Large scale electrodynamic and plasma density variations in the low latitude ionosphere have recently been associated with sudden stratospheric warming (SSW) events. We present average patterns of largely enhanced lunar semidiurnal equatorial vertical plasma drift perturbations during arctic winter low and high solar flux SSW events. These perturbations play a dominant role in the electrodynamic response of the low latitude ionosphere to SSWs. Our models indicate that the amplitudes of the enhanced lunar semidiurnal drifts are strongly local time and solar flux dependent, with largest values during early morning low solar flux SSW periods. These results suggest that ionospheric conductance strongly modulate low latitude ionospheric changes during SSWs. They also indicate that lunar semidiurnal effects need to be taken into account by global ionospheric models for their improved forecasting of the low latitude ionospheric response to SSW events, especially for low solar flux conditions.

We use the measurements by the Vector Electric Field Investigation (VEFI) on board the Communication/Navigation Outage Forecasting System (C/NOFS) satellite to study the local time and seasonal‐ and longitudinal‐dependent climatology of equatorial F region zonal plasma drifts during 2008–2011. These drifts are essentially westward during the day and eastward at night. Over Jicamarca Radio Observatory, the satellite measurements are in good agreement with incoherent scatter radar drifts. Our data show strong longitudinal variations, particularly in the South American sector during the solstices. The equinoctial data exhibit short‐lived and largely enhanced westward drifts near sunrise and wave‐4 structures from the early afternoon to late night equinoctial periods. The nighttime eastward drifts are largest near the western American sector at all seasons. The June solstice postmidnight eastward drifts decrease sharply at longitudes of about 310° and have much smaller values in the entire Eastern Hemisphere. We also briefly discuss the relationship between the longitude‐dependent vertical and zonal plasma drifts.

respectively. The monthly and semimonthly amplitudes decrease from early morning to afternoon and evening to morning with moderate to large increases near dusk and dawn.We also examined these perturbation drifts during periods of sudden stratospheric warmings (SSWs). Our results show, for the first time, the enhancements of the lunar semimonthly tidal effects associated with SSWs to occur at night, as well as during the day. Our results also indicate during SSWs, monthly tidal effects are not enhanced as strongly as the semimonthly effects. We also examined these perturbation drifts during periods of sudden stratospheric warmings (SSWs), which is a meteorological event where the polar vortex is displaced or splits and which has been known to be associated with a large increase in planetary wave activity. Our results show, for the first time, the enhancements of the lunar semimonthly tidal effects associated with SSWs to occur at night, as well as during the day. Our results also indicate during SSWs monthly tidal effects are not enhanced as strongly as the semimonthly effects.vii ACKNOWLEDGMENTS