Surges in the Ross Ice Shelf Air Stream due to topographically trapped waves

The Ross Ice Shelf Air Stream (RAS) is a prominent feature in the lower atmosphere over the Ross Ice Shelf region of West Antarctica. The northward flow associated with the RAS serves an important role in mass transport off the Antarctic continent. While the RAS is a consistent feature of the Ross Ice Shelf region, the strength and spatial extent of the RAS varies from day to day. Days when the RAS is particularly strong pose a hazardous threat to operations at McMurdo Station on Ross Island. The sparse quantity of observations in this region makes mesoscale modeling a challenging yet necessary endeavor for understanding the variability of the RAS. This talk will discuss results from simulations of the RAS performed with the University of Wisconsin – Nonhydrostatic Modeling System (UW-NMS). UW-NMS simulations demonstrate surges in the RAS due to the formation and propagation of topographically trapped waves. The topographically trapped waves are characterized by temperature drops of 10-20 degrees Celsius per hour and are followed by wind speeds in excess of 30 m/s. Automatic Weather Station (AWS) observations are consistent with the simulated progression of these events. The propagation of topographically trapped waves along the Transantarctic Mountains represents a new explanation for the variability of the RAS. Sensitivity experiments will be presented that demonstrate the role of Antarctic topography in controlling the spatial extent and propagation speed of these surges in the RAS.