SPECTRAL CHARACTERISTICS OF MAGNETIC STORM-INDUCED F-REGION SCINTILLATIONS EXTENDING INTO DAYTIME

Magnetic storm-induced F-region scintillations extending into daytime were recorded over Bombay, situated near the anomaly crest region in India, on 12 November 1991. The scintillations at 244 MHz using the radio beacon onboard FLEETSAT (73 degrees E), lasted till 1312 h IST (77.5 degrees E). Observations at Trivandrum, situated close to the magnetic equator also show strong daytime scintillations lasting till 1030 h. The scintillation event followed a sudden commencement at 1748 h UT (2318 h IST) on 11 November 1991 and the ionosonde observations, both over Ahmedabad in the anomaly crest region and Kodaikanal near the magnetic equator, show large upward drift of about 50 m s(-1) around 0300 h IST. The scintillation index S-4, autocorrelation function and power spectra have been computed from the digital data recorded at Bombay. The time variation of S, shows large fluctuations with a periodicity of about half an hour. The 50% decorrelation time of the signal fluctuations is of the order of seconds. The spectral index n, of the temporal power spectra, where P(f)alpha f(-n), varies between 1.5 and 5.0, with a mean value of 3.0, and shows a dependence on the S-4 index. These features are similar to those reported for night time scintillations recorded over Ahmedabad.