A study on the zonal movements of ionospheric irregularities using simultaneous geo-stationary satellite signals

The simultaneous recordings of the amplitude scintillations of VHF radio signals from two nearby geostationary satellites, FLEETSAT (73 degrees E) and SIRIO (65 degrees E), received at a low latitude station, Waltair (17.7 degrees N, 83.3 degrees E), have revealed systematic time-shifts in the onset and decay of the individual similar scintillation patches. A total of 143 individual similar patches identified in the simultaneous scintillation data recorded at 136 MHz and 244 MHz during a low solar activity period from September 1983 to August 1984 at Waltair are used to compute the velocity components and size of the irregularities. The sub-ionospheric points [SIRIO (16.9 degrees N, 81.9 degrees E); FLEETSAT (16.4 degrees N, 82.6 degrees E)] of the two ray-paths were separated by only about 80 km in the east-west (E-W) direction, in which distance the structure of the irregularities do not change much. The E-W drift of plasma irregularities thus computed from the onset time delays of these events revealed a drift velocity of 140 m/s in the early hours of night and decreasing to about 90 m/s during the later part of the night. Using the drift velocities and the corresponding patch durations, the sizes of the irregularities (east-west extent) are computed and are found to vary from a minimum of 50 km to a maximum of 1000 km with most probable values ranging between 50 and 250 km, which compare well with the results reported earlier.