• Allen, M. R., and A. W. Robertson, 1996: Distinguishing modulated oscillations from coloured noise in multivariate datasets. Climate Dyn.,12, 775–784.

  • Auer, S. J., 1987: Five-year climatological survey of the Gulf Stream system and its associated rings. J. Geophys. Res.,92, 11 709–11 726.

  • Cessi, P., and G. R. Ierley, 1995: Symmetry-breaking multiple equilibria in quasigeostrophic, wind-driven flows. J. Phys. Oceanogr.,25, 1196–1205.

  • Dijkstra, H. A., and C. Katsman, 1997: Temporal variability of the wind-driven quasi-geostrofic double gyre ocean circulation: Basic bifurcation diagrams. Geophys. Astrophys. Fluid Dyn.,85, 195–232.

  • ——, and M. J. Molemaker, 1999: Imperfections of the North-Atlantic wind-driven ocean circulation: Continental geometry and windstress shape. J. Mar. Res.,57, 1–28.

  • ——, ——, A. J. Van der Ploeg, and E. F. F. Botta, 1995: An efficient code to compute nonparallel flows and their linear stability. Comput. Fluids,24, 415–434.

  • Fuglister, F. C., 1972: Cyclonic rings formed by the Gulf Stream 1965–1966. Studies in Physical Oceanography, A. L. Gordon, Ed., Vol. 1, Gordon and Breach, 137–168.

  • Golubitsky, M., and D. Schaeffer, 1985: Singularities and Groups in Bifurcation Theory. Springer-Verlag, 533 pp.

  • Greenslade, D., D. Chelton, and M. Schlax, 1997: The midlatitude resolution capability of sea level fields constructed from single and multiple satellite altimeter datasets. J. Atmos. Oceanic Technol.,14, 849–870.

  • Hall, M., and N. Fofonoff, 1993: Downstream development of the Gulf Stream from 68° to 55°W. J. Phys. Oceanogr.,23, 225–249.

  • Hansen, D., 1970: Gulf Stream meanders between Cape Hatteras and the Grand Banks. Deep-Sea Res.,17, 495–511.

  • Hasselmann, K., 1976: Stochastic climate models. Part I. Theory. Tellus,28, 473–485.

  • ——, 1988: PIPs and POPs: The reduction of complex dynamical systems using principal interaction and oscillation patterns. J. Geophys. Res.,93, 11 015–11 021.

  • Jiang, S., F. Jin, and M. Ghil, 1995: Multiple equilibria and aperiodic solutions in a wind-driven double gyre, shallow water model. J. Phys. Oceanogr.,25, 764–786.

  • Johns, W., T. Shay, J. Bane, and D. Watts, 1995: Gulf Stream structure, transport and recirculation near 68°W. J. Geophys. Res.,100, 817–838.

  • Jones, M., M. Allen, T. Guymer, and M. Saunders, 1998: Correlations between altimetric sea surface height and radiometric sea surface temperature in the South Atlantic. J. Geophys. Res.,103, 8073–8087.

  • Kaese, R. H., and W. Krauss, 1996: The Gulf Stream, the North Atlantic Current, and the origin of the Azores Current. The Warmwatersphere of the North Atlantic Ocean, W. Krauss, Ed., Borntraeger, 291–337.

  • Katsman, C., H. Dijkstra, and S. Drijfhout, 1998: The rectification of wind-driven flow due to its instabilities. J. Mar. Res.,56, 559–587.

  • Kelly, K. A., M. J. Caruso, S. Singh, and B. Qiu, 1996: Observations of atmosphere–ocean coupling in midlatitude western boundary currents. J. Geophys. Res.,101, 6295–6312.

  • ——, S. Singh, and R. Huang, 1999: Seasonal variations of sea surface height in the Gulf Stream region. J. Phys. Oceanogr.,29, 313–327.

  • Lee, T., and P. Cornillon, 1995: Temporal variation of meandering intensity and domain-wide lateral oscillations of the Gulf Stream. J. Geophys. Res.,100 (C7), 13 603–13 613.

  • ——, and ——, 1996: Propagation and growth of Gulf Stream meanders between 75° and 45°W. J. Phys. Oceanogr.,26, 225–241.

  • Maul, G., P. DeWitt, A. Yanaway, and S. Baig, 1978: Geostationary satellite observations of Gulf Stream meanders: Infrared measurements and time series analysis. J. Geophys. Res.,83 (C12), 6123–6135.

  • Plaut, G., and R. Vautard, 1994: Spells of low-frequency oscillations and weather regimes in the Northern Hemisphere. J. Atmos. Sci.,51, 210–236.

  • Preisendorfer, R. W., 1988: Principal Component Analysis in Meteorology and Oceanography. Elsevier, 425 pp.

  • Qiu, B., 1994: Determining the mean Gulf Stream and its recirculations through combining hydrographic and altimetric data. J. Geophys. Res.,99, 951–962.

  • Reynolds, R. W., and T. M. Smith, 1994: Improved global sea surface temperature analysis using optimum interpolation. J. Climate,7, 929–948.

  • Richardson, P., 1985: Average velocity and transport of the Gulf Stream near 55°W. J. Mar. Res.,43, 83–111.

  • Semtner, A. J. J., and R. Chervin, 1992: Ocean general circulation from a global eddy-resolving model. J. Geophys. Res.,97, 5493–5550.

  • Speich, S., H. Dijkstra, and M. Ghil, 1995: Successive bifurcations in a shallow-water model applied to the wind-driven ocean circulation. Nonl. Proc. Geophys.,2, 241–268.

