WRF Simulations of Synoptic Flow Modification over Mountainous Terrain during MATERHORN Observation Periods

Large scale weather systems that traverse regions characterized by complex terrain become modified as they pass over and around terrain obstacles. The MATERHORN-X-2 (www.nd.edu/~dynamics/materhorn) spring field campaign setup was designed with the focus of measuring synoptically driven flow conditions in mountainous terrain. The Advanced Research version of the Weather Research and Forecasting (WRF) model was used to perform high resolution simulations for several Intense Observation Periods (IOP) conducted during the MATERHORN field experiments when the local flow was driven by synoptic conditions. Several IOPs with conditions corresponding to low Froude numbers were investigated. The WRF model output provides the full nonlinear response to flow over orography, including lee waves, and low-level effects such as flow blocking, flow separation, and vortex shedding. This work aims to provide an analysis of the three-dimensional flow over a single mountain, identify dynamics of fluid parcels traveling along streamlines under stable conditions, delineate characteristics of the lee waves, and study vortex shedding and other inertially driven phenomena. Simulations are compared with measurements taken using LiDAR, SODAR, microwave radiometer, and radiosondes.

This research was funded by Office of Naval Research Grant # N00014-11-1-0709.