Two Stable Equilibria of the Atlantic Subpolar Gyre

Born, Andreas; Stocker, Thomas (2014). Two Stable Equilibria of the Atlantic Subpolar Gyre. Journal of Physical Oceanography, 44(1), pp. 246-264. 10.1175/JPO-D-13-073.1

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The cyclonic circulation of the Atlantic subpolar gyre is a key mechanism for North Atlantic climate variability on a wide range of time scales. It is generally accepted that it is driven by both cyclonic winds and buoyancy forcing, yet the individual importance and dynamical interactions of the two contributions remain unclear. The authors propose a simplified four-box model representing the convective basin of the Labrador Sea and its shallow and deep boundary current system, the western subpolar gyre. Convective heat loss drives a baroclinic flow of relatively light water around the dense center. Eddy salt flux from the boundary current to the center increases with a stronger circulation, favors the formation of dense waters, and thereby sustains a strong baroclinic flow, approximately 10%–25% of the total. In contrast, when the baroclinic flow is not active, surface waters may be too fresh to convect, and a buoyancy-driven circulation cannot develop. This situation corresponds to a second stable circulation mode. A hysteresis is found for variations in surface freshwater flux and the salinity of the near-surface boundary current. An analytical solution is presented and analyzed.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Climate and Environmental Physics
10 Strategic Research Centers > Oeschger Centre for Climate Change Research (OCCR)

UniBE Contributor:

Born, Andreas and Stocker, Thomas

Subjects:

500 Science > 530 Physics

ISSN:

0022-3670

Language:

English

Submitter:

Doris Rätz

Date Deposited:

29 Sep 2014 16:15

Last Modified:

29 Sep 2014 16:15

Publisher DOI:

10.1175/JPO-D-13-073.1

Web of Science ID:

000335802100022

URI:

https://boris.unibe.ch/id/eprint/47327

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