Topographically Bound Balanced Flow over Antarctica

The large-scale winds in the lower troposphere in Antarctica appear to be topographically bound: while katabatic winds dominate in boundary layer, above that the flow tends to follow the contours of topography. A particularly clear example is the persistent easterly low-level jet along the east coast of Antarctica. We develop a simple dynamical model of this jet as a balanced flow that satisfies the potential vorticity invertibility
principle, based on local linear balance in spherical coordinates and expressed in isentropic coordinates. In this way, the easterly low-level jet is explained as the balanced flow associated with the topography of the Antarctic plateau, moderated by a shallow potential vorticity anomaly atop the plateau produced by radiative cooling. A similar analysis allows us to compute the corresponding meridional circulation driven by radiative cooling and katabatic winds, and understand its connection to the potential vorticity distribution which determines the balanced flow. Model results based on the simple theoretical arguments developed here are found to be consistent with high resolution ECMWF reanalysis data for the 2008-2010 period.