Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsa51d1972c&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SA51D-1972
Physics
[2730] Magnetospheric Physics / Magnetosphere: Inner, [2753] Magnetospheric Physics / Numerical Modeling, [2778] Magnetospheric Physics / Ring Current, [2788] Magnetospheric Physics / Magnetic Storms And Substorms
Scientific paper
The main phase of a geomagnetic storm is characterized by a decrease of the Dst index, which represents the northward magnetic field near the Earth's equator. This Dst decrease is attributed to the enhancement of the ring current. A sudden increase of the ring current, however, cannot instantaneously generate a southward component of magnetic field near the Earth's surface because the magnetospheric plasma is essentially diamagnetic with a plasma skin depth of around 5 km. This paper addresses the question how the magnetosphere loaded with a transiently enhanced ring current dynamically evolves toward equilibrium. Two cases with different values of the initial ring current are considered. In one case, the initial ring current is strong enough to create a magnetic island in the magnetosphere. The magnetic island readily reconnects with the earth-connected ambient field and is destroyed as the system approaches a steady equilibrium. In the other case, the initial ring current is not so strong, and the initial magnetic field configuration bears no magnetic island, but a wake of bent field lines, which is smoothed out through the relaxing evolution of the magnetosphere. The relaxation time of the magnetosphere is found to be about five to six minutes, over which the ring current is reduced to about a quarter of its initial value. Before reaching a steady state, the magnetosphere is found to undergo an overshooting expansion and a subsequent contraction. Fast and slow magnetosonic waves are identified to play an important role in the relaxation toward equilibrium.
Choe G.
Park Geumsook
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