Equatorward boundary of auroral ion precipitation

The data from the SSJ/4 detector on the Defense Meteorological Satellite Program (DMSP) F6 satellite are used to study the difference in the location of the equator ward boundaries of auroral ion and electron precipitation, and the variation in the difference with magnetic local time and activity. Large geometric factors of the ion sensors of the SSJ/4 detector make identification of the ion boundary unambiguous in most cases. In this study, approximately 900 boundaries each for electrons and ions were determined from all DMSP F6 auroral passes in January of 1983. The boundaries occur over local times from 0400 to 0700 on the morning side of the oval and from 1700 to 2100 on the eveningside. The ion and electron boundaries both move systematically to lower latitudes with increasing magnetic activity, as measured by Kp. Over the evening sector sampled, the ion boundary is on average 1.40 equatorward of the electron boundary, with the difference commonly ranging up to 30. For the morning sector sampled, the ion boundary is on average 2.60 poleward of the electron boundary with a significant number of cases with differences above 5.00. The separation between the electron and ion boundaries is not dependent on Kp but does increase with MLT from midnight toward noon on both the morningside and the eveningside of the oval. The separation in boundaries can be explained by motion in a large scale, quasi-static convection electric field if the time for development of the ion boundary is explicitly taken into account and if ion pitch angle diffusion is highly energy dependent. copyrightAmerican Geophysical Union 1987