Long Term Variations of Ionospheric Horizontal Drift and Anisotropy of E-region Irregularities at Waltair

The study of long term variation of drift and anisotropy parameters of E region irregularities is particularly important because of the fact that D1 method measures movements of ionization that corresponds with neutral air motion in this region and facilitates a comparison with other methods of measuring winds in this region. The study of horizontal movements of small scale ionospheric irregularities at Waltair (17.70 N; 83.30 E) using D1 technique was started as early as I.G.Y.period. In this paper we present the results of observations of the drift and anisotropy parameters of ionospheric irregularities during equinox season over a span of about 10 years from 1957 to 1966 covering both the I.G.Y.and I.Q.S.Y.periods.About 140 midday (10-14 hrs) E-region drift records taken on frequency of 2.4 MHz are selected for the present study. There is an overall increase observed in the velocity parameters Va, V and Vc with the increase of sunspot number. The structure size, a of the irregularities shows a negative variation with sunspot number, decreasing magnitude with increase in sunspot number. There seem to be seasonal variation in the long term variation of some of the drift parameters with respect to solar epoch at Waltair.