Analysis of Turbulent Characteristics of Sheared Convective Boundary Layer under Different Shear and Potential Temperature Gradients

Abstract

Effects of shear and potential temperature gradient on the formation mechanism and turbulence characteristics of the sheared convective boundary layer are studied through Large-Eddy Simulation (LES) experiments. Four cases with different velocity difference ΔU of 1.5ms-1 and 3.0ms-1 and different potential temperature gradient Γθ of 0.006Km-1 and 0.015Km-1 were conducted in the horizontal homogeneous atmospheric convective boundary layer of 6000m × 6000m × 2000m. The results show that the formation of the entrainment layer is affected integratedly by the horizontal shear effect and the vertical buoyancy effect, in which turbulence shows strong anisotropy and intermittent characteristics, wherein the mixed layer is dominated by stable small eddies, and the entrainment layer by strip-shaped large eddies. Compared with the pure buoyancy boundary layer, the entrainment flux ratio A f is 0.176∼0.385, and the height of the entrainment layer z i is shifted to the side with bigger velocity (U 2). ΔU promotes entrainment and Γθ inhibits, especially for the upper limit of the entrainment layer h 2. Obviously, the shear-shelter entrainment phenomenon appears under the weak shear and strong potential temperature gradient.