Plenary Speaker IV

Ágata Piffer Braga Umass Dartmouth

Title : Evolution of a mid-sized river plume front: from discharge to arrest 

Abstract : Data collected in the Merrimack River plume front, ranging from the near-field until the beginning of the mid-field region (Rossby number approximately 0.6), were analyzed. The dataset enabled tracking of the evolution of frontal structure in a front-following reference frame, including the velocity, density, and turbulent kinetic energy (TKE) dissipation rate structure. Our measurements were mostly obtained from a collection of sensors mounted on an autonomous underwater vehicle (AUV) known as the UMassD T-REMUS, augmented by several surface drifters and video footage from an aerial drone. The sampling captured the first 6-8 hours of frontal propagation outside the mouth, characterized by an initial phase of radial propagation and rapid expansion, with the eventual arrest of the front approximately 4-6 hours later. At the time of frontal arrest, the motion of drifters tracking the front becomes dominated by along front, rather than cross front velocities, and frontal features become less well defined. The evolution of terms in the cross-front momentum balance as the front evolves suggests that the arrest of radial expansion and forward propagation may be driven by the increasing importance of Coriolis forcing to the momentum balance. The process by which the front stalls may have important implications for connectivity between the source water and the front. In turn, source water interaction with the arrested front may contribute to the observed weakening of frontal features, which may also be affected by the release of frontal energy via internal waves.