East-west plasma bubble irregularity motion determined from spaced VHF polarimeters: Implications on velocity shear in the zonal F region bulk plasma motion

VHF electronic polarimeters were used to monitor Faraday rotation angle and amplitude of geostationary satellite (GOES 3) beacon signals, simultaneously at two stations, Cachoeira Paulista (22°41'S, 45°W) and São José dos Campos (23°12'S, 45°55'W), separated by 110 km exactly in the magnetic east-west direction in Brazil. The analysis of the data for a few months in the 1981-1982 period, carried out in this paper, shows TEC fluctuations correlated with range type spread F events in the local ionograms and amplitudes scintillation in the satellite beacon signals, thereby identifying themselves as plasma bubbles and associated structures in the equatorial ionosphere. The spaced polarimeter system has permitted determination of the east-west velocities of these plasma bubble structures whose nighttime variation pattern is in excellent agreement with those of the eastward bulk plasma measured by Jicamarca radar and with those of the plasma bubble irregularities obtained from different radio and optical measurements carried out in the equatorial and low-latitude regions. There exist, however, significant differences in the magnitude of the velocities in the different measurements, our results over low-latitude locations showing highest values of all. These differences are interpreted as suggesting the possibility of a latitudinal variation in the plasma zonal velocities, consistent with the already known existence of vertical shears in the bulk plasma zonal flow over the equator.