Editorial Type:
Article
Article Type:
Research Article

Generation and Stability of a Quasi-Permanent Vortex in the Lofoten Basin

Armin Köhl Institut für Meereskunde, Zentrum für Meeres- und Klimaforschung, Universität Hamburg, Hamburg, Germany

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Print Publication:
01 Nov 2007
DOI:
https://doi.org/10.1175/2007JPO3694.1
Page(s):
2637–2651
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Abstract

In the Nordic seas the Lofoten Basin is a region of high mesoscale activity. The generation mechanism and the conditions for the stability of a quasi-permanent vortex in the center of the Lofoten Basin are studied with a high-resolution ocean circulation model and altimeter data. The vortex and its generation mechanism manifest themselves by a pronounced sea surface height (SSH) signature and variability, which are found to be in agreement with altimeter data. The vortex results primarily from anticyclonic eddies shed from the eastern branch of the Norwegian Atlantic Current, which propagate southwestward. The large-scale bottom depression of the Lofoten Basin plays a crucial role for attracting anticyclones into the trough and for enabling the dynamical stability of the vortex. The water mass characteristics of the anticyclone lead to enhanced atmospheric interaction (heat loss) during wintertime. The cold water trapped in the upper part of the vortex preconditions convection in the following winter. This positive feedback mechanism tends to deepen convection progressively within the upper part of the vortex.

Corresponding author address: Armin Köhl, Institut für Meereskunde, Zentrum für Meeres- und Klimaforschung, Universität Hamburg, Bundesstr. 53, 20146 Hamburg, Germany. Email: koehl@ifm.uni-hamburg.de

Abstract

In the Nordic seas the Lofoten Basin is a region of high mesoscale activity. The generation mechanism and the conditions for the stability of a quasi-permanent vortex in the center of the Lofoten Basin are studied with a high-resolution ocean circulation model and altimeter data. The vortex and its generation mechanism manifest themselves by a pronounced sea surface height (SSH) signature and variability, which are found to be in agreement with altimeter data. The vortex results primarily from anticyclonic eddies shed from the eastern branch of the Norwegian Atlantic Current, which propagate southwestward. The large-scale bottom depression of the Lofoten Basin plays a crucial role for attracting anticyclones into the trough and for enabling the dynamical stability of the vortex. The water mass characteristics of the anticyclone lead to enhanced atmospheric interaction (heat loss) during wintertime. The cold water trapped in the upper part of the vortex preconditions convection in the following winter. This positive feedback mechanism tends to deepen convection progressively within the upper part of the vortex.

Corresponding author address: Armin Köhl, Institut für Meereskunde, Zentrum für Meeres- und Klimaforschung, Universität Hamburg, Bundesstr. 53, 20146 Hamburg, Germany. Email: koehl@ifm.uni-hamburg.de

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  • Benilov, E. S., 2005: Stability of a two-layer quasigeostrophic vortex over axisymmetric localized topography. J. Phys. Oceanogr., 35 , 123–130.

    • Search Google Scholar
    • Export Citation

  • Björk, G., B. G. Gustafsson, and A. Stigebrandt, 2001: Upper layer circulation of the Nordic seas as inferred from the spatial distribution of heat and freshwater content. Polar Res., 20 , 161–168.

    • Search Google Scholar
    • Export Citation

  • Blindheim, J., and F. Rey, 2004: Water-mass formation and distribution in the Nordic seas during the 1990s. ICES J. Mar. Sci., 61 , 846–863.

    • Search Google Scholar
    • Export Citation

  • Boyer, T., S. Levitus, H. Garcia, R. A. Locarnini, C. Stephens, and J. Antonov, 2005: Objective analyses of annual, seasonal, and monthly temperature and salinity for the world ocean on a ¼° grid. Int. J. Climatol., 25 , 931–945.

    • Search Google Scholar
    • Export Citation

  • Carnevale, G. F., P. Cavazza, P. Orlandi, and R. Purini, 1991a: An explanation for anomalous vortex merger in rotating-tank experiments. Phys. Fluids, 3A , 1411–1415.

    • Search Google Scholar
    • Export Citation

  • Carnevale, G. F., R. C. Kloosterziel, and G. J. F. van Heijst, 1991b: Propagation of barotropic vortices over topography in a rotating tank. J. Fluid Mech., 223 , 119–139.

    • Search Google Scholar
    • Export Citation

  • Dewar, W. K., and P. D. Killworth, 1995: On the stability of oceanic rings. J. Phys. Oceanogr., 25 , 1467–1487.

  • Emery, W. J., W. G. Lee, and L. Magaard, 1984: Geographic and seasonal distributions of Brunt–Väisälä frequency and Rossby radii in the North Pacific and North Atlantic. J. Phys. Oceanogr., 14 , 294–317.

    • Search Google Scholar
    • Export Citation

  • Gascard, J-C., A. J. Watson, M-J. Messias, K. A. Olsson, T. Johannessen, and K. Simonsen, 2002: Long-lived vortices as a mode of deep ventilation in the Greenland Sea. Nature, 416 , 525–527.

    • Search Google Scholar
    • Export Citation

  • Griffith, R. W., and E. J. Hopfinger, 1987: Coalescing of geostrophic vortices. J. Fluid Mech., 178 , 73–97.

