ISEE OBSERVATIONS OF LOW-FREQUENCY WAVES AND ION DISTRIBUTION FUNCTION EVOLUTION IN THE PLASMA SHEET BOUNDARY-LAYER

This paper describes ISEE plasma and magnetic fluctuation observations during two crossings of the plasma sheet boundary layer in the Earth's magnetotail. Distribution function observations show that the counterstreaming ion components undergo pitch‐angle scattering and evolve into a shell distribution in velocity space. This evolution is correlated with the development of low frequency, low amplitude magnetic fluctuations. However, the measured wave amplitudes are insufficient to accomplish the observed degree of ion pitch‐angle scattering locally; the near‐Earth distributions may be the result of processes occurring much farther down the magnetotail. Our results show a clear correlation between the ion component beta and the relative streaming speed of the two components, suggesting that electromagnetic ion/ion instabilities do play an important role in the scattering of PSBL ions. Copyright 1990 by the American Geophysical Union.