Remote sensing of a near-Earth neutral line during the 5 October 2000 substorm
In this paper we examined the continuous motions of a near-Earth neutral line during the recovery phase of the 5 October 2000 substorm. Estimation was based on the PSBL ion beam model proposed by Onsager (1991) and the Geotail observations. Estimated distances from the Earth ranged from 20 to 60 RE and retreated tailward at velocities of 250 and 300 km/s. This event initiated with the arrival of solar wind discontinuity. Simultaneous observations of electromagnetic field and electrons indicate the existence of earthward propagating waves associated with field-aligned currents. Based on these observations, we suggest that the source of the PSBL ion beams was the retreating near-Earth neutral line formed by the compression of the magnetosphere. Two scenarios of near-Earth neutral line motion in the tail dynamics are also proposed. One is the formation of plural neutral lines to create a long plasmoid. The other is the oscillation of one neutral line between the near-Earth region and the mid-tail stagnant plasmoid.