Thermosphere and F-region plasma dynamics in the equatorial region

Abstract

The dynamics of the equatorial thermosphere and the F-region ionospheric plasma are reviewed highlighting several features observed with in-situ satellite and ground-based experiments. Attention is given to the midnight temperature maximum (MTM) and related phenomena and to recent results on zonal neutral and plasma flows at F-region heights. The midnight temperature maximum and its midnight pressure bulge above 250 km altitude lead to neutral wind variations which significantly affect the F-region equilibrium height and its airglow emissions. During magnetically active periods, enhanced meridional winds from the poles lead to strong meridional intensity gradients (MIGs) in the atomic oxygen emission at 6300Å; MIGs have been used to estimate the magnitude of meridional wind gradients during active periods, and these estimates are consistent with measurements using incoherent scatter radar and optical Fabry-Perot interferometry. The pressure gradients which drive the thermospheric wind have been estimated using averaged density and temperature data, and the results have been used to check the consistency of the current data base in terms of the momentum equation. New analyses of the AE-E data are presented as further evidence of the effect of the MTM on the latitude-local time distribution of the meridional wind reversal. The tidal decomposition studies of the neutral temperature and of both ion and neutral flows are reviewed. The zonal plasma flow is found to be closely coupled to the zonal neutral wind as a consequence of the F-region dynamo, and more recently, the F-region dynamo has been found to play an important role in an anomaly in the latitudinal distribution of the equatorial zonal plasma flow.