Dynamics of steady ocean currents in the light of experimental fluid mechanics

The present investigation may be regarded as a part of a systematic effort to introduceinto meteorology and physical oceanography methods and results which for anumber of years have contributed to the rapid growth and increasing practical significanceof experimental fluid mechanics. This science has recognized that the exact characterof the forces controlling the motion of a turbulent fluid is not known and thatconsequently there is very little justification for a purely theoretical attack on problems of a practical character. For this reason fluid mechanics has been forced to develop a research technique all of its own, in which the theory is developed on the basis of experiments and then used to predict the behavior of fluids in cases which are not accessibleto experimentation. In oceanography it has long been regarded as an axiom that the movements of thewater are controlled by three forces, the horizontal pressure gradient, the deflecting force,and the frictional force resulting from the relative motion of superimposed strata. It issignificant that thirty-five years of intensive theoretical work on this basis have failedto produce a theory capable of explaining the major features of the observed oceaniccirculation below the pure drift current layer. The present investigation considers a force which has been completely disregardedby theoretical investigators although its existence has been admitted implicitly bypractically everyone who has approached physical oceanography from the descriptiveside, namely the frictional force resulting from large-scale horizontal mixing. The intro-. duction of this force permits us to see how motion generated in the surface layers may bediffused and finally dissipated without recourse to doubtful frictional forces at the bottomof the ocean.