Impact of midnight thermosphere dynamics on the equatorial ionospheric vertical drifts

Recent satellite and ground‐based observations have revealed the existence of upward drifts in the postmidnight equatorial ionosphere (~0–3 LT). The phenomenon has not been explained by theoretical models. Simulations using the Whole Atmosphere Model coupled with the Global Ionosphere Plasmasphere model have successfully reproduced the unusual nighttime upward drifts. The simulations and observations by the Ion Velocity Meter onboard the Communications/Navigation Outage Forecasting System also reveal substantial longitudinal dependence of the drifts. Our analysis indicates that the upward drifts are driven by thermosphere dynamics associated with the midnight temperature maximum (MTM). The MTM locally reverses the typical large‐scale zonal and meridional wind pattern, in turn affecting the nighttime F layer electrodynamics. In addition, the longitudinal variation of the drifts in different seasons depends on the magnitude and position of the MTM peak relative to the magnetic equator. Key Points Simulation reproduces the nighttime upward drift observed by C/NOFS The nighttime upward drift is caused by thermospheric dynamics related to MTM Longitudinal variations result from the MTM dynamics and magnetic field geometry