EXCHANGE GEOMETRY REVEALED BY FLOAT TRAJECTORIES IN THE GULF-STREAM

In an effort to understand the extent to which Lagrangian pathways in the Gulf Stream indicate fluid exchange between the stream and its sur roundings, trajectories of RAFOS floats are viewed in a frame of refer ence moving with the dominant zonal phase speed associated with nr per iodic flow. In such a frame, geometrical structures emerge that more c learly delineate the position of the parcel in relation to the jet cor e and its surroundings. The basic premise of this work is that the pat hways oi fluid parcels in the vicinity of stagnation points, as define d in the moving frame of reference, are susceptible to changes in thei r pathways, thereby facilitating fluid exchange between different regi ons of the flow field. Four representative RAFOS float trajectories ar e shown to exhibit the expected behavior in the vicinity of stagnation points. To further examine the mechanism of exchange in the vicinity of these geometrical features, concepts from dynamical systems theory are applied to a numerically simulated flow field. The entrainment and detrainment of parcels from the jet core are explained in the context of stable and unstable manifolds and their associated lobes. It is sh own that the Lagrangian pathways from the numerical flow and the obser vational trajectories exhibit a similarity based on the kinematics of a meandering flow field. Overall, this study provides the first look a t RAFOS float trajectories in a moving frame and provides insight as t o how the temporal variability of a jet creates chaotic exchange.