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Ice scallops: a laboratory investigation of the ice–water interface

Published online by Cambridge University Press:  28 June 2019

Mitchell Bushuk*
Affiliation:
Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, NJ 08540, USA Center for Atmosphere Ocean Science, Courant Institute of Mathematical Sciences, New York University, New York, NY 10012, USA
David M. Holland
Affiliation:
Center for Atmosphere Ocean Science, Courant Institute of Mathematical Sciences, New York University, New York, NY 10012, USA Center for Global Sea Level Change, New York University Abu Dhabi, P.O. 129188, UAE
Timothy P. Stanton
Affiliation:
Department of Oceanography, Naval Postgraduate School, Monterey, CA 93943, USA
Alon Stern
Affiliation:
Center for Atmosphere Ocean Science, Courant Institute of Mathematical Sciences, New York University, New York, NY 10012, USA
Callum Gray
Affiliation:
LaVision Inc., Ypsilanti, MI 48197, USA
*
Email address for correspondence: mitchell.bushuk@noaa.gov

Abstract

Ice scallops are a small-scale (5–20 cm) quasi-periodic ripple pattern that occurs at the ice–water interface. Previous work has suggested that scallops form due to a self-reinforcing interaction between an evolving ice-surface geometry, an adjacent turbulent flow field and the resulting differential melt rates that occur along the interface. In this study, we perform a series of laboratory experiments in a refrigerated flume to quantitatively investigate the mechanisms of scallop formation and evolution in high resolution. Using particle image velocimetry, we probe an evolving ice–water boundary layer at sub-millimetre scales and 15 Hz frequency. Our data reveal three distinct regimes of ice–water interface evolution: a transition from flat to scalloped ice; an equilibrium scallop geometry; and an adjusting scallop interface. We find that scalloped-ice geometry produces a clear modification to the ice–water boundary layer, characterized by a time-mean recirculating eddy feature that forms in the scallop trough. Our primary finding is that scallops form due to a self-reinforcing feedback between the ice-interface geometry and shear production of turbulent kinetic energy in the flow interior. The length of this shear production zone is therefore hypothesized to set the scallop wavelength.

Information

Type
JFM Papers
Copyright
© 2019 Cambridge University Press 

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