  • Stammer, D., R. Tokmakian, A. Semtner, and C. Wunsch, 1996: How well does a 1/4° global circulation model simulate large-scale oceanic observations? J. Geophys. Res.,101, 25 779–25 811.

  • Trenberth, K., J. Olson, and W. Large, 1989: A global ocean wind stress climatology based on ECMWF analyses. NCAR Tech. Note TN-338+Str, 93 pp. [Available from National Center for Atmospheric Research, 1850 Table Mesa Dr., Boulder, CO 80307.].

  • Vautard, R., and M. Ghil, 1989: Singular spectrum analysis in nonlinear dynamics with applications to paleoclimatic time series. Physica D,35, 395–424.

  • ——, P. Yiou, and M. Ghil, 1992: Singular spectrum analysis: A toolkit for short, noisy chaotic signals. Physica D,58, 95–126.

  • Vazquez, J., 1993: Observations on the long-period variability of the Gulf Stream downstream of Cape Hatteras. J. Geophys. Res.,98 (C11), 20 133–20 147.

  • ——, V. Zlotnicki, and L.-L. Fu, 1990: Sea level variabilities in the Gulf Stream between Cape Hatteras and 50° W: A Geosat study. J. Geophys. Res.,95 (C10), 17 957–17 964.

  • von Storch, H., G. Buerger, R. Schnur, and J.-S. von Storch, 1995: Principal oscillation patterns: A review. J. Climate,8, 377–400.

  • Vossepoel, F., 1995: Processing of altimeter and infrared radiometer data for eddy detection in the Gulf Stream. M.S. thesis, Faculty of Aerospace Engineering, Delft University of Technology, Delft, Netherlands, 133 + viii pp.

  • Wang, L., and C. Koblinsky, 1995: Low-frequency variability in regions of the Kuroshio Extension and the Gulf Stream. J. Geophys. Res.,100 (C9), 18 313–18 331.

  • ——, and ——, 1996: Annual variability of the subtropical recirculations in the North Atlantic and North Pacific: A TOPEX/Poseidon study. J. Phys. Oceanogr.,26, 2462–2479.

  • ——, ——, and S. Howden, 1998: Annual and intra-annual sea level variability in the region of the Kuroshio Extension from TOPEX/Poseidon and Geosat altimetry. J. Phys. Oceanogr.,28, 692–711.

  • Weare, B. C., and J. N. Nasstrom, 1982: Examples of extended empirical orthogonal function analyses. Mon. Wea. Rev.,110, 481–485.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 1 1 1
PDF Downloads 1 1 1

Physics of the 9-Month Variability in the Gulf Stream Region: Combining Data and Dynamical Systems Analyses

View More View Less
  • 1 Institute for Marine and Atmospheric Research Utrecht, Department of Physics and Astronomy, Utrecht University, Utrecht, Netherlands
Restricted access

Abstract

Using nonseasonal altimeter data and SST observations of the North Atlantic, and more specifically the Gulf Stream region, dominant patterns of variability are determined using multivariate time series analyses. A statistically significant propagating mode of variability with a timescale close to 9 months is found, the latter timescale corresponding to dominant variability found in earlier studies. In addition, output from a high resolution simulation of the Parallel Ocean Climate Model (POCM) is analyzed, which also displays variability on a timescale of 9 months, although not statistically significant at the 95% confidence level. The vertical structure of this 9-month mode turns out to be approximately equivalent barotropic. Following the idea that this mode is due to internal ocean dynamics, steady flow patterns and their instabilities are determined within a barotropic ocean model of the North Atlantic using techniques of numerical bifurcation theory. Within this model, there appear to be two different mean flow paths of the Gulf Stream, both of which become unstable to oscillatory modes. For reasonable values of the parameters, an oscillatory instability having a timescale of 9 months is found. The connection between results from the bifurcation analysis, from the analysis of the observations, and from the analysis of the POCM output is explored in more detail and leads to the conjecture that the 9-month variability is related to a barotropic instability of the wind-driven gyres.

Corresponding author address: Henk A. Dijkstra, Institute for Marine and Atmospheric Research Utrecht, Department of Physics and Astronomy, Utrecht University, Princetonplein 5, 3584 CC Utrecht, Netherlands.

Email: dijkstra@phys.uu.nl

Abstract

Using nonseasonal altimeter data and SST observations of the North Atlantic, and more specifically the Gulf Stream region, dominant patterns of variability are determined using multivariate time series analyses. A statistically significant propagating mode of variability with a timescale close to 9 months is found, the latter timescale corresponding to dominant variability found in earlier studies. In addition, output from a high resolution simulation of the Parallel Ocean Climate Model (POCM) is analyzed, which also displays variability on a timescale of 9 months, although not statistically significant at the 95% confidence level. The vertical structure of this 9-month mode turns out to be approximately equivalent barotropic. Following the idea that this mode is due to internal ocean dynamics, steady flow patterns and their instabilities are determined within a barotropic ocean model of the North Atlantic using techniques of numerical bifurcation theory. Within this model, there appear to be two different mean flow paths of the Gulf Stream, both of which become unstable to oscillatory modes. For reasonable values of the parameters, an oscillatory instability having a timescale of 9 months is found. The connection between results from the bifurcation analysis, from the analysis of the observations, and from the analysis of the POCM output is explored in more detail and leads to the conjecture that the 9-month variability is related to a barotropic instability of the wind-driven gyres.

Corresponding author address: Henk A. Dijkstra, Institute for Marine and Atmospheric Research Utrecht, Department of Physics and Astronomy, Utrecht University, Princetonplein 5, 3584 CC Utrecht, Netherlands.

Email: dijkstra@phys.uu.nl

Save