Dispersion of passive particles by a quasi-two-dimensional turbulent flow

Using the experimental data of Paret and Tabeling [Phys. Rev. Led. 79, 4162 (1997)] we consider in detail the dispersion of particle pairs by a two-di mensional turbulent flow and its relation to the kinematic properties of th e velocity field. We show that the mean square separation of a pair of part icles is governed by rather rare, extreme events and that the majority of i nitially close pairs are not dispersed by the flow. Another manifestation o f the same effect is the fact that the dispersion of an initially dense clu ster is not the result of homogeneously spreading the particles within the whole system. instead it proceeds through a splining into smaller but also dense clusters. The statistical nature of this effect is discussed, [S1063- 651X(93)09804-9].