Cooperative Institute for Research in Environmental Sciences

Science Rendezvous > 2009 Posters
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Gravity Wave Characteristics and Seasonal Variations in the 30-45 km at the South Pole and Rothera, Antarctica

Chihoko Yamashita¹, Xinzhao Chu¹, Han-Li Liu², Wentao Huang¹, Patrick J. Espy³, Graeme J. Nott⁴

¹ Cooperative Institute for Research in Environmental Sciences & Department of Aerospace Engineering Sciences, University of Colorado at Boulder, USA, ² National Center for Atmospheric Research, Boulder, Colorado, USA, ³ Department of Physics, Norwegian University of Science and Technology, Trondheim, Norway, ⁴ Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada

We present an observational study of stratospheric gravity wave (GW) spectra and seasonal variations of potential energy density at the South Pole (90°S) and Rothera (67.5°S, 68.0°W), Antarctica. GW spectra are derived from the atmospheric relative density perturbation in the 30-45 km detected with an iron Boltzmann/Rayleigh lidar. The obtained characteristics are comparable between the South Pole and Rothera with the annual mean vertical wavelength of ~5.7 km, vertical phase speed of ~0.8 m/s, and period of ~128 min. The GW potential energy density (GW-E_P) is then calculated from the relative density perturbation and Brunt-Väisälä frequency. Clear seasonal variations of GW-E_P are observed at Rothera with a maximum in winter and a minimum in summer, while no significant seasonal variations occur at the South Pole. We then examine the effects of GW sources (topography and jet stream) and critical level filtering on the observed GW-E_P seasonal variations. The correlation between stratospheric GW-E_P and topographical GW source is 68% in winter but zero in summer at Rothera. Stratospheric jet stream could be another important GW source at Rothera in winter, which is supported by a correlation between maximum wind speeds of jet stream and GW-E_P at Rothera of 59% and observed downward propagating waves resulting from GW source above our observational altitude (30-45 km). Less critical level filtering in winter allow more GW generated by topography to propagate upward, resulting in GW enhancement in winter at Rothera. At the South Pole, there are no significant seasonal variations of critical level filtering and GW sources, leading to no seasonal variations of GW-E_P.