Defining a simplified yet “realistic” equation of state for seawater
Defining a simplified yet “realistic” equation of state for seawater
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.
Circulation/Dynamics, Deep convection, Large-scale motions, Ocean circulation, Models and modeling, General circulation models, Ocean models, Applications, Education
2564-2579
Roquet, Fabien
df1aac99-2c3a-4497-a84d-63efec104bb3
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Brodeau, Laurent
f72d7333-bc09-4a6a-999d-afc48b928ef8
Nycander, J.
16e86f07-b62c-4bbe-bd21-576c7ac35626
October 2015
Roquet, Fabien
df1aac99-2c3a-4497-a84d-63efec104bb3
Madec, Gurvan
ffb28deb-4bbd-4a4c-914f-492f813e4864
Brodeau, Laurent
f72d7333-bc09-4a6a-999d-afc48b928ef8
Nycander, J.
16e86f07-b62c-4bbe-bd21-576c7ac35626
Roquet, Fabien, Madec, Gurvan, Brodeau, Laurent and Nycander, J.
(2015)
Defining a simplified yet “realistic” equation of state for seawater.
Journal of Physical Oceanography, 45 (10), .
(doi:10.1175/JPO-D-15-0080.1).
Abstract
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.
Text
jpo-d-15-0080%2E1.pdf
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Published date: October 2015
Keywords:
Circulation/Dynamics, Deep convection, Large-scale motions, Ocean circulation, Models and modeling, General circulation models, Ocean models, Applications, Education
Organisations:
Marine Systems Modelling
Identifiers
Local EPrints ID: 388137
URI: http://eprints.soton.ac.uk/id/eprint/388137
ISSN: 0022-3670
PURE UUID: dd57ed6e-6f4a-42f2-9ba7-a89e734ccbc2
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Date deposited: 18 Feb 2016 16:41
Last modified: 14 Mar 2024 22:52
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Contributors
Author:
Fabien Roquet
Author:
Gurvan Madec
Author:
Laurent Brodeau
Author:
J. Nycander
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