Numerical investigation of stratified anabatic flows in idealized valleys

Due to the diurnal cycle of heating and cooling, the atmospheric boundary layer in areas of complex terrain is dominated by downslope, or katabatic, flows during the evening cooling, and upslope, or anabatic, flows during the morning heating. In valleys, katabatic flows during the evening lead to the formation of a stably stratified layer at the base of the valley, whereas upslope flows in the morning lead to the destruction of the stable stratification. This study investigates the dynamics of anabatic flows in a stably stratified idealized valley through direct numerical simulations (DNS). We establish a novel set of dimensionless parameters controlling the dynamics of stratified valley flows. We identify new flow regimes within the valley, including regimes in which the symmetry of the problem breaks down and asymmetric flow profiles emerge. We also identify unique three-dimensional instabilities as functions of the dimensionless parameter space.