Richardson Pair Dispersion in Two-Dimensional Turbulence

We report the first experimental study of the dispersion of pairs of passive particles, performed in a controlled two-dimensional turbulent flow, in which Kolmogorov-Kraichnan scaling $E\left(k\right)\sim k^{-5\mathrm{}/3}$ holds. The Richardson $t^3$ law is observed, and strongly non-Gaussian behavior is obtained for the Lagrangian distributions of separations. The process is shown to be isotropic, and self-similar in time. The observations, which fit well in the Kolmogorov framework, jeopardize the relevance of the Lévy walk approach.