Signatures and Timing of Substorms in the Near-Earth Plasma Sheet

Details Signatures and Timing of Substorms in the Near-Earth Plasma Sheet Signatures and Timing of Substorms in the Near-Earth Plasma Sheet

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsm22a..16e&link_type=abstract

American Geophysical Union, Spring Meeting 2002, abstract #SM22A-16

Other

2736 Magnetosphere/Ionosphere Interactions, 2744 Magnetotail, 2760 Plasma Convection, 2788 Storms And Substorms

Scientific paper

CRRES observations revealed that substorms usually proceed in two stages [JGR, 105, 25,265, 2000]. During the first stage, electromagnetic energy was observed at CRRES released from the near-geosynchronous plasma sheet toward the ionosphere, often beginning before the start of ground/auroral activity and resulting in initiation of the substorm current wedge, dipolarization, and particle injection. Activity could then wane (a pseudobreakup) or poleward expansion of activity could occur in a second stage (substorm expansion), which could occur several minutes later. The second stage was characterized by a resumption of dipolarization resulting from the pileup of magnetic flux owing to flows spawned further downtail. We are engaged in an analysis of Geotail near-Earth plasma sheet data to determine if and how these two substorm stages are causally related. Here we provide an interim report. There is little evidence of an active near-Earth X-line prior to stage-2 substorm expansion. On the other hand, near X=-9RE it is not unusual to observe current disruption type activity and dipolarization near times of stage-1 ground/auroral activity. A bit further into the tail low-frequency wave activity is often observed to increase within a few minutes of stage-1 start and before X-line activation. Stage-2 substorm expansion appears to necessitate an active near-Earth X-line in the vicinity of -15 > X >-25. It is not uncommon to observe X-line activation as close as X=-13RE and quickly move tailward of the spacecraft, consistent with previous reports on the location of X-line formation. Events observed near Geotail's apogee (30RE) are complex but generally follow the classic Hone's picture of plasma sheet dropout and recovery.

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