Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm41a2005l&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM41A-2005
Physics
[2753] Magnetospheric Physics / Numerical Modeling, [2760] Magnetospheric Physics / Plasma Convection, [2778] Magnetospheric Physics / Ring Current, [2788] Magnetospheric Physics / Magnetic Storms And Substorms
Scientific paper
Statistical studies suggest that the solar wind dynamic pressure influences the development of the storm-time ring current, with increased dynamic pressure leading to increased ring current energy. But physical understanding of that relationship is lacking. While magnetospheric compressions drive adiabatic energization of plasma and thereby directly increase the ring current energy, this effect should be reversible, and dynamic pressure can vary rapidly in either direction during magnetic storms. Rather, the process of plasma transport from the plasma sheet to the ring current is affected by magnetopause currents that perturb the background field in the magnetosphere. This perturbation will affect both convective transport and gradient/curvature drift of plasma, which will subsequently further perturb the magnetic and electric fields. Using the Rice Convection Model with a force-equilibrated magnetic field (the RCM-E), we are able to simulate the ring current development in response to varying upstream conditions. This study contrasts the development of the ring current in response to different solar wind dynamic pressure inputs: sustained low dynamic pressure, sustained high dynamic pressure, and low dynamic pressure with a superposed pressure pulse. We quantitatively account for the processes that lead to variations in ring current development during these different upstream driving scenarios. These processes include the effect of the magnetopause currents (and ring and tail currents) on plasma drift paths, modifications of the convection electric field due to adiabatic energization of plasma (electric shielding), and the induction electric fields caused by changes in the magnetopause, ring, and tail currents. Our simulations separately investigate the extent to which ring current enhancements are driven by 1) the impact of the magnetopause currents on the magnetic and (indirectly) electric fields of the inner magnetosphere, 2) the coupling of the plasma sheet to the ring current due to relationships between the solar wind pressure and the plasma sheet density and temperature, and 3) the effect of the solar wind pressure on the convection electric field via energy coupling at the magnetopause. The results give physical understanding to empirical relationships between upstream parameters and the Dst index, and help researchers interpret modeling and observational studies of ring current development.
Chen Margaret W.
Guild Timothy B.
Lemon Colby
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