Flow Separation in Complex Terrain during Synoptically Dominated Wind Conditions

The wake structures that develop past complex terrain due to synoptic flows are not well resolved in mesoscale models of mountain meteorology. High resolution numerical models as well as laboratory experiments have been used to predict these flow structures, but whether they represent very high Reynolds number field situations is yet to be confirmed using field measurements. To better understand the intricacies of these wake dynamics, field experiments were conducted on Granite Mountain in Dugway Proving Grounds in May 2013 as part of the MATERHORN field campaign (www.nd.edu/~dynamics/materhorn/). Meteorological towers were located at the north and east of the mountain to capture the flow dynamics upwind of the mountain and near the separation point. These 32-meter meteorological towers were equipped with sonic anemometers, net radiometers, thermocouples, relative humidity sensors, and a hygrometer. A Doppler LiDAR was positioned near the separation point at the east of the mountain to capture additional flow features in conjunction with tower-based meteorological measurements. By using data from unstably stratified daytime periods and stably stratified nighttime periods, it was possible to determine the effects of flow stratification on the formation of these wake structures. In this presentation, we will present and interpret MATERHORN data on flow separation and vortex wake dynamics under synoptic flow conditions, particularly focusing on the Strouhal number of vortex shedding and its modification due to stratification, turbulence generation in the wakes, separation point change under different stability conditions. Comparisons will also be made with previous laboratory and numerical results, which are numerous.