Stability Dependence of the Turbulent Dissipation Rate in the Convective Atmospheric Boundary Layer

Turbulent dissipation rate (epsilon) is a crucial parameter in turbulence theory, and an essential component of higher-order planetary boundary layer schemes for numerical weather prediction and climate models. It is most often modeled diagnostically based on the dissipation scaling epsilon proportional to e(3/2)/L, where e and L are the turbulence kinetic energy (TKE) and the size of the largest turbulent eddies, respectively. Utilizing three-month-long vertically-extended observations accompanied by high resolution large-eddy simulations, scaling-based epsilon-models are evaluated, focusing on their stability dependence under daytime convective conditions. The analysis uncovers biases in the parameterized epsilon profiles that cannot be corrected through tuning of model constants. The biases are attributed to the limited and even opposing stability dependence of the modeled dissipation length. Close examination reveals violation of the dissipation scaling by the inclusion of TKE associated with organized convection. A self-similar dissipation length is obtained when only the isotropic component of TKE is considered.