Large-eddy simulation of the stably stratified planetary boundary layer

In this work, we study the characteristics of a stably stratified atmospheric boundary layer using large-eddy simulation (LES). In order to simulate the stable planetary boundary layer, we developed a modified version of the two-part subgrid-scale model of Sullivan et al. This improved version of the model is used to simulate a highly cooled yet fairly windy stable boundary layer with a surface heat flux of <wθ>(o) = -0.05 m K s^-1 and a geostrophic wind speed of U(g) = 15 m s^-1. Flow visualization and evaluation of the turbulence statistics from this case reveal the development of a continuously turbulent boundary layer with small-scale structures. The stability of the boundary layer coupled with the presence of a strong capping inversion results in the development of a dominant gravity wave at the top of the stable boundary layer that appears to be related to the most unstable wave predicted by the Taylor-Goldstein equation. As a result of the decay of turbulence aloft, a strong-low level jet forms above the boundary layer. The time dependent behaviour of the jet is compared with Blackadar's inertial oscillation analysis.