GLOBAL EQUATORIAL IONOSPHERIC VERTICAL PLASMA DRIFTS MEASURED BY THE AE-E SATELLITE

Ion drift meter observations from the Atmosphere Explorer E satellite during the period of January 1977 to December 1979 are used to study t he dependence of equatorial (dip latitudes less than or equal to 7.5 d egrees) F region vertical plasma drifts (east-west electric fields) on solar activity, season, and longitude. The satellite-observed ion dri fts show large day-to-day and seasonal variations. Solar cycle effects are most pronounced near the dusk sector with a large increase of the prereversal velocity enhancement from solar minimum to maximum. The d iurnal, seasonal, and solar cycle dependence of the longitudinally ave raged drifts are consistent with results from the Jicamarca radar exce pt near the June solstice when the AE-E nighttime downward velocities are significantly smaller than those observed by the radar. Pronounced presunrise downward drift enhancements are often observed over a larg e longitudinal range but not in the Peruvian equatorial region. The sa tellite data indicate that longitudinal variations are largest near th e June solstice, particularly near dawn and dusk but are virtually abs ent during equinox. The longitudinal dependence of the AE-E vertical d rifts is consistent with results from ionosonde data. These measuremen ts were also used to develop a description of equatorial F region vert ical drifts in four longitudinal sectors.