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Characteristics of bolus formation and propagation from breaking internal waves on shelf slopes

Published online by Cambridge University Press:  19 February 2016

Christine D. Moore ,
Jeffrey R. Koseff  and
Erin L. Hult
Christine D. Moore
Affiliation:
Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305, USA
Jeffrey R. Koseff*
Affiliation:
Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305, USA
Erin L. Hult
Affiliation:
Residential Buildings Systems Group, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
*
†Email address for correspondence: koseff@stanford.edu
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Abstract

A series of laboratory experiments was conducted to study the formation of internal boluses through the run up of periodic internal wave trains on a uniform slope/shelf topography in a two-layer stratified fluid system. In the experiments, the forcing parameters of the incident waves (wave amplitude and frequency) are varied for constant slope angle and layer depths. Simultaneous particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) measurements are used to calculate high resolution, two-dimensional velocity and density fields. Over the range of wave forcing conditions, four bolus formation types were observed: backward overturning into a coherent bolus, top breaking into a turbulent bolus, top breaking into a turbulent surge and forward breaking into a turbulent surge. Wave forcing parameters, including a wave Froude number $Fr$, a wave Reynolds number $Re$ and a wave steepness parameter $ka_{0}$, are used to relate initial wave forcing to a dominant bolus formation mechanism. Bolus characteristics, including the bolus propagation speed and turbulent components, are also related to wave forcing. Results indicate that for $Fr>0.20$ and $ka_{0}>0.40$, the generated boluses become more turbulent in nature. As wave forcing continues to increase further, boluses are no longer able to form.

JFM classification

Geophysical and Geological Flows: Internal waves Geophysical and Geological Flows: Stratified flows Geophysical and Geological Flows: Topographic effects
Type
Papers
Information
Journal of Fluid Mechanics , Volume 791 , 25 March 2016 , pp. 260 - 283
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Copyright
© 2016 Cambridge University Press 

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