Study of night time VHF ionospheric scintillations near the crest of equatorial Appleton anomaly Indian Station, Udaipur (24.6°N, 73.7°E)

Abstract

This paper presents the results of percentage occurrence of night time VHF ionospheric scintillations characteristics of radio beacon signals of 244/250 MHz transmitted from Fleet Satellite (positioned at 73°E Longitude) received over Udaipur (24.6°N, 73.7°E, Dip angle 35°) during different epochs of solar activity periods from March 1986 to April 2000. The long term observations of VHF scintillation phenomenon, spanning a solar cycle (1986 to 2000) which covers low, mid as well as high solar activity period, has shown the consistent nocturnal temporal hourly, seasonal and solar cycle variations in scintillation occurrences. The night time VHF radio wave scintillations has been found to be at maximum percentage occurrence during the equinoxes months and less during winter and the least during summer months in all the epochs of solar activity period. The monthly variations of percentage occurrences of VHF ionospheric scintillation activities are seen to be increased during high solar activity years and also showed that highest values of percentage of occurrences in equinoctials months during high solar activity years. The prominent feature of discrete patchy nature of night time VHF amplitude scintillations specifically, over Equatorial Appleton anomaly region, is also presented in the light of seasonal and solar activity dependence of scintillation occurrences and patches duration. The results of present observations are also compared with the earlier works of similar stations.