Hemispheric asymmetry of the ionospheric variation during major sudden stratospheric warming events

The hemispheric asymmetry of the ionospheric variation in the American sector (45°N~45°S, MLAT; 80°~60°W) is studied with total electron content (TEC) data during major sudden stratospheric warming events. The amplitude (A_M2) and relative strength (RS_M2) of the semi-diurnal lunar tidal component (M2) of TEC are analyzed. RS_M2 is the ratio between the energy of M2 and the energy of all the studied tidal components. The magnitudes of A_M2 and RS_M2 exhibit clear hemispheric and latitudinal variations. The A_M2 in the north of the magnetic equator tends to occur at lower magnetic latitudes than the A_M2 in the south of the magnetic equator. The RS_M2 exhibits similar features as the A_M2 but the difference is more distinct. We suggest that such hemispheric asymmetry of M2 parameters is related to the hemispheric asymmetry of the EIA and the latitudinal variation of the amplitude of the solar tidal components in winter.