Strength of the equatorial electro jet and geomagnetic activity control on VHF scintillations at the Indian longitudinal zone

Amplitude sc inti ll ations o n 244 MHz radi o signal s tran smitted fro m geo-stati onary satelli te, FLEETSAT (73°E), were continuo us ly record ed at a network exte nding from Ujjain (situated no rth of anomaly crest regio n) to th e equatorial stati o n. Trivandrum. by th e In di a n In stitut e of Geomagneti sm. Mumbai. Para mete rs of geomagne ti c activity like K-Alibag, AP and e lectrojet stre ngth are used to study th e association o f th e amplit ude sc intillation recordings a t th e equatorial station, Trivandrum ( dip 1° N ) and at Mumbai ( dip 26° N ). a stati o n outh of the anomaly crest regio n during the hi gh solar acti ity period 1989- 1991. It is observed that an increase in geomagnetic activity (K-Alibag o r Ap) suppresses the occurrence of scintill ati on activity at both th e stati o ns. whe reas the e lectro jet streng th is found to have no assoc iati o n o n the occ urre nce of scintill ati o ns. A total of 77 storms occurring during thi s pe ri od are classified into three types accordin g to Aaro ns c rit erio n. The time o f th e maximum inte ns ity of ring current appears to pl ay a role directly o r indirectl y in establi shin g th e conditi o ns necessary for th e equatorial F-layer in·eg ul arity gene rati o n and inhibition which, in turn. manifests it self in scintillati o n activity. However. the re is abo ut 30-40% of scintillati o n activity unaccounted by th e mag ne tosphe ric electri c field alo ne.