Meeting Abstracts
3D Lagrangian Coherent Structures in Oceanic Flows
Mohamed H. M. Sulman, Helga S. Huntley, B.L. Lipphardt, Jr., and A.D. Kirwan, Jr.
University of Delaware
(Abstract received 05/11/2012 for session D)
ABSTRACT
Over the last decade Finite-Time Lyapunov Exponents (FTLEs) have emerged as a standard tool for identifying Lagrangian Coherent Structures (LCS). Because vertical velocities are small and usually available from a diagnostic calculation, in most oceanic applications the FTLEs typically are calculated from 2x2 Cauchy-Green tensors that ignore both the vertical velocity and the vertical gradients of the horizontal velocities. Of course, LCS are 2D structures embedded in the three-dimensional ocean. Here we report on the effect of the vertical gradients of the horizontal velocities on the FTLEs calculated from two-dimensional gridded trajectories for oceanic flows, by analyzing computations based on a reduced 3x3 Cauchy-Green tensor. The analysis provides useful criteria for assessing the errors in estimates of the standard approach to calculating FTLEs.