A study of evolution/suppression parameters of equatorial postsunset plasma instability

Evening equatorial pre-reversal vertical ion E×B drift (VZP) and the peak of the ionospheric F2 maximum altitude (hmF2P) of the postsunset equatorial F-layer, which are the essential parameters requisite for the generation or inhibition of postsunset bottomside equatorial irregularities were deduced from ionosonde observations made in the Africa region (Ouagadougou: ~3° N dip latitude) between January 1987 and December 1990 for solar activity minimum, medium, and maxima (F10.7=85, 141, 214, and 190, respectively) for quiet geomagnetic conditions. We investigate variations of evening equatorial pre-reversal drift and the corresponding altitude at four levels of solar activity. Our observations show strong variations with solar variability. Correlation analysis between these parameters indicates that the correlation coefficient value between hmF2P versus VZP decreases considerably with increasing solar flux value. There seems to be no significant link between these parameters under high solar activity, especially for solar intensity F10.7>200 units. We conclude that meridional neutral wind in the F-region contributes substantially to the variations of the pre-reversal vertical plasma drifts enhancement and the peak hmF2, particularly the electrodynamics during twilight high solar flux conditions