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 mu similar to 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 it to the trapping time exponent gamma = 1 + mu. 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. (C) 2003 Elsevier Ltd. All rights reserved.