PARTICLE DIFFUSION IN A MEANDERING JET

The process of turbulent mixing across an ideal model of a meandering Gulf Stream is studied considering particle motion in two dimensions. The turbulent motion is modeled using a ''random flight'' model that a ssumes that the evolution of the turbulent velocity along trajectories is a Markov process, with the velocity at one time step depending lin early on the velocity at the previous step. This turbulent field is su perimposed on a meandering jet (similar to the one considered by Bower (1991)) propagating steadily eastward. In Bower's model the particles are constrained to move along streamlines in the translating frame; i n our model the turbulent motion allows the particles to cross streaml ines, resulting in an exchange between the different regions of the fl ow. The major exchange occurs between the ''jet core'' region and the ''recirculating'' regions moving with the meanders. Particles launched in the jet core tend to be lost from the jet in plumes at the extrema of the meanders and to be entrained in successive recirculation regio ns. When in the recirculation regions, particles tend to be trapped an d homogenized. The exchange between the jet and the ''far field'' depe nds only on diffusion mechanisms and is small for the short integratio n time considered. An application of the kinematic techniques consider s the distribution of biological species across the jet. The tendency for ''patches'' of organisms to develop in the recirculation regions i s observed. In a two-species case, where the species have affinities f or the environment on opposite sides of the jet, there is a linear cha nge in species composition across the jet. Patches forming on either s ide of the jet consist of an admixture of the two species, with the po pulation for the crest or trough environment dominating.