Low-Frequency Variability in the Midlatitude Atmosphere Induced by an Oceanic Thermal Front

Yizhak Feliks Department of Atmospheric Sciences, and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, California

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Michael Ghil Department of Atmospheric Sciences, and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, California

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Eric Simonnet Department of Atmospheric Sciences, and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, California

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Abstract

This study examines the flow induced in a highly idealized atmospheric model by an east–west-oriented oceanic thermal front. The model has a linear marine boundary layer coupled to a quasigeostrophic, equivalent- barotropic free atmosphere. The vertical velocity at the top of the boundary layer drives the flow in the free atmosphere and produces an eastward jet, parallel to the oceanic front's isotherms. A large gyre develops on either side of this jet, cyclonic to the north and anticyclonic to the south of it. As the jet intensifies during spinup from rest, it becomes unstable. The most unstable wave has a length of about 500 km, it evolves into a meander, and eddies detach from the eastern edge of each gyre.

The dependence of the atmospheric dynamics on the strength T∗ of the oceanic front is studied. The Gulf Stream and Kuroshio fronts correspond roughly, in the scaling used here, to T∗ ≅ 7°C. For weak fronts, T∗ ≤ 4°C, the circulation is steady and exhibits two large, antisymmetric gyres separated by a westerly zonal jet. As the front strengthens, 4 < T∗ < 5, the solution undergoes Hopf bifurcation to become periodic in time, with a period of 30 days, and spatially asymmetric. The bifurcation is due to the westerly jet's barotropic instability, which has a symmetric spatial pattern. The addition of this pattern to the antisymmetric mean results in the overall asymmetry of the full solution. The spatial scale and amplitude of the symmetric, internally generated, and antisymmetric, forced mode increase with the strength T∗ of the oceanic front. For T∗ ≥ 5°C, the solution becomes chaotic, but a dominant period still stands out above the broadband noise. This dominant period increases with T∗ overall, but the increase is not monotonic.

The oceanic front's intensity dictates the mean speed of the atmospheric jet. Two energy regimes are obtained. 1) In the low-energy regime, the SST front, and hence the atmospheric jet, are weak; in this regime, small meanders develop along the jet axis, and the dominant period is about 25 days. 2) In the high-energy regime, the SST front and the jet are strong; in it, large meanders and eddies develop along the jet, and the dominant oscillation has a period of about 70 days. The physical nature of the two types of oscillations is discussed, as are possible transitions between them when T∗ changes on very long time scales. The results are placed in the context of previous theories of ocean front effects on atmospheric flows, in which baroclinic phenomena are dominant.

Permanent affiliation: Mathematics Department, Israel Institute of Biological Research, Nes-Ziona, Israel

Additional affiliation: Départment Terre-Atmosphère-Océan, Ecole Normale Supérpieure, and Laboratoire de Météorologie Dynamique du CNRS, Paris, France

Permanent affiliation: Institut Non-Linéaire de Nice, CNRS, Nice, France

Corresponding author address: Michael Ghil, Dept. of Atmospheric Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, CA 90095-1567. Email: ghil@atmos.ucla.edu

Abstract

This study examines the flow induced in a highly idealized atmospheric model by an east–west-oriented oceanic thermal front. The model has a linear marine boundary layer coupled to a quasigeostrophic, equivalent- barotropic free atmosphere. The vertical velocity at the top of the boundary layer drives the flow in the free atmosphere and produces an eastward jet, parallel to the oceanic front's isotherms. A large gyre develops on either side of this jet, cyclonic to the north and anticyclonic to the south of it. As the jet intensifies during spinup from rest, it becomes unstable. The most unstable wave has a length of about 500 km, it evolves into a meander, and eddies detach from the eastern edge of each gyre.

The dependence of the atmospheric dynamics on the strength T∗ of the oceanic front is studied. The Gulf Stream and Kuroshio fronts correspond roughly, in the scaling used here, to T∗ ≅ 7°C. For weak fronts, T∗ ≤ 4°C, the circulation is steady and exhibits two large, antisymmetric gyres separated by a westerly zonal jet. As the front strengthens, 4 < T∗ < 5, the solution undergoes Hopf bifurcation to become periodic in time, with a period of 30 days, and spatially asymmetric. The bifurcation is due to the westerly jet's barotropic instability, which has a symmetric spatial pattern. The addition of this pattern to the antisymmetric mean results in the overall asymmetry of the full solution. The spatial scale and amplitude of the symmetric, internally generated, and antisymmetric, forced mode increase with the strength T∗ of the oceanic front. For T∗ ≥ 5°C, the solution becomes chaotic, but a dominant period still stands out above the broadband noise. This dominant period increases with T∗ overall, but the increase is not monotonic.

