Abstract
Despite years of research on the dynamics and mixing of gravity currents, there are relatively few detailed observations at geophysical scales. In this chapter, we present measurements of the frontal propagation, and distribution and structure of frontal turbulence and mixing, at a river plume front. The measurements are made using a novel platform that consists of a balloon‐mounted infrared camera in combination with a vessel‐mounted conductivity‐temperature sensor chain. The sampling vessel was deliberately trapped in the convergent front, and followed it seaward for almost three hours during the ebb tide, so that the measurements were fixed in the frame of reference following the front. In this mode, the infrared images have been processed to generate high‐resolution frontal velocity and turbulence fields, and a control volume approach is used to estimate the frontal mixing. We identify an approximately 16[t#]m band of elevated mixing near the front based on the decay of turbulent kinetic energy (TKE) and TKE dissipation rate (?). This region of frontal mixing is marked on the water surface by upwelling streaks of relatively cool water that extend landward from the front. Lobes and clefts were observed along the front that are characteristic of gravity currents observed in laboratory experiments. Turbulence is organized within the circulation of the lobes and clefts, with dissipation rates in the lobes being an order of magnitude higher than in the surrounding frontal regions.