Observations of field‐aligned currents at the plasma sheet boundary: An ISEE‐1 and 2 survey

Using ISEE‐1 and 2 magnetometer data we have performed a survey of field‐aligned currents at the boundary of the plasmasheet between 10 and 22 Earth radii down the magnetotail. Most cases are observed as the plasma sheet expands across the spacecraft. We find that the currents are most often observed flowing earthward throughout this region of the tail; however, a fraction of the cases correspond to tailward flowing currents and these tend to be found dawnward of midnight. Toward dusk no tailward currents are found. The currents at the plasma sheet boundary should map to the high latitude boundary of the auroral zone, and consequently one might expect them to have a Region 1 polarity; just the opposite is observed. Typical sheet current densities for these cases are roughly 5 mA/m.