Some new insights for inferring diapycnal (irreversible) diffusivity in stably stratified turbulence

New insight for inferring diapycnal diffusivity in stably stratified turbulent flows is obtained based on physical scaling arguments and tested using high-resolution direct numerical simulation data. It shown that the irreversible can be decomposed into a length scale represents an inner of turbulence velocity scale. Furthermore, it related to measurable Ellison (LE) outer vertical (w′) through Froude number analysis. The defined as Fr=ε/Nk, where ε rate dissipation kinetic energy, N buoyancy frequency, k energy. analysis suggests Kρ∼w′LE weakly regime (Fr >1) Kρ∼(w′LE)×Fr strongly <1).