Lagrangian particles in a stratified turbulent bottom Ekman layer

Particle dispersion in the stratified bottom Ekman Layer over a smooth surface is studied by direct numerical simulation. Neutral, stable and unstable stratifications are considered. The stable stratification tends both to suppress the turbulent fluctuations and to reduce the boundary layer thickness, while the opposite is observed for the unstable case. Therefore, stable stratification causes the increase of particle concentration in the near-wall region, while unstable stratification gives rise to a rapid diffusion of particles in the vertical direction. We show that, besides having a strong influence on the diffusion along the vertical, stratification also affects particle transport along horizontal directions.