The oceanic front's intensity dictates the mean speed of the atmospheric jet. Two energy regimes are obtained. 1) In the low-energy regime, the SST front, and hence the atmospheric jet, are weak; in this regime, small meanders develop along the jet axis, and the dominant period is about 25 days. 2) In the high-energy regime, the SST front and the jet are strong; in it, large meanders and eddies develop along the jet, and the dominant oscillation has a period of about 70 days. The physical nature of the two types of oscillations is discussed, as are possible transitions between them when T∗ changes on very long time scales. The results are placed in the context of previous theories of ocean front effects on atmospheric flows, in which baroclinic phenomena are dominant.

Permanent affiliation: Mathematics Department, Israel Institute of Biological Research, Nes-Ziona, Israel

Additional affiliation: Départment Terre-Atmosphère-Océan, Ecole Normale Supérpieure, and Laboratoire de Météorologie Dynamique du CNRS, Paris, France

Permanent affiliation: Institut Non-Linéaire de Nice, CNRS, Nice, France

Corresponding author address: Michael Ghil, Dept. of Atmospheric Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Los Angeles, CA 90095-1567. Email: ghil@atmos.ucla.edu

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  • Batchelor, G. K., 2000: An Introduction to Fluid Dynamics. Cambridge University Press, 615 pp.

  • Bjerknes, J., 1964: Atlantic air–sea interaction. Advances in Geophysics, Vol. 10, Academic Press, 1–82.

  • Branstator, G. W., 1987: A striking example of the atmosphere's leading traveling pattern. J. Atmos. Sci, 44 , 23102323.

  • Businger, J. A., and W. J. Shaw, 1984: The response of the marine boundary layer to mesoscale variations in sea-surface temperature. Dyn. Atmos. Oceans, 8 , 267281.

    • Search Google Scholar
    • Export Citation
  • Chao, Y., M. Ghil, and J. C. McWilliams, 2000: Pacific interdecadal variability in this century's sea surface temperatures. Geophys. Res. Lett, 27 , 22612264.

    • Search Google Scholar
    • Export Citation
  • Charney, J. G., 1971: Geostrophic turbulence. J. Atmos. Sci, 28 , 10871095.

  • Chen, Z-M., M. Ghil, E. Simonnet, and S. Wang, 2004: Hopf bifurcation in quasi-geostrophic channel flow. SIAM J. Appl. Math.,64, doi:10.1137/50036139902406164.

    • Search Google Scholar
    • Export Citation
  • Deser, C., and M. L. Blackmon, 1993: Surface climate variations over the North Atlantic Ocean during winter: 1900–1989. J. Climate, 6 , 17431753.

    • Search Google Scholar
    • Export Citation
  • Dickey, J. O., M. Ghil, and S. L. Marcus, 1991: Extratropical aspects of the 40–50 oscillation in length-of-day and atmospheric angular momentum. J. Geophys. Res, 96 , 2264322658.

    • Search Google Scholar
    • Export Citation
  • Doyle, J. D., and T. T. Warner, 1990: Mesoscale coastal processes during GALE IOP-2. Mon. Wea. Rev, 118 , 283308.

  • Doyle, J. D., and T. T. Warner, 1993: Nonhydrostatic simulations of coastal mesobeta-scale vortices and frontogenesis. Mon. Wea. Rev, 121 , 33713392.

    • Search Google Scholar
    • Export Citation
  • Feliks, Y., 1990: Isolated vortex evolution in 2 and 4 mode models. Deep-Sea Res, 37 , 571591.

  • Feliks, Y., and M. Ghil, 1996: Mixed barotropic–baroclinic eddies growing on an eastward midlatitude jet. Geophys. Astrophys. Fluid Dyn, 82 , 137171.

    • Search Google Scholar
    • Export Citation
  • Gallego, B., and P. Cessi, 2001: Decadal variability of two oceans and an atmosphere. J. Climate, 14 , 28152832.

  • Ghil, M., and K-C. Mo, 1991a: Intraseasonal oscillations in the global atmosphere. Part I: Northern Hemisphere and tropics. J. Atmos. Sci, 48 , 752779.

    • Search Google Scholar
    • Export Citation
  • Ghil, M., and K-C. Mo, 1991b: Intraseasonal oscillations in the global atmosphere. Part II: Southern Hemisphere. J. Atmos. Sci, 48 , 780790.

    • Search Google Scholar
    • Export Citation
  • Ghil, M., and A. W. Robertson, 2000: Solving problems with GCMs: General circulation models and their role in the climate modeling hierarchy. General Circulation Model Development: Past, Present and Future, D. Randall, Ed., Academic Press, 285–325.

