Evidence of fractional transport in point vortex flow

Advection properties of passive particles in flows generated by point vortices are considered. Transport properties are anomalous with characteristic transport exponent μ 1.5. This behavior is linked back to the presence of coherent fractal structures within the flow. A fractional kinetic analysis allows to link the characteristic transport exponent μ to the trapping time exponent γ=1+μ. The quantitative agreement is found for different systems of vortices investigated and a clear signature is obtained of the fractional nature of transport in these flows.