Variation of flow properties during a collision event of two mesoscale eddies in the Gulf Stream region from numerical simulation

Abstract

The temporal variation of the flow structure and consequent mixing process during the collision of two counter-rotating mesoscale eddies are investigated by analyzing the HYbrid Coordinate Ocean Model simulation for the Gulf Stream region using Eulerian parameters-Okubo-Weiss parameters and horizontal kinetic energy (KE)-and Lagrangian parameters-finite-size Lyapunov exponent (FSLE) and relative dispersion coefficients (K (r) ). During the collision process, a transport barrier constructed by FSLE ridges develops between the two eddies and hyperbolic points are formed at both ends of the barrier. High values of the shear components of strain (> mean + standard deviation) are observed around the hyperbolic points, indicating possible deformation of the eddy. The magnitudes of spatially averaged KE and FSLE values increase (20% and 25%, respectively) during the collision as the flows around the main eddy become more energetic and dispersive. The Eulerian measures-the relative vorticity and the shear components of strain-show different temporal evolutions. The former does not significantly vary (3%) while the latter has a peak value (34%) at the time of maximum impact of the collision. In contrast, the Lagrangian measures show a similar pattern of temporal variations as both FSLE and K (r) values generally increase (25% and 35%, respectively) during the collision, which indicates increased mixing due to the collision.