A statistical study of gravity waves in the polar regions based on operational radiosonde data

Gravity waves in the lower polar stratosphere are examined using operational radiosonde observations gathered from 33 stations over a period of 10 years. Both the potential and kinetic energies of the gravity waves vary annually and reach maxima in winter in the Arctic and in spring in the Antarctic. In the Antarctic spring a region of large gravity wave energy propagates downward following the movement of a zone of high static stability associated with Southern Hemispheric warming. Moreover, the enhanced energy region and the high stability zone coincide in the horizontal plane and move gradually from 135 degrees E, 50 degrees S to 45 degrees W, 70 degrees S over the South Pole. The vertical and horizontal directions of wave propagation are examined using hodograph analysis in the vertical. Most gravity waves transfer energy upward in the Arctic, while the percentage of downward energy propagation is relatively high in winter and spring in the Antarctic. Horizontally, gravity waves propagate westward relative to the mean wind in the Arctic, while in the Antarctic the dominant direction varies from station to station. The correlation between gravity wave energy in the lower stratosphere and the mean wind is also examined. In the Arctic, gravity wave energy is highly correlated with the surface wind, though in the Antarctic it correlates with the stratospheric wind. These results suggest that gravity waves observed in the Arctic are forced by topography, whereas in Antarctica some sources may exist in the stratosphere. One such source candidate is likely to be the polar night jet.