Issues of soil moisture coupling in MM5: Simulation of the diurnal cycle over the FIFE area

This study evaluates the issues of soil moisture coupling on the partitioni ng of surface fluxes at the diurnal timescale over a mesoscale domain from the First International Satellite Land Surface Climatology Project Field Ex periment (FIFE) in Kansas. A state-of-the-art atmospheric model (the Fifth- Generation Pennsylvania State University-National Center for Atmospheric Re search Mesoscale Model. or MM5) is used as a control run in which soil mois ture is prescribed by a time-invariant as well as time-varying moisture ava ilability function. Then, in a coupled model simulation, the atmospheric mo del is coupled with a detailed land surface model. Three days are simulated with progressively smaller surface soil moisture conditions to identify th e influence of interactive soil moisture on surface fluxes partitioning at the diurnal timescale. Preliminary results suggest that, for days with wett er surface soil moisture conditions and moderately high wind speed, a time- variant interactive soil moisture representation provides a more accurate p artitioning of surface fluxes. For drier surface conditions with relatively low wind speed, a constant soil moisture availability function may be adeq uate.