VHF amplitude scintillations and associated electron content depletions as observed at Arequipa, Peru

Abstract

Results of observations on occurrences and behavior of 137 MHz VHF amplitude scintillations and associated ionospheric electron content depletions obtained at Arequipa, Peru (16.4°S, 71.5°W, geogr.; 9°S dip) during the recent solar maximum period 1979–1980 are presented. The seasonal variation of scintillations shows the usual deep minimum during May–July and a prominent maximum in December, when scintillations also persist for a long period of time, sometimes even beyond sunrise. Ionospheric irregularities have been found to occur in distinct patches whose extent varies with season. During the December solstice the average VHF scintillation patch duration is about 6 h, while numerous patches of much shorter duration are observed in equinoctial months. The depletions in the height integrated ionospheric electron content associated with scintillations have a typical duration of 10–15 min and amplitude less than 5 × 10 16 el m −2, although depletions with an amplitude as large as 20 × 10 16 elm −2 and with a duration of more than 30 min are sometimes encountered. The pre-midnight amplitude scintillations and associated electron content depletions could be identified with range type spread- F, as established earlier, while the association of post-midnight VHF scintillations with frequency type spread- F is found to be a special feature observed during years of very high solar activity. The seasonal dependence of irregularity patch dimensions is examined in terms of variations of drifts in the post-sunset equatorial ionosphere.