Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsm31b1110z&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #SM31B-1110
Physics
2704 Auroral Phenomena (2407), 2716 Energetic Particles, Precipitating, 2778 Ring Current, 2784 Solar Wind/Magnetosphere Interactions, 2788 Storms And Substorms
Scientific paper
We have studied 11 magnetic storms (in 1997) that were induced by the smoothly varying Bz component of the interplanetary magnetic field typical of interplanetary magnetic clouds. It was found that there was a lack of substorm expansion phases for long periods of time (up to 7 hr) in 5 out of 11 storm main phases. In this paper, a relatively weak magnetic storm event (with minimum SYM-H at -47 nT) that occurred on July 15, 1997 is studied using ground-based magnetograms, polar cap potentials from SuperDARN, and LANL geosynchronous energetic particle data as well as the Polar UV imaging (for aurorae) and Wind (for the solar wind) data. It is shown that during the storm main phase, there was a lack of substorm expansion phase activity (from imaging and the ground-based data) and a lack of energetic particle injections at the geostationary orbit. The corresponding ring current intensification was weak. The most prominent auroral forms were north-south aligned auroral patches and torches. Dawn and dusk aurorae were more intense than the aurorae near midnight, where auroral gaps were seen. In addition, this paper shows that there was significant directly driven activity during the storm main phase when the IMF was continually southward. We argue that during this event the ring current intensification was more strongly associated with enhanced magnetospheric convection than with substorm-generated impulsive unloading of energy from the tail. Three scenarios are suggested to explain the relatively low-intensity of the magnetic storm induced by a magnetic cloud. They are: 1) weak nightside auroral zone ionospheric ion outflows (due to lack of substorms), 2) choked penetration of the tail plasma flow (due to lack of substorms), 3) retarded magnetospheric convection (due to reduced solar wind-magnetosphere reconnection). The observed saturation of the polar cap potential drop is consistent with this last mechanism.
Gonzalez Walter D.
Kamide Yohsuke
Lui T. Y.
Parks George K.
Reeves Galen
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