Model results of the effect of solar wind dynamic pressure enhancements on the auroral size and strength and comparison with observations

Details Model results of the effect of solar wind dynamic pressure enhancements on the auroral size and strength and comparison with observations Model results of the effect of solar wind dynamic pressure enhancements on the auroral size and strength and comparison with observations

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsm53a..06z&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #SM53A-06

Physics

2704 Auroral Phenomena (2407), 2736 Magnetosphere/Ionosphere Interactions (2431), 2776 Polar Cap Phenomena, 2784 Solar Wind/Magnetosphere Interactions

Scientific paper

Recent studies have suggested that solar wind dynamic pressure enhancements can cause energetically very significant perturbations in auroral precipitation and ionospheric currents, thus having the potential for significant energy input to the Earth's upper atmosphere. It has been reported that pressure enhancements can cause significant and rapid closure of the polar cap and open flux, widening and strengthening of the auroral oval at all local times, as well as an increase of the cross polar cap potential 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. We investigate the physics driving such responses by comparing the observations with the results of the OpenGGCM MHD model, and we identify to what extent the MHD model can reproduce the observed responses. We have isolated a small number of cases where the solar wind dynamic pressure enhancement occurs under negative or near-zero IMF Bz. Perhaps the most peculiar of the effects of pressure pulses is the rapid shrinkage of the polar cap as the increased solar wind dynamic pressure impacts the magnetosphere, at the same time when the cross polar cap potential increases. We investigate, through the model, the time development of the size of the open flux and of the auroral oval, and of the cross polar cap potential. Initial results from one case study give some closing of the polar cap, but not with the observed time sequence with respect to field-aligned current and cross-polar cap potential increases. In addition, it has been suggested that the closing of the polar cap is the result of enhanced tail reconnection. We study this suggestion through the model by tracing the magnetospheric topology of the separatrix and comparing dayside and nightside reconnection rates.

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