Large-Eddy Simulations of the Dividing Streamline in Stably Stratified Flow over and around a Mountain

The National Center for Atmospheric Research (NCAR) has developed a new large-eddy simulation (LES) model, FastEddy^®, that is designed to harness the calculation speeds of graphics processing units (GPUs). NCAR has timed the dry dynamical core of FastEddy^® at roughly six times the execution rates of alternative models run on central processing units (CPUs). FastEddy^® was developed, in part, to simulate phenomena in the atmospheric boundary layer at resolutions high enough to represent explicitly the relevant processes while keeping execution times short enough for some operational applications. Consistent with that motivation, the authors will present a preliminary evaluation of FastEddy^® using data from field experiments conducted in May 2013 as part of the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program. During the experiments, smoke was released on the slopes of a semi-isolated hill on the northwestern edge of Granite Peak, UT to test agreement with recent modifications to equations for the dividing streamline that in stably stratified flow separates the upper layer of air that rises over a mountain from the lower layer that skirts around the mountain. The authors will describe FastEddy^®, how it was configured and executed to approximate the conditions of the field experiments, and how the model results compare to the observed results of the smoke releases.