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Investigating the observational signatures of magnetic cloud substructure

Steed, K; Owen, CJ; Demoulin, P; Dasso, S; (2011) Investigating the observational signatures of magnetic cloud substructure. Journal of Geophysical Research: Space Physics , 116 (A1) , Article A01106. 10.1029/2010JA015940. Green open access

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Abstract

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.

Type: Article
Title: Investigating the observational signatures of magnetic cloud substructure
Open access status: An open access version is available from UCL Discovery
DOI: 10.1029/2010JA015940
Publisher version: http://dx.doi.org/10.1029/2010JA015940
Language: English
Additional information: Copyright © 2011 by the American Geophysical Union.
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of the Built Environment
URI: https://discovery.ucl.ac.uk/id/eprint/154286
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