INCOHERENT-SCATTER RADAR, IONOSONDE, AND SATELLITE MEASUREMENTS OF EQUATORIAL F-REGION VERTICAL PLASMA DRIFTS IN THE EVENING SECTOR

Studies of equatorial F region evening vertical plasma drifts using di fferent measurement techniques have produced conflicting results. We e xamine the relationship of incoherent scatter radar and ionosonde drif t observations over the Peruvian equatorial region, and AE-E satellite drifts for different geophysical conditions. Our data show that there is large day-to-day variability on the ratios of radar and ionosonde drifts, but on the average the measurements from these two techniques are in fair agreement during low and moderate solar flux conditions. F or high solar activity, however, the Jicamarca evening drifts during e quinox and December solstice are significantly larger than the ionoson de drifts. These results can be explained by the different height rang es of the radar and ionosonde measurements, and the increase of the up ward drift velocity with height below the F region peak. This altitudi nal variation is related to the longitudinal gradient of the zonal pla sma drifts as a result of the curl-free electric field condition. Our results also indicate that during equinox the increase of the vertical prereversal velocity enhancement with solar activity is largely longi tude independent.