• Login
    About WHOAS
    View Item 
    •   WHOAS Home
    • Woods Hole Oceanographic Institution
    • Academic Programs
    • WHOI Theses
    • View Item
    •   WHOAS Home
    • Woods Hole Oceanographic Institution
    • Academic Programs
    • WHOI Theses
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of WHOASCommunities & CollectionsBy Issue DateAuthorsTitlesKeywordsThis CollectionBy Issue DateAuthorsTitlesKeywords

    My Account

    LoginRegister

    Statistics

    View Usage Statistics

    Impacts of double-diffusive processes on the thermohaline circulation

    Thumbnail
    View/Open
    JubaoZhang_thesis.pdf (5.344Mb)
    Date
    1998-08
    Author
    Zhang, Jubao  Concept link
    Metadata
    Show full item record
    Citable URI
    https://hdl.handle.net/1912/4787
    DOI
    10.1575/1912/4787
    Keyword
     Thermoclines; Ocean circulation 
    Abstract
    Double-diffusive processes are studied and parameterized, and their impacts on the oceanic thermohaline circulation are investigated by single-hemisphere numerical models and scaling analysis. Scaling analysis on the thermohaline circulation has been done under three types of surface boundary conditions. (a) Under "relaxation" conditions, there is a two-thirds power law dependence of the meridional overturning rate (and the poleward heat transport) on the diapycnal diffusivity. For any given external forcing, there is only one equilibrium state for the thermohaline circulation. (b) Under "flux" boundary conditions, there is a half power law dependence of the meridional overturning rate on the diapycnal diffusivity. Only one mode is possible for given external forcing. (c) Under "mixed" boundary conditions, multiple equilibria become possible. For given thermal forcing, the existence of multiple equilibria depends on the relative contributions of diapycnal diffusivity and the hydrologic forcing. Numerical experiments are implemented to test the above scaling arguments. Consistent results have been obtained under the above three types of boundary conditions. These provide a basis for understanding how the thermohaline circulation depends on the diapycnal diffusivity, which we know is influenced by the double-diffusive processes of "salt fingering" and "diffusive layering" in some parts of the ocean. In order to examine this issue, the double-diffusive processes are parameterized by diapycnal eddy diffusivities for heat and salt that are different and depend on the local density ratio, Rp= αTz/βSz. A background diffusivity is applied to represent turbulent mixing in the stratified environment. The implementation of this double-diffusive - parameterization in numerical models has significant impacts on the thermohaline circulation. (a) Under "relaxation" boundary conditions, the meridional overturning rate and the poleward heat transport are reduced, and water mass properties are also changed. Similar results are obtained under "flux" boundary conditions. (b) Under "mixed" boundary conditions, the critical freshwater flux for the existence of the thermal mode becomes smaller with the double-diffusive parameterization. The extent to which the thermohaline circulation is affected by double-diffusive processes depends on the magnitude of the freshwater forcing.
    Description
    Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1998
    Collections
    • Physical Oceanography (PO)
    • WHOI Theses
    Suggested Citation
    Thesis: Zhang, Jubao, "Impacts of double-diffusive processes on the thermohaline circulation", 1998-08, DOI:10.1575/1912/4787, https://hdl.handle.net/1912/4787
     

    Related items

    Showing items related by title, author, creator and subject.

    • Thumbnail

      Instabilities of an eastern boundary current with and without large-scale flow influence 

      Wang, Jinbo (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2011-06)
      Eastern oceanic boundary currents are subject to hydrodynamic instability, generate small scale features that are visible in satellite images and may radiate westward into the interior, where they can be modified by the ...
    • Thumbnail

      Oceanic fluxes of mass, heat, and freshwater : a global estimate and perspective 

      Macdonald, Alison M. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1995-08)
      Data from fifteen globally distributed, modern, high resolution, hydrographic oceanic transects are combined in an inverse calculation using large scale box models. The models provide estimates of the global meridional ...
    • Thumbnail

      Adaptive error estimation in linearized ocean general circulation models 

      Chechelnitsky, Michael Y. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1999-06)
      Data assimilation methods, such as the Kalman filter, are routinely used in oceanography. The statistics of the model and measurement errors need to be specified a priori. In this study we address the problem of estimating ...
    All Items in WHOAS are protected by original copyright, with all rights reserved, unless otherwise indicated. WHOAS also supports the use of the Creative Commons licenses for original content.
    A service of the MBLWHOI Library | About WHOAS
    Contact Us | Send Feedback | Privacy Policy
    Core Trust Logo