HR: 0800h
AN: SM51A-0344    [Abstracts]
TI: Case Study of the Evolution of Global Ionospheric Convection during Substorms
AU: * Hashimoto, K K
EM: hashi@kiui.ac.jp
AF: Kibi International University, 8 Igacho,Takahashi, Okayama, 716-8508 Japan
AU: Lyons, L
EM: larry@atmos.ucla.edu
AF: University of California, Los Angeles, 405 Hilgard Ave., Los Angeles, CA 90095-1565
AU: Kikuchi, T
EM: kikuchi@nict.go.jp
AF: National Institute of Information and Communications Technology, 4-2-1 Nukui-kita, Koganei, Tokyo, 184-8795 Japan
AB: Evolution of global ionospheric convection is investigated for a substorm event on February 2, 2002 with unusually good SuperDARN radar echo coverage. Global magnetometer chains from the polar cap to the dip-equator show the development of the DP2 electric field during the growth phase, which followed a sudden southward turning of the IMF. Three DP2 reductions were observed during the 90 min substorm growth phase, the first two of which were followed by further DP2 enhancement. Electron precipitation measured by the IMAGE FUV/SI13 at 16-17 MLT at 70-75 degrees magnetic latitudes was coherent with these changes of DP2, and the dusk-side proton precipitation measured by the IMAGE FUV/SI12 showed more gradual changes reflecting the overall DP2 changes. The DP2 convection changes were seen clearly in the SuperDARN data. Prior to the second two convection reductions, but not prior to the first, flow shear of the Harang discontinuity was observed to develop in the post-midnight sector. The Harang discontinuity shifted equatorward from 75 to 68 degrees magnetic latitudes as the growth phase developed. The second and the third reductions in convection led to the pseudo break-up and the expansion phase onset, respectively, both of which initiated within the Harang flow-shear region and were associated with large weakening of the Harang flow shear. Our results suggest that both auroral activity on the night-side and auroral precipitation on the afternoon-to-dusk region are strongly controlled by global convection, that reduction in convection leads to substorm expansion or pseudo break-up only under the condition of a well-developed Harang flow shear, and that an enhancement of convection prior to full expansion-phase development leads to termination of the expansion phase (i.e. a pseudo breakup) and reformation of the Harang shear.
DE: 2455 Particle precipitation
DE: 2463 Plasma convection
DE: 2736 Magnetosphere/ionosphere interactions
DE: 2788 Storms and substorms
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting