Editorial Type:
Article
Article Type:
Research Article

A Note on the Stability Indicator of the Atlantic Meridional Overturning Circulation

Wei Liu Center for Climatic Research, University of Wisconsin—Madison, Madison, Wisconsin

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Zhengyu Liu Key Laboratory of Meteorological Disaster of Ministry of Education, School of Marine Sciences, Nanjing University of Information Science and Technology, Nanjing, and Laboratory for Climate, Ocean and Atmosphere Studies, Peking University, Beijing, China, and Center for Climatic Research, University of Wisconsin—Madison, Madison, Wisconsin

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Print Publication:
15 Jan 2014
DOI:
https://doi.org/10.1175/JCLI-D-13-00181.1
Page(s):
969–975
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Abstract

This study examines the validity of the net freshwater transport ΔMov as a stability indicator of the Atlantic meridional overturning circulation (AMOC) in a low-resolution version of the NCAR Community Climate System Model, version 3 (CCSM3). It is shown that the sign of ΔMov indicates the monostability or bistability of the AMOC, which is based on a hypothesis that a collapsed AMOC induces a zero net freshwater transport. In CCSM3, this hypothesis is satisfied in that the collapsed AMOC, with a nonzero strength, induces a zero net freshwater transport ΔMov across the Atlantic basin by generating equivalent freshwater export MovS and freshwater import MovN at the southern and northern boundaries, respectively. Because of the satisfaction of the hypothesis, ΔMov is consistent with a generalized indicator L for a slowly evolving AMOC, both of which correctly monitor the AMOC stability.

Corresponding author address: W. Liu, Scripps Institution of Oceanography, CASPO, 9500 Gilman Dr., La Jolla, CA, 92093. E-mail: wel109@ucsd.edu

Abstract

This study examines the validity of the net freshwater transport ΔMov as a stability indicator of the Atlantic meridional overturning circulation (AMOC) in a low-resolution version of the NCAR Community Climate System Model, version 3 (CCSM3). It is shown that the sign of ΔMov indicates the monostability or bistability of the AMOC, which is based on a hypothesis that a collapsed AMOC induces a zero net freshwater transport. In CCSM3, this hypothesis is satisfied in that the collapsed AMOC, with a nonzero strength, induces a zero net freshwater transport ΔMov across the Atlantic basin by generating equivalent freshwater export MovS and freshwater import MovN at the southern and northern boundaries, respectively. Because of the satisfaction of the hypothesis, ΔMov is consistent with a generalized indicator L for a slowly evolving AMOC, both of which correctly monitor the AMOC stability.

Corresponding author address: W. Liu, Scripps Institution of Oceanography, CASPO, 9500 Gilman Dr., La Jolla, CA, 92093. E-mail: wel109@ucsd.edu
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  • Bryan, F., 1986: High-latitude salinity effects and interhemispheric thermohaline circulations. Nature, 323, 301–304.

  • Cimatoribus, A. A., S. S. Drijfhout, M. den Toom, and H. A. Dijkstra, 2012: Sensitivity of the Atlantic meridional overturning circulation to South Atlantic freshwater anomalies. Climate Dyn., 39, 2291–2306, doi:10.1007/s00382-012-1292-5.

    • Search Google Scholar
    • Export Citation

  • de Vries, P., and S. L. Weber, 2005: The Atlantic freshwater budget as a diagnostic for the existence of a stable shut down of the meridional overturning circulation. Geophys. Res. Lett., 32, L09606, doi:10.1029/2004GL021450.

    • Search Google Scholar
    • Export Citation

  • Dijkstra, H. A., 2007: Characterization of the multiple equilibria regime in a global ocean model. Tellus, 59A, 695–705.

  • Drijfhout, S. S., S. L. Weber, and E. van der Swaluw, 2010: The stability of the MOC as diagnosed from model projections for pre-industrial, present and future climates. Climate Dyn., 37, 1575–1586, doi:10.1007/s00382-010-0930-z.

    • Search Google Scholar
    • Export Citation

  • Hawkins, E., R. S. Smith, L. C. Allison, J. M. Gregory, T. J. Woollings, H. Pohlmann, and B. de Cuevas, 2011: Bistability of the Atlantic overturning circulation in a global climate model and links to ocean freshwater transport. Geophys. Res. Lett., 38, L10605, doi:10.1029/2011GL047208.

    • Search Google Scholar
    • Export Citation

  • Huisman, S. E., M. Den Toom, H. A. Dijkstra, and S. S. Drijfhout, 2010: An indicator of the multiple equilibria regime of the Atlantic meridional overturning circulation. J. Phys. Oceanogr., 40, 551–567.

    • Search Google Scholar
    • Export Citation

  • Liu, W., and Z. Liu, 2013: A diagnostic indicator of the stability of the Atlantic meridional overturning circulation in CCSM3. J. Climate, 26, 1926–1938.

    • Search Google Scholar
    • Export Citation

  • Liu, W., Z. Liu, and A. Hu, 2013: The stability of an evolving Atlantic meridional overturning circulation. Geophys. Res. Lett., 40, 1562–1568, doi:10.1002/grl.50365.

    • Search Google Scholar
    • Export Citation

  • Manabe, S., and R. J. Stouffer, 1988: Two stable equilibria of a coupled ocean–atmosphere model. J. Climate, 1, 841–866.

  • Rahmstorf, S., 1996: On the freshwater forcing and transport of the Atlantic thermohaline circulation. Climate Dyn., 12, 799–811.

  • Rahmstorf, S., and Coauthors, 2005: Thermohaline circulation hysteresis: A model intercomparison. Geophys. Res. Lett., 32, L23605, doi:10.1029/2005GL023655.

    • Search Google Scholar
    • Export Citation

  • Stommel, H., 1961: Thermohaline convection with two stable regimes of flow. Tellus, 2, 244–230.

  • Weaver, A. J., and Coauthors, 2012: Stability of the Atlantic meridional overturning circulation: A model intercomparison. Geophys. Res. Lett., 39, L20709, doi:10.1029/2012GL053763.

    • Search Google Scholar
    • Export Citation

  • Yeager, S. G., C. A. Shields, W. G. Large, and J. J. Hack, 2006: The low-resolution CCSM3. J. Climate, 19, 2545–2566.

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