Interpreting Patterns of Concentric Rings within Small Buoyant River Plumes

George Marmorino,Thomas Evans

doi:10.3390/rs13071361

Abstract

High-resolution imagery of small buoyant plumes often reveals an extensive pattern of concentric rings spreading outward from near the discharge point. Recent remote sensing studies of plumes from rivers flowing into the Black Sea propose that such rings are internal waves, which form near a river mouth through an abrupt deceleration of the current, or hydraulic jump. The present study, using numerical simulations, presents an alternative viewpoint in which no hydraulic jump occurs and the rings are not internal waves, but derive instead through shear instability. These two differing dynamical views point to a clear need for additional field studies that combine in-water measurements and time-sequential remote sensing imagery.

Highlights

Rivers flowing into the sea add momentum and buoyancy that influence coastal dynamics; and they carry sediment, nutrients, and contaminants, which impact the coastal ecosystem
An intriguing feature often found in buoyant plumes from small rivers is a distinctive pattern of nearly concentric bands, or “rings”, which appear to emanate from near the river mouth [3,4,5]
This study has attempted to achieve a clearer understanding of patterns of concentric rings occurring within small buoyantariver plumes, as has been revealed of recently in

Summary

Introduction

Rivers flowing into the sea add momentum and buoyancy that influence coastal dynamics; and they carry sediment, nutrients, and contaminants, which impact the coastal ecosystem. An important objective of studies of river plumes, as well as their laboratory analogs, has been to quantify the mixing of the buoyant layer with the ambient fluid [1,2]. An intriguing feature often found in buoyant plumes from small rivers is a distinctive pattern of nearly concentric bands, or “rings”, which appear to emanate from near the river mouth [3,4,5]. Similar ring-like patterns have been found to occur in a near-surface discharge of heating water from an electric power-generating plant [6]. In the literature, such features have been referred to as internal bands, fronts, and bores (e.g., reference [2])

Methods

Results

Conclusion