3.4    Improved Subgrid Drag or Hyper PBL/Horizontal Resolution:        What Improves PBL Wind Biases in WRF?

Mass, Clifford, University of Washington

A major issue with WRF, and many other modeling systems, is the tendency for high wind biases and overmixing under stable conditions.  In this presentation a variety of approaches are tested to deal with such PBL issue in WRF.   First, an improved subgrid scale parameterization is tested, one that increases drag based on the subgrid-scale terrain variance, but which decreases its impact as stability decreases or wind speed increases. Second, ultra high vertical resolution is tested for a range of cases to determine whether this improves the definition of low-level inversions and thus decreases mixing under stable conditions.   Finally, the influence of running WRF at ultra-high resolution (1.3 km horizontal grid spacing) is evaluated.  This presentation will present a summary of these experiments and suggest the most fruitful avenues for further research and testing.