Dynamics of Convective Entrainment in a Heterogeneously Stratified Atmosphere with Wind Shear

University Of Oklahoma Norman Campus, Norman OK

Investigators

Abstract

This research focuses on the nonsteady evolution of the convective boundary layer (CBL) in an atmosphere with complex vertical structure. As the CBL grows, air from the free atmosphere is entrained into the top of the CBL by turbulent mixing. The structure of the entrainment layer and the entrainment dynamics depend on the static stability of the atmosphere, as measured by the temperature profile, and the vertical wind shear. Convective entrainment in conditions when the wind and temperature vary smoothly with height has been studied extensively in laboratory tanks, numerical large-eddy simulations (LES), and simple bulk models of the CBL. Less studied is the development of the CBL in fluids with more complex stratification, though there is evidence that the CBL in such cases grows in an unsteady way, passing through a sequence of transition regimes accompanied by strong variations in the intensity and vertical structure of the entrainment. In this study, the CBL entrainment dynamics will be investigated numerically, by means of high-resolution LES, and compared with observations from atmospheric, laboratory, and other numerical studies. Emphasis will be placed on the influence of discrete and nonlinear temperature stratification on the entrainment characteristics with and without wind shear. Elements of the work include: (1) improvement of the characterization of subgrid-scale turbulence in LES models; (2) numerical studies of convective entrainment in conjunction with analysis of observational and experimental data; (3) developing a parameterization of convective entrainment in a heterogeneously stratified atmosphere with wind shear.