Fundamental Framework and Experiments of the Third Generation of IAP/LASG World Ocean General Circulation Model
Jin Xiangze;Zhang Xuehong(State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG); Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100080)Zhou Tianjun(Department of Geophysics,Peking
A new generation of the IAP/LASG world ocean general circulation model is designed and presentedbased on the previous 20-layer model, with enhanced spatial resolutions and improved parameterizations.The model uses a triangular-truncated spectral horizontal grid system with its zonal wave number of 63(T63) to match its atmospheric counterpart of a T63 spectral atmosphere general circulation model in aplanned coupled ocean-atmosphere system. There are 30 layers in vertical direction, of which 20 layers arelocated above 1000 m for better depicting the permanent thermocline. As previous ocean models developedin IAP/LASG, a free surface (rather than "rigid-lid" approximation) is included in this model. Comparedwith the 20-layer model, some more detailed physical parameterizations are considered, including thealong/cross isopycnal mixing scheme adapted from the Gent MacWilliams scheme.The model is spun up from a motionless state. Initial conditions for temperature and salinity are takenfrom the three-dimensional distributions of Levitus' annual mean observation. A preliminary analysis ofthe first 1000-year integration of a control experiment shows some encouraging improvements comparedwith the twenty-layer model, particularly in the simulations of permanent thermocline, thermohaline circulation, meridional heat transport, etc. resulted mainly from using the isopycnal mixing scheme. However,the use of isopycnal mixing scheme does not significantly improve the simulated equatorial thermocline. Aseries of numerical experiments show that the most important contribution to the improvement of equatorial thermocline and the associated equatorial under current comes from reducing horizontal viscosity in theequatorial regions. It is found that reducing the horizontal viscosity in the equatorial Atlantic Ocean mayslightly weaken the overturning rate of North Atlantic Deep Water.