Equatorial ionospheric plasma bubble irregularity occurrence and zonal velocities under quiet and disturbed conditions, from Polarimeter observations

Abstract

Amplitude scintillation and Faraday rotation angle fluctuations of satellite VHF beacons registered by electronic polarimeters operated at two stations spaced 110 km apart in the magnetic east‐west direction namely, Cachoeira Paulista, 22°41′S, 45°W, dip angle of −26°, and São José dos Campos, 23°12′S, 45°51′W, dip angle of −26°, in Brazil are analyzed for equinoctial and summer months of 1982–1983 to determine the irregularity patch occurrence characteristics and their zonal velocities under varying levels of magnetic disturbances. The scintillation patch occurrences and total electron content fluctuations representing plasma depletion structures decrease during premidnight hours and are enhanced in the postmidnight period. The occurrences often extend to morning hours, with increasing magnetic activity index. While the night events are associated with eastward irregularity patch motion, the morning events have westward velocities (the reversal) occurring around 0400 LT, reflecting the morning velocity reversal in the F region bulk plasma motion reported earlier from Jicamarca radar measurements. The westward plasma bubble motions reported here represent the first observation of this kind. Another important finding from the present investigation is a clear tendency for the zonal plasma motion, namely, the equatorial meridional electric field, to become enhanced mainly in the premidnight hours immediately following strong magnetic activity.