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A Tailward Moving Current Sheet Normal Magnetic Field Front Followed by an Earthward Moving Dipolarization FrontA case study is presented using measurements from the Cluster spacecraft and ground-based magnetometers that show a substorm onset propagating from the inner to outer plasma sheet. On 3 October 2005, Cluster, traversing an ion-scale current sheet at the near-Earth plasma sheet, detected a sudden enhancement of Bz, which was immediately followed by a series of flux rope structures. Both the local Bz enhancement and flux ropes propagated tailward. Approximately 5 min later, another Bz enhancement, followed by a large density decrease, was observed to rapidly propagate earthward. Between the two Bz enhancements, a significant removal of magnetic flux occurred, possibly resulting from the tailward moving Bz enhancement and flux ropes. In our scenario, this flux removal caused the magnetotail to be globally stretched so that the thinnest sheet formed tailward of Cluster. The thinned current sheet facilitated magnetic reconnection that quickly evolved from plasma sheet to lobe and generated the later earthward moving dipolarization front (DF) followed by a reduction in density and entropy. Ground magnetograms located near the meridian of Cluster's magnetic foot points show two-step bay enhancements. The positive bay associated with the first Bz enhancement indicates that the substorm onset signatures propagated from the inner to the outer plasma sheet, consistent with the Cluster observation. The more intense bay features associated with the later DF are consistent with the earthward motion of the front. The event suggests that current disruption signatures that originated in the near-Earth current sheet propagated tailward, triggering or facilitating midtail reconnection, thereby preconditioning the magnetosphere for a later strong substorm enhancement.
Document ID
20150007928
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
doi:10.1002/2013JA019657
Authors
Hwang, K.-J. (Maryland Univ. Baltimore County Baltimore, MD, United States)
Goldstein, M. L. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Moore, T. E. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Walsh, B. M. (California Univ. Berkeley, CA, United States)
Baishev, D. G. (Academy of Sciences (USSR) Yakutsk, Russian Federation)
Moiseyev, A. V. (Academy of Sciences (USSR) Yakutsk, Russian Federation)
Shevtsov, B. M. (Academy of Sciences (USSR) Leningrad, Russian Federation)
Yumoto, K. (Kyushu Univ. Fukuoka, Japan)
Date Acquired
May 12, 2015
Publication Date
July 1, 2014
Publication Information
Publication: Journal of Geophysical Research: Space Physics
Publisher: American Geophysical Union Publications
Volume: 119
Issue: 7
Subject Category
Solar Physics
Report/Patent Number
GSFC-E-DAA-TN22212
Funding Number(s)
CONTRACT_GRANT: NNG11PL02A
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
Dipolarization Front
Reconnection
Substorm

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