On the reversal of drift direction at Thumba 0.6.DEG.S dip) in the F-region.

Abstract

The characteristics of the horizontal drift vector in the F-region over the equatorial station Thumba around the times of morning and evening reversals are discussed in detail. The fading of the reflected signal is found to become extremely slow at these timings and the usual spaced antenna technique of determining the horizontal drift is found to be not applicable. The drift vector shows a more or less sudden reversal of direction and there is no indication of its going through north-south in the intervening time. The morning reversal of drift is found to occur at a time when the transverse size of the F-region irregularities is maximum, while the evening reversal shows a close correspondence with occurrence of the maximum virtual height (h′F) of the F layer.The appearence and disappearence of the sporadic-E layer at Thumba is also found to be dependent on the timings of F-region horizontal drift reversal. The sudden reversals of the drift in the F-region during day time is also found to result in the disappearence of Es ionization at Thumbe for the corresponding short period. Both these effects are well correlated to the changes in the electrojet current direction.