Magnetic twist profile inside magnetic clouds derived with a superposed epoch analysis |
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Pascal Demoulin Submitted: 2020-03-12 04:42
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.
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.
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.
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.
Authors: Lanabere V., Dasso S., Démoulin P., Janvier M., Rodriguez L. and Masías-Meza J.J.
Projects: Wind
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Publication Status: A&A 635, A85 (2020)
Last Modified: 2020-03-12 14:25
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Properties of ICME-Induced Forbush decreases at Earth and Mars |
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Pascal Demoulin Submitted: 2020-03-11 12:07
Forbush decreases (FDs), which are short-term drops in the flux of galactic cosmic rays
(GCR), 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 (CIRs). Such events can
be observed at Earth, e.g. using neutron monitors, but also at many other locations
in the solar system, such as on the surface of Mars with the Radiation Assessment
Detector (RAD) instrument onboard Mars Science Laboratory (MSL). They are often
used as a proxy for detecting the arrival of ICMEs or CIRs, 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 modelling 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.
Authors: Freiherr von Forstner, J.L., Guo, J., Wimmer-Schweingruber, R.F., Dumbovic, M., Janvier, M., Demoulin, P., Veronig, A., Temmer, M., Papaioannou, A., Dasso, S., Hassler, D.M., Zeitlin, C.J.,
Projects: None
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Publication Status: JGR, in press
Last Modified: 2020-03-11 13:17
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Re-analysis of Lepping's Fitting Method for Magnetic Clouds: Lundquist Fit Reloaded |
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Pascal Demoulin Submitted: 2019-12-20 08:10
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, Jones, and Burlaga, 1990, J. Geophys. Res. 95, 11957) 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.
Then, 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 0 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 have 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 flatten FR cross-sections.
Authors: P. Demoulin, S. Dasso, M. Janvier, V. Lanabere
Projects: Wind
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Publication Status: 2019, Solar Physics, 294, 172
Last Modified: 2019-12-21 23:20
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Exploring the biases of a new method based on minimum variance for interplanetary magnetic clouds |
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Pascal Demoulin Submitted: 2018-09-03 04:12
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).
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.
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.
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 compromise in size of this sub-FR is achieved.
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 degrees) and is present mostly on the angle between the flux rope axis and the plane perpendicular to the Sun-Earth direction.
Authors: Pascal Démoulin, Sergio Dasso, Miho Janvier
Projects: ACE
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Publication Status: A&A, in press
Last Modified: 2018-09-04 09:19
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Quantitative model for the generic 3D shape of ICMEs at 1 AU |
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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
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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 |
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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 Nançay 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
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Publication Status: ApJ, in press
Last Modified: 2016-03-15 11:25
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Solar filament eruptions and their physical role in triggering Coronal Mass Ejections |
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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
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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 |
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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
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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? |
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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
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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 |
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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
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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 |
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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
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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 |
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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
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Publication Status: in press, ApJ
Last Modified: 2012-03-09 21:05
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Nonlinear Force-Free Extrapolation of Emerging Flux with a Global Twist and Serpentine Fine Structures |
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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
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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 |
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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
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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 |
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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
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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 |
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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
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Publication Status: in press, ApJ
Last Modified: 2011-02-07 12:31
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