GLOBAL EXPRESSIONS FOR SEASONAL TEMPERATURES OF THE SEA-SURFACE AND AMBIENT AIR - THE INFLUENCE OF TIDAL CURRENTS AND WATER DEPTH

A 'single point' coupled ocean-atmosphere model is formulated to study seasonal temperature cycles with particular application to shelf seas . The simplified atmospheric module is consistent with the physical pr ocesses described by Gill [4] while the vertical exchange of heat in t he ocean module is determined via a turbulence closure model. The vari ous empirical coefficients in the atmospheric module were determined b y fitting the model output to North Atlantic observational data over t he latitude range 0 degrees to 65 degrees N. The model is then applied to the shallow, strongly tidal North Sea. The general validity of the model is demonstrated, thereby indicating that the seasonal cycles of the sea surface, T-s, and ambient air, T-a, are generally governed by a localised equilibrium. In shallow water (< 200 m) the amplitude of this seasonal cycle is modulated by both the water depth and tidal cur rent amplitude. North Sea observational data confirm these model indic ations that large tidal currents decrease seasonal amplitudes. This st udy provides, for the first time, a quantitative estimate of this infl uence of shallow seas on adjacent coastal climates. It is shown how th e model results can be sensibly approximated by generalised expression s - illustrating that mean values of both T-s and T-a vary with the co sine of latitude (up to 65 degrees N) while their seasonal amplitudes vary directly with latitude and inversely with an exponent of water de pth. Thus these generalised expressions can be conveniently used to pr ovide boundary conditions in generalised ecological models. The model can also be used for (small amplitude) sensitivity analyses to examine , for example, the effect of changes in storminess or cloud cover. (C) Elsevier, Paris.