Characteristics of VHF scintillations in the Indian equatorial and low latitude stations

158-169The VHF scintillation data from three different locations, namely, Pondicherry (11o N, 78°E, dip 7.6°N), a near equatorial station, and Waltair (17.7°N, 83.3°E, dip 20°N) and Mumbai (19°N, 73°E, dip 25°N), the two anomaly crest region stations, are considered for the study of some typical characteristic features and geophysical effects on the occurrence of VHF scintillations both on short and long term basis. The data pertaining to the period of increasing sunspot years of 1998 and 1999 from the three different locations are considered for these studies. The percentage occurrences of scintillations revealed that the occurrence is mo re at the equatorial stat ion, Pondicherry, compared to those at the two off equatorial stations, Waltair and Mumbai. The onset of scintillations, in most cases, is found to occur first at the equatorial station, and later at the two off-equatorial stations. However, there are some occasions when the occurrence of scintillations is first seen at Waltair and Mumbai without their prior occurrence at the equatorial station, Pondicherry. These cases are believed to be associated with the generation of irregularities at the anomaly crest regions. Further, it is found that the scintillation occurrence increases as the sunspot number increases at all the three stations with increasing latitude, suggesting the widening o f the scintillation activity belt with the increase of solar activity. The suppression effects of magnetic activity on the occurrence of scintillations seem to be more evident during the pre-midnight hours than during post-mid night hours