A Local-Closure Turbulent Mixing Parameterization for Applications in Atmospheric Modeling

A parameterization for the coefficient of vertical eddy diffusivity for momentum based on a new velocity scale, the square root of turbulent kinetic energy, and depth of the atmospheric boundary layer (ABL) is developed for applications in atmospheric modeling. The coefficient of vertical eddy diffusivity for heat is calculated as a function of the coefficient of vertical eddy diffusivity for momentum and the ratio of nondimensional functions for the heat and momentum. We also developed a formulation for the coefficient of vertical eddy diffusivity for moisture as a function of coefficient of vertical eddy diffusivity for heat and Bowen's ratio at the surface. Turbulence mixing in the free atmosphere is also included by adapting a simple formulation based on vertical buoyancy and shear.

We performed three numerical simulations to study the performance of this new turbulent mixing parameterization using a 1-D ABL-Chemistry model. Simulated urbulent mixing features and their effects on pollutant concentrations are presented. Also, results obtained from using this new scheme are compared with a 1.5-order local-closure scheme and observations.