Effects of Horizontal Wind Structure on a Gravity Wave Event in the Middle Atmosphere Over Syowa (69^°S, 40^°E), the Antarctic

Nightly mean potential energy of gravity waves (GWs) per unit mass (E_p) over Syowa Station (69°S, 40°E) was calculated from temperature profiles observed by the Rayleigh/Raman lidar from 2011 to 2015. The E_p values in the upper stratosphere and lower mesosphere were significantly enhanced on 8–21 August 2014, except on 12 August. A ray-tracing analysis showed that large-scale GWs emitted from various latitudes could be refracted and forced to converge above Syowa due to the poleward tilting of the polar night jet with altitude. It should be noted that E_p on 12 August was smaller than the other values during the enhancement, despite similar polar night jet conditions. A synoptic-scale disturbance, which passed on 12 August, could have blocked the GWs from propagating upward through critical level filtering. These results suggest that convergence of the wave should be considered as a part of the intermittency of the GWs.