Multiscale Atmospheric Simulations Over a Complex and Heterogeneous Terrain: Surface Variability and Land-Atmosphere Interactions

Multiscale atmospheric simulations are performed from the mesoscale (~10 km) to the urban scales (~50 m) using the Weather Research and Forecasting model, coupled with NOAH Land surface model and Kusaka et al. Urban Canopy Model. Simulations are performed over a complex and heterogeneous terrain. We test the model sensitivity to the choice of turbulence model and input data source (NCEP Eta products: NARR and GCIP); while the turbulence closure technique is found to have little effect on the results, the forcing input data displays significant differences that propagate to the smaller scales resolved by the model. The results of nested Large Eddy Simulations are then analyzed and confronted to measurements of a meteorological station measuring eddy covariance surface fluxes and air and surface properties (soil moisture, temperature, relative humidity, etc). We are specifically investigating two distinctive summer-time study cases: a cloud-free day and four days of surface drying after a day of precipitation. The spatial and turbulent variability are analyzed for the urban and non-urban environments, different soil types and water surface over a 25 km2 area. The agreement of the model with the measurements is found to vary significantly, even during a single diurnal cycle.