Coupling of the MM5 regional atmospheric model with a physically-based regional land surface model.

摘要

It is important to couple a regional atmospheric model to a land surface model because the land surface greatly influences the atmosphere through the atmospheric boundary layer. The land surface provides the heat fluxes and moisture to the atmosphere while the atmosphere determines the temperature, relative humidity and land surface wetness of the land surface. The atmospheric model used in this study is MM5 (Fifth Generation Mesoscale Model) which was developed by the National Center for Atmospheric Research (NCAR) and PENN State University (PSU). The land surface model is based on the areal-average behavior of land surface processes over a computational grid of the mesoscale atmospheric model. Once the two models are fully coupled, it is possible to provide the hydrological model with the spatial distribution of soil moisture content, soil water storage, precipitation and evapotranspiration.; Two simulations are used in this study to validate the fully coupled MM5 with the land surface model. The first simulation period is from August 3rd to August 6th, 1997 and the second simulation period is from March 1st 1998 to May 31st, 1998. The modeling domain for both simulations is in southern California. Four dimensional data assimilation is used in the first simulation for updating initial conditions. Blackadar planetary boundary layer scheme is used to couple the land surface model with MM5 in both simulations. The fully coupled model shows improvement for the surface wind speed, surface temperature and precipitation over the original MM5 model when compared to the observational data. In addition, the evapotranspiration is introduced in the coupled model which the original MM5 is lacking. The evapotranspiration description in the coupled model has shown good agreement with the observations.