Numerical investigation of the influence of river flow on the atmospheric boundary layer under stably stratified conditions

We report on Large Eddy Simulation of a stably stratified atmospheric boundary layer with a simplified river flow at the bottom boundary. The shear generated by the friction of water surface leads to creation of the air flow in a thin layer above water surface. Stratification prevents vertical motion due to negative buoyancy effects, and the flow expands in horizontal direction. This leads to accumulation of kinetic energy of the flow in a narrow layer near the surface (about 10 meters), where the air velocity may reach about a half of the velocity of the river surface. In case of strong inversion magnitude (20 degrees C/km) the effect of formation of large-scale vortices was found for such configuration. These vortices significantly intensify heat and mass transfer in horizontal direction. The formation of these vortices is attributed to the process of inverse spectral transfer of turbulent energy, possible because of a quasi-two-dimensional structure of the flow.