The influence of two-dimensional turbulence on diffusion

The validity of laws governing contaminant cloud diffusion or particle pair dispersion in forced, stationary, two-dimensional turbulence is shown to remain when considering free-decaying two-dimensional turbulence. The predictions of the theories are compared with data taken in diffusion measurements made in quasi-two-dimensional flows, both steady and unsteady. It is shown that the laws can be used for predicting the behavior of nonentrained two-dimensional turbulent flows, and a numerical value is proposed as a universal constant in the diffusion laws. The diffusion law is compared with the results from measurements of the three-dimensional wind field on a large scale, for the diffusion of a spot of dye in a rotating fluid, and for turbulent MHD diffusion.