文章基本信息

标题：The role of turbulence and internal waves in the structure and evolution of a near-field river plume
本地全文：下载
作者：McPherson, Rebecca A. ; Stevens, Craig L. ; O'Callaghan, Joanne M. 等
期刊名称：Ocean Science
印刷版ISSN：1812-0784
电子版ISSN：1812-0792
出版年度：2020
卷号：16
期号：4
页码：799-815
DOI：10.5194/os-16-799-2020
出版社：Copernicus Publications
摘要：An along-channel momentum budget is quantified in the near-field plume region of a controlled river flow entering Doubtful Sound, New Zealand. Observations include highly resolved density, velocity and turbulence, enabling a momentum budget to be constructed over a control volume. Estimates of internal stress ( τ ) were made from direct measurements of turbulence dissipation rates ( ϵ ) using vertical microstructure profiles. High flow speeds of the surface plume over 2 m s −1 and strong stratification ( N 2 ∼ 10 - 1 s −2 ) resulted in enhanced turbulence dissipation rates ( ϵ > 10 - 3 W kg −1 ) and internal stress ( τ > 10 - 2 m 2 s −2 ) at the base of the surface layer. Internal waves were observed propagating along the base of the plume, potentially released subsequent to a hydraulic jump in the initial 1 km downstream of the plume discharge point. The momentum flux divergence of these internal waves suggests that almost 15 % of the total plume momentum can be transported out of the system by wave radiation, therefore playing a crucial role in the redistribution of momentum within the near-field plume. Observations illustrate that the evolution of the momentum budget components vary between the distinct surface plume layer and the turbulent, shear-stratified interfacial layer. Within the surface plume, a momentum balance was achieved. The dynamical balance demonstrates that the deceleration of the plume, driven by along-channel advection, is controlled by turbulence stress from the plume discharge point to as far as 3 km downstream. In the interfacial layer, however, the momentum equation was dominated by the turbulence stress term and the balance was not closed. The redistribution of momentum within the shear-stratified layer by internal wave radiation and other hydraulic features could account for the discrepancy in the budget.