Multistation VHF scintillation studies at low latitudes

Amplitude scintillations data at 244 MHz (FLEETSAT, 73 E) recorded from a network of three stations at Waltair (177°N, 83.3°E), Nuzvid (16.8°N, 80.8°E) and Payyanur (12°N, 75.8°E) from August 1991 to April 1993 are used to study the characteristics of ionospheric irregularities at low and near-equatorial latitudes in the Indian sector. The occurrence and patch durations are found to be higher at the near-equatorial station Payyanur, when compared to the occurrence at the other two low latitude stations. Equinoctial maxima are seen at all three stations followed by secondary maxima in winter. However during summer, significant scintillations were present at Payyanur, while the occurrence is much reduced at the other two low latitude stations. Seintillations are also inhibited during magnetically disturbed days. The scintillation patches recorded at the two nearby low latitude stations (Waltair and Nuzvid) show similarities during post-sunset hours, while their characteristics are found to differ after midnight. From a comparison of similar patches simultaneously recorded at the above two nearby stations, the velocity components of the drift of ionospheric irregularities are found to show predominent eastward movements with velocities varying between 80 and 280 ms−1. The occurretice of daytime scintillations is found to be higher in summer months.