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Sensitivity of basinwide meridional overturning to diapycnal diffusion and remote wind forcing in an idealized Atlantic–Southern Ocean geometry

Sensitivity of basinwide meridional overturning to diapycnal diffusion and remote wind forcing in an idealized Atlantic–Southern Ocean geometry
Sensitivity of basinwide meridional overturning to diapycnal diffusion and remote wind forcing in an idealized Atlantic–Southern Ocean geometry
Recent numerical experiments indicate that the rate of meridional overturning associated with North Atlantic Deep Water is partially controlled by wind stress in the Southern Ocean, where the zonal periodicity of the domain alters the nature of the flow. Here, the authors solve the cubic scale relationship of Gnanadesikan to find a simple expression for meridional overturning that is used to clarify the relative strength of the wind-forced component. The predicted overturning is compared with coarse-resolution numerical experiments with an idealized Atlantic Ocean–Southern Ocean geometry. The scaling accurately predicts the sensitivity to forcing for experiments with a level model employing isopycnal diffusion of temperature, salinity, and “layer thickness.” A layer model produces similar results, increasing confidence in the numerics of both models. Level model experiments with horizontal diffusivity have similar qualitative behavior but somewhat different sensitivity to forcing. The paper highlights the difference in meridional overturning induced by changes in wind stress or vertical diffusivity. Strengthening the Southern Ocean wind stress induces a circulation anomaly in which most of the water is subducted in the Ekman layer of the wind perturbation region, follows isopycnals down into the thermocline, and changes density again when the isopycnals near the surface in the Northern Hemisphere. Approximating the circulation anomaly by this subduction route allows for a surprisingly accurate prediction of the resulting heat transport anomaly, based on the surface temperature distribution. Some of the induced flow follows a second, near-surface northward route through low-latitude water that is lighter than the subducted flow. Overturning anomalies far from the wind stress perturbations are not completely determined by wind stress in the zonally periodic Southern Ocean: wind stress outside the periodic region strongly influences the transport of heat across the equator primarily by changing the temperature of the flow across the equator.
0022-3670
249-266
Klinger, Barry A.
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Drijfhout, Sybren
a5c76079-179b-490c-93fe-fc0391aacf13
Marotzke, Jochem
b4b295a3-5568-4f63-94b6-6fa92ab27cf3
Scott, Jeffery R.
0a5b123f-280a-443e-b026-7a010bbe33b5
Klinger, Barry A.
0be849df-8abd-463c-a560-7715cb9f7475
Drijfhout, Sybren
a5c76079-179b-490c-93fe-fc0391aacf13
Marotzke, Jochem
b4b295a3-5568-4f63-94b6-6fa92ab27cf3
Scott, Jeffery R.
0a5b123f-280a-443e-b026-7a010bbe33b5

Klinger, Barry A., Drijfhout, Sybren, Marotzke, Jochem and Scott, Jeffery R. (2003) Sensitivity of basinwide meridional overturning to diapycnal diffusion and remote wind forcing in an idealized Atlantic–Southern Ocean geometry. Journal of Physical Oceanography, 33 (1), 249-266. (doi:10.1175/1520-0485(2003)033<0249:SOBMOT>2.0.CO;2).

Record type: Article

Abstract

Recent numerical experiments indicate that the rate of meridional overturning associated with North Atlantic Deep Water is partially controlled by wind stress in the Southern Ocean, where the zonal periodicity of the domain alters the nature of the flow. Here, the authors solve the cubic scale relationship of Gnanadesikan to find a simple expression for meridional overturning that is used to clarify the relative strength of the wind-forced component. The predicted overturning is compared with coarse-resolution numerical experiments with an idealized Atlantic Ocean–Southern Ocean geometry. The scaling accurately predicts the sensitivity to forcing for experiments with a level model employing isopycnal diffusion of temperature, salinity, and “layer thickness.” A layer model produces similar results, increasing confidence in the numerics of both models. Level model experiments with horizontal diffusivity have similar qualitative behavior but somewhat different sensitivity to forcing. The paper highlights the difference in meridional overturning induced by changes in wind stress or vertical diffusivity. Strengthening the Southern Ocean wind stress induces a circulation anomaly in which most of the water is subducted in the Ekman layer of the wind perturbation region, follows isopycnals down into the thermocline, and changes density again when the isopycnals near the surface in the Northern Hemisphere. Approximating the circulation anomaly by this subduction route allows for a surprisingly accurate prediction of the resulting heat transport anomaly, based on the surface temperature distribution. Some of the induced flow follows a second, near-surface northward route through low-latitude water that is lighter than the subducted flow. Overturning anomalies far from the wind stress perturbations are not completely determined by wind stress in the zonally periodic Southern Ocean: wind stress outside the periodic region strongly influences the transport of heat across the equator primarily by changing the temperature of the flow across the equator.

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Published date: 2003
Organisations: Ocean and Earth Science

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Local EPrints ID: 349181
URI: http://eprints.soton.ac.uk/id/eprint/349181
ISSN: 0022-3670
PURE UUID: ae85173a-7b56-4cc8-b6fb-4f89072c24bb

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Date deposited: 26 Feb 2013 11:40
Last modified: 08 Jan 2022 09:06

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Contributors

Author: Barry A. Klinger
Author: Jochem Marotzke
Author: Jeffery R. Scott

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