VHF ionospheric scintillations near the equatorial anomaly crest: solar and magnetic activity effects

Abstract

The paper presents a study of solar and magnetic activity effects on VHF ionospheric scintillations recorded during three and half years at Bhopal, a station near the northern crest of the equatorial anomaly in India. During E- (equinox) and D- (winter) months, scintillations occur mainly in the pre-midnight period whereas during J- (summer) months their occurrence is larger in the post-midnight period. Very intense scintillations (>20 dB) mainly occur in the pre-midnight period, and in the post-midnight period, the scintillations are generally moderate (5–10 dB) or weak (<5 dB). The nocturnal scintillation occurrence decreases with the decrease in solar activity from 1989 to 1992. Monthly mean scintillation occurrence changes according to solar activity during E- and D-months but not so during J-months. The effects of magnetic activity on scintillations vary with season and, in general, inhibit the scintillation occurrence in the pre-midnight period and enhance it a little in the post-midnight period, especially after 0300 hours IST (Indian Standard Time). For most of the severe magnetic storms in which Dst goes below −125 nT and the recovery phase starts in the post-midnight to dawn local time sector, strong post-midnight scintillations, which sometimes extend for several hours beyond the local sunrise, are observed.