Geomagnetic activity control on VHF scintillations over an Indian low latitude station, Waltair (17.7°N, 83.3°E, 20°N dip)

Using the data of amplitude scintillations recorded at 244 MHz from the geostationary satellite, FLEETSAT (73 degrees E) at a low latitude station, Waltair (17.7 degrees N, 83.3 degrees E; 20 degrees N dip), during the increasing sunspot activity period of 1997-2000, the effect of the geomagnetic storms on the occurrence of ionospheric scintillations has been studied. A total of 60 SC storms studied during this period, following the Aarons' criterion, reveals that the local time of onset of the recovery phase of the geomagnetic storms play an important role in the generation or inhibition of the ionospheric irregularities. Out of the 60 storms studied, nearly 60 to 70% satisfied the categories I, II and III of Aarons' criteria. However, in the remaining 30 to 40% of the cases, no consistent results were observed. Thus, there is a necessity for further investigation of the effect of geomagnetic storms on ionospheric irregularities, particularly with reference to the altitude variations of the F-layer (h'F) relating to the changes in the local electric fields.