A New Second-Order Turbulence Closure Scheme for the Planetary Boundary Layer

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Abstract
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 kinetic energy. Other second-order moments are determined diagnostically 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-gradient term. The counter-gradient term turns out to be a combination of well-established formulations with an additional new term. The performance of the new scheme is tested in a variety of cloud-free PBL conditions by comparing the results with corresponding LES simulations. The scheme is able to accurately reproduce the LES results of the mean as well as the turbulent quantities including third moments. Abstract 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 kinetic energy. Other second-order moments are determined diagnostically 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-gradient term. The counter-gradient term turns out to be a combination of well-established formulations with an additional new term. The performance of the new scheme is tested in a variety of cloud-free PBL conditions by comparing the results with corresponding LES simulations. The scheme is able to accurately reproduce the LES results of the mean as well as the turbulent quantities including third moments.

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