Transient Plasma Flow Response to Solar Wind Dynamic Pressure Change as Observed by SuperDARN and Magnetometers

Takashi KIKUCHI, Kumiko HASHIMOTO, Tetsuo MOTOBA
Communications Research Laboratory, Japan.
Mike RUOHONIEMI
(JHU/APL, USA)

Super DARN radars observed a counter-clockwise plasma flow vortex centered at 72° geomagnetic latitude in the 14 MLT meridian during initial 10 min of the geomagnetic sudden impulse (SI) on April 21, 1997. The ionospheric plasma flow vortex may be generated by an earthward magnetospheric plasma flow inside the subsolar magnetopause due to a solar wind dynamic pressure increase. Ground magnetometer data from the Greenland stations (14.5 MLT) indicate magnetic deflections consistent with the ionospheric plasma flow vortex. Magnetometer observations in the high latitude evening sector (IMAGE) and at the dayside dip equator (Ancon, Peru) indicate negative magnetic deflections consistent with the preliminary reverse impulse (PRI) of a SI caused by a global DP2 ionospheric current system. The flow vortex observed by SuperDARN is thus an afternoon part of the twin vortices associated with field-aligned currents predicted theoretically by Tamao (1964) during the PRI. On the other hand, plasma flow enhancement took place in the cusp, suggesting an enhanced reconnection triggered by the solar wind pressure pulse.

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