Surface airflow around Windless Bight, Ross Island, Antarctica

Abstract

AbstractRoss Island, Antarctica is located along the Transantarctic Mountains and is subjected to a strong southerly mountain‐parallel wind regime. Despite this, Windless Bight on the island's southern coast is a region of anomalous calm. The atmospheric boundary layer dynamics that gives rise to this phenomenon is analysed both theoretically and observationally. It is the strong static stability of the boundary layer air encountering the high steep topography of Ross Island, that causes a stagnation zone resulting in the calm conditions of Windless Bight.Direct and proxy observations of boundary layer winds provide a detailed description of airflow around the island. The anomalous (with respect to the synoptic pressure field) but persistent north‐easterly winds at Scott Base are due to the deflection of highly stable, low‐level air around Hut Point Peninsula. By contrast, the less frequent, strong southerly winds which override the peninsula are associated with the influx of warm maritime air from cyclonic systems to the east. It is inferred that flow of air around the terrain of Ross Island gives rise to locally strong winds; these are responsible for the ice breakout and polynya occurrences in McMurdo Sound.The surface airflow past Ross Island can be modelled by a two‐dimensional, steady, frictionless, irrotational, incompressible flow past an obstacle, with a shape based on an island height contour. The flow is assumed to separate from the eastern and western sides of the island and form a wake downstream. A solution for this flow is presented, based on potential theory for streaming motion past an obstacle. The streamline and isobar patterns clearly depict the stagnation region in Windless Bight. For approaching winds of 20 ms−1 the local pressure field is perturbed by several millibars.