Improvements in Landuse Specification in MM5/PLACE

Sensitivity tests were performed on the Parameterization for Land-Atmosphere-Cloud Exchange (PLACE) module of the Pennsylvania State University – National Center for Atmospheric Research Mesoscale Model version 5 (MM5) in order to determine the importance of the individual landuse parameters. The coverage and thickness of green vegetation (as manifested by the fractional green vegetation and LAI values) had the greatest effect on the relative magnitudes of sensible and latent heat fluxes, which in turn determine the depth and character of the daytime boundary layer. Variations in albedo and surface roughness length were found to have much smaller effects on the surface fluxes.

Landuse parameters derived from the Advanced Very High Resolution Radiometer (AVHRR) sensor were then inserted into PLACE and the improvements in model-predicted surface energy fluxes in Oklahoma during July 1997 were documented. Two-week average values for fractional vegetation coverage, albedo, and leaf area index at 1-km resolution were all available for use. Since PLACE allows for incorporation of 12 separate surface energy budgets (mosaic tiles) within each model grid box, it is possible to take advantage of this high-resolution landuse data set. Previous land-surface models have simply used climatological values of these crucial landuse parameters. The ability to improve model predictions of surface energy fluxes in a diagnostic sense provides promise for future attempts at ingesting pseudo-real-time land use data into numerical models. These model improvements would be most helpful in predictions of extreme temperature events, where current numerical weather prediction models often perform poorly.