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Quantitative model for the generic 3D shape of ICMEs at 1 AU  

Pascal Demoulin   Submitted: 2016-09-05 05:51

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. 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. 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. 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. 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.

Authors: P. Demoulin, M. Janvier, J.J. Masias-Meza and S. Dasso
Projects: ACE

Publication Status: A&A, in press
Last Modified: 2016-09-07 12:12
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Homologous solar events on 2011 January 27: Build-up and propagation in a complex coronal environment  

Pascal Demoulin   Submitted: 2016-03-11 09:14

In spite of the wealth of imaging observations at extreme-ultraviolet, X-ray, and radio wavelengths, there are still a relatively small number of cases where the whole imagery becomes 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 formation of shocks, and on their propagation. We have analyzed the interactions of a couple of homologous CME events with the ambient coronal structures. Both events were launched in a direction far from the local vertical, and exhibited a radical change of their direction of propagation during their progression from the low corona into higher altitudes. Observations at extreme ultraviolet wavelengths from the Atmospheric Imaging Assembly instrument onboard the Solar Dynamic Observatory were used to track the events in the low corona. The development of the events at higher altitudes was followed with the white light coronagraphs onboard the Solar and Heliospheric Observatory. Radio emissions produced during the development of the events were well recorded by the Nancay solar instruments. By detecting accelerated electrons, the radio observations are an important complement to the extreme ultraviolet imaging. They allowed us to characterize the development of the associated shocks, and helped unveil the physical processes behind the complex interactions between the CMEs and ambient medium (e.g., compression, reconnection).

Authors: M. Pick, G. Stenborg, P. Demoulin, P. Zucca, A. Lecacheux
Projects: Nançay Radioheliograph

Publication Status: ApJ, in press
Last Modified: 2016-03-15 11:25
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Magnetic Flux and Helicity of Magnetic Clouds  

Pascal Demoulin   Submitted: 2015-08-31 04:23

Magnetic clouds (MCs) are formed by flux ropes (FRs) launched from the Sun as part of coronal mass ejections (CMEs). They carry away an important amount of magnetic flux and helicity. The main aim of this study is to quantify these quantities from insitu 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 crossing the sphere of radius of 1 AU, centered at the Sun, per year and during a solar cycle. We also include in the study two sets of small FRs which 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. They carry in one year 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 comparable to the one estimated for the solar dynamo and the one measured in emerging active regions.

Authors: Demoulin P., Janvier M., Dasso S.
Projects: Wind

Publication Status: Solar Physics (in press)
Last Modified: 2015-08-31 09:42
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Evolution of interplanetary coronal mass ejections and magnetic clouds in the heliosphere  

Pascal Demoulin   Submitted: 2013-09-04 02:50

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.

Authors: Demoulin P.
Projects: STEREO

Publication Status: submitted, IAU S300 proceedings
Last Modified: 2013-09-04 11:42
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Solar filament eruptions and their physical role in triggering Coronal Mass Ejections  

Pascal Demoulin   Submitted: 2012-12-17 07:45

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. In order to initiate eruptions, different mechanisms have been proposed: new emergence of flux, and/or dispersion of the external magnetic field, and/or reconnection of field lines below or above the flux rope. These mechanisms reduce the downward magnetic tension and favor the rise of the flux rope. Another mechanism is the kink instability when the configuration is twisted too much. In this paper we open a forum of discussions revisiting observational and theoretical papers to understand which mechanisms trigger the eruption. We conclude that all the above quoted mechanisms could bring the flux rope to an unstable state. However, the most efficient mechanism for CMEs is the loss-of-equilibrium or torus instability, when the flux rope has reached an unstable threshold determined by a decay index of the external magnetic field.

Authors: Schmieder B., Demoulin P., Aulanier G.
Projects: None

Publication Status: in press, Advances in Space Research
Last Modified: 2012-12-17 11:09
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The 3D geometry of active region upflows deduced from their limb-to-limb evolution  

Pascal Demoulin   Submitted: 2012-11-28 02:51

We analyse 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 centre, we deduce their 3D geometrical properties as inclination and angular spread in three coronal lines (SiVII, FeXII, FeXV). 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 centre. 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 SiVII , FeXII and FeXV 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. We propose that, at any given time, we observe the superposition of flows created by successive reconnections, leading to a broad velocity distribution. Movies are at: http://www.lesia.obspm.fr/perso/pascal-demoulin/13/Movies_Vevol.zip

Authors: Demoulin, P., Baker, D., Mandrini, C.H., Van Driel-Gesztelyi, L.
Projects: Hinode/EIS

Publication Status: Solar Physics (in press)
Last Modified: 2012-11-28 09:41
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Does the spacecraft trajectory strongly affect the detection of magnetic clouds?  

