Potential vorticity of flow along the Alps

Abstract

Observations from the German Front Experiment are presented here that show the existence - in conditions with a dominant flow component parallel to the main Alpine chain - of a mesoscale region to the north of the Alps where the absolute and potential vorticity (PV) are substantially negative. These structures exist before the front arrives to the Alps and appear to be affected little by the passage of the front. A dynamical explanation for these and other mesoscale structures is sought by considering a simple unsheared airflow impinging on the Alps from the west. A linear frictionless model for the steady-state response is used as well as a full nonlinear numerical model with and without friction. A vastly simplified Alpine orography is considered as well as one that adequately describes its mesoscale detail. (from Authors)