On the Spatial Variation of the Vertical Thermal Diffusion Coefficient in A Simple Ocean Model
Mathematical Proceedings of the Royal Irish Academy
Numerical experiments were conducted on a simple model of the North Atlantic ocean consisting of a thermocline region above an abyssal region with the surface mixing (Ekman) layer excluded. The western ocean boundary (in both the thermocline and abyss) layers are also excluded. It is also assumed that zonal variations in temperature can be neglected. The model temperature field is required to agree with the observed ocean temperature field as given in the Levitus' climatological atlas of the
... cal atlas of the world ocean. This requirement results in a spatial variation for the vertical thermal diffusion coefficient over the combined thermocline/abyss, with values for this coefficient of : 1.35r10 x4 m 2 s x1 in the tropical thermocline ; 0.675r10 x4 m 2 s x1 in the combined subpolar/subtropical thermocline ; and a range of 1.49-1.69r10 x4 m 2 s x1 in the abyss. These values are similar in magnitude to previous calculations, and result from the assumption that the typical upwelling velocity from the abyss into the thermocline is of order 2r10 x7 m 2 s x1 . Webb and Suginohara suggest that some abyssal mass rises along isothermals in the southern ocean, with the resultant need for a decrease in diathermal upwelling over the remainder of the global ocean. This implies a smaller value for the typical abyssal upwelling velocity, and if it is reduced by a factor of 5 from the above value, then the resulting values for the vertical thermal diffusion coefficient are close to 3r10 x5 m 2 s x1 (representing the average over the whole ocean). Webb and Suginohara suggest that this is more consistent with existing ocean measurements.