A model of diffusion produced by a cellular surface flow

A model of diffusion induced by the joint action of random cells of two different sizes (granulation and supergranulation) is developed. The basic properties of the model are defined by the dimensionless ratio = (the life time)/(characteristic size/velocity) constructed for these two types of cells. An analytical expression for the diffusivity as a function of is derived. It is estimated that for the standard parameters used the contribution of granulation to the joint diffusion is small. A comparison between the model and numerical simulations of the kinematic diffusion of magnetic fields on the solar surface is made.