A NEW 2ND-ORDER TURBULENCE CLOSURE SCHEME FOR THE PLANETARY BOUNDARY-LAYER

A new turbulence formulation for the planetary boundary layer (PBL) is presented and compared with large-eddy simulations (LES) for the dry PBL. The new scheme contains a prognostic equation for the turbulent k inetic energy. Other second-order moments are determined diagnosticall y through a parameterization of the third-order moments that is based on a convective mass-flux argument. For the heat flux this leads to a nonlocal formulation with the usual down-gradient term and a counter-g radient term. The counter-gradient term turns out to be a combination of well-established formulations with an additional new term. The perf ormance of the new scheme is tested in a variety of cloud-free PBL con ditions by comparing the results with corresponding LES simulations. T he scheme is able to accurately reproduce the LES results of the mean as well as the turbulent quantities including third moments.