Diagnosing the Observed Seasonal Cycle of Atlantic Subtropical Mode Water Using Potential Vorticity and Its Attendant Theorems

Guillaume Maze Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts

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John Marshall Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts

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Abstract

Analyzed fields of ocean circulation and the flux form of the potential vorticity equation are used to map the creation and subsequent circulation of low potential vorticity waters known as subtropical mode water (STMW) in the North Atlantic. Novel mapping techniques are applied to (i) render the seasonal cycle and annual-mean mixed layer vertical flux of potential vorticity (PV) through outcrops and (ii) visualize the extraction of PV from the mode water layer in winter, over and to the south of the Gulf Stream. Both buoyancy loss and wind forcing contribute to the extraction of PV, but the authors find that the former greatly exceeds the latter. The subsequent path of STMW is also mapped using Bernoulli contours on isopycnal surfaces.

Current affiliation: Laboratoire de Physique des Océans, IFREMER, Plouzané, France.

Corresponding author address: Guillaume Maze, Laboratoire de Physique des Océans, IFREMER, BP70, 29280 Plouzané, France. E-mail: gmaze@ifremer.fr

Abstract

Analyzed fields of ocean circulation and the flux form of the potential vorticity equation are used to map the creation and subsequent circulation of low potential vorticity waters known as subtropical mode water (STMW) in the North Atlantic. Novel mapping techniques are applied to (i) render the seasonal cycle and annual-mean mixed layer vertical flux of potential vorticity (PV) through outcrops and (ii) visualize the extraction of PV from the mode water layer in winter, over and to the south of the Gulf Stream. Both buoyancy loss and wind forcing contribute to the extraction of PV, but the authors find that the former greatly exceeds the latter. The subsequent path of STMW is also mapped using Bernoulli contours on isopycnal surfaces.

Current affiliation: Laboratoire de Physique des Océans, IFREMER, Plouzané, France.

Corresponding author address: Guillaume Maze, Laboratoire de Physique des Océans, IFREMER, BP70, 29280 Plouzané, France. E-mail: gmaze@ifremer.fr
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  • Brambilla, E., L. D. Talley, and P. E. Robbins, 2008: Subpolar Mode Water in the northeastern Atlantic. Part II: Origin and transformation. J. Geophys. Res., 113, C04026, doi:10.1029/2006JC004063.

    • Search Google Scholar
    • Export Citation
  • Bretherton, C. S., and C. Schär, 1993: Flux of potential vorticity substance: A simple derivation and a uniqueness property. J. Atmos. Sci., 50, 18341836.

    • Search Google Scholar
    • Export Citation
  • Cerovecki, I., and J. Marshall, 2008: Eddy modulation of air–sea interaction and convection. J. Phys. Oceanogr., 38, 6583.

  • Cushman-Roisin, B., and M. Manga, 1994: Introduction to Geophysical Fluid Dynamics. Prentice Hall, 320 pp.

  • Czaja, A., and U. Hausmann, 2009: Observations of entry and exit of potential vorticity at the sea surface. J. Phys. Oceanogr., 39, 22802294.

    • Search Google Scholar
    • Export Citation
  • Forget, G., 2010: Mapping ocean observations in a dynamical framework: A 2004–06 ocean atlas. J. Phys. Oceanogr., 40, 12011221.

  • Forget, G., G. Maze, M. Buckley, and J. Marshall, 2011: Estimated seasonal cycle of North Atlantic Eighteen Degree Water volume. J. Phys. Oceanogr., 41, 269286.

    • Search Google Scholar
    • Export Citation
  • Hanawa, K., and L. Talley, 2001: Mode waters. Ocean Circulation and Climate: Observing and Modelling the Global Ocean, G. Siedler, J. Church, and J. Gould, Eds., Academic Press, 373–386.

    • Search Google Scholar
    • Export Citation
  • Haynes, P., and M. McIntyre, 1987: On the evolution of vorticity and potential vorticity in the presence of diabatic heating and frictional or other forces. J. Atmos. Sci., 44, 828841.

