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A tailward moving current sheet normal magnetic field front followed by an earthward moving dipolarization front
Author(s) -
Hwang K.J.,
Goldstein M. L.,
Moore T. E.,
Walsh B. M.,
Baishev D. G.,
Moiseyev A. V.,
Shevtsov B. M.,
Yumoto K.
Publication year - 2014
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2013ja019657
Subject(s) - plasma sheet , substorm , current sheet , physics , front (military) , magnetometer , magnetic field , magnetic flux , magnetic reconnection , flux (metallurgy) , plasma , earth's magnetic field , geophysics , magnetosphere , magnetohydrodynamics , materials science , meteorology , quantum mechanics , metallurgy
A 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 B z , which was immediately followed by a series of flux rope structures. Both the local B z enhancement and flux ropes propagated tailward. Approximately 5 min later, another B z enhancement, followed by a large density decrease, was observed to rapidly propagate earthward. Between the two B z enhancements, a significant removal of magnetic flux occurred, possibly resulting from the tailward moving B z 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 B z 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.