Diffusion or dispersion due to the effects of turbulent motions. When quantifying turbulent diffusion, it is important to distinguish between two types of measurement: 1) single-particle diffusion, where we measure the distances between diffusing particles at a fixed point or a point moving with the mean fluid velocity, and where the mean-square particle displacement initially increases rapidly with time (e. G. , linearly); and 2) two-particle diffusion, where we measure the distances between particle pairs or the dimensions of a cloud of diffusing particles. Here the mean-square distance initially increases more slowly (e. G. , as the 5/ 2 power of the time).