Impact of the vertical dynamics on the thermosphere at low and middle latitudes: GITM simulations

The equatorial ionization anomaly and the equatorial thermosphere anomaly (ETA) are well reproduced in the simulation when the electric fields are included. The term analysis of the continuity equation of the neutral mass density shows that the daytime upward vertical wind near the geomagnetic equator tends to increase the local neutral mass density at 400km altitude, while the divergence in the meridional wind associated with the meridional ion-drag force tends to transport the neutral mass density away from the geomagnetic equator which might contribute to the formation of the ETA trough.

The vertical dynamics is modulated by the vertical forces including ion-drag force and pressure gradient force acting on the neutrals, and the changing vertical dynamics can also feedback to vertical ion-drag and pressure gradient forces, particularly near the geomagnetic equator. The daytime vertical ion-drag force near the geomagnetic equator is generally upward, while the daytime vertical pressure gradient force near the geomagnetic equator is reduced at most times after adding in the electric fields at low and middle latitudes.