magnetic fields, along a given magnetic field line, implies that the singularity in Maxwell's equation is of mathematical rather than of physical origin. Thus, requiring also the vanishing of the numerator at P(0) leads to an undetermined form for alpha. By using Taylor's expansions in two variables (x and y) about P(0) for both numerator and denominator, the actual value for alpha, namely alpha (P(0), is obtained. The procedure is tested on the case of the analytical model proposed by Low (1982). Title: Instability of a prominence supported in a linear force-free field. II - Effect of twist or flux conservation Authors: Demoulin, P.; Ferreira, J.; Priest, E. R. Bibcode: 1991A&A...245..289D Altcode: Ideal MHD equations are used to study the vertical stability of a prominence in a linear force-free field in two dimensions. The prominence is modeled by a line current in equilibrium at a height between the background magnetic force, the repulsion of image currents and gravity. Attention is given to boundary conditions, current evolution, parameters, stability results with boundary conditions, and the effects of lateral boundaries. Title: Ground-Based Infrared Measurements of HNO3 Total Column Abundances: Long-Term Trend and Variability Authors: Rinsland, C. P.; Zander, R.; Demoulin, P. Bibcode: 1991JGR....96.9379R Altcode: The long-term trend and variability of the total column amount of atmospheric nitric acid (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. Bibcode: 1991gamp.conf..281D Altcode: A rapid overview of observations is given, and then it is tried to understand thermal and magnetic processes that lead to prominence formation. One section is devoted to what we can learn about the Sun, from prominences. The support and eruption of prominences are totally omitted. Title: Solar Prominences Authors: Demoulin, P. Bibcode: 1991assm.conf..281D Altcode: No abstract at ADS Title: The creation of the magnetic environment for prominence formation in a coronal arcade Authors: Amari, T.; Démoulin, P.; Browning, P.; Hood, A.; Priest, E. Bibcode: 1991A&A...241..604A Altcode: The possibility of prominence formation in sheared coronal arcades is investigated. The creation of a dip at the summit of field lines is a likely requirement before a prominence can form; then dense plasma can be supported against gravity by the Lorentz force. It is proved that, in fact, no shear profile can create a dip in a two-dimensional force-free arcade if the photospheric field is bipolar. However, numerical investigations show that shearing an arcade can induce very flat field lines. It is investigated, in order of magnitude, how this flattening of the field can increase the free fall time of a dense plasma. Also, the interaction between shear and twist is analyzed; the critical twist needed to have a dip is a decreasing function of shear. Title: How to Form a Dip in a Magnetic Field Before the Formation of a Solar Prominence Authors: Démoulin, P.; Priest, E. R. Bibcode: 1990LNP...363..269D Altcode: 1990doqp.coll..269D; 1990IAUCo.117..269D Magnetic fields with downward curvature are not favourable for prominence formation since the presence of a small quantity of dense material at the summit of a low-beta arcade cannot deform sufficiently the magnetic field lines to remain there in a stable manner. Thus a dip at the field line summit is needed before a prominence can form. We investigate different ways of forming such an upward curvature. Results with a twisted flux tube or a sheared arcade are reviewed, and a third possibility, namely a quadrupolar region is proposed. Title: Relationship between a spot and a filament observed during spacelab 2 mission Authors: Schmieder, B.; Dere, K. P.; Raadu, M. A.; Démoulin, P.; Alissandrakis, C. E. Bibcode: 1990AdSpR..10i.195S Altcode: 1990AdSpR..10..195S During the Spacelab 2 Mission, an active region including a sunspot, plages, fibrils and a filament which disappears during the observation period, was observed in Hα and in the C IV lines. The analysis of the observations leads to several conclusions. Shear in the active region filament is observed before its disappearance. Hα and C IV upflows in the filament are well correlated spatially, but the transition zone (C IV) velocities are an order of magnitude larger than the Hα chromospheric ones. Over the sunspot, the reverse-Evershed effect is observed in Hα and in C IV Dopplershift images while strong downflows are also detected in the C IV profiles.

