22-29The VHF scintillation
observations made at a chain of stations in India during February-March 1993
under AICPITS (third campaign), using the 244 MHz radio beacon from FLEETSAT,
and analysed jointly by all participating investigators at a workshop held at Raj
kot are described. The occurrence features of scintillations during the third campaign
were similar to those observed during the first campaign of March-April 1991.
The maximum occurrence was, however, reduced to some extent due to the lower solar
activity. The latitudinal variations showed an increased occurrence in the region
of about 17-18o latitude. The data during the night of 19-20 Feb. 1993
when an extensive ‘Ionisation Hole Campaign’ was undertaken showed scintillations
marked by earlier onset and longer duration at stations Waltair and Nuzvid than
at the stat ions close to the magnetic equator. However, based on the average
variations during February-March 1993 the onset at Tiruchendur, Anantpur and Walt
air was at nearly the same time. The vertical rise velocity of the plasma
depletions, estimated from the time delays in the onset of scintillations at latitudes
away from the dip equator, was found to range from 40 m/s to 420 m/s in the altitude
region 300-1350 km