Estimation of Tail Reconnection Lines by AKR Onsets and Plasmoid Entries Observed with Geotail Spacecraft

T. Murata, H. Matsumoto, H. Kojima, A. Fujita, T. Nagai, T. Yamamoto, R.R. Anderson.
Geophys. Res. Lett., 22, 1849-1852, 1995.

We estimate the location of the reconnection line and plasmoid size in the geomagnetic tail using data from the Plasma Wave Instrument onboard the GEOTAIL spacecraft. We first compare AKR onset events with high energy particle observations at geosynchronous orbit. We determine the plasmoid ejection (reconnection) time by the AKR enhancement only when it correspond to energetic particle enhancement within five minutes. The traveling time of the plasmoid from the X-line to the spacecraft is calculated by the difference in time of the AKR onset and that of the plasmoid encounter with GEOTAIL. Assuming the plasmoid propagates with the Alfven velocity in the tail lobe as MHD simulations predict, we estimate the location of the reconnections line in 11 events. The results show that the most probable location of the plasmoid edge is distributed around x = -60 RE in the GSE coordinates. The estimated size of the plasmoids ranges from 10 to 50 RE in the x direction. If we apply this result to the alternative plasmoid model in which the evolution of the tearing instability causes the generation of plasmoids, the X-line should be approximately at x= -35 RE.