Dynamical Regimes and Clustering of Small Neutrally Buoyant Inertial Particles in Stably Stratified Turbulence

Inertial particles in stably stratified flows play a fundamental role in geophysics, from the dynamics of nutrients in the ocean to the dispersion of pollutants in the atmosphere. We consider the Maxey-Riley equation for small neutrally buoyant inertial particles in the Boussinesq approximation and discuss its limits of validity. The main motivation is the study of phytoplankton and oceanic particles in turbulent flows. We show that particles behave as forced damped oscillators, with different regimes depending on the particles Stokes number and the fluid Brunt-Vaisala frequency. Using direct numerical simulations we study their dynamics and show that small neutrally buoyant particles in these flows tend to cluster in regions of low local vorticity. The particles, albeit small, behave fundamentally differently than tracers.