VHF radio scintillations at Bombay

Abstract

The simultaneous recordings of the amplitude scintillations of VHF radio signals from nearby geostationary satellites FLEETSAT (at 73°E long.) and SIRIO (at 65°E) received at Bombay (geog. lat. 19°N, geog. long. 73°E, mag. lat. 15°N) have revealed systematic time shifts in the starting and the ending of the individual scintillation events. The ionosphere crossover points of the two transmission paths were separated by only 80 km in the east-west direction, which was smaller than the average size of the irregularity patches. Scintillations normally started after 1930 h, reached a maximum at 2200 h and slowly decreased till 1000 h, after which no scintillations were observed. The speed of the irregularity patches computed from the time shifts of these events was about 150 m s^-1 in the early hours of the night, decreasing to about 100 m s^-1 by midnight and showing much lower velocities in the post-midnight hours.