• An, S-I., , and F-F. Jin, 2000: An Eigen analysis of the interdecadal changes in the structure and frequency of ENSO mode. Geophys. Res. Lett., 27 , 25732576.

    • Search Google Scholar
    • Export Citation
  • Battisti, D. S., , and A. C. Hirst, 1989: Interannual variability in the tropical atmosphere–ocean system: Influence of the basic state, ocean geometry, and non-linearity. J. Atmos. Sci., 46 , 16871712.

    • Search Google Scholar
    • Export Citation
  • Bergman, J. W., , H. Hendon, , and K. M. Weickmann, 2001: Intraseasonal air–sea interactions at the onset of El Niño. J. Climate, 14 , 17021718.

    • Search Google Scholar
    • Export Citation
  • Bjerknes, J., 1969: Atmospheric teleconnections from the equatorial Pacific. Mon. Wea. Rev., 97 , 820829.

  • Blanke, B., , J. D. Neelin, , and D. Gutzler, 1997: Estimating the effect of stochastic wind stress forcing on ENSO irregularity. J. Climate, 10 , 14731486.

    • Search Google Scholar
    • Export Citation
  • Boulanger, J. P., , and C. Menkes, 1995: Propagation and reflection of long equatorial waves in the Pacific Ocean during the 1992–1993 El Nino. J. Geophys. Res., 100 , 2504125059.

    • Search Google Scholar
    • Export Citation
  • Boulanger, J. P., , and C. Menkes, 1999: Long equatorial wave reflection in the Pacific Ocean from TOPEX/Poseidon data during the 1992–1998 period. Climate Dyn., 15 , 205225.

    • Search Google Scholar
    • Export Citation
  • Eckert, C., , and M. Latif, 1997: Predictability of a stochastically forced hybrid coupled model of El Niño. J. Climate, 10 , 14881504.

    • Search Google Scholar
    • Export Citation
  • Farrell, B. F., , and P. J. Ioannou, 1996a: Generalized stability theory. Part I: Autonomous operators. J. Atmos. Sci., 53 , 20252040.

  • Farrell, B. F., , and P. J. Ioannou, 1996b: Generalized stability theory. Part II: Nonautonomous operators. J. Atmos. Sci., 53 , 20412053.

    • Search Google Scholar
    • Export Citation
  • Fedorov, A. V., 2002: The response of the coupled tropical ocean–atmosphere to westerly wind bursts. Quart. J. Roy. Meteor. Soc., 128 , 123.

    • Search Google Scholar
    • Export Citation
  • Fedorov, A. V., , and S. G. H. Philander, 2000: Is El Niño changing? Science, 288 , 19972002.

  • Gill, A., 1980: Some simple solutions for the heat-induced tropical circulation. Quart. J. Roy. Meteor. Soc., 106 , 447462.

  • Gill, A., 1982: The Tropics. Atmosphere–Ocean Dynamics. Academic Press, 429–491.

  • Gill, A., , and E. M. Rasmusson, 1983: The 1982–1983 climate anomaly in the equatorial Pacific. Nature, 305 , 229234.

  • Kalnay, E., and Coauthors. 1996: NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77 , 437441.

  • Kessler, W. S., 2001: EOF representation of the Madden–Julian oscillation and its connection with ENSO. J. Climate, 14 , 30553061.

  • Kessler, W. S., , M. J. McPhaden, , and K. M. Weickmann, 1995: Forcing of intraseasonal Kelvin waves in the equatorial Pacific. J. Geophys. Res., 100 , 1061310631.

    • Search Google Scholar
    • Export Citation
  • Kirtman, B. P., , and P. S. Schopf, 1998: Decadal variability in ENSO predictability and prediction. J. Climate, 11 , 28042822.

  • Kleeman, R., 1989: A modelling study of the effect of the Andean mountains on the summertime circulation of tropical South America. J. Atmos. Sci., 46 , 33443362.

