A numerical study on the dynamics of non-inertial and inertial particles in geophysical flows

We consider the dynamics of non-inertial and inertial particles in several types of geophysical flows. The underlying structures of the flow fields are examined via their associated Lagrangian coherent structures, which are found by computing the finite-time Lyapunov exponent (FTLE) field. For inertial particles with finite size and mass, the Maxey-Riley equation is used to describe the particles' motion and to find the inertial FTLE field. We compare the behavior and FTLE fields of massless non-inertial particles and light (bubbles) and heavy (aerosols) inertial particles using the velocity fields from the double-gyre flow, Bickley jet, and eddy-quadrupole models, as well as an ocean dataset of Monterey Bay, California. In addition, we explore the preferential aggregation of inertial particles in these flows and show that inertia affects particle transport: aerosols accumulate along maximal FTLE ridges, and bubbles cluster inside vortex cores, where the clustering depends on the density ratio and the Stokes number. Inclusion of the Coriolis force further influences the dynamics via ejection of particles between cyclonic and anticyclonic structures, where the rate of aggregation onto these rotational attractors increases with the strength of rotation. We also study the validity of ignoring the Faxén correction and an often used assumption whereby the material derivative is set equal to the total derivative. The Faxén correction has a negligible effect for these flows, while the material derivative simplification changes the timescale on which inertial particles aggregate onto their attractors.