Defining a simplified yet “realistic” equation of state for seawater

Roquet, Fabien; Madec, Gurvan; Brodeau, Laurent; Nycander, J.. 2015 Defining a simplified yet “realistic” equation of state for seawater. Journal of Physical Oceanography, 45 (10). 2564-2579. 10.1175/JPO-D-15-0080.1

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Text © Copyright 2015 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act September 2010 Page 2 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (http://www.ametsoc.org/) or from the AMS at 617-227-2425 or copyrights@ametsoc.org. jpo-d-15-0080%2E1.pdf - Published Version Download (14MB) | Preview

Abstract/Summary

There is a growing realization that the nonlinear nature of the equation of state has a deep impact on the global ocean circulation; however, the understanding of the global effects of these nonlinearities remains elusive. This is partly because of the complicated formulation of the seawater equation of state making it difficult to handle in theoretical studies. In this paper, a hierarchy of polynomial equations of state of increasing complexity, optimal in a least squares sense, is presented. These different simplified equations of state are then used to simulate the ocean circulation in a global 2°-resolution configuration. Comparisons between simulated ocean circulations confirm that nonlinear effects are of major importance, in particular influencing the circulation through determination of the static stability below the mixed layer, thus controlling rates of exchange between the atmosphere and the ocean interior. It is found that a simple polynomial equation of state, with a quadratic term in temperature (for cabbeling), a temperature–pressure product term (for thermobaricity), and a linear term in salinity, that is, only four tuning parameters, is enough to simulate a reasonably realistic global circulation. The best simulation is obtained when the simplified equation of state is forced to have an accurate thermal expansion coefficient near the freezing point, highlighting the importance of polar regions for the global stratification. It is argued that this simplified equation of state will be of great value for theoretical studies and pedagogical purposes.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1175/JPO-D-15-0080.1
ISSN:	0022-3670
Additional Keywords:	Circulation/Dynamics, Deep convection, Large-scale motions, Ocean circulation, Models and modeling, General circulation models, Ocean models, Applications, Education
Date made live:	18 Feb 2016 16:47 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/513019

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