Comparison of in-situ PV banner observations against high-resolution numerical simulations during MAP

Many of the PV banner scientific objectives within the Mesoscale Alpine Programme (MAP) require detailed information on the dynamics of flow-splitting over highly complex terrain -- information which is difficult or even impossible to directly extract from observational data. A two-stage strategy was thus developed early within the planning process, which is geared towards validating high-resolution numerical simulations against observational data, and subsequent use of the model data to address the dynamical questions under consideration.

In this study high-resolution numerical simulations of the Alpine PV banner event from October 1, 1999 (MAP IOP 4) are presented and intercompared against observational data collected during the MAP field phase. The simulations are conducted with the Canadian MC2 model. This model was used as a real-time forecasting tool during MAP SOP at a horizontal resolution of 3 km and with 50 levels in the vertical. Consideration will be given to both (real-time) forecast and hindcast integrations, with the former being driven by a forecast chain involving the German and Swiss NWP models, and the latter being driven by the operational ECMWF analysis. The simulations are compared against in-situ aircraft and dropsonde data. Both primary and secondary banners are considered. Results suggest that the model did reasonably well capture the structure and width of the banners. This suggests that high-resolution model simulations may provide a useful tool to assess the dynamics of PV banner formation. Some associated dynamical questions relating to the width and structure of the banners will also be addressed.