Abstract
Abstract. The damping of water surface standing waves (seiche modes) and the associated excitation of baroclinic internal waves are studied experimentally in a quasi-two-layer laboratory setting with a topographic obstacle at the bottom representing a seabed sill. We find that topography-induced baroclinic wave drag contributes markedly to seiche damping in such systems. Two major pathways of barotropic–baroclinic energy conversions were observed: the stronger one – involving short-wavelength internal modes of large amplitudes – may occur when the node of the surface seiche is situated above the close vicinity of the sill. The weaker, less significant other pathway is the excitation of long waves or internal seiches along the pycnocline that may resonate with the low-frequency components of the decaying surface forcing.
Highlights
Energy conversion over bathymetric formations is a key component of global ocean dynamics and mixing (Wunsch and Ferrari, 2004)
We analyzed the coupling between surface seiche modes and internal wave dynamics in a quasitwo-layer stratified system and the effect of a topographic obstacle on the damping of the surface seiche
The “direct” excitation of shortwavelength propagating internal waves via the horizontal velocity shear emerging in the vicinity of the obstacle
Summary
Energy conversion over bathymetric formations is a key component of global ocean dynamics and mixing (Wunsch and Ferrari, 2004). The coupling between barotropic tidal waves at the sea surface and internal gravity waves facilitates heat and material exchange between the uppermost and deeper layers (Garrett, 2003; Lelong and Kunze, 2013; Morozov, 2018; Vic et al, 2019; Rippeth and Green, 2020; Stanev and Ricker, 2020) This largely interconnected dynamic is pertinent in semi-enclosed basins, bays, and fjords with density profiles characterized by sharp gradients (Rattray, 1960; Niiler, 1968; Bell, 1975; Stigebrandt, 1980; Stigebrandt and Aure, 1989; Chapman and Giese, 1990; Münnich, 1996; Parsmar and Stigebrandt, 1997; Stigebrandt, 1999; Antenucci and Imberger, 2001, 2003; Inall et al, 2004; Cushman-Roisin et al, 2005; Johnsson et al, 2007; Boegman and Ivey, 2012; Park et al, 2016; Staalstrøm and Røed, 2016; Castillo et al, 2017; Roget et al, 2017; Stanev and Ricker, 2020; Xue et al, 2020). Even tsunamis and other seismic disturbances, are known to generate large inflows into coastal harbors and may yield strong seiche activity (Chapman and Giese, 2001)
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