Climate and the Ocean Circulation1

The effect of the hydrology of the earth's surface is incorporated into a numerical model of the general circulation of the atmosphere developed at the Geophysical Fluid Dynamics Laboratory of the Environmental Science Services Administration (ESSA). The primitive equation of motion is used for this study. The nine levels of the model are distributed so as to resolve the surface boundary layer and stratosphere. The depletion of solar radiation and the transfer of the terrestrial radiation are computed taking into consideration cloud and atmospheric absorbers such as water vapor, carbon dioxide, and ozone. The scheme treating the hydrology of our model involves the prediction of water vapor in the atmosphere and the prediction of soil moisture and snow cover. In order to represent the mositure-holding capacity of soil, the continent is assumed to be covered by boxes, which can store limited amounts of water. The ocean surface is idealized to be a completely wet surface without any heat capacity. The temperature of the earth's surface is determined in such a way that it satisfies the condition of heat balance. To facilitate the analysis and the interpretation of the results, a simple and idealized distribution of the ocean and the continental region is chosen for this study. The numerical integrations are performed for the annual mean distribution of solar insolation. In general, the qualitative features of hydrologic and thermodynamic regimes at the earth's surface are successfully simulated. Particularly, the horizontal distribution of rainfall is in excellent qualitative agreement with the observations. For example, the typical subtropical desert, the break of the subtropical dry belt along the east coast of the continent, and the equatorial rain belt emerged as the result of numerical time integration. Some features of the spatial distributions of heat and water balance components at the earth's surface also agree well with those obtained by Budyko for the actual atmosphere. Owing to the lack of seasonal variation of solar insolation and lack of poleward transport of heat by ocean currents in the model, excessive snow cover develops at higher latitudes. Accordingly, the temperature in the polar region is much lower than the annual mean temperature observed in the actual atmosphere. This investigation constitutes a preliminary study preceding the numerical integration of the general circulation model of joint ocean-atmosphere interaction, in which the transport of heat by ocean currents plays an important role.