Pascal Demoulin   Submitted: 2012-11-28 02:50

Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs) where a magnetic flux rope is detected. Is the difference between MCs and ICMEs without detected flux rope intrinsic or rather due to an observational bias? 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 and Wu (2010) confirmed that it is a strongly decreasing function of the estimated impact parameter. Is a flux rope more frequently undetected for larger impact parameter? 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. We find that the distribution of the twist within the flux rope, the non-detection due to too low field rotation angle or magnitude are only weakly affecting 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 in 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. We conclude that either most of the non-MC ICMEs are encountered outside their flux rope or near the leg region, or they do not contain any.

Authors: Demoulin, P., Dasso, S., Janvier, M.
Projects: ACE

Publication Status: A&A in press
Last Modified: 2012-11-28 09:41
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Magnetic topology of Active Regions and Coronal Holes: Implications for Coronal Outflows and the Solar Wind  

Pascal Demoulin   Submitted: 2012-07-20 10:23

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 interplanetary 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 in 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.

Authors: L. van Driel-Gesztelyi, J. L. Culhane, D. Baker, P. Démoulin, C.H. Mandrini, M.L. DeRosa, A. P. Rouillard, A. Opitz, G. Stenborg, A. Vourlidas, D. H. Brooks
Projects: Hinode/EIS

Publication Status: Solar Physics (in press)
Last Modified: 2012-07-20 11:37
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Expansion of magnetic clouds in the outer heliosphere  

Pascal Demoulin   Submitted: 2012-04-17 09:55

A large amount of magnetized plasma are frequently ejected from the Sun as Coronal Mass Ejections (CMEs). A part of these ejections are detected in the solar wind as magnetic clouds (MCs) which have flux rope signatures. MCs are typically expanding structures in the inner heliosphere. The aim of this work is to derive the expansion properties of MCs in the outer heliosphere from 1 to 5 AU and to compare them to the ones in the inner heliosphere. 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 implies a self-similar expansion and a MC size that locally follows a power-law of the solar distance with an exponent called zeta. We derive the value of zeta from the in situ velocity data. We analyze separately the non-perturbed MCs (cases presenting a linear velocity profile almost for the full event), and perturbed MCs (cases presenting a strongly distorted velocity profile). We find that non-perturbed MCs expand with a similar non-dimensional expansion rate (zeta = 1.05 ± 0.34), i.e. slightly faster than the solar distance and than in the inner heliosphere (zeta = 0.91± 0.23). The subset of perturbed MCs expands, as in the inner heliosphere, with a significant lower rate and with a larger dispersion (zeta = 0.28 ± 0.52) as expected from the temporal evolution found in numerical simulations. This local measure of the expansion is also in agreement with the distribution with distance of MC size, mean magnetic field and plasma parameters. The MCs in interaction with a strong field region, e.g. another MC, have the most variable expansion rate (ranging from compression to over-expansion).

Authors: A.M. Gulisano, P. Demoulin, S. Dasso, L. Rodriguez
Projects: None

Publication Status: in press, A&A
Last Modified: 2012-04-17 13:54
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Initiation and Development of the white-light and radio CME on 15 April 2001  

Pascal Demoulin   Submitted: 2012-03-09 06:35

The 2001 April 15 event was one of the largest of the last solar cycle. A former study (Maia et al., 2007) 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. i) The radio CME corresponds to the white light flux rope cavity. ii) 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. iii) Radio imaging reveals an important lateral over expansion in the low corona; this over expansion is at the origin of compression regions where type II and III bursts are imaged. iv) Already in the initiation phase, radio images reveal large scale interactions of the source active region with its surroundings, including another active region and open magnetic fields. Thus, these complementary radio, EUV, white light data validate the flux rope eruption model of CMEs.

