A NEW 2ND-ORDER TURBULENCE CLOSURE SCHEME FOR MODELING THE OCEANIC MIXED-LAYER

A new second-order turbulence closure scheme is proposed for the ocean ic 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 tur bulence quantity treated prognostically with the others determined dia gnostically. The main difference lies in the treatment of the turbulen t fluxes. While momentum fluxes are assumed to be downgradient, the ot her turbulent fluxes allow for nonlocal and countergradient contributi ons. The model was tested against several idealized forcing experiment s for wind-deepening, heating and cooling cases, and also against obse rvational data taken from Ocean Weather Stations November and Papa. Th e simulations reveal good agreement with other models. The present sch eme also performs reasonably well in reproducing the observed sea surf ace temperature and boundary layer depth for the year 1961 at stations November and Papa. Also proposed are ways of incorporating near-surfa ce processes such as Langmuir circulation and wave breaking. Simulatio ns have shown that wave breaking leads to negligible deepening of the mixed layer, while the inclusion of Langmuir circulations causes furth er deepening to occur