Observations of fast Faraday polarization fluctuations at VHF and amplitude scintillations at VHF and UHF near the equatorial anomaly crest in the Indian sector

摘要

Simultaneous measurements of fast Faraday polarization fluctuations (FPF's) and amplitude scintillations at 136 MHz during April 1977 to February 1980 and of amplitude scintillations at 136 MHz and 244 MHz during August 1981 to December 1982 made at Calcutta (27° dip subionospheric) have been utilized to investigate the nature of ionospheric irregularities during different seasons near the equatorial anomaly crest in the Indian sector. The irregularities occurring in the equinoxes under high solar activity conditions are found to be responsible for intense VHF/UHF scintillations and FPF's. The June solstice is characterized by irregularities producing slow and moderate to weak VHF scintillations but no significant FPF's and UHF scintillations. The occurrence of FPF's is mostly confined to premidnight hours and reduces significantly with respect to the amplitude scintillation occurrence in postmidnight hours. The results are assessed in terms of the strength of irregularities and the longitudinal behavior of global equatorial scintillation activities.