  • Isachsen, P. E., J. H. LaCasce, C. Mauritzen, and S. Häkkinen, 2003: Wind-driven variability of the large-scale recirculating flow in the Nordic seas and Arctic Ocean. J. Phys. Oceanogr., 33 , 2534–2550.

    • Search Google Scholar
    • Export Citation

  • Ivanov, V., and A. Korablev, 1995a: Formation and regeneration of the pycnocline lens in the Norwegian Sea. Russ. Meteor. Hydrol., 9 , 62–69.

    • Search Google Scholar
    • Export Citation

  • Ivanov, V., and A. Korablev, 1995b: Interpycnocline lens dynamics in the Norwegian Sea. Russ. Meteor. Hydrol., 10 , 32–37.

  • Jakobsen, P. K., M. H. Ribergaard, D. Quadfasel, T. Schmith, and C. W. Hughes, 2003: Near-surface circulation in the northern North Atlantic as inferred from Lagrangian drifters: Variability from the mesoscale to interannual. J. Geophys. Res., 108 .3251, doi:10.1029/2002JC001554.

    • Search Google Scholar
    • Export Citation

  • Kara, A. B., P. A. Rochford, and H. E. Hurlburt, 2002: Naval Research Laboratory mixed layer depth (NMLD) climatologies. NRL Rep. NRL/FR/7330-02-9995, 26 pp.

  • Köhl, A., R. H. Käse, D. Stammer, and N. Serra, 2007a: Causes of changes in the Denmark Strait overflow. J. Phys. Oceanogr., 37 , 1678–1696.

    • Search Google Scholar
    • Export Citation

  • Köhl, A., D. Stammer, and B. Cornuelle, 2007b: Interannual to decadal changes in the ECCO global synthesis. J. Phys. Oceanogr., 37 , 313–337.

    • Search Google Scholar
    • Export Citation

  • Large, W. G., and S. Pond, 1981: Open ocean momentum flux measurements in moderate to strong winds. J. Phys. Oceanogr., 11 , 324–336.

  • Large, W. G., and S. Pond, 1982: Sensible and latent heat flux measurements over the ocean. J. Phys. Oceanogr., 12 , 464–482.

  • Large, W. G., J. C. Williams, and S. C. Doney, 1994: Ocean vertical mixing: A review and a model with a nonlocal boundary layer parameterization. Rev. Geophys., 32 , 363–403.

    • Search Google Scholar
    • Export Citation

  • Levitus, S., and T. P. Boyer, 1994: Temperature. Vol. 4, World Ocean Atlas 1994, NOAA Atlas NESDIS 4, 117 pp.

  • Levitus, S., R. Burgett, and T. P. Boyer, 1994: Salinity. Vol. 3, World Ocean Atlas 1994, NOAA Atlas NESDIS 3, 99 pp.

  • 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 , 5753–5766.

    • 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 , 5733–5752.

    • Search Google Scholar
    • Export Citation

  • Melander, M. V., N. J. Zabusky, and J. C. McWilliams, 1988: Symmetric vortex merger in two dimensions: Causes and conditions. J. Fluid Mech., 195 , 303–340.

    • Search Google Scholar
    • Export Citation

  • Nilsen, J. E. O., and E. Falck, 2006: Variation of mixed layer properties in the Norwegian Sea for the period 1948–1999. Prog. Oceanogr., 70 , 58–90.

    • Search Google Scholar
    • Export Citation

  • Nycander, J., and J. H. LaCasce, 2004: Stable and unstable vortices attached to seamounts. J. Fluid Mech., 507 , 71–94.

  • Orvik, K. A., 2004: The deepening of the Atlantic water in the Lofoten Basin of the Norwegian Sea, demonstrated by using an active reduced gravity model. Geophys. Res. Lett., 31 .L01306, doi:10.1029/2003GL018687.

    • Search Google Scholar
    • Export Citation

  • Orvik, K. A., and P. Niiler, 2002: Major pathways of Atlantic water in the northern North Atlantic and Nordic seas toward Arctic. Geophys. Res. Lett, 29 .1896, doi:10.1029/2002GL015002.

    • Search Google Scholar
    • Export Citation

  • Pedersen, O. P., M. Zhou, K. S. Tande, and A. Evardsen, 2005: Eddy formation on the coast of North Norway—Evidenced by synoptic sampling. ICES J. Mar. Sci., 62 , 615–628.

    • Search Google Scholar
    • Export Citation

  • Poulain, P-M., A. Warn-Varnas, and P. P. Niiler, 1996: Near-surface circulation of the Nordic seas as measured by Lagrangian drifters. J. Geophys. Res., 101 , 18237–18258.

    • Search Google Scholar
    • Export Citation

  • Rodionov, V. B., 1992: On the mesoscale structure of the frontal zones in the Nordic seas. J. Mar. Syst., 3 , 127–139.

  • Send, U., and J. Marshall, 1995: Integral effects of deep convection. J. Phys. Oceanogr., 25 , 855–872.

  • Zhang, J. L., and D. Rothrock, 2000: Modeling Arctic sea ice with an efficient plastic solution. J. Geophys. Res., 105 , 3325–3338.

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