Progressive Transformation of a Flux Rope to an ICME

Dasso, S.; Nakwacki, M. S.; Démoulin, P.; Mandrini, C. H.

doi:10.1007/s11207-007-9034-2

Cited by 148 publications

(177 citation statements)

References 46 publications

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“…In some cases, both MCs even travel consecutively and the flux rope signatures are preserved . On the other hand, Dasso et al [2007] also considered whether the substructure could be explained by a small twisted flux tube with opposite helicity sign in the center of the flux rope and concluded that the formation of such a structure is not possible in the corona. It is, however, possible for two flux ropes with the same sign of helicity to interact in interplanetary space, but the symmetrical nature of the 13 April 2006 flux rope signature in B y,cloud implies that the flux ropes would have to be very similar to reproduce the observed substructure signatures, and it is very improbable that this is the case.…”

Section: Discussionmentioning

confidence: 99%

“…[26] Dasso et al [2007] also suggested the simplest interpretation of the observed substructure may be spatial oscillations of the magnetic field, introduced as a result of interactions between a magnetic cloud and the ambient solar wind as the cloud propagates into interplanetary space. They proposed that close to the minimum approach of the magnetic cloud center, the spacecraft trajectory would be nearly tangential to the magnetic flux surfaces of the flux rope.…”

Section: Discussionmentioning

confidence: 99%

“…We herein use the term "substructure" to refer only to the region of a magnetic cloud that exhibits this signature. Dasso et al [2007] suggest that in a magnetic flux rope structure, the magnetic flux surfaces of an MC could become "warped" as a result of its fast evolution and interaction with the ambient solar wind, giving rise to the observed magnetic field fluctuations. However, this and other possible causes of this kind of substructure have not, as yet, been investigated further.…”

Section: Introductionmentioning

confidence: 99%

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Investigating the observational signatures of magnetic cloud substructure

et al. 2011

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

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Investigating the observational signatures of magnetic cloud substructure

et al. 2011

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“…However, this effect can be corrected, and it is usually not the main cause of the observed asymmetry between the front and back of MCs . Moreover, even removing the aging effect, a front/back asymmetry can still be observed in some MCs Dasso et al 2007). Finally, we find that the deformation of the flux-rope core decreases with higher spatial frequency deformations of the boundary.…”

Section: Discussionmentioning

confidence: 99%

Magnetic cloud models with bent and oblate cross-section boundaries

Démoulin¹,

Dasso

2009

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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.

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“…One significant difference is the inclusion or not of a region of strong magnetic field without much rotation at the "back" of the MC (until 02:40 on November 8). Previous studies (Dasso et al, 2006;Dasso et al, 2007;Möstl et al, 2008) have discussed how reconnection between a MC and the ambient solar wind during the ICME propagation may result in this type of regions which, actually, belong to the MC. Each researcher decided exactly where to end the MC.…”

Section: Event 27mentioning

confidence: 99%

Magnetic Field Configuration Models and Reconstruction Methods for Interplanetary Coronal Mass Ejections

et al. 2013

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This study aims to provide a reference to different magnetic field models and reconstruction methods for interplanetary coronal mass ejections (ICMEs). In order to understand the differences in the outputs of those models and codes, we analyze 59 events from the Coordinated Data Analysis Workshop (CDAW) list, using four different magnetic field models and reconstruction techniques; force-free fitting (Goldstein, 1983; Burlaga, 1988;Lepping, Burlaga, and Jones, 1990), magnetostatic reconstruction using a numerical solution to the Grad-Shafranov equation (Hu and Sonnerup, 2001), fitting to a self-similarly expanding cylindrical configuration (Marubashi and Lepping, 2007) and elliptical, non-force free fitting (Hidalgo, 2003). The resulting parameters of the reconstructions for the 59 events are compared statistically, as well as in selected case studies. The ability of a method to fit or reconstruct an event is found to vary greatly: the Grad-Shafranov reconstruction is successful for most magnetic clouds (MCs) but for less than 10% of the non-MC ICMEs; the other three Al-Haddad et al methods provide a successful fit for more than 65% of all events. The differences between the reconstruction and fitting methods are discussed, and suggestions are proposed as to how to reduce them. We find that the magnitude of the axial field is relatively consistent across models but not the orientation of the axis of the ejecta. We also find that there are a few cases for which different signs of the magnetic helicity are found for the same event when we do not fix the boundaries, illustrating that this simplest of parameters is not necessarily always well constrained by fitting and reconstruction models. Finally, we look at three unique cases in depth to provide a comprehensive idea of the different aspects of how the fitting and reconstruction codes work.

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Progressive Transformation of a Flux Rope to an ICME

Cited by 148 publications

References 46 publications

Investigating the observational signatures of magnetic cloud substructure

Investigating the observational signatures of magnetic cloud substructure

Magnetic cloud models with bent and oblate cross-section boundaries

Magnetic Field Configuration Models and Reconstruction Methods for Interplanetary Coronal Mass Ejections

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