How does your model generate potential vorticity banners? Proposal for a model intercomparison project

PV banners, elongated filaments of anomalous potential vorticity, are frequently seen to develop downstream of topography. The generation of these PV banners is the result of dissipation in flow-splitting/separation and/or gravity-wave breaking events. It is not clear how these processes are resolved in mesoscale numerical models. For instance, the influence of turbulence parametrization, as well as explicit and implicit numerical diffusion are not properly understood.

The idea of the PV banner intercomparison project (PVBIP) is to compare PV generation in different mesoscale numerical models using a common (idealized) setup and to identify the key parameters influencing the structure of the wake and the strength and shape of the PV anomalies. The proposed setup is that of a stratified flow past an isolated, Gaussian-shaped mountain with an upstream profile of uniform wind speed and constant stratification. To further simplify the problem free-slip lower boundary conditions are used.

The poster will present the detailed setup for the study, suggestions for the intercomparison procedures and data exchange, and some preliminary results for two models, namely ARPS (the Advanced Regional Prediction System from the Center for Analysis and Prediction of Storms at University of Oklahoma) and COAMPS (Coupled Ocean/Atmosphere Mesoscale Prediction System from the Naval Research Laboratory). We invite all groups interested in participation to further discussions.