Seasonal and magnetic activity variations of nighttime ionospheric F-region vertical plasma drifts at Ibadan

Abstract

Nighttime F-region vertical electrodynamic drifts at Ibadan (lat. 7.4ºN, long. 3.9ºE; –6º dip) are obtained from the hourly-recorded ionosonde h′F data during 1957-58 International Geophysical Year (IGY) under geomagnetic quiet and disturbed conditions. The present results indicate strong seasonal variations in the drifts, even during quiet geomagnetic conditions. The downward nighttime average electrodynamic drift is found to be nearly 10 m/s. The drifts are consistently downward between ~2100 and 0500 hrs LT sector. The evening reversal time from upward daytime to downward nighttime does not vary much except during the June solstice months when it is found to be least, while it occurs early in December solstice and equinox. An equinoctial maximum in pre-reversal enhancements of the vertical drift is also noted. The present results are found to be completely consistent with some results obtained for some low latitude ionospheric stations, Jicamarca (lat. 11.9ºS, long. 76.8ºW; 1ºN dip), and Trivandrum (lat. 8.36ºN, long. 76.6ºE; 0.5ºN dip) that use different measurement techniques. Possible sources of the quiet-time variability in the electrodynamics can arise from changes in the global wind system and their resultant dynamo conditions, and changes in conductivity due to solar flux variability.