Interannual variability of mean winds and the semidiurnal tide in the Antarctic summer mesosphere-lower thermosphere

Long-term observations at southern polar latitudes in the summertime mesosphere–lower thermosphere (MLT) reveal persistent nonmigrating semidiurnal tides, with the zonal wavenumber-1 ($s$=1) component being particularly dominant. Using nearly two decades of meteor radar wind measurements (80–100 km) from Davis Station (East Antarctica) and King Sejong Station (Antarctic Peninsula), we find strong agreement in mean zonal and meridional wind structures and their interannual variability. However, near the summer solstice, the semidiurnal tide exhibits pronounced longitudinal asymmetry: large amplitudes at Davis but weak at King Sejong. This disparity is attributed to interference between the westward-propagating $s$=1 and $s$=2 components, analyzed via singular value decomposition. The decomposed $s$=1 tide shows interannual variability similar to that of the mean summertime zonal winds, with both variations highly correlated with the size and depth of the Antarctic ozone hole. Modal analysis indicates that, prior to solstice, the $s$=1 and $s$=2 tides correspond to the (2,1,4) and (2,2,6) Hough modes, respectively.