Study of Nighttime Vertical Drifts in F-region over Waltair Using Phase-path Technique

Abstract

Nighttime F-region phase-path records taken at Waltair (dip 20°N; 83° 18'E), a low latitude station, are used to calculate vertical drifts. Vertical speed is upward around 1800 hrs LT, undergoing a post-sunset reversal around 1900 hrs LT; the layer then moves downwards till 2050 hrs LT. Vertical speed is positive again between 2050 and 2330 hrs LT and later the F-layer moves downwards ti1sunrise hours. These observations are consistent at this station and are different from the nighttime vertical speeds noticed at equatorial and midlatitude stations. Upward and downward movements at Waltair seem to closely fol1ow the F-region height variations at Ahmedabad (dip 34°N; 72°36'E). The post-sunset reversal at Waltair is very similar to the E x B drift reversal at post-sunset times reported for the equatorial F-region. The upward motion of the F-region for about two and half hours prior to midnight is noticed to be a regular feature at this station and the dominance of neutral wind effect on the motion of the F-layer at that time appears to be a possible explanation. Vertical drifts on all spread-F days, observed before the post-sunset reversal, are noticed to be large when compared to those on no spread-F days.