The relationship between topography and the Ross Ice Shelf Air Stream

The Ross Ice Shelf Air Stream (RAS) is one of the most pronounced features in the lower atmosphere over the Ross Ice Shelf in West Antarctica. The RAS plays an important role in the northward transport of mass off of the Ross Ice Shelf. The Transantarctic Mountains are adjacent to the Ross Ice Shelf and provide a formidable barrier that is critical for developing the RAS. As the RAS flows northward the topography modifies the RAS though both direct influences and through topographically induced phenomena. This work examines three ways that the Ross Ice Shelf Air Stream is modified by topography: (a) topographical barriers such as Ross Island, (b) katabatic circulations that transport mass from East Antarctica down the valleys of the Transantarctic Mountains and (c) through "surges" produced by coastally trapped waves that propagate along the Transantarctic Mountains.; Numerical simulations were performed using the University of Wisconsin-Nonhydrostatic Modeling System. Topography directly modifies the RAS through topographical barriers such as Ross Island. A series of five nested grids, with horizontal grid spacing as small as 500m, showed a flow separation to the RAS when it encounters Ross Island. Due to the lack of observations near Ross Island, this work provides the first look at the many microscale circulations that form when the RAS flows around Ross Island.{09}Topography modifies the RAS indirectly by the influence of topographically generated katabatic flows. From infrared satellite imagery, the RAS appears as a "river" with the katabatic flows as "tributaries". The topography along the Transantarctic Mountains was modified to prevent the katabatic flows from developing. The katabatic flows where shown to modify the spatial extent and location of the RAS, however the intensity of the RAS was maintained in the absence of the katabatic flows. While the katabatic flows of the Transantarctic Mountains do not appear to modify the intensity of the RAS, "surges" in the RAS were observed in simulations and verified by observations due to cold, coastally trapped waves that propagate southward along the Siple Coast and create a "surge" in the RAS upon reaching the barrier of the Transantarctic Mountains.