Reconstruction of the 2007 May 22 Magnetic Cloud: How Much Can We Trust the Flux-Rope Geometry of CMEs?

Liu, Y.; Luhmann, J. G.; Huttunen, Kerttu; Lin, R. P.; Bale, S. D.; Russell, C. T.; Galvin, A. B.

doi:10.1086/587839

Cited by 83 publications

(90 citation statements)

References 20 publications

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“…We also confirm the results of Vandas & Romashets (2003) who derived an analytical solution of a linear force-free field contained inside an elliptical boundary. We find that the configuration of the core inherits the oblate shape of the boundary but with a significantly lower aspect ratio, in agreement with previous observations (e.g., Dasso et al 2005a;Liu et al 2008;Möstl et al 2009). …”

Section: Discussionsupporting

confidence: 92%

“…by a smoothing procedure). The method was recently tested successfully with MCs crossed by two spacecraft (Liu et al 2008;Möstl et al 2009). …”

Section: Introductionmentioning

confidence: 99%

“…Moreover, using combined observations of several spacecraft, some recent analyses have shown that the core of the MCs is significantly more circular than their oblate outer part (Liu et al 2008;Kilpua et al 2009;Möstl et al 2009). Still, the Lundquist solution is known to have difficulties in fitting the magnetic field strength, in particular it was found that it frequently overestimates the axial component of the field near the flux-rope axis (e.g., Gulisano et al 2005).…”

Section: Introductionmentioning

confidence: 99%

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Magnetic cloud models with bent and oblate cross-section boundaries

Démoulin¹,

Dasso

2009

A&A

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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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Section: Discussionsupporting

confidence: 92%

“…by a smoothing procedure). The method was recently tested successfully with MCs crossed by two spacecraft (Liu et al 2008;Möstl et al 2009). …”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Magnetic cloud models with bent and oblate cross-section boundaries

Démoulin¹,

Dasso

2009

A&A

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“…One of the potential issues with the Grad-Shafranov technique is the stability of the integration and the influence of the solver and stabilization procedure on the results. However, Grad-Shafranov reconstruction has been tested by using observations of ICMEs by two spacecraft at a significant separation with respect to the ICME size (Liu et al, 2008;. Some of the stability issues have also been recently addressed in Isavnin, Kilpua, and Koskinen (2011).…”

Section: Grad-shafranov Reconstruction Techniquementioning

confidence: 99%

“…Therefore, this model does not only use the magnetic field measurements but also measurements of the plasma pressure, and it is only applicable to a structure possessing axial symmetry. The Grad-Shafranov technique has been tested using multi-spacecraft measurements (Liu et al, 2008;Kilpua et al, 2009; and, recently, improvement to the algorithm have been presented by Isavnin, Kilpua, and Koskinen (2011).…”

Section: Introductionmentioning

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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Comparing generic models for interplanetary shocks and magnetic clouds axis configurations at 1 AU

et al. 2015

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

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Reconstruction of the 2007 May 22 Magnetic Cloud: How Much Can We Trust the Flux-Rope Geometry of CMEs?

Cited by 83 publications

References 20 publications

Magnetic cloud models with bent and oblate cross-section boundaries

Magnetic cloud models with bent and oblate cross-section boundaries

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

Comparing generic models for interplanetary shocks and magnetic clouds axis configurations at 1 AU

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