Ionosphere variability at mid latitudes during sudden stratosphere warmings

Variability of the mid latitude ionosphere and thermosphere during the 2009 and 2013 sudden stratosphere warmings (SSWs) is investigated in the present study using a combination of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) observations and model simulations. The simulations are performed using the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) and Ionosphere Plasmasphere Electrodynamics (IPE) model. Both the COSMIC observations and TIME-GCM simulations reveal perturbations in the F-region peak height (hmF2) at Southern Hemisphere mid latitudes during SSW time periods. The perturbations are ~20-30 km, which corresponds to 10-20% variability in hmF2. The TIME-GCM simulations and COSMIC observations of the hmF2 variability are in overall good agreement, and the simulations can thus be used to understand the physical processes responsible for the hmF2 variability. The simulation results demonstrate that the mid lattiude hmF2 variability is primarily driven by the propagation of the migrating semidiurnal lunar tide (M2) into the thermosphere where it modulates the field aligned neutrals winds, which in-turn raise and lower the F-region peak height. The importance of the thermosphere neutral winds on generating the ionosphere variability at mid latitudes during SSWs is supported by IPE simulations performed both with and without the neutral wind variability. Though there are subtle differences, the consistency of the behavior between the 2009 and 2013 SSWs suggests that variability in the Southern Hemisphere mid latitude ionosphere and thermosphere is a consistent feature of the SSW impact on the upper atmosphere.