LAUSR

AbstractRecent progress in direct numerical simulations (DNS) of stratified turbulent flows has led to increasing attention to the validity of the constancy of the dissipation flux coefficient Г in the Osborn’s eddy diffusivity model. Motivated by lack of observational estimates of Г particularly under weakly stratified deep-ocean conditions, this study estimates Г using deep microstructure profiles collected in various regions of the North Pacific and the Southern Ocean. It is shown that Г is not constant but varies significantly with the Ozmidov/Thorpe scale ratio ROT in a fashion similar to that obtained by previous DNS studies. Efficient mixing events with Г ~ O(1) and ROT ~ O(0:1) tend to be frequently observed in the deep ocean (i.e., weak stratification), while moderate mixing events with Г ~ O(0:1) and ROT ~ O(1) tend to be observed in the upper ocean (i.e., strong stratification). The observed negative relationship between Г and ROT is consistent with a simple scaling that can be derived from cla...