Modeling the ionospheric prereversal enhancement by using coupled thermosphere-ionosphere data assimilation

We report that assimilating total electron content (TEC) into a coupled thermosphere-ionosphere model by using the ensemble Kalman filter results in improved specification and forecast of eastward prereversal enhancement (PRE) electric field (E field). Through data assimilation, the ionospheric plasma density, thermospheric winds, temperature, and compositions are adjusted simultaneously. The improvement of duskside PRE E field calculation over the prior state is achieved primarily by intensification of eastward neutral wind. The improved E field calculation promotes a stronger plasma fountain and deepens the equatorial trough. As a result, the horizontal gradients of Pedersen conductivity and eastward wind are increased due to greater zonal electron density gradient and smaller ion drag at dusk, respectively. Such modifications provide preferable conditions and obtain a strengthened PRE magnitude closer to the observation. The adjustment of PRE E field is enabled through self-consistent thermosphere and ionosphere coupling processes captured in the model. This study suggests that the PRE E field that is critical in driving the evening equatorial plasma instability could be better forecasted by assimilation of TECs in the 10 min cycling.