    • Search Google Scholar
    • Export Citation
  • Jenkins, W. J., 1982: Oxygen utilization rates in North Atlantic subtropical gyre and primary production in oligotrophic systems. Nature, 300, 246248, doi:10.1038/300246a0.

    • Search Google Scholar
    • Export Citation
  • Joyce, T. M., L. N. Thomas, and F. Bahr, 2009: Wintertime observations of Subtropical Mode Water formation within the Gulf Stream. Geophys. Res. Lett., 36, L02607, doi:10.1029/2008GL035918.

    • Search Google Scholar
    • Export Citation
  • Keffer, T., 1985: The ventilation of the world’s oceans: Maps of the potential vorticity field. J. Phys. Oceanogr., 15, 509523.

  • Kwon, Y., and S. Riser, 2004: North Atlantic subtropical mode water: A history of ocean-atmosphere interaction 1961–2000. Geophys. Res. Lett., 31, L19307, doi:10.1029/2004GL021116.

    • Search Google Scholar
    • Export Citation
  • Marshall, J., and J. G. Nurser, 1992: Fluid dynamics of oceanic thermocline ventilation. J. Phys. Oceanogr., 22, 583595.

  • Marshall, J., A. Adcroft, C. Hill, L. Perelman, and C. Heisey, 1997a: A finite-volume, incompressible Navier Stokes model for studies of the ocean on parallel computers. J. Geophys. Res., 102 (C3), 57535766.

    • Search Google Scholar
    • Export Citation
  • Marshall, J., C. Hill, L. Perelman, and A. Adcroft, 1997b: Hydrostatic, quasi-hydrostatic, and nonhydrostatic ocean modeling. J. Geophys. Res., 102 (C3), 57335752.

    • Search Google Scholar
    • Export Citation
  • Marshall, J., D. Jamous, and J. Nilsson, 1999: Reconciling thermodynamic and dynamic methods of computation of water-mass transformation rates. Deep-Sea Res., 46, 545572.

    • Search Google Scholar
    • Export Citation
  • Marshall, J., D. Jamous, and J. Nilsson, 2001: Entry, flux and exit of potential vorticity in ocean circulation. J. Phys. Oceanogr., 31, 777789.

    • Search Google Scholar
    • Export Citation
  • Marshall, J., and Coauthors, 2009: The CLIMODE field campaign: Observing the cycle of convection and restratification over the Gulf Stream. Bull. Amer. Meteor. Soc., 90, 13371350.

    • Search Google Scholar
    • Export Citation
  • Maze, G., G. Forget, M. Buckley, J. Marshall, and I. Cerovecki, 2009: Using transformation and formation maps to study the role of air–sea heat fluxes in North Atlantic Eighteen Degree Water formation. J. Phys. Oceanogr., 39, 18181835.

    • Search Google Scholar
    • Export Citation
  • McDowell, S., P. Rhines, and T. Keffer, 1982: North Atlantic potential vorticity and its relation to the general circulation. J. Phys. Oceanogr., 12, 14171436.

    • Search Google Scholar
    • Export Citation
  • Schär, C., 1993: A generalization of Bernoulli’s theorem. J. Atmos. Sci., 50, 14371443.

  • Speer, K. G., and E. Tziperman, 1992: Rates of water mass formation in the North Atlantic Ocean. J. Phys. Oceanogr., 22, 93104.

  • Thomas, L., 2005: Destruction of potential vorticity by winds. J. Phys. Oceanogr., 35, 24572466.

  • Walin, G., 1982: On the relation between sea-surface heat flow and thermal circulation in the ocean. Tellus, 34, 187195.

  • Worthington, L. V., 1959: The 18° Water in the Sargasso Sea. Deep-Sea Res., 5, 297305.

  • Worthington, L. V., 1972: Negative oceanic heat flux as a cause of water-mass formation. J. Phys. Oceanogr., 2, 205211.

  • Worthington, L. V., 1976: On the North Atlantic Circulation. The Johns Hopkins University Press, 110 pp.

  • Wunsch, C., and P. Heimbach, 2007: Practical global oceanic state estimation. Physica D, 230 (1–2), 197208.

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