    • Search Google Scholar
    • Export Citation
  • Kleeman, R., 1991: A simple model of the atmospheric response to ENSO sea surface temperature anomalies. J. Atmos. Sci., 48 , 318.

  • Kleeman, R., 1993: On the dependence of hindcast skill on ocean thermodynamics in a coupled ocean–atmosphere model. J. Climate, 6 , 20122033.

    • Search Google Scholar
    • Export Citation
  • Kleeman, R., , and A. M. Moore, 1997: A theory for the limitations of ENSO predictability due to stochastic atmospheric transients. J. Atmos. Sci., 54 , 753767.

    • Search Google Scholar
    • Export Citation
  • Lau, K. M., 1985: Elements of a stochastic dynamical theory of the long-term variability of the El Niño/Southern Oscillation. J. Atmos. Sci., 42 , 15521558.

    • Search Google Scholar
    • Export Citation
  • Lau, K. M., , and P. H. Chan, 1986: The 40–50 day oscillation and the El Niño/Southern Oscillation: A new perspective. Bull. Amer. Meteor. Soc., 67 , 533534.

    • Search Google Scholar
    • Export Citation
  • McCreary, J. P., 1983: A model of tropical ocean–atmosphere interaction. Mon. Wea. Rev., 111 , 370387.

  • McPhaden, J. M., 1999: Genesis and evolution of the 1997–98 El Niño. Science, 283 , 950954.

  • McPhaden, J. M., and Coauthors. 1998: The Tropical Ocean–Global Atmosphere system: A decade of progress. J. Geophys. Res., 103 , 1416914240.

    • Search Google Scholar
    • Export Citation
  • Miller, L., , R. Cheney, , and B. C. Douglas, 1988: GEOSAT altimeter observations of Kelvin waves and the 1986–87 El Niño. Science, 239 , 5254.

    • Search Google Scholar
    • Export Citation
  • Moore, A. M., , and R. Kleeman, 1996: The dynamics of error growth and predictability in a coupled model of ENSO. Quart. J. Roy. Meteor. Soc., 122 , 14051446.

    • Search Google Scholar
    • Export Citation
  • Moore, A. M., , and R. Kleeman, 1997: The singular vectors of a coupled ocean–atmosphere model of ENSO. Quart. J. Roy. Meteor. Soc., 123 , 953981.

    • Search Google Scholar
    • Export Citation
  • Moore, A. M., , and R. Kleeman, 1999a: Stochastic forcing of ENSO by the intraseasonal oscillation. J. Climate, 12 , 11991220.

  • Moore, A. M., , and R. Kleeman, 1999b: The non-normal nature of El Niño and intraseasonal variability. J. Climate, 12 , 29652982.

  • Moore, A. M., , and R. Kleeman, 2001: The Differences between the optimal perturbations of coupled models of ENSO. J. Climate, 14 , 138163.

    • Search Google Scholar
    • Export Citation
  • Moore, D. W., , and S. G. H. Philander, 1977: Modelling of the tropical ocean circulation. The Sea, Vol. 6, E. A. Goldberg et al., Eds., Marine Modeling, Vol. 6, Wiley and Sons, 319–361.

    • Search Google Scholar
    • Export Citation
  • Penland, C., 1996: A stochastic model of IndoPacific sea surface temperature anomalies. Physica D, 98 , 534558.

  • Penland, C., , and L. Matrosova, 1994: A balance condition for stochastic numerical models with application to the El Niño–Southern Oscillation. J. Climate, 7 , 13521371.

    • Search Google Scholar
    • Export Citation
  • Penland, C., , and L. P. D. Sardeshmukh, 1995: The optimal growth of tropical sea surface temperature anomalies. J. Climate, 8 , 19992024.

    • Search Google Scholar
    • Export Citation
  • Penland, C., , M. Flügel, , and P. Chang, 2000: Identification of dynamical regimes in an intermediate coupled ocean–atmosphere model. J. Climate, 13 , 21052115.

