Longitudinal variation of ionospheric vertical drifts during the 2009 sudden stratospheric warming

The Whole Atmospheric Model (WAM) initialized with a data assimilation scheme is capable of simulating real sudden stratospheric warming (SSW) events. The electrodynamics in the Coupled Thermosphere Ionosphere and Plasmasphere with Electrodynamics model (CTIPe) was driven by the WAM thermospheric winds in January 2009 to study the response of ionospheric drifts during the SSW. Simulation results are compared with observations of the vertical drift at Jicamarca and the equatorial electrojet (EEJ) in the Asian sectors. Early morning upward drift and afternoon downward drift are reproduced in all longitudes in the simulations, and are consistent with the available observations. Results also show that the occurrence time of the early morning upward drift and afternoon downward drift have significant phase differences between different longitudes. Simulations suggest that during the SSW the longitude dependence of the amplitude and phase of the equatorial vertical plasma drift is caused by the changing magnitudes of the migrating tides modulated by the geometry of the geomagnetic field. Some additional day-to-day variability and modulation of the phase structures at different longitudes in ionospheric vertical drifts during the SSW are possibly produced by the short-term changes in the non-migrating tides and by planetary waves.