Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsm23b..02z&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SM23B-02
Physics
2704 Auroral Phenomena (2407), 2753 Numerical Modeling, 2776 Polar Cap Phenomena, 2784 Solar Wind/Magnetosphere Interactions
Scientific paper
Recent studies have shown that solar wind dynamic pressure enhancements can cause very significant perturbations in auroral precipitation and ionospheric currents. It has been reported that 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. Perhaps the most peculiar of the effects is the rapid shrinkage of the polar cap, which occurs together with an increase in the CPCP, as the increased solar wind dynamic pressure impacts the magnetosphere. We investigate the physics driving these responses by comparing observations from the Polar, DMSP, and FAST Spacecraft with the results of the OpenGGCM MHD model, and we identify to what extent the MHD model can reproduce the observed responses. We focus specifically on the CPCP, the area of open flux, and the dynamic evolution of the separatrix boundary. 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. We have selected a number of cases where the solar wind dynamic pressure enhancement occurs under negative or near-zero IMF Bz. Initial results indicate that when IMF Bz is steady, either southward or near zero, the model reproduces very well the direction and timing of the change of the open flux and that of the CPCP after the compression. During more dynamic times, specifically when the IMF is varying, the comparisons between the model and observations appear to be less realistic and more work is needed to sort out the different effects.
Boudouridis Athanasios
Larson David J.
Lummerzheim Dirk
Lyons Larry
Raeder Joachim
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