Post-SSW Quasi-Biweekly Oscillations Sustained by Wave-Mean Flow Feedback in the Southern Hemisphere

Abstract. A quasi-biweekly oscillation developed in the Southern Hemisphere following the 2024 sudden stratospheric warming (SSW) events, rather than a monotonic recovery. Although recurrent tropospheric planetary-wave activity preceded the warming episodes, the much stronger stratospheric response suggests that lower-level forcing alone cannot explain the oscillation. We show that planetary-wave propagation, the polar vortex, and the stratospheric waveguide were linked through a coupled feedback: enhanced upward wave propagation before the warming peaks weakened and contracted the polar vortex, shifting the strongest waveguide structure poleward and reducing its overlap with the main 50° S–70° S wave-activity region. The subsequent weakening of upward propagation allowed the westerly flow and polar vortex to partially recover, restoring favorable propagation conditions and enabling the next cycle. These results suggest that Antarctic post-SSW variability can be sustained from late winter into early spring by internally modulated wave-mean flow interactions.