Fundamental aspects of stable atmospheric boundary layer turbulence and implications for the modeling of polar and mid-lattitude PBLs

Stably stratified atmospheric flows are usually characterized by weak and highly anisotropic turbulence, gravity waves, instabilities, and meandering motions that are not observed in neutral or convective atmospheric flows. These features complicate both modeling and measurements in stable atmospheric boundary layers, with important implications for polar, and also mid-latitude nighttime, weather and climate modeling. The dynamics of the stable ABL evolve over small temporal and spatial scales that cannot be explicitly represented in coarse atmospheric models, thus requiring simple parameterizations of these dynamics. In this talk, using a combination of experimental and turbulence-resolving (large-eddy) simulations, we investigate some of the common assumptions and parameterizations of stable ABLs. The aim being to improve the representation of the stable ABL in large-scale models, we also use the single-column model of the geophysical fluid dynamics laboratory (GFDL), to test some of the developments and improvements suggested by our a-priori, experimental and numerical studies. Results show that the basic eddy-visocisty/diffusivity closure works well under stable conditions. Nevertheless, the choice of the appropriate diffusivity (actually its modeling) is complicated by positive feedbacks, sensitivity to grid resolution, and other factors.