Frequency variation of equatorial ionospheric scintillations

Abstract

The fluctuations in the signal strength of v.h.f. and u.h.f. transmissions from satellites received at ground level contain valuable information about ionospheric irregularities. These fluctuations, usually called scintillations, depend on the frequency of transmission, characteristics of the irregularities and the angle of incidence. At equatorial latitudes, there have as yet been few such observations, and there are reasons to expect the scintillation characteristics at equatorial latitudes to be quite different from those at higher latitudes because the ionospheric irregularities (mainly spread F irregularities) responsible for scintillations differ widely in their characteristics with latitude. It is also well recognised that the equatorial region is a strong scintillation zone. At Trivandrum (dip 0°57′S, geographic longitude 76°57′E), a station close to the magnetic equator, amplitude and phase scintillations of the radio beacon transmissions on 40, 140 and 360 MHz as well as the amplitude scintillations of the 860–MHz television downlink from the geostationary satellite ATS–6 have been recorded since August 1975. Here we present preliminary results on the frequency variation of the scintillation index.