Authors: P. Demoulin, A. Vourlidas, M. Pick, A. Bouteille
Projects: Nançay Radioheliograph

Publication Status: in press, ApJ
Last Modified: 2012-03-09 21:05
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Interplanetary magnetic structure guiding relativistic particles  

Pascal Demoulin   Submitted: 2011-10-24 09:17

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: Masson S., Demoulin P., Dasso S., and Klein K.-L.
Projects: None

Publication Status: A&A in press
Last Modified: 2011-10-25 12:39
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Dynamical evolution of a magnetic cloud from the Sun to 5.4 AU  

Pascal Demoulin   Submitted: 2011-09-16 11:48

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: Nakwacki M.S., Dasso S., Demoulin P., Mandrini C.H., and Gulisano A.M.
Projects: SoHO-MDI

Publication Status: A&A in press
Last Modified: 2011-09-19 05:23
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Nonlinear Force-Free Extrapolation of Emerging Flux with a Global Twist and Serpentine Fine Structures  

Pascal Demoulin   Submitted: 2011-09-16 07:25

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: G. Valori, L.M. Green, P. Demoulin, S. Vargas Dominguez, L. van Driel-Gesztelyi, A. Wallace, D. Baker, M. Fuhrmann
Projects: Hinode/EIS,Hinode/SOT,Hinode/XRT

Publication Status: Solar Physics (in press)
Last Modified: 2011-09-16 08:40
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Investigating the observational signatures of magnetic cloud substructure  

Pascal Demoulin   Submitted: 2011-02-07 06:51

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.

Authors: K. Steed, C. J. Owen, P. Demoulin, and S. Dasso
Projects: None

Publication Status: JGR 116, A01106
Last Modified: 2011-02-07 12:31
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Twisted Flux Tube Emergence Evidenced in Longitudinal Magnetograms: Magnetic Tongues  

Pascal Demoulin   Submitted: 2011-02-07 06:40

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 Omega-loop emergence, trailing the solar rotation, which was proposed earlier to explain other asymmetries in bipolar ARs.

Authors: M.L. Luoni, P. Demoulin, C.H. Mandrini, L. van Driel-Gesztelyi
Projects: SoHO-MDI

Publication Status: Solar Physics (in press)
Last Modified: 2011-02-07 12:31
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Initiation and early development of the 2008 April 26 Coronal Mass Ejection  

Pascal Demoulin   Submitted: 2011-02-07 06:37

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, are tracing 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 to trace the extension and orientation of the flux rope which is later detected in the interplanetary space. Moreover, combining the radio images at various frequency with fast EUV imaging permits to characterize in space and time the processes involved in the CME launch.

Authors: J. Huang, P. Demoulin, M. Pick, F. Auchere, Y.H. Yan, A. Bouteille
Projects: STEREO

Publication Status: in press, ApJ
Last Modified: 2011-02-07 12:31
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Criteria for Flux Rope Eruption: Non Equilibrium versus Torus Instability  

Pascal Demoulin   Submitted: 2010-06-09 07:05

The coronal magnetic configuration of an active region typically evolves quietly during few days before becoming suddenly eruptive and launching a coronal mass ejection (CME). The precise origin of the eruption is still debated. Among several mechanisms, it has been proposed that a loss of equilibrium, or an ideal magneto-hydrodynamic (MHD) instability such as the torus instability, could be responsible for the sudden eruptivity. Distinct approaches have also been formulated for limit 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 time scale is governed by ideal MHD. We show analytically first 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 instability of circular and straight current channels. Indeed, they are just two particular limiting case 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, (d ln |Bp|) / (d ln h) is larger than a critical value. At the limit of very thin current channels, previous analysis found a critical decay index of 1.5 and 1 for circular and straight current channels, respectively. However, with current channels being deformable and as thick as expected in the corona, we show that this critical index has similar values for circular and straight current channels, typically in the range [1.1,1.3].

Authors: P. Demoulin and G. Aulanier
Projects: None

Publication Status: in press, ApJ
Last Modified: 2010-06-09 12:02
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Criteria for Flux Rope Eruption: Non Equilibrium versus Torus Instability  

Pascal Demoulin   Submitted: 2010-06-09 07:05

The coronal magnetic configuration of an active region typically evolves quietly during few days before becoming suddenly eruptive and launching a coronal mass ejection (CME). The precise origin of the eruption is still debated. Among several mechanisms, it has been proposed that a loss of equilibrium, or an ideal magneto-hydrodynamic (MHD) instability such as the torus instability, could be responsible for the sudden eruptivity. Distinct approaches have also been formulated for limit 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 time scale is governed by ideal MHD. We show analytically first 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 instability of circular and straight current channels. Indeed, they are just two particular limiting case 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, (d ln |Bp|) / (d ln h) is larger than a critical value. At the limit of very thin current channels, previous analysis found a critical decay index of 1.5 and 1 for circular and straight current channels, respectively. However, with current channels being deformable and as thick as expected in the corona, we show that this critical index has similar values for circular and straight current channels, typically in the range [1.1,1.3].