    • Search Google Scholar
    • Export Citation
  • Ghil, M., and Coauthors, 2002a: Advanced spectral methods for climatic time series. Rev. Geophys.,40, 1003, doi:10.1029/ 2000GR000092.

    • Search Google Scholar
    • Export Citation
  • Ghil, M., Y. Feliks, and L. Sushama, 2002b: Baroclinic and barotropic aspects of the wind-driven ocean circulation. Physica D, 167 , 135.

    • Search Google Scholar
    • Export Citation
  • Giordani, H., and S. Planton, 2000: Modeling and analysis of ageostrophic circulation over the Azores oceanic front during the SEMAPHORE experiment. Mon. Wea. Rev, 128 , 22702287.

    • Search Google Scholar
    • Export Citation
  • Haidvogel, D. B., A. R. Robinson, and E. E. Schulman, 1980: The accuracy, efficiency and stability of three numerical models with application to open ocean problems. J. Comput. Phys, 34 , 153.

    • Search Google Scholar
    • Export Citation
  • Haltiner, G. J., and R. T. Williams, 1979: Numerical Prediction and Dynamic Meteorology. 2d ed. John Wiley & Sons, 477 pp.

  • Holton, J. R., 1992: An Introduction to Dynamic Meteorology. 3d ed. Academic Press, 511 pp.

  • Hsu, H., 1987: Study of linear steady atmospheric flow above a finite surface heating. J. Atmos. Sci, 44 , 186199.

  • Jin, F-F., and M. Ghil, 1990: Intraseasonal oscillations in the extratropics: Hopf bifurcation and topographic instabilities. J. Atmos. Sci, 47 , 30073022.

    • Search Google Scholar
    • Export Citation
  • Jin, F-F., J. D. Neelin, and M. Ghil, 1994: El Niño on the Devil's Staircase: Annual subharmonic steps to chaos. Science, 264 , 7072.

    • Search Google Scholar
    • Export Citation
  • Jin, F-F., J. D. Neelin, and M. Ghil, 1996: El Niño/Southern Oscillation and the annual cycle: Subharmonic frequency-locking and aperiodicity. Physica D, 98 , 442465.

    • Search Google Scholar
    • Export Citation
  • Keppenne, C. L., S. Marcus, M. Kimoto, and M. Ghil, 2000: Intraseasonal variability in a two-layer model and observations. J. Atmos. Sci, 57 , 10101028.

    • Search Google Scholar
    • Export Citation
  • Kuo, H. L., 1973: Dynamics of quasi-geostrophic flows and instability theory. Adv. Appl. Mech, 13 , 247330.

  • Kushnir, Y., 1987: Retrograding wintertime low-frequency disturbances over the North Pacific Ocean. J. Atmos. Sci, 44 , 27272742.

  • Kushnir, Y., 1994: Interdecadal variations in North Atlantic sea surface temperature and associated atmospheric conditions. J. Climate, 7 , 141157.

    • Search Google Scholar
    • Export Citation
  • Kushnir, Y., W. A. Robinson, I. Blade, N. M. J. Hall, S. Peng, and R. Sutton, 2002: Atmospheric GCM response to extratropical SST anomalies: Synthesis and evolution. J. Climate, 15 , 22332256.

    • Search Google Scholar
    • Export Citation
  • Lau, N-C., and M. J. Nath, 1987: Frequency dependence of the structure and temporal development of wintertime tropospheric fluctuations—Comparison of a GCM simulation with observations. Mon. Wea. Rev, 115 , 251271.

    • Search Google Scholar
    • Export Citation
  • Lee, T., and P. Cornillon, 1996: Propagation of Gulf Stream meanders between 74° and 70°W. J. Phys. Oceanogr, 26 , 205224.

  • Lott, F., A. W. Robertson, and M. Ghil, 2001: Mountain torques and atmospheric oscillations. Geophys. Res. Lett, 28 , 12071210.

  • Lott, F., A. W. Robertson, and M. Ghil, 2004a: Mountain torques and Northern Hemisphere low-frequency variability. Part I: Hemispheric aspects. J. Atmos. Sci, in press.

    • Search Google Scholar
    • Export Citation
  • Lott, F., A. W. Robertson, and M. Ghil, 2004b: Mountain torques and Northern Hemisphere low-frequency variability. Part II: Regional aspects. J. Atmos. Sci, in press.

    • Search Google Scholar
    • Export Citation
  • Madden, R. A., and P. R. Julian, 1971: Detection of a 40–50-day oscillation in the zonal wind in the tropical Pacific. J. Atmos. Sci, 28 , 702708.

    • Search Google Scholar
    • Export Citation
  • Madden, R. A., and P. R. Julian, 1994: Observations of the 40–50-day tropical oscillation—A review. Mon. Wea. Rev, 122 , 814837.

