A Dynamical Explanation of the Topographically Bound Easterly Low-Level Jet Surrounding 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, this 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.  The dynamical connection of the jet with katabatic winds can be understood through the meridional circulation equation.  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.