    • Search Google Scholar
    • Export Citation
  • Picaut, J., , and T. Delcroix, 1995: Equatorial wave sequence associated with warm pool displacements during the 1986–1989 El Niño–La Niña. J. Geophys. Res., 100 , 1839318408.

    • Search Google Scholar
    • Export Citation
  • Rasmusson, E. M., , and T. H. Carpenter, 1982: Variations in tropical sea surface temperature and surface wind fields associated with the Southern Oscillation/El Niño. Mon. Wea. Rev., 110 , 354384.

    • Search Google Scholar
    • Export Citation
  • Reynolds, R. W., , and T. M. Smith, 1994: Improved global sea surface temperature analyses using optimal interpolation. J. Climate, 7 , 929948.

    • Search Google Scholar
    • Export Citation
  • Roulston, M. S., , and J. D. Neelin, 2000: The response of an ENSO model to climate noise, weather noise, and intraseasonal forcing. Geophys. Res. Lett., 27 , 37233726.

    • Search Google Scholar
    • Export Citation
  • Smith, T. M., , R. W. Reynolds, , R. E. Livezy, , and D. C. Stokes, 1996: Reconstruction of historical sea surface temperatures using empirical orthogonal functions. J. Climate, 9 , 14031420.

    • Search Google Scholar
    • Export Citation
  • Strang, G., 1988: Linear Algebra and Its Applications. Harcourt Brace Jovanovich College, 505 pp.

  • Suarez, M. J., , and P. S. Schopf, 1988: A delayed action oscillator for ENSO. J. Atmos. Sci., 45 , 32833287.

  • Thompson, C. J., , and D. S. Battisti, 2000: A linear stochastic dynamical model of ENSO. Part I: Model development. J. Climate, 13 , 28182832.

    • Search Google Scholar
    • Export Citation
  • Trefethen, L. N., 1997: Pseudospectra of linear operators. SIAM Rev., 39 , 383406.

  • Van Oldenburgh, G. J., 2000: What caused the onset of the 1997–98 El Niño? Mon. Wea. Rev., 128 , 26012607.

  • Vialard, J., , C. Menkes, , J-P. Boulanger, , P. Delecluse, , E. Guilyardi, , M. J. McPhaden, , and G. Madec, 2001: A model study of oceanic mechanisms affecting equatorial Pacific sea surface temperature during the 1997–98 El Niño. J. Phys. Oceanogr., 31 , 16491675.

    • Search Google Scholar
    • Export Citation
  • Wang, C., , and R. H. Weisenberg, 2000: The 1997–98 El Niño evolution relative to previous El Niño events. J. Climate, 13 , 488501.

  • Webster, P. J., 1972: Response of the tropical atmosphere to local, steady forcing. Mon. Wea. Rev., 100 , 518541.

  • Webster, P. J., , and T. N. Palmer, 1997: The past and the future of El Niño. Nature, 390 , 562564.

  • Zebiak, S. E., 1989: On the 30–60-day oscillation and the prediction of El Niño. J. Climate, 2 , 13811387.

  • Zebiak, S. E., , and M. A. Cane, 1987: A model of El Niño–Southern Oscillation. Mon. Wea. Rev., 115 , 22622278.

  • Zhang, C., , and J. Gottschalck, 2002: SST anomalies of ENSO and the Madden–Julian oscillation in the equatorial Pacific. J. Climate, 15 , 24292445.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 101 101 3
PDF Downloads 16 16 5

The Response of a Coupled Model of ENSO to Observed Estimates of Stochastic Forcing

View More View Less
  • 1 Program in Atmospheric and Oceanic Sciences and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado
  • | 2 Courant Institute for Mathematical Sciences, New York University, New York, New York
© Get Permissions Rent on DeepDyve
Restricted access

