Other
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsm13b1318z&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SM13B-1318
Other
2704 Auroral Phenomena (2407), 2723 Magnetic Reconnection (7526, 7835), 2753 Numerical Modeling, 2760 Plasma Convection (2463), 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
Recent studies have clearly demonstrated the significant effect solar wind dynamic pressure enhancements have on auroral precipitation, ionospheric and magnetospheric currents, and convection. Sudden pressure enhancements can cause significant and rapid closure of the polar cap and thus reduction in the open flux, widening and strengthening of the auroral oval at all local times, as well as an increase of the cross polar cap potential (CPCP) and the efficiency of coupling of the solar wind to the magnetosphere. The effects are most dramatic during periods of strongly southward IMF Bz but are evident at various degrees under most IMF conditions. MHD model simulations of two events, using the Open GGCM model, have also shown increase in the CPCP, but the reduction of open flux was only reproduced in one of the two cases. What seems to be the deciding factor is whether dayside or nightside reconnection dominates. We now simulate a larger number of events that occur under various IMF conditions and compare the results with observations. We use observations from the DMSP and FAST low-altitude spacecraft and auroral images from the Polar UVI instrument. We focus specifically on the CPCP, the area of open flux, the dynamic evolution of the separatrix boundary, and convection. With the larger number of events simulated we focus on the question of why these properties (i.e., the CPCP, open flux, etc) respond differently for different IMF conditions, and how well does the model reproduce such differences. Does the model reproduce the global closure of the polar cap during strong southward IMF Bz as opposed to closure only on the nightside for near-zero IMF Bz, and how are the associated CPCP changes reproduced? Does the dayside or nightside reconnection rate dominate in the changes observed? Can the model reproduce other significant features, like the propagation of the auroral precipitation enhancement from dayside to nightside under zero or positive IMF Bz, or the added effects of dynamic pressure aurora and a simultaneous substorm at nightside. Finally, we also use the model to predict various properties (like the precipitating flux) along virtual spacecraft (DMSP and FAST) passes of the oval and compare them directly with the actual observations of DMSP and FAST.
Boudouridis Athanasios
Larson David J.
Lummerzheim Dirk
Lyons Larry
Raeder Joachim
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