Time of evening zonal drift reversal in F- region and its implications for post sunset ionosphere

Abstract

The study analyses the delayed occurrence of the F- region ionospheric manifestations like peak vertical drift and Equatorial Spread F onset in summer solstice of low solar activity years, using the ionosonde data at the magnetic equatorial station Trivandrum (8.5° N, 76.9° E) and Republic of China Satellite-1 data. The analysis reveals the unambiguous role of the time of ionospheric F- region zonal plasma drift/wind reversal in modifying the above-mentioned phenomena. The direct control of equatorial Spread F onset by the F- region drift/wind reversal is clearly established on a day-to-day basis in summer season. The role of the time of zonal wind/drift reversal in modulating the ESF onset is examined quantitatively by exploring its effect on the growth rate of Rayleigh - Taylor instability. Further, the study brings out the solar activity variation of the time of F- region zonal plasma drift/wind reversal for all seasons. The results highlight the need to have systematic neutral wind measurements to better address the enigmatic and multi-dimensional problem of equatorial Spread F day-to-day variability.