Multiple diffusion of heat and scalar in rotating stratified turbulence

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Multiple diffusion of heat and scalars in stratified rotating turbulence have been studied by RDT (rapid distortion theory), direct numerical simulation (RDT) and turbulent vortex-wave model. In the previous studies, double diffusion problem has been studied as a stability problem of fluid motion and its effects on turbulent transfer and diffusion have not been studied. This is because the system is very complex even with a single active scalar. In this study we have used RDT and obtained the solution for two active scalars. Particular attention is paid to the effects of (1) the difference of molecular diffusion, (2) vertical temperature gradient and vertical concentration gradient, (3)vertical mean shear, (4)the wave mode intrinsic to stratified rotating turbulence. We have further developed a numerical code for the transport of heat and scalar, and investigated the mechanisms and examined the quantitative results from the view point of both the theory and the numerical simulations. The results of the theory (RDT) gave good agreement with the results of DNS and experiments. This shows that in the ocean interior away from the surface and the bottom slope (e.g., abyssal ocean) where the strength of turbulence is relatively weak, linear effects are important.