Chaotic transport in zonal flows in analogous geophysical and plasma systems

Zonal flows occur naturally in geophysical fluids. Important examples include Jupiter's zonal flows, large scale jets in the earth's stratosphere, and oceanic jets like the Gulf Stream. These zonal flows create transport barriers that have a crucial influence on mixing and confinement. On the other hand, zonal flows have also been observed in fusion plasmas and their role in the reduction of transport has been widely recognized. Based on the analogy between Rossby waves in quasigeostrophic flows and drift waves in magnetically confined plasmas, recent models and laboratory experiments developed for studying transport in geophysical fluid dynamics are discussed in the context of plasma physics. The flows considered are not turbulent and are dominated by large scale coherent structures which we describe with simple deterministic Hamiltonian models that exhibit chaotic transport. Two transport problems are studied: the role of drift/Rossby waves in the destruction of transport barriers, and the statistics of test particle motion. It is shown that non-monotonic zonal flows close to marginal stability typically exhibit robust transport barriers at the peak velocity where the shear locally vanishes. Also, it is shown that the trapping effect of vortices combined with the zonal flows gives rise to anomalous diffusion and Levy (non-Gaussian) statistics. The models are compared with fluid laboratory experiment. (C) 2000 American Institute of Physics. [S1070-664X(00)95805-1].