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Multi-Spacecraft Study of the 21 January 2005 ICME - Evidence of Current Sheet Substructure Near the Periphery of a Strongly Expanding, Fast Magnetic Cloud

Multi-Spacecraft Study of the 21 January 2005 ICME - Evidence of Current Sheet Substructure Near the Periphery of a Strongly Expanding, Fast Magnetic Cloud

Publication date: 30 May 2007

Authors: Foullon, C. et al.

Journal: Solar Physics
Volume: Online First
Year: 2007

Copyright: Springer

We examine the near-Earth Interplanetary Coronal Mass Ejection (ICME) apparently related to the intense Solar Energetic Particle (SEP) event of 20 January 2005. Our purpose is to contribute to the understanding of the macroscopic structure, evolution and dynamics of the solar corona and heliosphere. Using Cluster, ACE and Wind data in the solar wind, and Geotail data in the magnetosheath, we perform a multi-spacecraft analysis of the ICME-driven shock, post-shock magnetic discontinuities and ejecta. Traversals by the well-separated near-Earth spacecraft provide a coherent picture of the ICME geometry. Following the shock, the ICME sequence starts with a hot pileup, i.e., a sheath, followed by a fast ejecta characterised by a non-compressive density enhancement (NCDE), which is caused essentially by an enrichment in helium. The plasma and magnetic observations of the ejecta are consistent with the outskirts of a structure in strong expansion, consisting of nested magnetic loops still connected to the Sun. Within the leading edge of the ejecta, we establish the presence of a tilted current sheet substructure. An analysis of the observations suggests that the tilted current sheet is draped within the overlying cloud canopy, ahead of a magnetic cloud-like structure. The flux rope interpretation of this structure near L1, confirmed by observations of the corresponding magnetic cloud, provided by Ulysses at 5.3 AU and away from the Sun-Earth line, indicates that the bulk of the cloud is in the northwest sector as seen from the Earth, with its axis nearly perpendicular to the ecliptic. - Remainder of abstract truncated -

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