Paper#: 135
Poster #: 5
Session Name: Poster Session 2
Room: East Ballroom
Day: Thursday
Time: 10:10 a.m.-Noon
Abstract Title: Distinct Magnetospheric Responses to Southward IMF in Two Substorms
PresentSurname: El-Alaoui, M.
All Authors: M. El-Alaoui, M. Ashour-Abdalla, R.L. Richard, L.A. Frank, W.R. Paterson, John B. Sigwarth
Abstract : Two intervals with substorms reveal two very different magnetospheric and ionospheric responses to southward interplanetary magnetic field (IMF) conditions. Spacecraft observations and results from global magnetohydrodynamic (MHD) simulations were used to analyze these two events, one that occurred on September 4, 1996, and one that occurred on July 2, 1996. During the September 4 event the IMF By was directed dawnward with a magnitude of 7 nT. At about 2135 UT on that day, GEOTAIL observed a tailward flow on the dawnside that was accompanied by a negative Bz magnetic-field component. During the July 2 event the IMF was duskward with a magnitude of 10 nT. During this event GEOTAIL was located on the dusk side. GEOTAIL measured plasma sheet parameters throughout the expansion phase of these substorms. Measurements taken upstream of the Earth by the Wind spacecraft were used as input to MHD simulations for each event. After assessing the validity of the models' results by comparing simulated time series with GEOTAIL and Polar observations, we consider the time evolution of the magnetosphere and ionosphere. During the September 4 case the calculated power seemed to correlate well with upstream conditions, while during the July 2 case there were large scale variations in the calculated power that did not seem to correlate with any IMF variations. The results for July 2 suggest a state of steady magnetospheric convection prior to the substorm, while the September 4 event reveals a more conventional driven response.