PATCHINESS - A NEW DIAGNOSTIC FOR LAGRANGIAN TRAJECTORY ANALYSIS IN TIME-DEPENDENT FLUID-FLOWS

In 2-D time-dependent fluid hows, a patch represents a localized regio n in space that has a significantly different average velocity compare d to its surroundings. We show that one can obtain important informati on about the Lagrangian particle motion in such flows by studying the nature, long-term evolution, and statistical characteristics of the pa tchiness behavior. For example, the dispersion of passive tracers at a ny time is directly related to the distribution of patches in the how. We thoroughly investigate the transport properties of the Lagrangian trajectories associated with a cellular flow previously used as a mode l for time-dependent Rayleigh-Benard convection, and a kinematic model of a meandering jet (originally due to Bower [1991]). In both cases, we examine the statistical attributes of the patchiness, their relatio nship with the geometric features of the stable and unstable manifolds , and the effect of noise on the structure of patchiness. We uncover s ome interesting features associated with the origin of these patches a nd their influence on Lagrangian transport.