Authors: P. Demoulin and G. Aulanier
Projects:

Publication Status: Astrophysical Journal 718 (2010) 1388-1399
Last Modified: 2010-07-16 07:11
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Interaction of ICMEs with the Solar Wind  

Pascal Demoulin   Submitted: 2009-09-09 07:08

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. Such interaction is reviewed by comparing the results obtained from in situ observations and with numerical simulations. Like fast ships in the ocean, fast ICMEs drive an extended shock in front. However, their interaction with the SW is much more complex than that of the ship analogy. For example, as they expand in all directions while traveling away from the Sun, a sheath of SW plasma and magnetic field accumulates in front, which partially reconnects with the ICME magnetic field. Furthermore, not only 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).

Authors: Demoulin P.
Projects: None

Publication Status: submitted, SW12 proceedings
Last Modified: 2009-09-09 09:37
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Magnetic cloud models with bent and oblate cross-section boundary  

Pascal Demoulin   Submitted: 2009-09-09 07:06

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 (SW). 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. 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. 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. 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 mostly the magnetic field strength. The measure of how much the field strength peaks along the crossing provides an estimation for 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 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. 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.

Authors: Demoulin P., Dasso S.
Projects: None

Publication Status: in press, A&A
Last Modified: 2009-09-09 09:37
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Quantitative model for the generic 3D shape of ICMEs at 1 AU
Homologous solar events on 2011 January 27: Build-up and propagation in a complex coronal environment
Magnetic Flux and Helicity of Magnetic Clouds
Evolution of interplanetary coronal mass ejections and magnetic clouds in the heliosphere
Solar filament eruptions and their physical role in triggering Coronal Mass Ejections
The 3D geometry of active region upflows deduced from their limb-to-limb evolution
Does the spacecraft trajectory strongly affect the detection of magnetic clouds?
Magnetic topology of Active Regions and Coronal Holes: Implications for Coronal Outflows and the Solar Wind
Expansion of magnetic clouds in the outer heliosphere
Initiation and Development of the white-light and radio CME on 15 April 2001
Interplanetary magnetic structure guiding relativistic particles
Dynamical evolution of a magnetic cloud from the Sun to 5.4 AU
Nonlinear Force-Free Extrapolation of Emerging Flux with a Global Twist and Serpentine Fine Structures
Investigating the observational signatures of magnetic cloud substructure
Twisted Flux Tube Emergence Evidenced in Longitudinal Magnetograms: Magnetic Tongues
Initiation and early development of the 2008 April 26 Coronal Mass Ejection
Criteria for Flux Rope Eruption: Non Equilibrium versus Torus Instability
Criteria for Flux Rope Eruption: Non Equilibrium versus Torus Instability
Interaction of ICMEs with the Solar Wind
Magnetic cloud models with bent and oblate cross-section boundary
Why Temperature and Velocity have Different Relationships in the Solar Wind and in Interplanetary Coronal Mass Ejections?
Causes and consequences of magnetic cloud expansion
Modeling and Observations of Photospheric Magnetic Helicity
Subject will be restored when possible
Expected in Situ Velocities from a Heirarchical Model for Exapnding Interplanetary Coronal Mass Ejections
Subject will be restored when possible
Where will efficient energy release occur in 3D magnetic configurations?
Recent theoretical and observational developments in magnetic helicity studies
A Multiple flare scenario where the classic long duration flare was not the source of a CME
Decametric N burst: a consequence of the interaction of two coronal mass ejections
Magnetic topologies: where will reconnection occur ?
Extending the Concept of Separatrices to QSLs for Magnetic Reconnection
Radio and X-ray signatures of magnetic reconnection behind an ejected flux rope
Amplitude and orientation of prominence magnetic fields from constant-alpha magnetohydrostatic models
Obervations of magnetic helicity
Magnetic energy and helicity fluxes at the photospheric level
The scalings of the coronal plasma parameters with the mean photospheric magnetic field: The long-term evolution of AR 7978
Testing coronal heating models: The long-term evolution of AR 7978
What is the source of the magnetic helicity shed by CMEs. The long-term helicity budget of AR 7978
The magnetic helicity injected by shearing motions

Related Pages
MSU Solar Physics.
Max Millennium Science Mail Archive.
Max Millennium Message of the Day Mail Archive.
Max Millennium Flare Catalog

Archive Maintainer
Alisdair Davey



© 2003 Solar Physics Group - Montana State University