The chromospheric network - (A) network evolution viewed as a diffusion process

Autocorrelation and cross-correlation techniques have been applied to obtai n quantitative information about the dynamics of magnetic flux on the solar surface. The speed of network magnetic elements and the diffusion coeffici ent associated with their random motion is derived. The speed is found to b e about 0.1 km s(-1), independent of activity level. However, the diffusion coefficient shows a strong activity dependence: it is about 370-500 km(2) s(-1) in the quiet network and 135-210 km(2) s(-1) in the enhanced network. It is found that the lifetime of the enhanced network relative to the quie t network is compatible with that suggested by a comparison of their respec tive diffusion coefficients. This supports the proposition that a diffusion -like dispersion of magnetic flux is the dominant factor in the large-scale , long-term evolution of the network.