Airborne Observations of Shoaling and Breaking Internal Waves

Abstract

Internal waves (IW) are crucial contributors to the transport of sediment, heat, and nutrients in coastal areas. While IW have been extensively studied using point measurements, their spatial variability is less well understood. In this paper we present a unique set of high-resolution infrared imagery collected from a helicopter, hovering over very energetic shoaling and breaking IW. We compute surface velocities by tracking the evolution of thermal structures at the ocean surface and find horizontal velocity gradients with magnitudes that are more than 100 times the Coriolis frequency. Under the assumption of no vertical shear we determine vertical velocities from the obtained horizontal divergence estimates and identify areas of the wave undergoing breaking. The spatial variability of the internal wave occurs on scales from a few to a few hundred meters. These results highlight the need to collect spatio-temporal observations of the evolution of IW in coastal areas.