Validation of a non-hydrostatic numerical model to simulate stratified wind fields over complex topography

摘要

A non-hydrostatic numerical model developed from a general purpose Navier-Stokes solver (CFDS-FLOW3D) has been proposed in order to simulate atmospheric flows over complex topography. In the validation tests presented here, the 3D numerical model has been run to simulate neutral and stratified wind fields over a 2D theoretical bell-shaped mountain. Model results have been compared to analytical solutions, obtained from linear mountain wave theory for the two approximations of (a) neutral flow and (b) stratified flow with atmospheric conditions leading to hydrostatic waves production. In both cases, the model results were in very good agreement with the analytical solution. For atmospheric conditions were non-hydrostatic effects become dominant, the model also proved to be able to reproduced trapped lee waves located downwind of the mountain. For highly non-linear atmospheric conditions, we have tried to reproduce the well-documented severe windstorm which was registered in January 1972 in the region of Boulder (Colorado), during which extreme horizontal wind values of more than 60 m/s were measured. To this purpose, the model was initialised with temperature and wind speed profiles from the meteorological soundings registered at Grand Junction station, located 300 km upwind of Boulder. A comparison of the model calculated potential temperature and horizontal wind component with the observations for this event shows the model ability to reproduce the very strong tropospheric air descent and flow acceleration over the mountain.