Oceanic Influence on North Atlantic Climate Variability

Peili Wu Hadley Centre for Climate Prediction and Research, Met Office, Bracknell, Berkshire, United Kingdom

Search for other papers by Peili Wu in
Current site
Google Scholar
PubMed
Close
and
Chris Gordon Hadley Centre for Climate Prediction and Research, Met Office, Bracknell, Berkshire, United Kingdom

Search for other papers by Chris Gordon in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

The role of ocean dynamics in low-frequency climate variability in the North Atlantic is investigated using the Hadley Centre coupled climate model (HadCM3). An ensemble of three 100-yr experiments, in which low-frequency damping is applied below 500 m in the North Atlantic Ocean, is compared with the HadCM3 control integration that shows realistic variability in both SST and the North Atlantic Oscillation (NAO). All three damped runs have shown significantly reduced SST and NAO variability on decadal timescales, while interannual variability remains unchanged or even increased. A significance test of the ensemble mean low-frequency variance, against any three random 100-yr segments from the full HadCM3 control run, gives a confidence level above 95%. It is therefore concluded that ocean dynamics does play an active role in low-frequency variability of both the SST and the NAO at decadal and interdecadal timescales.

By comparing mechanisms in the control and damped experiments it is also possible to find out how ocean dynamics affect the long-term variability of the SST and the NAO. The deep ocean damping leads to reduced variability of the meridional overturning and its associated northward heat transport, as well as constraining the position and strength changes of the Gulf Stream/North Atlantic Current (NAC) system. The study has also confirmed that the surface tripole mode is largely an ocean response to NAO forcing. Ocean dynamics comes into play through a Gulf Stream mode in the autumn forcing of the winter NAO. By constraining the Gulf Stream/NAC, it is possible to effectively reduce the low-frequency variability of SST and associated surface heat flux, and therefore cause the NAO to lose its red spectrum.

Corresponding author address: Dr. Peili Wu, Hadley Centre for Climate Prediction and Research, Met Office, London Road, Bracknell, Berkshire RG12 2SY, United Kingdom. Email: peili.wu@metoffice.com

Abstract

The role of ocean dynamics in low-frequency climate variability in the North Atlantic is investigated using the Hadley Centre coupled climate model (HadCM3). An ensemble of three 100-yr experiments, in which low-frequency damping is applied below 500 m in the North Atlantic Ocean, is compared with the HadCM3 control integration that shows realistic variability in both SST and the North Atlantic Oscillation (NAO). All three damped runs have shown significantly reduced SST and NAO variability on decadal timescales, while interannual variability remains unchanged or even increased. A significance test of the ensemble mean low-frequency variance, against any three random 100-yr segments from the full HadCM3 control run, gives a confidence level above 95%. It is therefore concluded that ocean dynamics does play an active role in low-frequency variability of both the SST and the NAO at decadal and interdecadal timescales.

By comparing mechanisms in the control and damped experiments it is also possible to find out how ocean dynamics affect the long-term variability of the SST and the NAO. The deep ocean damping leads to reduced variability of the meridional overturning and its associated northward heat transport, as well as constraining the position and strength changes of the Gulf Stream/North Atlantic Current (NAC) system. The study has also confirmed that the surface tripole mode is largely an ocean response to NAO forcing. Ocean dynamics comes into play through a Gulf Stream mode in the autumn forcing of the winter NAO. By constraining the Gulf Stream/NAC, it is possible to effectively reduce the low-frequency variability of SST and associated surface heat flux, and therefore cause the NAO to lose its red spectrum.

Corresponding author address: Dr. Peili Wu, Hadley Centre for Climate Prediction and Research, Met Office, London Road, Bracknell, Berkshire RG12 2SY, United Kingdom. Email: peili.wu@metoffice.com

Save
  • Battisti, D. S., U. S. Bhatt, and M. A. Alexander, 1995: A modeling study of the interannual variability in wintertime North Atlantic Ocean. J. Climate, 8 , 30673083.

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

  • Cattle, H., and J. Crossley, 1995: Modelling Arctic climate-change. Philos. Trans. Roy. Soc. London, 352A , 201213.

