On the mutual adjustment of pressure and velocity distributions in certain simple current systems

Abstract

The writer (Rossby 1936) recently advanced the hypothesis that the horizontal pressure gradients observed in the current systems of the atmosphere and the ocean to a large extent must be interpreted as reactions to the Coriolis’ forces impressed upon these systems by the rotation of the earth. Observational support for this point of view was found in the fact that both the temperature-salinity and oxygen-salinity correlation curves obtained from stations on both sides of the Gulf Stream in the region between Nova Scotia and Bermuda are very nearly identical, even though the individual isotherms may drop as much as 700 meters between the slope water basin and the Sargasso Sea. This mass distribution and the resulting pressure distribution are most readily interpreted as the result of a continuous banking process caused by the action of the Coriolis’ forces on the moving masses of the Gulf Stream system. Theoretical support was found in a theorem by Taylor (1932), according to which any purely two-dimensional motion which can occur in a non-rotating system is equally possible also when the system rotates at uniform speed around an axis normal to the plane of motion, the deflecting forces due to the rotation then being offset by the reaction of the fluid system in the form of a superimposed “Coriolian” pressure field. It is easily shown that this nullification of the Coriolis’ forces is possible only when the prescribed motion is purely two-dimensional..