Effects Caused by Varying the Strength of the Capping Inversion Based on a Large Eddy Simulation Model of the Shear-Free Convective Boundary Layer

Abstract

Effects caused by variation of the potential temperature lapse rate Γ in the free atmosphere are examined based on a ?large eddy simulation? model of the shear-free convective atmospheric boundary layer. The obtained results show that only near the top of the boundary layer are the statistical moments involving temperature strongly sensitive to changes of the parameter Γ. Furthermore, the moments involving only the vertical velocity are practically independent of Γ. The ratio R of the heat fluxes at the top and the bottom of the mixed layer increases when Γ increases. For the values of Γ from 1 to 10 K/km, typically observed in the atmosphere, the heat flux ratio R varies in the range ?0.2 to ?0.3. When Γ increases by an order of magnitude to 100 K/km, R increases only slightly to about ?0.4. When Γ decreases to zero, the heat flux Hi, at the top of the mixed layer also decreases to zero. In this case, the thermal structure of the atmospheric boundary layer is found to be similar to nonpenetrative ?solid lid? convection in a tank.