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

Abstract

Amplitude scintillations on 244 MHz radio signals transmitted from geo-stationary satellite, FLEETSAT (73°E), were continuously recorded at a network extending from Ujjain (situated north of anomaly crest region) to the equatorial station, Trivandrum, by the Indian Institute of Geomagnetism, Mumbai. Parameters of geomagnetic activity like <i>K</i>-Alibag, <i>A</i>_p and electrojet strength are used to study the association of the amplitude scintillation recordings at the equatorial station, Trivandrum (dip 1° N ) and at Mumbai (dip 26°N), a station south of the anomaly crest region during the high solar activity period 1989-1991. It is observed that an increase in geomagnetic activity (<i>K</i>-Alibag or <i>A</i>_p) suppresses the occurrence of scintillation activity at both the stations, whereas the electrojet strength is found to have no association on the occurrence of scintillations. A total of 77 storms occurring during this period are classified into three types according to Aarons criterion. The time of the maximum intensity of ring current appears to play a role directly or indirectly in establishing the conditions necessary for the equatorial F-layer irrgularity generation and inhibition which, in turn, manifests itself in scintillation activity. However, there is about 30-40% of scintillation activity unaccounted by the magnetospheric electric field alone.