Large-eddy simulation of the stably stratified planetary boundary layer

In this work, we study the characteristics of a stably stratified atmospher ic boundary layer using large-eddy simulation (LES). In order to simulate t he stable planetary boundary layer, we developed a modified version of the two-part subgrid-scale model of Sullivan et al. This improved version of th e model is used to simulate a highly cooled yet fairly windy stable boundar y layer with a surface heat flux of [w theta](o) = -0.05 m K s(-)1 and a ge ostrophic 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 co ntinuously turbulent boundary layer with small-scale structures. The stabil ity of the boundary layer coupled with the presence of a strong capping inv ersion 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 w ave 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. T he time dependent behaviour of the jet is compared with Blackadar's inertia l oscillation analysis.