How open ocean dynamics affects coastal sea level, an investigation of the influence of the continental shelf and slope

Large scale, annual to decadal period motions in the deep ocean drive large scale gradients in dynamic sea level that are important as baseline levels with the potential to amplify short term sea level fluctuations from extreme events such as storm surges. Model projections assessing flood risk ther...

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Bibliographic Details
Main Author: Wise, Anthony
Other Authors: Polton, Jeff, Hughes, Chris, Huthnance, John, Holt, Jason, Harle, James
Format: Thesis
Language:English
Published: 2019
Subjects:
Online Access:http://livrepository.liverpool.ac.uk/3085550/
http://livrepository.liverpool.ac.uk/3085550/1/201127745_Apr2020.pdf
Description
Summary:Large scale, annual to decadal period motions in the deep ocean drive large scale gradients in dynamic sea level that are important as baseline levels with the potential to amplify short term sea level fluctuations from extreme events such as storm surges. Model projections assessing flood risk therefore depend on accurately simulating both short and long term variability. The decreasing depth of the bathymetry from the deep ocean to the shallow coastal zone tends to produce an insulating effect between the deep ocean and the coast. Nevertheless, studies show coherence between signals on- and off-shore over vast distances, implying that remote driving of the coastal sea level by deep ocean forcing is important. Western boundaries of ocean basins are of particular interest as the rotation and curvature of the Earth result in the intensification of currents and sea level gradients adjacent to the coastal zone. This thesis seeks to develop an improved physical understanding of how coastal sea level along a western boundary is related to the open ocean and to what extent this relationship depends on bottom topography h, the effects of the Coriolis parameter f, and friction. To investigate these questions, a hierarchy of idealized models is developed. Analytic and numerical solutions are sought for the linearised problem, while an idealized configuration of the NEMO General Ocean Circulation Model is developed to probe more realistic scenarios in the North Atlantic. For a homogeneous ocean layer above sloping topography that is uniform alongshore, the β-effect and bottom topography result in the mean dynamic sea level tending to follow h/f contours. The inclusion of friction allows sea level to cross these contours, with steeper topography and a larger friction parameter promoting penetration to the coast. This leads to the equatorward displaced and attenuated coastal sea level (relative to the open ocean) that is seen in observations. Fluctuations in the open ocean are shown to generate a new type of leaky Slope ...