Particle trajectories below surface gravity wavepackets —Ton van den Bremer, University of Oxford & Colin Whittaker, University of Auckland

Owing to the interplay between forward Stokes drift and a backward return flow, Lagrangian particles underneath surface wavepackets can follow different trajectories. The image shows records from Particle Tracking Velocimetry experiments in which particles are illuminated by a LED light box (Van den Bremer et al., 2019, J. Fluid Mech.).