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    Dynamical origin of low-frequency variability in a highly nonlinear midlatitude coupled model

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    JCLI3976.1.pdf (2.223Mb)
    Date
    2006-12-15
    Author
    Kravtsov, Sergey K.  Concept link
    Berloff, Pavel S.  Concept link
    Dewar, William K.  Concept link
    Ghil, M.  Concept link
    McWilliams, James C.  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/4182
    As published
    https://doi.org/10.1175/JCLI3976.1
    DOI
    10.1175/JCLI3976.1
    Keyword
     Climate variability; Rossby waves; Climate models 
    Abstract
    A novel mechanism of decadal midlatitude coupled variability, which crucially depends on the nonlinear dynamics of both the atmosphere and the ocean, is presented. The coupled model studied involves quasigeostrophic atmospheric and oceanic components, which communicate with each other via a constant-depth oceanic mixed layer. A series of coupled and uncoupled experiments show that the decadal coupled mode is active across parameter ranges that allow the bimodality of the atmospheric zonal flow to coexist with oceanic turbulence. The latter is most intense in the regions of inertial recirculation (IR). Bimodality is associated with the existence of two distinct anomalously persistent zonal-flow modes, which are characterized by different latitudes of the atmospheric jet stream. The IR reorganizations caused by transitions of the atmosphere from its high- to low-latitude state and vice versa create sea surface temperature anomalies that tend to induce transition to the opposite atmospheric state. The decadal–interdecadal time scale of the resulting oscillation is set by the IR adjustment; the latter depends most sensitively on the oceanic bottom drag. The period T of the nonlinear oscillation is 7–25 yr for the range of parameters explored, with the most realistic parameter values yielding T ≈ 20 yr. Aside from this nonlinear oscillation, an interannual Rossby wave mode is present in all coupled experiments. This coupled mode depends neither on atmospheric bimodality, nor on ocean eddy dynamics; it is analogous to the mode found previously in a channel configuration. Its time scale in the model with a closed ocean basin is set by cross-basin wave propagation and equals 3–5 yr for a basin width comparable with the North Atlantic.
    Description
    Author Posting. © American Meteorological Society 2006. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 19 (2006): 6391–6408, doi:10.1175/JCLI3976.1.
    Collections
    • Physical Oceanography (PO)
    Suggested Citation
    Journal of Climate 19 (2006): 6391-6408
     

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