HR: 0800h
AN: SM31A-0389    [Abstracts]
TI: Relationship Between Substorm Onset and Reconnection in The Magnetotail
AU: Stickle, A
EM: astickle@u.washington.edu
AF: University of Washington, Dept. of Earth and Space Sciences, Seattle, WA 98195-1310
AU: * Winglee, R M
EM: winglee@ess.washington.edu
AF: University of Washington, Dept. of Earth and Space Sciences, Seattle, WA 98195-1310
AU: Harnett, E M
EM: eharnett@ess.washington.edu
AF: University of Washington, Dept. of Earth and Space Sciences, Seattle, WA 98195-1310
AB: The timing of tail reconnection relative to substorm onset is critical to tying auroral processes with magnetospheric processes. Global multi-fluid simulations are used to study this problem. These simulations provide important into this problem because they include light and heavy ionospheric outflows in addition to ion cyclotron effects which control the reconnection rate. It is shown that in the ideal MHD limit where the ion skin is assumed to be very much smaller than the grid spacing, a stagnant near-Earth neutral line forms for persistent southward IMF without any significant nightside auroral currents and as such the substorm/reconnection relationship is ambiguous at best. However, with a full incorporation of the ion cyclotron/skin depth effects the reconnection is seen to be substantially more dynamic. While tail reconnection occurs with southward turning of the IMF, the reconnection region eventually moves out beyond 25 R_E. During this period there is very little enhancement of the auroral currents near midnight and as such this reconnection is more related to a pseudo-breakup as opposed to a true substorm. Internal triggering of substorm activity with enhanced auroral currents at midnight can occur for steady southward IMF over periods greater than about 100 mins for nominal solar wind conditions. This onset occurs via disruption of plasma flows at the inner edge of the plasma sheet and reconnection does not play a role in triggering the substorm. When the IMF becomes more northerly (but not necessarily northward), it is demonstrated that disruption of the plasma flows at the inner edge of the plasma sheet occurs prior to the formation a near-Earth neutral sheet. This timing appears to be consistent with recent inferences of substorm onset and Geotail observations of reconnection.
DE: 2723 Magnetic reconnection (7526, 7835)
DE: 2744 Magnetotail
DE: 2753 Numerical modeling
DE: 2790 Substorms
SC: SPA-Magnetospheric Physics [SM]
MN: Fall Meeting 2005