Investigating Unique Observations of Middle-Upper Atmosphere Planetary-Scale Wave Events Observed by Lidar above McMurdo, Antarctica

We investigate upward phase progressing planetary-scale wave events observed above Antarctica by the McMurdo (77.84°S, 166.67°E) lidar systems during a 15-year campaign monitoring the middle atmosphere (30-80 km) and mesosphere and lower thermosphere (80-120 km). Two cases of waves having greater-than-inertial ground-based periods, planetary-scale horizontal wavelengths, and upward phase progression were observed in July 2016 and July 2024. Most planetary waves observed above McMurdo by the lidar and in MERRA-2 have a downward phase progression, making these observations somewhat unique throughout years of lidar observations. In these events, a wedge-like structure is observed in which waves with downward phase progression meet upward phase progressing waves at a "knee" in the middle atmosphere, where both upward and downward phase progressing waves have similar frequency and vertical wavenumber. These waves are explored using both lidar observations and the MERRA-2 reanalysis model, where we determine the spatial/temporal span and spectra of these waves during each of these events, theorize upon their sources/generation mechanisms, and assess any impact on lidar observed gravity waves (GWs) propagating on these unusual backgrounds. The July 2024 event is of particular interest as it occurs one week before a rare southern hemisphere sudden stratospheric warming, thus the role of this wave event in that warming is also investigated.