We study the formation of clusters of passive Lagrangian tracers in anon-smooth turbulent flow in a flat free-slip surface as a model for particledynamics on free surfaces. Single particle and pair dispersion show differentbehavior for short and large times: on short times particles clusterexponentially rapidly until patches of the size of the divergence correlationlength are depleted; on larger times the pair dispersion is dominated by almostballistic hopping between clusters. We also find that the distribution ofparticle density is close to algebraic and can trace this back to theexponential distribution of the divergence field of the surface flow.
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