Paper#: 107
Poster #: 18
Session Name: Poster Session 2
Room: East Ballroom
Day: Thursday
Time: 10:10 a.m.-Noon
Abstract Title: Signatures and Timing of Local Substorm Onsets in the Near-Earth Plasma Sheet
PresentSurname: Erickson, G.M.
All Authors: G.M. Erickson, N.C. Maynard, G.R. Wilson
Abstract : The types and times of signatures of local substorm onsets observed at Geotail (9 Re < R < 30 Re) are catalogued with respect to ground substorm times. In the neighborhood of 10 Re in the tail, wave activity and dipolarization, akin to current disruption, begin a few minutes before or at ground onset. Earthward flows associated with flux pileup occur at or within 2 minutes following ground onset. Usually current disruption signatures precede local earthward flow onset, but occasionally flux pileup is the first signature. In the vicinity of 12 Re, arrival of earthward flow and flux pileup is the more usual signature, initiating local onset and occurring at or within 2 minutes following ground onset. It is not unusual, however, for this signature to be preceded by brief tailward flow with northward Bz, indicative of ballooning earthward of the observation point. In the vicinity of 15 Re and tailward, the signature of local onset may be one of several consistent with formation of a near-Earth neutral line: sudden plasma sheet dropout and recovery, tailward flow with southward Bz, plasma sheet dropout, or plasma sheet recovery with earthward flow. Local onset occurs at or up to a few minutes following a major ground onset or intensification, i.e., a substorm main phase. Rarely is a local onset signature observed prior to ground onset. These findings are consistent with findings from an earlier CRRES study that suggests that substorm onset is associated with ballooning/current disruption in the near-geosynchronous plasma sheet. The substorm main phase, i.e., intensification and poleward expansion, follows and is associated with near-Earth neutral line formation. These two substorm stages, when they both occur, can be separated by a few to 10s of minutes. How the first stage triggers the main (second) phase requires additional study.