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A new second-order turbulence closure scheme is proposed for the oceanic mixed layer. The scheme is similar in complexity to a Mellor-Yamada level 2.5 scheme in that the turbulent kinetic energy is the only turbulence quantity treated prognostically with the others determined diagnostically. The main difference lies in the treatment of the turbulent fluxes. While momentum fluxes are assumed to be downgradient, the other turbulent fluxes allow for nonlocal and countergradient contributions. The model was tested against several idealized forcing experiments for wind-deepening, heating and cooling cases, and also against observational data taken from Ocean Weather Stations November and Papa. The simulations reveal good agreement with other models. The present scheme also performs reasonably well in reproducing the observed sea surface temperature and boundary layer depth for the year 1961 at stations November and Papa. Also proposed are ways of incorporating near-surface processes such as Langmuir circulation and wave breaking. Simulations have shown that wave breaking leads to negligible deepening of the mixed layer, while the inclusion of Langmuir circulations causes further deepening to occur.

A new surface-flux par~ete~~tion is presented and its impact on climate simulations with the Canadian Centre for Climate Modelling and Analysis (CCCMA) general circulation model (GCM) is discussed. The parameterization is based on the Monin-Obukhov similarity theory using well established flux-profile relationships for the unstable conditions. However, recently proposed new relationships are used in stable conditions. The new formulation allows different roughness lengths for heat and momentum, and gives transfer coefficients that are in agreement with MoninObukhov similarity theory. It also includes a p~amete~ation for the free-convective boundary layer, which often occurs over warm surfaces within light winds. In circ~s~ces where the surface layer is not neutrally stratified the proposed flux parameterization yields surface transfer coefficients that are different from those resulting from the standard surface flux formulation used in the GCM. The most marked effects of implementing the new formulation in the GCM are found over land and adjacent oceanic regions in winter where significant differences are found in the surface heat and moisture fluxes and surface temperatures.