Impact of Midnight Thermosphere Dynamics on the Equatorial Ionosphere

Abstract:

During the recent solar minimum, a large amount of C/NOFS satellite measurements have revealed an upward drift that occurs during the post-midnight period (~2-3 LT). The upward drift is also frequently shown in radar measurements. The phenomenon has not yet been explained and the physics are still unknown. Our simulations have successfully reproduced the unusual upward drift using the coupled Whole Atmosphere Model and Global Ionosphere Plasmasphere Model (WAM/GIP). Model produces significant day-to-day variability in the nighttime equatorial ionosphere. Simulations also reveal strong seasonal and longitudinal dependence of the upward drift. 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. The longitudinal variation of the drifts depends on the magnitude and position of the MTM peak relative to the magnetic equator. In this talk, we will present the morphology and characteristics of the post-midnight upward drift shown in the simulations and explain its causal mechanism.