Plasma drifts inferred from thermospheric neutral parameters during geomagnetic storms at 23°S

Abstract

Abstract Nighttime thermospheric neutral winds and temperatures are derived from measurements of Doppler shifts and widths of the OI 630.0 nm airglow emission line, respectively, using a Fabry-Perot interferometer at Cachoeira Paulista (23°S, 45°W, 16°S dip latitude), Brazil. The observed nighttime East–West and North–South temperature gradients and neutral wind velocity variations are presented for two geomagnetic storm periods 7–10 July 1991 and 4–9 August 1991. Zonal plasma drifts inferred during an intense geomagnetic storm, from the nighttime neutral wind velocities and temporal temperature gradient variations, suggested that a strong zonal plasma drift (−240 m⧹s) on 9–10 July 1991 changed the direction of the zonal winds to westward at 01:30. Also it was noticed that, during the geomagnetic storm, the zonal temperature gradients were not well defined like those observed during quiet time. The meridional wind was towards the pole for the whole night during the geomagnetic storm of 9–10 July, a behaviour which is unusual during winter time (southern hemisphere) at Cachoeira Paulista. However, the meridional plasma drifts inferred did not show significant differences during the quiet and disturbed periods. The method presented to infer plasma drifts using the observed neutral parameters showed results comparable with those observed by incoherent scatter radar measurements at Arecibo.