Semidiurnal Tide Modulation by Ozone and Nonlinear Interaction With Planetary Wave During the 2024 Southern Hemisphere Sudden Stratospheric Warmings

We investigate the neutral wind and semidiurnal tide (SDT) variations in the mesosphere and lower thermosphere (MLT) during two consecutive minor Southern Hemisphere (SH) sudden stratospheric warmings (SSWs) that occurred unusually early in July–August 2024. Zonal and meridional winds from four meteor radar stations at 50–70°S were analyzed. Zonal winds reversed from eastward to westward between 80 and 100 km altitude during both events, showing a more distinct reversal in the second event. The SDT amplitudes increased and exhibited longitudinal differences around the second event. To elucidate the mechanisms responsible, we analyzed ozone observations from Aura/MLS along with MERRA-2 shortwave heating. Positive ozone anomalies at 10 hPa (∼32 km) in the SH polar region around each event coincide with enhanced SDT amplitudes from meteor radars. In addition, the shortwave heating rate shows an enhanced 12-hr component at SH high-latitudes above 40 km during these events, supporting an ozone-related radiative contribution to the SDT variability. Using phase-differences from longitudinally separated meteor radars, we estimated the zonal wavenumber. Based on this analysis, we propose that nonlinear interaction between the quasi-16-day zonal wavenumber-2 planetary wave (Q16DW2) and the migrating semidiurnal tide (SW2) contributed to the observed longitudinal differences in SDT amplitude. Furthermore, nonlinear advection associated with Q16DW2–SDT interactions is examined and shows clear longitudinal differences that lead to longitudinal asymmetry in SDT amplitude. These findings show the strong modulation of the SDT by SH SSWs and underscore the combined roles of ozone variability and nonlinear wave interactions in modulating upper-atmospheric tidal responses.