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Global MHD Simulation of Interaction between the Solar Wind and the Earth's Magnetosphere

Earth's magnetosphere is influenced by the solar wind and interplanetary magnetic field (IMF). Dynamics of the magnetosphere are dominantly controlled by magnetic reconnection, which favorably occurs under the anti-parallel condition. The behavior of magnetic reconnection is very complicated when the IMF and the solar wind vary as a function of time.

We have carried out a high resolution 3-dimensional magnetohydrodynamic (MHD) simulation of interaction between the solar wind and earth's magnetosphere in order to study response of the magnetosphere to variations of the IMF and the solar wind. When the IMF turns from northward to southward, tail reconnection starts and generates strong earthward and tailward flows. It takes 6-8 minutes from the onset of tail reconnection to the expansion onset corresponding to the generation of strong flows. In the interval the tail reconnection proceeds for the closed field lines. When the last closed field lines are suffered the tail reconnection, the expansion onset suddenly starts to generate strong plasma flows and increase temperature in the plasma sheet. This suggests that tail reconnection is effective to energize plasmas in the plasma sheet.

The reconnection site at the magnetopause quickly shifts in a few minutes when the IMF suddenly changes its orientation. During the transition interval, structure of magnetic field lines becomes very complex. Magnetospheric convection in the dayside magnetosphere and around the cusp also varies quickly to generate disturbances of plasma pressure and electromagnetic fields in the magnetosphere and ionosphere. The disturbances propagate along magnetospheric convection and are relaxed in the tail region. The ionospheric convection in the polar cap is controlled by the IMF By component as well as the IMF Bz component. The IMF By component has dominant effect on flow direction in the entrance region of polar convection for northward IMF. Thus a quick variation of the IMF By component may produce a considerable disturbance.

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