Michael Cox (1941–1989): His Pioneering Contributions to Ocean Circulation Modeling

Abstract

Michael Cox was a pioneer in the development and application of numerical models to the study of the ocean circulation. His simulation of the response of the Indian Ocean to the monsoons was one of the first applications of a numerical model to seasonal changes in circulation near the equator. Cox's finding that the seasonal reversal of the Somali Current was primarily due to local monsoon-driven coastal upwelling challenged a popular theory that the effects of remote forcing, propagating westward along the equatorial waveguide, were the most important mechanism. In a detailed follow-up study, he was able to demonstrate that remote forcing could only be important near the equator along the Somali Coast and that local driving was the only viable mechanism to explain the amplitude and phase of the main features of the seasonal reversal of the Somali Current. In another pioneering calculation, Cox was the first to simulate the seasonal changes of the eastern equatorial Pacific, including the Legeckis waves between the South Equatorial Current and the Equatorial Counter Current. From his analysis, he concluded that the Legeckis waves were due to both baroclinic and barotropic instability. Using observed temperature and salinity data, Cox carried out a new type of diagnostic study of the circulation of the World Ocean. His calculations demonstrated the great importance of adjusting the observed density field in a manner compatible with the constraints imposed by the conservation of mass, temperature, and salinity. In a detailed comparison of simulations of ocean circulation in eddy- and noneddy-resolving models of simplified geometry, Cox was able to demonstrate that mesoscale eddies could have some very important effects on midlatitude thermocline ventilation by wind-driven downwelling. In particular, the mixing by mesoscale eddies along isopycnal surfaces could be strong enough to erase tracer and potential vorticity gradients over trajectories of less than 2000 km. On the other hand, Cox found that poleward transport of buoyancy was approximately the same in similar runs, which did, or did not, include mesoscale eddies. He concluded that this was due to eddy-time mean flow compensation. A similar phenomenon exists in the weakly driven flows of the earth's stratosphere.