Passive admixture transport in a random velocity field

An approximate method allowing the mean concentration to be described with a diffusion equation for regular media is considered. An equation is obtained for a function D(t) representing the coefficient of the Laplace operator in an isotropic homogeneous random field of local velocities. The function D(t) is analyzed assuming Gaussian correlation for the velocity field in a ''locally frozen'' turbulent atmosphere. The spreading of an admixture cloud in a turbulent medium with the power-law spectrum of fluctuations is investigated.