Ionospheric storm of 4–5 August 1972 in the Asia-Australia-Pacific sector

Abstract

The ionospheric storm of 4–5 August 1972 is analyzed using data from 35 middle and low latitude ionospheric stations and 7 magnetic stations in the Asia-Australia-Pacific longitude sector. The largest ionospheric and geomagnetic disturbances were both observed in the mid-Pacific. Strong upward electrodynamic drifts occurred in the western Pacific during the initial phase of the storm. True-height profiles of electron density in the Pacific area show that the ionosphere was raised during the first several hours after the geomagnetic storm sudden commencement, that large variations later occurred in the mid-Pacific, possibly caused by wave-like thermospheric winds, and that the F-layer was reduced in density and raised in height during the main phase of the storm on the following day. Synoptic pictures of the variations in foF2 are presented, showing that electron density enhancements occurred during the storm initial phase in the western Pacific at middle latitudes, peaking in the 20°–45° geomagnetic latitude range, and becoming density deficits during the storm main phase. The observed variations are interpreted in terms of possible physical mechanisms.