  • Moron, V., R. Vautard, and M. Ghil, 1998: Trends, interdecadal and interannual oscillations in global sea-surface temperatures. Climate Dyn, 14 , 545569.

    • Search Google Scholar
    • Export Citation
  • Neelin, J. D., and W. Weng, 1999: Analytical prototypes for ocean– atmosphere interaction. Part I: Coupled feedbacks as a sea surface temperature dependent stochastic process. J. Climate, 12 , 697721.

    • Search Google Scholar
    • Export Citation
  • Pedlosky, J., 1987: Geophysical Fluid Dynamics. 2d ed. Springer- Verlag, 710 pp.

  • Plaut, G., and R. Vautard, 1994: Spells of low-frequency oscillations and weather regimes in the Northern Hemisphere. J. Atmos. Sci, 51 , 210236.

    • Search Google Scholar
    • Export Citation
  • Rhines, P. B., 1975: Waves and turbulence on a beta-plane. J. Fluid Mech, 69 , 417443.

  • Robertson, A. W., M. Ghil, and M. Latif, 2000: Interdecadal changes in atmospheric low-frequency variability with and without boundary forcing. J. Atmos. Sci, 57 , 11321140.

    • Search Google Scholar
    • Export Citation
  • Robinson, A. R., Ed.,. 1983: Eddies in Marine Science. Springer- Verlag, 609 pp.

  • Rogers, D. P., 1989: The marine boundary layer in the vicinity of an ocean front. J. Atmos. Sci, 46 , 20442062.

  • Salmon, R., 1998: Lectures on Geophysical Fluid Dynamics. Oxford University Press, 378 pp.

  • Saravanan, R., and J. C. McWilliams, 1995: Multiple equilibria, natural variability, and climate transitions in an idealized ocean– atmosphere model. J. Climate, 8 , 22962323.

    • Search Google Scholar
    • Export Citation
  • Schlichting, H., and K. Gersten, 1999: Boundary-Layer Theory. Springer-Verlag, 799 pp.

  • Shapiro, R., 1970: Smoothing, filtering, and boundary effects. Rev. Geophys. Space Phys, 8 , 359387.

  • Simmons, A. J., J. M. Wallace, and G. W. Branstator, 1983: Barotropic wave propagation and instability, and atmospheric teleconnection patterns. J. Atmos. Sci, 40 , 13631392.

    • Search Google Scholar
    • Export Citation
  • Speich, S., H. Dijkstra, and M. Ghil, 1995: Successive bifurcations in a shallow-water model, applied to the wind-driven ocean circulation. Nonlin. Proc. Geophys, 2 , 241268.

    • Search Google Scholar
    • Export Citation
  • Stommel, H. M., 1965: The Gulf Stream: A Physical and Dynamical Description. 2d ed. University of California Press, 248 pp.

  • Stommel, H. M., and K. Yoshida, Eds.,. 1972: Kuroshio: Physical Aspects of the Japan Current. University of Washington Press, 517 pp.

  • Strong, C. M., F-F. Jin, and M. Ghil, 1993: Intraseasonal variability in a barotropic model with seasonal forcing. J. Atmos. Sci, 50 , 29652986.

    • Search Google Scholar
    • Export Citation
  • Strong, C. M., F-F. Jin, and M. Ghil, 1995: Intraseasonal oscillations in a barotropic model with annual cycle, and their predictability. J. Atmos. Sci, 52 , 26272642.

    • Search Google Scholar
    • Export Citation
  • Sweet, W., R. Fett, J. Kerling, and P. LaViolette, 1981: Air–sea interaction effects in the lower troposphere across the north wall of the Gulf Stream. Mon. Wea. Rev, 109 , 10421052.

    • Search Google Scholar
    • Export Citation
  • Tziperman, E., L. Stone, M. Cane, and H. Jarosh, 1994: El Niño chaos: Overlapping of resonances between the seasonal cycle and the Pacific ocean–atmosphere oscillator. Science, 264 , 7274.

    • Search Google Scholar
    • Export Citation
  • Warner, T. T., M. N. Lakhtakia, J. D. Doyle, and R. A. Pearson, 1990: Marine atmospheric boundary layer circulations forced by Gulf Stream sea surface temperature gradients. Mon. Wea. Rev, 118 , 309323.

    • Search Google Scholar
    • Export Citation
  • Weng, W., and J. D. Neelin, 1999: Analytical prototypes for ocean– atmosphere interaction at midlatitudes. Part II: Mechanisms for coupled gyres modes. J. Climate, 12 , 27572774.

    • Search Google Scholar
    • Export Citation
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