New model of plasma convection during transpolar arc events

概要

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A transpolar arc (TPA) event occurred on December 10, 1996, is examined using auroral images from the Polar UVI. Before the appearance of the TPA, the total pressure of the magnetotail observed at X〜-24 R_E had been increasing for about three hours. Since the IMF Bz was strongly positive during this period, the viscous-like interaction probably contributed to the increase in the total pressure of the magnetotail. A clear TPA appeared in association with fluctuations in the IMF By component. A subsequent decrease in the IMF Bz component caused a significant equatorward shift of the dawnside auroral oval, probably resulting in the duskward movement of the TPA. The nightside termination of the TPA, however, was fixed at around local midnight of the auroral oval. This observation indicates that a quasi-stable structure existed in the magnetospheric convection pattern. To account for the present observations, a new model for the formation of TPAs is proposed. The model assumes that the interactions between the viscous convection cells and the merging cell occur in the magnetotail, and predicts that the TPA is mapped along magnetic field lines onto a plasma flow channel that branches off from the earthward plasma convection toward the flank of the magnetotail.
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