Dynamics of Orographic Gravity Waves from Subantarctic Islands As Observed and Modeled During the Deep Propagating Gravity Wave Experiment (DEEPWAVE)

Global climate and weather prediction models contain a persistent cold-pole bias in the Antarctic polar winter stratosphere, characterized by a vortex that is too cold, vortex-edge westerlies that are too strong, and a final springtime stratospheric warming that occurs weeks later than observed. These model biases affect climate predictions of Antarctic climate and stratospheric ozone loss and recovery. One the many scientific motivations of the Deep Propagating Gravity Wave Experiment (DEEPWAVE) was to test the hypothesis that one source of these model biases could be missing orographic gravity-wave drag from tiny chains of subantarctic islands scattered across the Southern Ocean. We review this hypothesis, then discuss a DEEPWAVE research flight over Auckland Island, located ~1000 km south of New Zealand, which observed deep propagation of orographic gravity waves from this island archipelago and huge drag effects in the mesosphere. We then present high-resolution satellite observations of stratospheric gravity waves from other subantarctic islands during DEEPWAVE, and use them together with global data assimilation fields, gravity-wave drag parameterizations and regional gravity-wave modeling to delineate some new and unusual aspects of stratospheric wave propagation and wave breaking from these islands during DEEPWAVE. Implications of these findings for the stratospheric cold-pole hypothesis and gravity-wave drag parameterization are discussed.