Remedies for artificial diapycnal mixing in a sigma co-ordinated model of Tokyo Bay

False diapycnal mixing often occurs due to horizontal diffusion in the simu lation of heat, salinity, or water quality in estuaries by using a sigma co -ordinated ocean model. The Princeton ocean model (POM) is used as a basic cr co-ordinated model and is applied to Tokyo Bay. Only river discharges ar e introduced into the model as external forces. Two remedies recommended in the POM, Stelling's horizontal diffusion approximation, Huang's new diffus ion formula, Song and Haidvogel's s co-ordinates, and Smolarkiewicz advecti on scheme have all been examined for suppressing the false diapycnal mixing . The conclusions are that the simultaneous use of POM's remedy and Stellin g's approximation and the simultaneous use of POM's remedy and s co-ordinat es are the most effective. Copyright (C) 2001 John Wiley & Sons, Ltd.