EWM 26: Clustering and chaotic transport in deforming oceanic eddies by Anu V. S. Nath

Clustering and chaotic transport in deforming oceanic eddies by Anu V. S. Nath (Ecole Normale Sup´erieure de Lyon) Understanding how coherent oceanic eddies transport and disperse material is central to problems such as search-and-rescue operations, pollutant spreading, and plankton dynamics. Motivated by this, we study the motion of heavy inertial particles in the flow generated by an isolated, non-axisymmetric vortex. We use the Kirchhoff vortex as a minimal model of a balanced eddy, and its strained counterpart, the Kida vortex, to represent the effect of interacting vortices or large-scale deformation. While heavy particles are typically expelled from vortical regions, we show that non-axisymmetry can instead promote clustering near co-rotating attractors. As particle inertia increases, these attractors migrate, merge, and eventually disappear through bifurcations. When external strain is present, chaotic transport emerges, reflecting the competition between coherent eddy trapping and deformation-induced dispersion. A Melnikov analysis reveals that sufficiently large particle inertia can suppress chaotic transport. These results provide a simple theoretical framework to understand how balanced eddies interacting with background strain influence material transport, mixing, and irreversible pathways, with implications for parameterising subgrid-scale transport in oceanic flows.