A Simple Ocean-Atmosphere Climate Model: Basic Model and a Simple Experiment

Abstract

A simple model is developed with the aim of studying large-scale and long-term interactions between the various components of the earth-ocean-atmosphere system. The general three-dimensional structure of the system is simplified by division into a number of domains, so chosen as to isolate regions of similar character or similar lower boundary conditions. The governing primitive equations and boundary conditions are averaged in longitude between the limits of each domain and neighboring domains are allowed to interact via east-west interdomain fluxes of heat and momentum and lateral interdomain work terms, or, in the case of the adjacent oceanic and atmospheric domains, via vertical heat and momentum exchanges. From this processes, sets of two-dimensional coupled equations evolve in latitude-height space for both the atmosphere and the ocean. Dynamic coupling of adjacent atmospheric domains is accomplished by the development of a new parameterization based on the theory of slowly varying or quasi-stationary modes. The character of the parameterization is such that it reduces to fluxes of quasi-geostrophic nature in middle and higher latitudes, whereas at low latitudes the fluxes are consistent with those associated with circulations confined to the longitude-height plane. Zonal fluxes of heat and momentum within each domain are handled by the baroclinic eddy parameterizations of Stone, Green and Wiin-Nielson and Sela. Results are presented for the three-domain version of the domain-averaged model. The three domains, each of which extend from pole to pole, consist of an atmospheric domain surmounting a continental region and an atmospheric domain which lies over an interactive and dynamic ocean domain. The ocean is represented by a simple variable depth and temperature mixed layer model modified by a large-scale? thermohaline? circulation. Converged results for the dry model using equinoctial and Northern Hemisphere solsticial forcing are presented. Field magnitudes and distributions appear consistent with the implied boundary conditions. Differences between the two domains during the equinox are relatively small although surface temperatures over land are considerably warmer than over the ocean at low latitudes, whereas at high latitudes the reverse is apparent. At the solstice large variations occur in both hemispheres especially in the summer hemisphere, where a low-latitude easterly maximum occurs surmounting a weaker low-level westerly flow. In the subtropics near the region of maximum heating, the meridional flux of heat is from over land to over the ocean with heating rates of about 2 K day?1, which is similar in magnitude to the poleward heat flux by the transient eddies in the winter hemisphere.