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The Ocean Circulation in Thermohaline Coordinates

The Ocean Circulation in Thermohaline Coordinates
The Ocean Circulation in Thermohaline Coordinates
The thermohaline streamfunction is presented. The thermohaline streamfunction is the integral of transport in temperature–salinity space and represents the net pathway of oceanic water parcels in that space. The thermohaline streamfunction is proposed as a diagnostic to understand the global oceanic circulation and its role in the global movement of heat and freshwater. The coordinate system used filters out adiabatic fluctuations. Physical pathways and ventilation time scales are naturally diagnosed, as are the roles of the mean flow and turbulent fluctuations. Because potential density is a function of temperature and salinity, the framework is naturally isopycnal and is ideal for the diagnosis of water-mass transformations and advective diapycnal heat and freshwater transports. Crucially, the thermohaline streamfunction is computationally and practically trivial to implement as a diagnostic for ocean models. Here, the thermohaline streamfunction is computed using the output of an equilibrated intermediate complexity climate model. It describes a global cell, a warm tropical cell, and a bottom water cell. The streamfunction computed from eddy-induced advection is equivalent in magnitude to that from the total advection, demonstrating the leading-order importance of parameterized eddy fluxes in oceanic heat and freshwater transports. The global cell, being clockwise in thermohaline space, tends to advect both heat and salt toward denser (poleward) water masses in symmetry with the atmosphere’s poleward transport of moisture. A reprojection of the global cell from thermohaline to geographical coordinates reveals a thermohaline circulation reminiscent of the schematized “global conveyor.”
Hydrologic cycle, Meridional overturning circulation, Streamfunction, Thermohaline circulation, Water masses, Coordinate systems
0022-3670
708-724
Zika, Jan D.
1843cce7-77ce-4ef6-9f79-bcf4f9db30e5
England, Matthew H.
420875c0-8efb-4d92-9dca-249cfe5927b9
Sijp, Willem P.
c9ef7770-5649-46b9-b92e-c73babca2a77
Zika, Jan D.
1843cce7-77ce-4ef6-9f79-bcf4f9db30e5
England, Matthew H.
420875c0-8efb-4d92-9dca-249cfe5927b9
Sijp, Willem P.
c9ef7770-5649-46b9-b92e-c73babca2a77

Zika, Jan D., England, Matthew H. and Sijp, Willem P. (2012) The Ocean Circulation in Thermohaline Coordinates. Journal of Physical Oceanography, 42, 708-724. (doi:10.1175/JPO-D-11-0139.1).

Record type: Article

Abstract

The thermohaline streamfunction is presented. The thermohaline streamfunction is the integral of transport in temperature–salinity space and represents the net pathway of oceanic water parcels in that space. The thermohaline streamfunction is proposed as a diagnostic to understand the global oceanic circulation and its role in the global movement of heat and freshwater. The coordinate system used filters out adiabatic fluctuations. Physical pathways and ventilation time scales are naturally diagnosed, as are the roles of the mean flow and turbulent fluctuations. Because potential density is a function of temperature and salinity, the framework is naturally isopycnal and is ideal for the diagnosis of water-mass transformations and advective diapycnal heat and freshwater transports. Crucially, the thermohaline streamfunction is computationally and practically trivial to implement as a diagnostic for ocean models. Here, the thermohaline streamfunction is computed using the output of an equilibrated intermediate complexity climate model. It describes a global cell, a warm tropical cell, and a bottom water cell. The streamfunction computed from eddy-induced advection is equivalent in magnitude to that from the total advection, demonstrating the leading-order importance of parameterized eddy fluxes in oceanic heat and freshwater transports. The global cell, being clockwise in thermohaline space, tends to advect both heat and salt toward denser (poleward) water masses in symmetry with the atmosphere’s poleward transport of moisture. A reprojection of the global cell from thermohaline to geographical coordinates reveals a thermohaline circulation reminiscent of the schematized “global conveyor.”

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JPO-D-11-0139.1 - Version of Record
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Published date: May 2012
Additional Information: Publishers version pdf available 6 months after publication
Keywords: Hydrologic cycle, Meridional overturning circulation, Streamfunction, Thermohaline circulation, Water masses, Coordinate systems
Organisations: Physical Oceanography

Identifiers

Local EPrints ID: 339663
URI: https://eprints.soton.ac.uk/id/eprint/339663
ISSN: 0022-3670
PURE UUID: 2f05dccd-434d-4691-a17a-ec999767b354

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Date deposited: 28 May 2012 14:00
Last modified: 18 Jul 2017 05:53

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