Evolution of Cusp Plasma Flow and Convection Vortex

K. HASHIMOTO, T. KIKUCHI
Communications Research Laboratory, Japan
M. RUOHONIEMI
JHU/APL, USA.
RIDLEY
University of Michigan, USA.
P. STAUNING
(DMI)

Contribution of ionospheric plasma flows in the day-side cusp to development of the large-scale convection electric field was investigated by applying the APL convection map model [Ruohoniemi and Greenwald, 1998] to the SuperDARN observation in the wide local time range (10-22 MLT) at 18-20 UT on November 17, 1996. The magnetic field data from the CANOPUS and West Greenland magnetometer arrays are used for identifying the timing of convection flow changes. During the period of the northward IMF, small-scale twin vortices were observed at higher latitude (78-83^o geomagnetic latitude) of the cusp region in the 10-14 MLT sector in addition to large-scale convection vortex centered in the 18-20 MLT sector. The twin vortices consist of a clockwise vortex in the pre-noon and counter-clockwise one in the post-noon, indicating cusp field-aligned currents. The large-scale convection vortex was intensified with a center in the 15-16 MLT sector at 78-80^o magnetic latitude after the IMF turned southward. As the southward IMF increased, the convection vortex developed over the magnetic local time of 11-20 MLT, but its center remained in the 15-16 MLT sector at 78-80^o magnetic latitude. The small-scale twin vortices in the cusp region remained for 4 minutes after the development of large-scale convection vortex. We discuss our observations in comparing with the MHD simulation result of Tanaka [1995] investigating the current generator for the Region-1 field aligned current.

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