The dynamics of buoyant, rotational river plumes.

摘要

River plumes are an important and dynamic component of the coastal landscape, delivering nutrients, contaminants, marine organisms, and sediments to shelf waters and shaping habitats that support some of the most diverse and productive ecosystems on earth. In this dissertation, I address the following question. In large-scale rotational plumes, what determines the flux of river water away from the river mouth?; Evidence from satellite and field data suggests that many river plumes exhibit a regime in which an anticyclonic bulge forms at the mouth. This regime has been reproduced in a number of numerical studies forced only by a steady, buoyant inflow. In these models the bulge is identified as an unsteady feature that accumulates a fraction of the inflowing river water, thereby decreasing the transport of river water along the coast. I conduct experiments on a 2-meter rotating table, combining Digital Particle Image Velocimetry (DPIV) and Planar Laser Induced Fluorescence (PLIF) to obtain simultaneous measurements of density and velocity in an idealized buoyant plume. The goal of these experiments is to understand how the structure of the anticyclonic bulge depends on the relative strength of buoyant and rotational forcing of the plume and to determine how they modify the transport away from the river mouth in the coastal current.; The results of these experiments provide three principal contributions to the understanding of river plume dynamics. First, they confirm that the unsteady plume structure observed in numerical models is an accurate description of an idealized buoyant rotational plume. Second, they define time dependent scales for the radius and depth of the bulge and show that they are consistent with the observed reduction in coastal current transport. The bulge radius and depth are characterized by inertial and geostrophic scales, respectively. Third, they demonstrate that the structure and alongshore transport in river plumes are strongly modified by the inflow angle and that plumes with low inflow angles are steady.