Variability of tidal vertical structures in the Antarctic MLT region: 11-Year observations over King Sejong Station (62.22°S, 58.78°W)

The mesosphere and lower thermosphere (MLT) region is greatly affected by tidal waves. The vertical structure of MLT tides in the Antarctic region is poorly understood. In the present study, we investigate the seasonal, annual and inter-annual variations of characteristics of MLT tides (24h,12h, and 8h) using long-term solar cycle neutral wind observations using meteor radar over King Sejong Station (KSS) (62.22°S, 58.78°W) during January 2007 and December 2017. Our analysis reveals ter-diurnal tide (8h) (TDT) and semi-diurnal tides (12) (SDT) are most significant tidal components than the diurnal tides (24h) (DT) over the present observational region and with diverse vertical structures. The variability in the tidal amplitudes is significant at and above 90 km than the lower MLT region. Both TDT and SDT reached their maximum amplitudes during southern hemisphere (SH) spring and winter at and above 90 km, whereas such features are not seen in the DT amplitudes. The zonal and meridional wind components are 90^o phase-shifted, with similar amplitude in most of the seasons, and this behavior is dominant in SDT than the others and at above 90 km. Further, the phase structure reveals a dominant upward propagating mode in SH summer and downward propagating mode in SH winter above 90 km, this feature is more predominant in the SDT. Most of the observed features differ from those reported in the Arctic, indicating large hemispheric asymmetry in MLT tidal characteristics. We have also investigated the solar cycle effect on the MLT tides over the present observational region. The present 11-year KSS meteor radar observations provide new constrains and benchmark for models that seek to understand MLT tidal forcing mechanisms in polar regions.