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Experiments with mixing in stratified flow over a topographic ridge
Author(s) -
Dossmann Yvan,
G. Rosevear Madelaine,
Griffiths Ross W.,
McC. Hogg Andrew,
Hughes Graham O.,
Copeland Michael
Publication year - 2016
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2016jc011990
Subject(s) - mixing (physics) , geology , abyssal zone , turbulence , stratification (seeds) , wake , internal wave , ridge , mechanics , turbulence kinetic energy , stratified flow , stratified flows , flow (mathematics) , physics , meteorology , oceanography , seed dormancy , paleontology , germination , botany , quantum mechanics , dormancy , biology
Abstract The interaction of quasi‐steady abyssal ocean flow with submarine topography is expected to generate turbulent mixing in the ocean. This mixing may occur locally, close to topography, or via breaking quasi‐steady lee waves that can carry energy into the ocean interior. There is currently no theoretical, or empirically derived, prediction for the relative amounts of local and interior mixing. We report measurements of the mixing rate in laboratory experiments with a topographic ridge towed through a density stratification. The experiments span three parameter regimes including linear lee waves, nonlinear flow and an evanescent regime in which wave radiation is weak. Full field density measurements provide the depth‐dependence of energy loss to turbulent mixing, allowing separation of the local mixing in the turbulent wake and remote mixing by wave radiation. Remote mixing is significant only for a narrow band of forcing parameters where the flow speed is resonant with internal waves; in all other parameter regimes local mixing close to the topography is dominant. The results suggest that mixing by local nonlinear mechanisms close to abyssal ocean topography may be much greater than the remote mixing by quasi‐steady lee waves.