Mats Bentsen and Helge Drange, Nansen Environmental Center
In preparing the Bergen Climate Model for simulations to be considered in the next IPCC report, various changes were made to MICOM. The main motivations for the modifications were to reduce model drift, overcome the need for flux adjustments, and improve the simulated sea-ice extent and volume. To improve the conservation properties of MICOM, two main issues were addressed. First, we have improved conservation of mass within each layer, which is fundamental to conserving other layer variables. Second, we use both salinity and temperature as prognostic variables in all layers. In MICOM this leads to the problem of maintaining the reference density in isopycnic layers, and how we cope with this problem will be discussed. The parameterizations of various physical processes have been modified or included. This concerns the convective adjustment process, diapycnal mixing which now includes shear instability mixing and gravity current entrainment, and absorption of short-wave radiation beneath the mixed layer. Improvements of the computation of air-sea fluxes will be briefly mentioned.