AN UPPER-OCEAN GENERAL-CIRCULATION MODEL FOR THE NORTH PACIFIC - PRELIMINARY EXPERIMENTS

A model with two active layers, a mixed layer and a pyonocline layer, over a semipassive deep ocean is described. The model is used to simulate a climatological seasonal cycle in the upper North Pacific. The formulation is similar to that in Cherniawsky et al. (1990). The model resolution is 1-degrees latitude by 1.5-degrees longitude, extending from 62-degrees-N to the equator. It is driven with monthly wind stress (Hellerman and Rosenstein, 1983) and with Newtonian heat and freshwater fluxes, which were inferred from climatological (Levitus, 1982) sea-surface monthly temperatures and annual mean salinities. The monthly temperature anomalies (without the annual mean) are multiplied by a prescribed gain factor and advanced in time, compensating for time delay in the response of the mixed layer. No-slip and no-flux constraints are applied on north, east, west and land boundaries, while the following open boundary conditions are used at the equator; (a) free-slip on zonal velocities in the two layers; (b) a prescribed meridional transport, due to local curl of the wind stress, in the mixed layer; (c) an antisymmetric meridional velocity plus a small flux-balancing term in the second layer; and (d) across-equator symmetry for layer depths, temperatures and salinities. Sensitivity to two aspects of parameterization is investigated: (1) the change to horizontal diffusion/viscosity coefficients that depend on the velocity deformation field (as in Smagorinsky, 1963), and (2) the use of idealized piecewise-linear profiles for second-layer temperatures and salinities for calculating mixed layer entrainment fluxes.