Implementation of TKE-Scalar Variance Mixing Scheme into COSMO

We report on the development and testing of a turbulence kinetic energy – scalar variance (TKESV) mixing scheme, and its implementation into the COSMO model. A summary of results obtained within the framework of the COSMO Priority Project UTCS is given, including a brief outline of the TKESV scheme, a discussion of the scheme performance in various clear and cloudy boundary-layer regimes as revealed by off-line single-column tests, details of the implementation of the new scheme into COSMO, and some results from numerical experiments with the full-fledged COSMO model. Future challenges are briefly discussed. In what follows, standard notation is used, where t is the time, xi are the space co-ordinates, and ui are the velocity components (the subscript “3” refers to the vertical direction). The angle brackets denote a (grid-box) mean quantity, and a prime denotes a fluctuation about the mean. 2 Outline of the TKESV scheme A turbulence kinetic energy – scalar variance mixing scheme for the COSMO model is developed. The scheme is formulated in terms of two scalars that are approximately conserved for phase changes in the absence of precipitation. These are the total water specific humidity qt and the liquid water potential temperature θl. The TKESV scheme carries prognostic transport equations for the turbulence kinetic energy (TKE), 1 u ′2