Turbulence Closure Modelling in Coastal Waters

摘要

In this paper the use of turbulence closure models in coastal ocean models is reviewed. Two-equation turbulence closure models are argued to be an optimal compromise between efficiency and accuracy for the purpose of calculating diapycnal fluxes of momentum, heat and tracers in coastal ocean modelling. They provide enough degrees of freedom to be calibrated to the most prominent properties of coastal ocean mixing, but are still numerically robust and computationally efficient. Isopycnal mixing schemes are briefly reviewed as well. Major implementational and numerical aspects are presented, with some focus on the inherent problem of numerically-induced mixing which together with the physically-induced mixing gives the effective mixing in ocean models. Vertically adaptive coordinates are presented as one possibility to reduce numerical mixing. Finally, three coastal ocean simulation examples from the General Estuarine Transport Model (GETM) which is coupled to the turbulence module of the General Ocean Turbulence Model (GOTM) are given. These examples include thermocline mixing in the Northern North Sea, physically and numerically induced mixing in the Western Baltic Sea as well as basin-wide mixing in the Central Baltic Sea. All three examples highlight the importance of using well-calibrated turbulence closure models together with vertically adaptive coordinates.