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Robustness of nearshore vortices

Published online by Cambridge University Press:  09 July 2018

James C. McWilliams Open the ORCID record for James C. McWilliams [Opens in a new window] ,
Cigdem Akan  and
Yusuke Uchiyama
James C. McWilliams*
Affiliation:
Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095-1565, USA
Cigdem Akan
Affiliation:
College of Computing, Engineering and Construction, University of North Florida, Jacksonville, FL, USA
Yusuke Uchiyama
Affiliation:
Department of Civil Engineering, Kobe University, Kobe, Japan
*
†Email address for correspondence: [email protected]
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Abstract

Coherent vortices with horizontal swirl arise spontaneously in the wave-driven nearshore surf zone. Here, a demonstration is made of the much greater robustness of coherent barotropic dipole vortices on a sloping beach in a 2D shallow-water model compared with fully 3D models either without or with stable density stratification. The explanation is that active vortex tilting and stretching or instability in 3D disrupt an initially barotropic dipole vortex. Without stratification in 3D, the vorticity retains a dipole envelope structure but is internally fragmented. With stratification in 3D, the disrupted vortex reforms as a coherent but weaker surface-intensified baroclinic dipole vortex. An implication is that barotropic or depth-integrated dynamical models of the wave-driven surf zone misrepresent an important aspect of surf-eddy behaviour.

JFM classification

Geophysical and Geological Flows: Topographic effects Vortex Flows: Vortex dynamics Vortex Flows: Vortex Flows
Type
JFM Rapids
Information
Journal of Fluid Mechanics , Volume 850 , 10 September 2018 , R2
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Copyright
© 2018 Cambridge University Press 

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