"Anomalous diffusion in quasi-geostrophic flow", J. S. Urbach, E. R. Weeks, and H. L. Swinney, in Chaos, Kinetics, and Nonlinear Dynamics in Fluids and Plasmas, eds. S. Benkadda and G. Zaslavsky (Springer-Verlag, 1998), pp. 171-197.

We review a series of experimental investigations of anomalous transport in quasi-geostrophic flow. Tracer particles are tracked for long periods of time in two-dimensional flows comprised of chains of vortices generated in a rapidly rotating annular tank. The tracer particles typically follow chaotic trajectories, alternately sticking in vortices and flying long distances in the jets surrounding the vortices. Probability distribution functions (PDFs) are measured for the sticking and flight times. The flight PDFs are found to be power laws for most time-dependent flows with coherent vortices. In many cases the PDFs have a divergent second moment, indicating the presence of Levy flights. The variance of an ensemble of particles is found to vary in time as sigma^2 ~ t^ z, with z > 1 (superdiffusion). The dependence of the variance exponent z on the flight and sticking PDFs is studied and found to be consistent with calculations based on a continuous time random walk model.