Variations of equatorial electrodynamics during sudden stratospheric warming events

We have used plasma drift and magnetic field measurements during the 2000-2012 December solstices to study, for the first time, the longitudinal dependence of equatorial ionospheric electrodynamic perturbations during sudden stratospheric warmings (SSWs). Jicamarca radar measurements during these events show large dayside downward drift (westward electric field) perturbations followed by large morning upward and afternoon downward drifts that systematically shift to later local times. Ground-based magnetometer measurements in the American, Indian, and Pacific equatorial regions show strongly enhanced electro jet currents in the morning sector and large reversed currents (i.e., counterelectro jets) in the afternoon sector with onsets near new and full moons during northern winter warming periods. CHAMP satellite and ground-based magnetic field observations indicate the onset of these equatorial afternoon counterelectrojets is longitude dependent. Our results indicate these large electrodynamic perturbations during SSW periods are due to strongly enhanced semidiurnal wave effects. We have also studied variations in plasma drifts and the magnetic field during the September 2002 equinox and July 2010 June solstice warming events. Plasma drift variations during these events indicate a strong effect due to enhanced multi-day oscillations. Lunar semidiurnal variations are shown to be highly dependent on season, with the strongest enhancements of the lunar tide around the December solstice and the weakest around the June solstice. The results of our study can be used for forecasting the occurrence and evolution of these electrodynamic perturbations during warming events.;We also 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 during SSWs. Our models indicate the amplitudes of the enhanced lunar semidiurnal drifts are strongly local time and solar flux dependent, with the largest values during early morning low solar flux SSW periods. These results suggest ionospheric conductance strongly modulate low-latitude ionospheric changes during SSWs. They also indicate 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.