  We report new measurements of single particle dispersion in turbulent
two-dimensional (2D) flows. Laboratory experiments in electromagnetically
driven and Faraday wave driven turbulence reveal a transition from weakly
dispersing superdiffusive regime to strongly dispersing Brownian diffusion as
the flow energy is increased in a broad range. The transition to fully
developed 2D turbulence is characterized by the topological changes in the
fluid particle trajectories and the development of self-similar diffusion. The
degree of 2D turbulence development can be quantified by a parameter describing
the deviation of single particle dispersion from the Taylor dispersion.