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. Bibcode: 1990LNP...363..232S Altcode: 1990doqp.coll..232S; 1990IAUCo.117..232S The evolution of the active region AR4682 observed in 1985 during six rotations was dominated by three different phenomena: . the large scale pattern activity: relationship between two active regions, formation of a quiescent filament during the decay phase of the active region, . the presence of two pivot points along the filament surrounding the sunspot-with the long term one is associated the existence of the filament, with the short term one the activity with partial disappearance, . the magnetic shear during one rotation. The magnetic field lines have been extrapolated from photospheric data using Alissandrakis code (1981). The magnetic configuration with the existence of a dip favors the formation of a filament. We note that the shearing of the sunspot region and of the filament are both well described by force-free magnetic fields with the same constant α. This suggests that they are both a consequent of the same shear process. Title: A three-dimensional model for solar prominences Authors: Démoulin, P.; Priest, E. R.; Anzer, U. Bibcode: 1990LNP...363..268D Altcode: 1990doqp.coll..268P; 1990LNP...363..268P; 1990IAUCo.117..268P We suggest here a model for the 3D structure of quiescent prominences by a superposition of two fields. A 3D force-free field with constant is assumed to exist in the corona prior to the prominence formation. The prominence itself is represented by a line current which interacts with the coronal field. The three-dimensional field is represented by analytical functions and concentration of the magnetic field at the photospheric level by convection cells is taken into account. When the field created by the photospheric pattern supports the prominence, the prominence feet are found to be located at supergranule centres otherwise; they are located at cell boundaries. Title: A three-dimensional model for solar prominences Authors: Demoulin, P.; Priest, E. R.; Anzer, U. Bibcode: 1989A&A...221..326D Altcode: In an attempt to model the external force field of a prominence, a three-dimensional linear force-free field configuration was studied. The model consists of a fundamental together with a harmonic that is periodic along the prominence. The variation of the prominence height along the prominence is calculated and it is suggested that feet occur where the prominence sags down to low heights. Title: A twisted flux model for solar prominences. II - Formation of a dip in a magnetic structure before the formation of a solar prominence Authors: Demoulin, P.; Priest, E. R. Bibcode: 1989A&A...214..360D Altcode: The possibility of dip formation in a linear force-free field before the formation of a filament is investigated. The creation of a dip prior to prominence formation requires a greatly sheared magnetic field and a particular magnetic base flux. In the present work, attention is given to a bipolar region devoid of parasite polarity. Title: Dynamics of a filament at the boundary of a SPOT region with magnetic shear Authors: Schmiedler, B.; Demoulin, P.; Raadu, M. A.; Dere, K. P. Bibcode: 1989A&A...213..402S Altcode: H-alpha (MSDP), magnetograph (Meudon), and C IV (HRTS) observations are used to investigate the relationship between the dynamics of a solar filament and a spot region with vortex structure. Comparisons are made between the structures in H-alpha and C IV intensity and Doppler-shift images. These show filament shearing and a good correlation between H-alpha and C IV upflow, the C IV filament being very dynamic (+ or - 50 km/s). Magnetograph data for the whole region including the sunspot are used to calculate linear force-free fields. The magnetic structure at the filament is found to be favorable for support. Title: The magnetic field around quiescent solar prominences computed from observational boundary conditions Authors: Demoulin, P.; Malherbe, J. M.; Priest, E. R. Bibcode: 1989A&A...211..428D Altcode: A generalization of Anzer's model (1972) for quiescent prominence support is presented. The coronal field is assumed to be current-free except inside the prominence where currents support dense material against gravity. The prominence is taken to be an infinitely thin current sheet of finite extent along the vertical axis. The hypothesis of two-dimensional fields allows the use of complex functions to solve the mixed boundary problem which is defined by the observed vertical field in the photosphere and the horizontal magnetic field in the prominence. These boundary conditions are not sufficient to determine a unique solution for the magnetic field. The indeterminacy is decreased by physical considerations, and some models for Normal (N) and Inverse (I) configurations are presented. In both cases it is possible to find field configurations which can support the fintie prominence against gravity. Title: Structure et stabilité thermique et magnétique des protubérances solaires Title: Structure et stabilité thermique et magnétique des protubérances solaires Title: Thermal and magnetic structure and stability of solar prominences; Authors: Démoulin, Pascal Bibcode: 1989PhDT.......141D Altcode: No abstract at ADS Title: How to Form a Dip in a Magnetic Field Before the Formation of a Solar Prominence Authors: Demoulin, P.; Priest, E. R. Bibcode: 1989HvaOB..13..261D Altcode: No abstract at ADS Title: A Three-Dimensional Model for Solar Prominences Authors: Demoulin, P.; Priest, E. R.; Anzer, U. Bibcode: 1989HvaOB..13..253D Altcode: No abstract at ADS Title: Formation of a Filament around a Magnetic Region Authors: Schmieder, B.; Demoulin, P.; Ferreira, J.; Alissandrakis, C. E. Bibcode: 1989HvaOB..13....1S Altcode: No abstract at ADS Title: Instability of a prominence supported in a linear force-free field Authors: Demoulin, P.; Priest, E. R. Bibcode: 1988A&A...206..336D Altcode: The authors analyse the