Earthward Flow Bursts in the Magnetotail Driven by Solar Wind Pressure Impulse

On August 31, 2001, similar to 1705 - 1718 UT, Cluster was located near the midnight magnetotail, GSE (x, y, z) similar to (-19, -2, 2) RE, and observed fast earthward flow bursts in the vicinity of the neutral sheet. They occurred while the tail magnetic field suddenly increased. Using simultaneous measurements in the solar wind, at geosynchronous orbit, and on the ground, it is confirmed that tail magnetic field enhancement is due to an increased solar wind pressure. In the neutral sheet region, strongly enhanced earthward flow bursts perpendicular to the local magnetic field ( V-perpendicular to x) were observed. Auroral brightenings localized in the pre-midnight sector (- 2200 - 2400 MLT) occurred during the interval of the V-perpendicular to x enhancements. The V-perpendicular to x bursts started similar to 2 minutes before the onset of auroral brightenings. Our observations suggest that the earthward flow bursts are associated with tail reconnection directly driven by a solar wind pressure impulse and that V-perpendicular to x caused localized auroral brightenings.