ON A POSSIBLE MECHANISM OF ANOMALOUS DIFFUSION BY ROSSBY WAVES

We study the advection of passive tracers by traveling plane Rossby wa ves of finite amplitude. In distinction with previous studies the nonl inearity of the wave field is taken into account in the first order of perturbation theory by considering the Lagrangian transport by resona nt wave triads. Using the waves' phases as new dynamical variables we reduce the problem to the study of a specific one-and-a-half degree of freedom Hamiltonian system with nonharmonic modulation. By using a sy mplectic integrator we study this system numerically and find an inter esting series of bifurcations of its phase portrait as the nonlinearit y increases. As is standard in the systems of this type we commonly se e a chaotic sea with elliptic islands in the phase space, which means that in the physical space the resonant triads give rise to chaotic mi xing and ballistic transport, respectively. The relevance of these res ults to the transport properties of beta(-)plane turbulence is discuss ed. (C) 1998 American Institute of Physics. [S1070-6631(98)02712-3].