CHARACTERISTICS OF VHF SCINTILLATIONS IN THE EQUATORIAL ANOMALY CRESTREGION IN INDIA

The characteristic of ionospheric scintillations at Rajkot in the equa torial anomaly crest region in India are described for the years 1987- 1991 by monitoring the 244-MHz transmission from the satellite FLEETSA T. This period covers the ascending phase of solar cycle 22. Scintilla tions occur predominantly in the pre-midnight period during equinoxes and winter seasons and in the post-midnight period during summer seaso n. During equinoxes and winter, scintillations occurrence increases wi th solar activity, whilst in summer it is found to decrease with solar activity. Statistically, scintillation occurrence is suppressed by ma gnetic activity. The characteristics observed during winter and equino xes are similar to those seen at the equatorial station, Trivandrum. T his, coupled with the nature of the post-sunset equatorial F-region dr ift and h'F variations, supports the view that at the anomaly crest st ation, scintillations are of equatorial origin during equinox and wint er, whilst in summer they may be of mid-latitude type. The variations in scintillation intensity (in dB) with season and solar activity are also reported.