Abstract:In the boundary layer parameterization scheme of numerical model, the critical Richardson number is for diagnosing turbulence state and boundary layer height. The critical Richardson number changes with the change of atmospheric stability, but it is set as a constant in most current models. Based on WRF (weather research and forecasting) mesoscale numerical prediction model and ysu (Yonsei University) boundary layer parameterization scheme (hereinafter referred to as WRF / ysu), this paper studies the influence of the change of critical Richardson number on meteorological field and boundary layer turbulence against the background of a sunny weather process in summer. The results show that: (1) When the critical Richardson number increases, the height of the boundary layer in a large area will increase. It can be reflected in time and space. In space, the height distribution of the boundary layer is uneven. In terms of time, the height of the boundary layer is most affected in the afternoon;(2) As the critical value of Richardson number increases, the turbulent diffusion coefficient increases, the water vapor mixing ratio increases, and the overall surface heat flux increases, which will further increase the height of the boundary layer; (3) The turbulent diffusion equation in ysu scheme consists of a local term, a nonlocal term and a entrainment term. For heat flux, the contribution of entrainment term to total heat flux is equivalent to that of local term and nonlocal term. For water vapor and momentum fluxes, the local term and entrainment flux term are the largest in the boundary layer.