An oceanic general circulation model in pressure coordinates

A new oceanic general circulation model in pressure coordinates is formulat ed. Since the bottom pressure changes with time, the vertical coordinate is actually a pressure-sigma coordinate. The numerical solution of the model is based on an energy-conservation scheme of finite difference. The most im portant new feature of the model is that it is a truly compressible ocean m odel and it is free of the Boussinesq approximations. Thus, the new model i s quite different from many existing models in the following ways: 1) the e xact form of mass conservation, 2) the in-situ instantaneous pressure and t he UNESCO equation of state to calculate density, 3) the in-situ density in the momentum. equations, 4) finite difference schemes that conserve the to tal energy. Initial tests showed that the model code runs smoothly, and it is quite sta ble. The quasi-steady circulation patterns generated by the new model compa re well with existing models, but the time evolution of the new model seems different from some existing models. Thus, the non-Boussinesq models may p rovide more accurate information for climate study and satellite observatio ns.