Stratospheric gravity wave characteristics and seasonal variations observed by lidar at the South Pole and Rothera, Antarctica

We present an observational study of stratospheric gravity wave spectra and seasonal variations of potential energy density at the South Pole (90°S) and Rothera (67.5°S, 68.0°W), Antarctica. The gravity wave spectra are derived from the atmospheric relative density perturbation in the altitude range of 30-45 km measured by an iron Boltzmann lidar. The ground-relative wave characteristics obtained at each location are comparable, with an annual mean vertical wavelength of ∼4.1 km, vertical phase speed of ∼0.7 m s ^-1, and period of ∼104 min. Approximately 44% of the observed waves show an upward phase progression while the rest display a downward phase progression in ground-based reference for both locations. Gravity wave potential energy density (GW-Ep) at Rothera is ∼4 times higher than the South Pole in winter but is comparable in summer. Clear seasonal variations of GW-Ep are observed at Rothera with the winter average being 6 times larger than that of summer. The seasonal variations of GW-E_P at the South Pole are significantly smaller than those at Rothera. The absence of seasonal variations in wave sources and critical level filtering at the South Pole is likely to be responsible for the nearly constant GW-Ep. The minimum critical level filtering in winter at Rothera is likely to be a main cause for the winter enhanced GW-Ep, as this would allow more orography-generated waves to reach the 30 to 45 km range. The stratospheric jet streams may also contribute to the winter enhancement at Rothera.