Calibration of Soil Moisture for Large-Eddy Simulations over the FIFE Area

A case day, 11 October 1987, was chosen for simulation using the Regional Atmospheric Modeling System (RAMS). The day was unique from other ‘‘golden’’ days of the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) in that the surface wind speeds were light in terms of magnitude. Numerous datasets were used to initialize the meteorology, vegetation, canopy height, roughness length, topography, and soil properties. The simulation was performed using the RAMS nested grid feature. First, the large-scale flow reproduced by RAMS was evaluated against the observations taken during FIFE and archived data available at the National Center for Atmospheric Research. Next, a large-eddy simulation (LES) was integrated for a 6-h period starting at 1500 UTC 11 October 1987. FIFE surface flux and surface thermodynamic and dynamic data were then used to evaluate the LES. It was found that LES fluxes were in poor spatial agreement with the observations, although domain-averaged values were in good agreement. A technique for initializing the near-surface to surface soil moisture was then developed after finding a nearlinear relationship between 6-h averaged latent heat and the initial model-gridded soil moisture obtained from an objective analysis of field data. The LES was performed again using the new soil moisture obtained from the relationship. The evaluation showed significant improvement in the model’s ability to represent spatial heterogeneity of surface fluxes present on 11 October 1987.