equilibrium of a prominence by modelling it as a line of current under the action of gravity and of a two-dimensional constant force-free field. They show that a region of non-equilibrium may occur, if the field strength is great enough, for some distribution of the base flux. This occurs for both Kippenhahn-Schlüter and Kuperus-Raadu topologies and the region of non-equilibrium increases with the shear. Title: Some dynamical aspects of a quiescent filament Authors: Schmieder, B.; Demoulin, P.; Poland, A.; Thompson, B. Bibcode: 1988A&A...197..281S Altcode: A typical quiescent filament was observed on the disk in the Hα and C IV lines during a period of approximately one hour. Vertical velocities (<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. Bibcode: 1988dssp.conf...93D Altcode: The aim of this work is to clarify definitely the conditions under which the transition region is stabilized and to show that there exist instabilities which can lead to the formation of a prominence. Title: Non equilibrium of a prominence current in a linear force free field. Authors: Demoulin, P.; Priest, E. Bibcode: 1988dssp.conf...45D Altcode: The authors analyse the equilibrium of a prominence by modelling it as a line of current under the action of gravity and of a two dimensional constant force free field. They show that a region of non equilibrium may occur, if the field strength is great enough, for some distribution of the base flux. This occurs for both Kippenhahn-Schluter and Kuperus-Raadu topologies and the region of non equilibrium increases with the shear. Title: Fine structures in solar filaments. I - Observations and thermal stability Authors: Demoulin, P.; Malherbe, J. M.; Schmieder, B.; Raadu, M. A. Bibcode: 1987A&A...183..142D Altcode: Limb observations of quiescent prominences show very fine structures of less than one arcsecond. Here H-alpha observations on the disk, made with the Multichannel Subtractive Double Pass spectrograph operating at the Observatoire du Pic du Midi are presented. They show long fine structures in the body of the filament, both in intensity and velocity maps. Many prominence models ignore such fine structures and suppose that the quiescent filament is a uniform body such as is seen in unresolved images. It has been suggested that in a current-sheet model of a prominence, fine structures may be produced as a consequence of the tearing mode coupled to thermal instability. Here the role of parallel and orthogonal conduction on the stability of a periodic fine structure is investigated. Equilibrium conditions are found and growth rates determined for linear perturbations. Title: Nonequilibrium of a Prominence Current in a Linear Force-Free Field Authors: Demoulin, P.; Priest, E. R. Bibcode: 1987dssp.work...45D Altcode: 1987ASSL..150...45D No abstract at ADS Title: Can a Thermal Instability Form a Prominence Authors: Demoulin, P.; Einaudi, G. Bibcode: 1987dssp.work...93D Altcode: 1987ASSL..150...93D No abstract at ADS Title: Thermal stability analysis of the fine structure of solar prominences. Authors: Demoulin, Pascal; Malherbe, Jean-Marie; Schmieder, Brigitte; Raadu, Mickael A. Bibcode: 1986NASCP2442..143D Altcode: The authors analyse the linear thermal stability of a 2D periodic structure (alternatively hot and cold) in a uniform magnetic field. The energy equation includes wave heating (assumed proportional to density), radiative cooling and both conduction parallel and orthogonal to magnetic lines. The equilibrium is perturbed at constant gas pressure. The results compared with observations show that the computations suggest that the size of the unresolved threads could be of the order of 10 km only. Title: Constraints on filament models deduced from dynamical analysis. Authors: Simon, G.; Schmieder, B.; Demoulin, P.; Malherbe, J. M.; Poland, A. I. Bibcode: 1986NASCP2442..177S Altcode: 1986copp.nasa..177S The conclusions deduced from simultaneous observations with the Ultra-Violet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission satellite, and the Multichannel Subtractive Double Pass (MSPD) spectrographs at Meudon and Pic du Midi observatories are presented. The observations were obtained in 1980 and 1984. All instruments have almost the same field of view and provide intensity and velocity maps at two temperatures. The resolution is approx. 0.5 to 1.5" for H alpha line and 3" for C IV. The high resolution and simultaneity of the two types of observations allows a more accurate description of the flows in prominences as functions of temperature and position. The results put some contraints on the models and show that dynamical aspects must be taken into account. Title: Dynamics of solar filaments. VI - Center-to-limb study of H-alpha and C IV velocities in a quiescent filament Authors: Simon, G.; Schmieder, B.; Demoulin, P.; Poland, A. I. Bibcode: 1986A&A...166..319S Altcode: The rotation of a stable quiescent filament from near disk center to the limb has been observed. Observations of intensity and velocity were made in H-alpha and C IV, and compared with magnetic field measurements. From the H-alpha observations, it is concluded that the filament is made up of many small scale magnetic features that are not coherently aligned along the neutral line. They are especially convoluted at the apparent 'footpoints'. The measured velocities are of the order of a few kilometers per second in both lines. However, the comparison of the standard deviations of the C IV velocities in and out of the filament as it rotates toward the limb shows that the vertical velocities in the filament are greater than the horizontal velocities. Measurements of velocity do not make it possible to distinguish between the Raadu-Kuperus (1973) or Kippenhahn-Schluter (1957) models for prominences because neither theory is adequately developed for this comparison. However, the observation of the many fine loops brings into question the correctness of either model.