A Long-Term Shift in Flow Regimes over the Antarctic Peninsula

Abstract Surface warming in the polar regions has important consequences for the stability of the lowest layers of the atmosphere and for atmospheric vertical movement. Here, using ERA5 reanalysis data and in situ measurements, we quantify the evolving static stability of the lowest 1 km of the Antarctic atmosphere and show that the Brunt–Väisälä frequency, a measure of atmospheric stability, has been steadily decreasing since the 1950s. Using satellite observations, reanalysis, and targeted climate simulations, we find that this reduced stability has prompted a shift in prevailing flow regimes over the Antarctic Peninsula by altering regional wind flow and enhancing the generation of orographic gravity waves. Increased gravity wave forcing from the Antarctic Peninsula can have important implications for global-scale circulation, polar vortex strength, ozone depletion, and midlatitude weather. Significance Statement We present consequences of Antarctic surface warming for the stability of the lower atmosphere since the 1950s. We show that the surface atmosphere over the Antarctic Peninsula has become less stable, and that this reduced stability favors the generation of atmospheric gravity waves from the Peninsula, one of the major sources of atmospheric waves on the planet. We provide a physically based explanation (i.e., a shift in flow regimes) for the increased gravity wave forcing that we find in an unprecedented set of reanalysis products, satellite observations, and model simulations, and that we present here for the first time. Gravity wave forcing changes can have profound ramifications for the global climate, from polar vortex strength to ozone depletion and midlatitude weather.