Numerical simulation of stably stratified turbulent flows over flat and urban surfaces

Stably stratified turbulent flows over surfaces with explicit roughness elements simulating an urban built-up area have been calculated using an LES model. A method of conducting numerical experiments allowing turbulent flows with specified values of the Obukhov scale L to reach a quasisteady state at the surface has been proposed. It has been shown that, to calculate both temperature and wind-velocity profiles over such objects, one can use the same universal dependences that are used for a flat surface. It has been found that stable stratification does not affect the roughness parameter z _0u and the displacement height D.