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    Onset of time-dependence in a double-gyre circulation : barotropic basin modes versus classical baroclinic modes

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    Date
    2010-03-01
    Author
    Hristova, Hristina G.  Concept link
    Dijkstra, Henk A.  Concept link
    Spall, Michael A.  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/4348
    As published
    https://doi.org/10.1357/002224010793721424
    DOI
    10.1357/002224010793721424
    Abstract
    Using a fully-implicit high-resolution two-layer quasi-geostrophic model combined with pseudo-arclength continuation methods, we perform a bifurcation analysis of double-gyre ocean flows to study their initial oscillatory instabilities. In this model, both wind- and thermally-forced flows can be represented. We demonstrate that on the branch of anti-symmetric steady-state solutions the ratio, Ω, of the flow advective speed to the long internal Rossby wave speed determines the type of oscillatory modes to first become unstable. This is the same nondimensional parameter that controls the shape of the geostrophic contours in the linear limit of the circulation. For large values of Ω, the first Hopf bifurcations correspond to the classical baroclinic modes with inter-monthly time periods arising from shear instability of the flow. For small values of Ω, the first Hopf bifurcations correspond instead to barotropic Rossby modes with shorter, monthly periods arising from mixed barotropic-baroclinic instability of the flow. By considering both a wind-forced and a thermally-forced ocean, we show that this is a robust feature that does not depend on the type of forcing driving the circulation.
    Description
    Author Posting. © Sears Foundation for Marine Research, 2010. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 68 (2010): 215-236, doi:10.1357/002224010793721424.
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    • Physical Oceanography (PO)
    Suggested Citation
    Journal of Marine Research 68 (2010): 215-236
     
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