Eddy diffusion

Eddy diffusion, eddy dispersion, multipath, or turbulent diffusion is any diffusion process by which substances are mixed in the atmosphere or in any fluid system due to eddy motion. In another definition it is mixing that is caused by eddies that can vary in size from the small Kolmogorov microscales to subtropical gyres.

Because the microscopic processes responsible for atmospheric mixing are too complex to model in detail, atmospheric modelers generally treat atmospheric mixing as a macroscopic "eddy" diffusion process. In this approach, the diffusion rate at each pressure level is parameterized by a quantity known as the eddy diffusion coefficient, K (also sometimes called eddy diffusivity, with units of m² s⁻¹).