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A Numerical Study of Climatic Oscillations Using a Coupled Atmosphere–Ocean Primitive Equation Model

Xiong-Shan ChenNational Center for Atmospheric Research, Boulder, CO 80307

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Abstract

A coupled atmosphere-ocean primitive equation model is developed. It is a free-dimensional general circulation model, with two layers in the atmosphere and two layers in the ocean and includes solar radiation, longwave radiation, sensible heating, latent heating and diffusion. Momentum and heat flux exchanges between the atmosphere and the ocean are also considered. Using the zonal mean climatic values as the initial conditions, the coupled model is integrated up to 15 years. In the lower layer of the atmosphere and the mixed layer of the ocean within the zonal belt of midlatitudes, disturbances which are caused by the boundaries of the ocean become large-scale disturbances in both atmosphere and ocean, and the monthly mean anomalies of these large-scale disturbances lock together to produce a very stable coupled system to move westwards at a speed of 5000 km per year. The periods of climatic oscillations are about two years. The initial inserted mixed-layer sea temperature anomaly in the equatorial region cannot last a long time but can influence the time evolution of monthly mean climatic anomalies in midlatitudes. The Coriolis parameter varying with latitude and the oceanic motion may be important to the westward movement of the various climatic anomalies in midiatitudes in the special coupled atmosphere-ocean model in which there is no continent and the oceans are only separated by boundaries.

Abstract

A coupled atmosphere-ocean primitive equation model is developed. It is a free-dimensional general circulation model, with two layers in the atmosphere and two layers in the ocean and includes solar radiation, longwave radiation, sensible heating, latent heating and diffusion. Momentum and heat flux exchanges between the atmosphere and the ocean are also considered. Using the zonal mean climatic values as the initial conditions, the coupled model is integrated up to 15 years. In the lower layer of the atmosphere and the mixed layer of the ocean within the zonal belt of midlatitudes, disturbances which are caused by the boundaries of the ocean become large-scale disturbances in both atmosphere and ocean, and the monthly mean anomalies of these large-scale disturbances lock together to produce a very stable coupled system to move westwards at a speed of 5000 km per year. The periods of climatic oscillations are about two years. The initial inserted mixed-layer sea temperature anomaly in the equatorial region cannot last a long time but can influence the time evolution of monthly mean climatic anomalies in midlatitudes. The Coriolis parameter varying with latitude and the oceanic motion may be important to the westward movement of the various climatic anomalies in midiatitudes in the special coupled atmosphere-ocean model in which there is no continent and the oceans are only separated by boundaries.

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