COMPARISON OF LOW-LATITUDE ION AND NEUTRAL ZONAL DRIFTS USING DE-2 DATA

We have used data from the ion drift meter and the wind and temperatur e spectrometer on the DE 2 spacecraft to make statistical comparisons of the zonal ion and neutral drifts at dip latitudes (DLAT) in the +/- 35 degrees range over all local times. Fourier analysis indicates tha t the superrotation and the diurnal components of both flows are stron gly peaked at the dip equator, with the superrotation term becoming ne gative for \DLAT\ greater than or equal to 20 degrees. One interesting feature is the presence of a period (2200-0500 solar local time) in t he 300-400 km altitude region near the dip equator where the ion drift is more strongly eastward than the neutral flow. This would seem to i ndicate the presence of an electric field source of greater strength t han the F region dynamo elsewhere along the geomagnetic field line. Mo del calculations indicate that a possible mechanism for this source li es in the vertical shear in the zonal neutral wind in the 100-200 km a ltitude region.