SEASONAL, SOLAR AND MAGNETIC ACTIVITY EFFECTS ON EVENING F-REGION VERTICAL PLASMA DRIFTS

A study of the seasonal, solar and magnetic activity dependence of the evening F region vertical plasma drifts using HF Doppler radar observ ations conducted during the period 1984-89 at the equatorial station T rivandrum (dip. 0.5-degrees-N) is presented. The observations show tha t (1) during magnetically quiet days of moderate solar activity condit ions, the characteristic pre-reversal enhancement in vertical plasma d rift attains a maximum during equinox and is higher than the winter an d summer values, which are not much different from each other, by abou t a factor of 2, (2) during equinox, the pre-reversal enhancement peak is sensitively, dependent on solar activity for both magnetically qui et and disturbed conditions, and (3) magnetic activity does not seem t o have a pronounced effect on the pre-reversal enhancement peak veloci ty. The results presented here are found to be in broad agreement with those reported for Jicamarca.