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

Abstract

Abstract On August 31, 2001,UT, Cluster was located near the midnight mag-netotail, GSE (x, y, z) RE, and observed fast earthwardflow bursts inthe vicinity of the neutral sheet. They occurred while the tail magnetic field suddenlyincreased. Using simultaneous measurements in the solar wind, at geosynchronousorbit, and on the ground, it is confirmed that tail magnetic field enhancement is dueto an increased solar wind pressure. In the neutral sheet region, strongly enhancedearthward flow bursts perpendicular to the local magneticfield Auroral brightenings localized in the pre-midnight sector ( were observed. MLT) oc-curred during the interval of the minutes before the onset of auroral brightenings. Our observations suggest that the enhancements. The bursts startedearthward flow bursts are associated with tail reconnection directly driven by a solarwind pressure impulse and thatcaused localized auroral brightenings. Keywords : substorm, solar wind pressure impulse, magnetotail 1. Introduction Magnetic reconnection in the near-earth region of the magnetotail is one of main processesfor magnetotail dynamics. Accelerated earthward and tailward plasma flows within the near-tailplasma sheet have been usually taken as evidence for reconnection (e.g., Nagai et al. 1998). Fastflows in the central plasma sheet are mostly earthward at