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A new multiply nested primitive equation ocean model is presented. The model employs a two-way interactive nesting technique successfully applied for many years in the Geophysical Fluid Dynamics Laboratory–NOAA hurricane prediction model. The formulation of the mesh nesting algorithm allows flexibility in deciding the number of meshes and the ratio of grid resolutions between adjacent meshes. Other advanced features include realistic coastline geometry and spatially variable grid spacing. The results of various idealized experiments indicate good performance of the nesting technique.

The most important feature of the model is the ability to combine large-scale and regional-scale predictions. The model is tested as a general circulation model (GCM) in a 3-yr spinup experiment of the large-scale circulation in the tropical Pacific Ocean. It demonstrates skill comparable to that of other recently developed GCMs. The resulting large-scale fields are then used in the nested configuration as initial conditions for simulations of the ocean response to a westerly wind burst and a tropical cyclone. Significant improvements over a coarse, single-mesh model have been achieved in resolving finescale features of the wind-induced current and temperature fields. These results highlight the importance of model resolution for realistic simulations of mesoscale ocean variability.