Structure of stable stratified boundary layers: study with of nonlocal turbulence model

Two types of vertical structure of turbulence are identified in the atmospheric boundary layer. One is the "traditional" boundary layer, in which turbulence is generated near the surface and is transported upward, in contrast to the second type, where turbulence is transported downward to the surface from a source aloft in the boundary layer. The latter can be called as the "upside-down boundary layer". In this case, the turbulence can be transferred downward to the surface, e.g., as random process. In this study, the boundary layer is upside down if turbulence increases with height and the transport of turbulence energy is downward toward the surface. Presumably, a similar structure can develop within the flow of air over a surface with large-scale roughness (city), when the horizontal temperature gradient between the heated air above the city and the air on the adjacent colder surface of the environment generates turbulent thermal circulation. If this turbulence generation is substantially larger than the generation of turbulence due to surface processes (wind shear), then the vertical transport of turbulence is downward toward the surface. In the present study, the vertical profiles of wind speed, temperature and turbulent quantities in the nocturnal urban boundary layer, calculated by means of the improved..soscale model, are analyzed to understand the vertical structure of this layer.