HR: 1330h
AN: SM32B-1150    [PDF]
TI: Effect of Solar Wind Pressure Enhancement on Ring Current Asymmetry During Strong Storms
AU: * Shi, Y
EM: yongshi@atmos.ucla.edu
AF: UCLA Dept.of Atmospheric Sciences, 405 Hilgard Ave, Los Angeles, CA 90095 United States
AU: Zesta, E
EM: ezesta@atmos.ucla.edu
AF: UCLA Dept.of Atmospheric Sciences, 405 Hilgard Ave, Los Angeles, CA 90095 United States
AU: Lyons, L
EM: larry@atmos.ucla.edu
AF: UCLA Dept.of Atmospheric Sciences, 405 Hilgard Ave, Los Angeles, CA 90095 United States
AB: During storms, solar wind dynamic pressure enhancements can significantly increase the Chapman-Ferraro, ring current and other magnetospheric and ionospheric current systems. The effect of the compression on the ring current could be asymmetric due to the ring current being stronger on the dusk side than on the dawn side. Variations of these current systems can be evaluated from the response of ground magnetometers. Typical response to compressions at low-latitude ground magnetometers is a positive increase of the horizontal magnetic field component, known as the main impulse (MI). In this study, a few strong storms (with Dst$<$-200nT) have been selected to investigate the effect of pressure enhancement on ring current asymmetry. We examined IMF data, ground geomagnetic data, and the ASY-H and SYM-H indices for each event. All cases studied show negative bays at low latitude over a large MLT sector around the dayside and dusk side, which is opposite to the typical MI response. This implies that the magnetic effect of the enhanced ring current exceeded that due to the enhanced Chapman Ferraro current. Only on the dawn side do we find the typical MI positive increase, which implies that the Chapman-Ferraro current effect there exceeded the ring current effect. This finding suggests that solar wind pressure enhancements asymmetrically increase an already asymmetric storm-time ring current. Consistent with this, the ASY-H index shows that the ring current, which has become asymmetric at the beginning of the storm, becomes even more asymmetric following a sudden increase in solar wind dynamic pressure. A moderate storm has also been investigated for comparison with the strong storms. For this storm, the effect of the enhancement of Chapman-Ferraro current at low latitudes is everywhere stronger than that of the ring current, although we also found enhancement of the ring current and its asymmetry. Therefore, we conclude that the storm-time ring current gets enhanced and more asymmetric due to the compression by solar wind dynamic pressure enhancements, and the stronger the storm, the more the ring current is enhanced.
DE: 2409 Current systems (2708)
DE: 2708 Current systems (2409)
DE: 2784 Solar wind/magnetosphere interactions
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting