HF Doppler radar observations of sporadic E at an Indian low latitude station, Visakhapatnam

Abstract. 5.5 MHz HF Doppler radar observations of Sporadic E over an Indian low latitude station, Visakhapatnam (17.7° N, 83.3° E and Dip 20°) with 10 s resolution showed quasi-periodic variations of the echo strength and Doppler velocity variations with periods of a few minutes to a few tens of minutes. The echo strength and Doppler velocity variations with time in different range bins of the E_S echo showed variations which are some times similar and some times significantly different in successive range bins at intervals of 7.5 km. The E_S echo occurs with the height of maximum echo strength in the range of 100 km to 120 km and some times at 130 km. The altitude variation of the average Doppler velocity is highly variable and the height of maximum echo strength is not the same as the height of maximum Doppler velocity. Observations of E_S echoes at different times of the day are presented to bring out the differences between the day and night time E_S echoes. The relationship between Radar and E_S parameters derived from Ionograms is poorer than that of mid latitudes which is quite consistent with the expectations based on gradient drift instability.