HR: 1340h
AN: SM13A-1115 [Abstracts]
TI: The Role of Low-Entropy Flux Tubes During Geomagnetic Activity
AU: * Savoie, A M
EM: asavoie@pvamu.edu
AF: Solar Observatory, Prairie View A&M University, MS 2250,
PO Box 519, Prairie View, TX 77446-0519, United States
AU: Erickson, G M
EM: gmerickson@pvamu.edu
AF: Solar Observatory, Prairie View A&M University, MS 2250,
PO Box 519, Prairie View, TX 77446-0519, United States
AB:
This investigation uses plasma and magnetic field observations taken onboard the Geotail satellite near perigee
(-9 RE > XGSE > -12 RE) in the midnight sector of the plasma sheet during geomagnetic
bays (driven activity) and near times of substorm onsets and pseudobreakups (unloading activity). Injections are
comprised of low-entropy flux tubes ("bubbles") that have lower pV5/3 than their pre-onset predecessors.
Interchange with their surroundings result in their injection earthward. Injected flux tubes have pV5/3 ≤
0.08 nPa(RE/nT)5/3, a value observed at geosynchronous altitude during injections. In
pseudobreakups, observed pV5/3 returns to its larger, pre-onset values within a few minutes, whereas for
substorm expansions, pV5/3 remains at depressed levels through the expansion phase. Geomagnetic
bays are episodes of driven activity evidenced by enhanced eastward and westward electrojets, enhanced
convection and a stable auroral band across the nightside. Steady magnetospheric convection (SMC) intervals
are geomagnetic bays that do not show unloading activity. During geomagnetic bays, pV5/3 < 0.08
nPa(RE/nT)5/3 in the near-Earth plasma sheet, typical of low-entropy, expansion-phase flux tubes rather
than high-content, growth-phase flux tubes. While we cannot say how such low-entropy flux tubes were formed
during geomagnetic bays and SMCs, their presence allows Earthward convection to proceed into the inner
plasma sheet without encountering the pressure-balance catastrophe.
DE: 2740 Magnetospheric configuration and dynamics
DE: 2760 Plasma convection (2463)
DE: 2764 Plasma sheet
DE: 2790 Substorms
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting