A Linear Theory Perspective of Mountain Wave Characteristics around 600 S

Over the past decade, the global distribution of stratospheric gravity wave variances has been examined by several studies using satellite-based observations, and a striking maximum in the gravity wave activity over the Drake Passage is evident. The crucial role of the stratospheric wave drag over mid- to high-latitude areas in the Southern Hemisphere is further highlighted recently by McLandress et al. (2012), who suggest that the missing orographic wave drag near 600 S is likely the cause of stratospheric wind biases in global models. In this study, vertically propagating gravity waves excited by tropospheric winds passing over topography between 500 and 700 S are examined using linear theory and large-scale winds interpolated from the ERA-Interim reanalysis, with an emphasis on stratospheric wave drag around 600 S (SD60S). Our results suggest that SD60S includes contributions from several local sources, i.e., the small islands scattered around 60 0S, and non-local sources, such as the Patagonian peaks in the southern Andes (~500 S) and the topography on the Antarctic Peninsula (to the south of 650 S). For example, under certain large-scale wind conditions, a fraction of the wave momentum flux originating from the Patagonian peaks is able to propagate southward and reach 600 S in the stratosphere. In general, the intense westerly flow associated with the polar vortex plays a constructive role in the southward wave refraction and delaying wave breaking. The relative importance of the local and non-local orographic wave sources and seasonal variations of SD60S will be addressed.