Spatial, temporal, and amplitude characteristics of parallel electric fields associated with subsolar magnetic field reconnection

Abstract

The electric field experiment on the Polar satellite collected bursts of data at rates of 1600 and 8000 samples/second to measure the parallel and perpendicular components of the vector electric field. Because data at these rates are required for full resolution measurements of the parallel component associated with subsolar magnetic field reconnection, some 150 such bursts from 2000 through 2003 were examined during 5 month intervals when the spacecraft was on the dayside of the Earth and the apogee of 9.5 RE was near the equator. Seventeen events were found at reconnecting magnetopauses with perpendicular electric field components as large as 200 mV/m and parallel electric field components as large as 80 mV/m. The parallel electric fields were associated with significant plasma density depletions, and they all appeared on the magnetospheric side of the current sheet. The large magnitudes of the parallel fields and their anticorrelations with plasma density are not found in simulations. For one example, the speed of the parallel electric field structure was 1.2 times the local Alfven speed. The directions of the parallel fields were such as to accelerate electrons moving along the magnetic field toward the reconnection site. The full widths at half maxima of the parallel field events ranged from less than 0.2 to 15 ms, in general agreement with simulations. Although the events occurred over ±20 degrees of magnetic latitude and for clock angles of 100 to 180 degrees, their statistics suggest that the X line for these events was within a few degrees of the magnetic equator.