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Spontaneous wave generation at strongly strained density fronts

Accepted version
Peer-reviewed

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Authors

Shakespeare, CJ 
Taylor, JR 

Abstract

jats:titleAbstract</jats:title>jats:pA simple analytical model is presented describing the spontaneous generation of inertia–gravity waves at density fronts subjected to strong horizontal strain rates. The model considers fronts of arbitrary horizontal and vertical structure in a semi-infinite domain, with a single boundary at the ocean surface. Waves are generated because of the acceleration of the steady uniform strain flow around the density front, analogous to the generation of lee waves via flow over a topographic ridge. Significant wave generation only occurs for sufficiently strong strain rates jats:italicα</jats:italic> > 0.2jats:italicf</jats:italic> and sharp fronts jats:italicH</jats:italic>/jats:italicL</jats:italic> > 0.5jats:italicf</jats:italic>/jats:italicN</jats:italic>, where jats:italicf</jats:italic> is the Coriolis parameter, jats:italicN</jats:italic> is the stratification, and jats:italicH</jats:italic> and jats:italicL</jats:italic> are the height and width scales of the front, respectively. The frequencies of the generated waves are entirely determined by the strain rate. The lowest-frequency wave predicted to be generated via this mechanism has a Lagrangian frequency jats:italicω</jats:italic> = 1.93jats:italicf</jats:italic> as measured in a reference frame moving with the background strain flow. The model is intended as a first-order description of wave generation at submesoscale (1 to 10 km wide) fronts where large strain rates are commonplace. The analytical model compares well with fully nonlinear numerical simulations of the submesoscale regime.</jats:p>

Description

Keywords

Circulation, Dynamics, Frontogenesis, frontolysis, Fronts, Inertia-gravity waves, Internal waves

Journal Title

Journal of Physical Oceanography

Conference Name

Journal ISSN

0022-3670
1520-0485

Volume Title

46

Publisher

American Meteorological Society
Sponsorship
Natural Environment Research Council (NE/J010472/1)
CJS was supported by a Gates Cambridge Scholarship. JRT was supported by a grant from the Natural Environment Research Council, Award NE/J010472/1.