Gravity waves in the middle atmosphere above South Pole, Antarctica

Abstract

In the winter months, the stable southern polar vortex creates a unique environment around South Pole, isolating it from mid-latitude air masses and weather systems. The absence of mountains in the vicinity of the Pole, lack of convection and the low wind speeds in the stratosphere eliminate typical local sources of gravity waves. This is in contrast to the southern tip of South America near the edge of the polar vortex, where strong low-level winds excite the strongest orographic gravity waves above the Southern Andes. The lidar in Rio Grande, Tierra del Fuego, Argentina regularly observes temperature perturbations in excess of 20 K in the stratosphere in winter. Interestingly, at the Amundsen-Scott station at South Pole, simultaneous measurements with a twin lidar instrument reveal a continuous presence of gravity waves throughout the stratosphere and mesosphere during the entire winter season, although of lower magnitude. We find that the gravity wave potential energy density in the stratosphere and mesosphere above South Pole is about a factor of 3 lower than at Rio Grande, and the temporal evolution at both lidar sites, separated by 4000 km, is uncorrelated. Notably, however, the intermittency of daily mean values of potential energy density is comparable at both sites with the exception of the upper mesosphere, where the distribution is more uniform at South Pole. We find evidence of mountain waves in the stratosphere that might be linked to catabatic winds crossing the transantarctic mountains. With our lidar measurements, which started in winter 2023, we complement the OH airglow observations acquired by the advanced temperature mapper and hope to characterize gravity waves from near surface up to the OH layer.