Abstract
We document the development and Sensitivity testing of a numerical model designed to predict diurnal cycles of boundary-layer flows of synoptic horizontal scale above sloping terrain. This application requires detailed vertical resolution of low-level jets, mixed layers and sharp inversions above terrain with large pointwise variations. The truncation errors of the pressure gradient term are of special concern. This term is computed using a thermodynamic state carried as a deviation from a standard state. Turbulent mixing is based upon a simplified diagnostic treatment. The final model produces rather stable solutions because of the rather careful pressure gradient calculation and strong physical dissipation.
Sensitivity testing indicates that the model prediction of diurnal convergence cycles depends upon soil parameters. Results are also sensitive to absolute rotation and mixing parameterizations, but not equally sensitive to longwave radiative flux divergence. Applications over complex North America terrain and coasts produce boundary-layer ascents that are generally in phase with observed summer diurnal thunderstorm distributions, where data on the latter are available. Equatorward of ∼30° latitude, the phase is ∼3–6 h retarded with respect to the response poleward of 30°.
