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Abstract
VHF intensity scintillations associated with equatorial spread- F were recorded at SHAR (dip 13°N), India, using the 136.1 MHz beacon from the geostationary satellite ETS-2. The observations were made during the periods 12 March–26 April 1986 and later from 15 September to 5 October 1988. The maximum hourly occurrence frequency of scintillations was about 50% during March 1986 and 30% during April 1986. It increased to about 85% during September–October 1988. The onset time of scintillations was generally between 20 and 21 h IST (77.5°E) during 1986 and between 1900 and 1930 h IST during 1988. Scintillations lasted for a longer duration of night in 1988 than in 1986. Data for a few nights were analysed to study the temporal variation of the scintillation index S 4, computed at close time intervals. Wave-like fluctuations with a dominant periodicity of about 1 h and another periodicity of about 20 min were seen. Power spectra were studied for 225 data samples of 100 s duration each for the night of 4–5 October 1988. The spectral index p[P(ƒ) ∞ ƒ −p] ranged between 2 and 6.8 with a mean value of 4. The temporal variation of the spectral index ( p) also showed a periodic fluctuation. The higher the S 4 index the steeper were the spectral slopes.
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