Abstract

In this work the role that observed intraseasonal atmospheric variability may play in controlling and maintaining ENSO variability is examined. To this end, an asymptotically stable intermediate coupled model of El Niño–Southern Oscillation (ENSO) is forced with observed estimates of stochastic forcing, which are defined to be the part of the atmospheric variability that is apparently independent of the ocean circulation. The stochastic forcing (SF) was estimated from 51 yr (1950–2000) of NCEP–NCAR reanalyses of surface winds and net surface heat flux, 32 yr (1950–81) of reconstructed sea surface temperatures (SST), and 19 yr (1982–2000) of Reynolds SST in the tropical Pacific. The deterministic component of the surface wind and heat flux anomalies that can be linearly related to SST anomalies was estimated using the singular value decomposition of the covariance between the anomaly fields, and was then removed from the atmospheric anomaly fields to recover the stochastic component of the ocean surface forcing. Principal component analysis reveals that the stochastic component has no preferred mode of variability, exhibits decorrelation times of a few days, and has a spectrum that is indistinguishable from red noise. A 19-yr stochastically forced coupled model integration qualitatively shows some similarities with the observed equatorial SST. The robustness of this result is checked by performing different sensitivity experiments. The model mostly exhibits a linear (and nonnormal) response to the low-frequency tail of SF. Using the ideas of generalized linear stability theory, the dynamically important contributions of the SF are isolated, and it is shown that most of the variability in the stochastically forced model solution is produced by stochastically induced Kelvin waves forced in the western and central Pacific. Moreover, the two most dynamically important patterns of stochastic forcing (which account for 71% of the expected variance in the model response) describe eastward propagation of the forcing similar to the MJO. The results of this study support the hypothesis that a significant fraction of ENSO variability may be due to SF, and suggest that a better understanding of the influence of SF on the ocean surface in the western/central Pacific may be required in order to understand the predictability of ENSO.

Corresponding author address: Dr. Javier Zavala-Garay, Div. of Meteorology and Phys. Oceanography, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Cswy., Miami, FL 33149-1098. Email: javier@orca.rsmas.miami.edu

Abstract

In this work the role that observed intraseasonal atmospheric variability may play in controlling and maintaining ENSO variability is examined. To this end, an asymptotically stable intermediate coupled model of El Niño–Southern Oscillation (ENSO) is forced with observed estimates of stochastic forcing, which are defined to be the part of the atmospheric variability that is apparently independent of the ocean circulation. The stochastic forcing (SF) was estimated from 51 yr (1950–2000) of NCEP–NCAR reanalyses of surface winds and net surface heat flux, 32 yr (1950–81) of reconstructed sea surface temperatures (SST), and 19 yr (1982–2000) of Reynolds SST in the tropical Pacific. The deterministic component of the surface wind and heat flux anomalies that can be linearly related to SST anomalies was estimated using the singular value decomposition of the covariance between the anomaly fields, and was then removed from the atmospheric anomaly fields to recover the stochastic component of the ocean surface forcing. Principal component analysis reveals that the stochastic component has no preferred mode of variability, exhibits decorrelation times of a few days, and has a spectrum that is indistinguishable from red noise. A 19-yr stochastically forced coupled model integration qualitatively shows some similarities with the observed equatorial SST. The robustness of this result is checked by performing different sensitivity experiments. The model mostly exhibits a linear (and nonnormal) response to the low-frequency tail of SF. Using the ideas of generalized linear stability theory, the dynamically important contributions of the SF are isolated, and it is shown that most of the variability in the stochastically forced model solution is produced by stochastically induced Kelvin waves forced in the western and central Pacific. Moreover, the two most dynamically important patterns of stochastic forcing (which account for 71% of the expected variance in the model response) describe eastward propagation of the forcing similar to the MJO. The results of this study support the hypothesis that a significant fraction of ENSO variability may be due to SF, and suggest that a better understanding of the influence of SF on the ocean surface in the western/central Pacific may be required in order to understand the predictability of ENSO.

Corresponding author address: Dr. Javier Zavala-Garay, Div. of Meteorology and Phys. Oceanography, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Cswy., Miami, FL 33149-1098. Email: javier@orca.rsmas.miami.edu

Save