  • Cayan, D., 1992: Latent and sensible heat flux anomalies over the Northern Oceans: Driving the sea surface temperature. J. Phys. Oceanogr., 22 , 859881.

    • Search Google Scholar
    • Export Citation
  • Christoph, M., U. Ulbrich, J. M. Oberhuber, and E. Roeckner, 2000: The role of ocean dynamics for low-frequency fluctuations of the NAO in a coupled ocean–atmosphere GCM. J. Climate, 13 , 25362549.

    • Search Google Scholar
    • Export Citation
  • Cooper, C., and C. Gordon, 2002: North Atlantic oceanic decadal variability in the Hadley Centre coupled model. J. Climate, 15 , 4572.

    • Search Google Scholar
    • Export Citation
  • Curry, R. G., and M. S. McCartney, 2001: Ocean gyre circulation changes associated with the North Atlantic Oscillation. J. Phys. Oceanogr., 31 , 33743400.

    • Search Google Scholar
    • Export Citation
  • Curry, R. G., and T. M. Joyce, 1998: Oceanic transport of subpolar climate signals to mid-depth subtropical waters. Nature, 391 , 575577.

    • Search Google Scholar
    • Export Citation
  • Delworth, T., S. Manabe, and R. J. Stouffer, 1993: Interdecadal variations of the thermohaline circulation in a coupled ocean–atmosphere model. J. Climate, 6 , 19932011.

    • 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
  • Dickson, R., J. Lazier, J. Meinke, P. Rhines, and J. Swift, 1996: Long-term co-ordinated changes in the convective activity of the North Atlantic. Progress in Oceanography, Vol. 38, Pergamon, 241–295.

    • Search Google Scholar
    • Export Citation
  • Dong, B., R. Sutton, S. Jewson, A. O'Neill, and J. Slingo, 2000: Predictable winter climate in the North Atlantic sector during the 1997–1999 ENSO cycle. Geophys. Res. Lett., 27 , 985988.

    • Search Google Scholar
    • Export Citation
  • Frankignoul, C., G. Coëtlogon, and T. M. Joyce, 2001: Gulf Stream variability and ocean–atmosphere interactions. J. Phys. Oceanogr., 31 , 35163529.

    • Search Google Scholar
    • Export Citation
  • Gordon, C., C. Cooper, C. A. Senior, H. Banks, J. M. Gregory, T. C. Johns, J. F. B. Mitchell, and R. A. Wood, 2000: The simulation of SST, sea ice extents and ocean heat transports in a version of the Hadley Centre coupled model without flux adjustments. Climate Dyn., 16 , 147168.

    • Search Google Scholar
    • Export Citation
  • Hall, M. M., and H. L. Bryden, 1982: Direct estimates and mechanisms of ocean heat transport. Deep-Sea Res., 29 , 339359.

  • Halliwell, G. R., 1998: Simulation of North Atlantic decadal/multidecadal winter SST anomalies driven by basin-scale atmospheric circulation anomalies. J. Phys. Oceanogr., 28 , 521.

    • Search Google Scholar
    • Export Citation
  • Hasselmann, K., 1976: Stochastic climate models. Part I: Theory. Tellus, 28 , 473485.

  • Hurrell, J. W., 1995: Decadal trends in the North Atlantic Oscillation: Regional temperatures and precipitation. Science, 269 , 676679.

    • Search Google Scholar
    • Export Citation
  • Joyce, T. M., C. Deser, and M. Spall, 2000: The relation between decadal variability of subtropical mode water and the North Atlantic Oscillation. J. Climate, 13 , 25502569.

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

    • Search Google Scholar
    • Export Citation
  • Latif, M., and T. P. Barnett, 1994: Causes of decadal climate variability over the North Pacific and North America. Science, 266 , 634637.

    • Search Google Scholar
    • Export Citation
  • Levitus, S., and T. B. Boyer, 1994: Temperature. Vol. 4, World Ocean Atlas 1994, NOAA Atlas NESDIS 4, 117 pp.

  • Luksch, U., 1996: Simulation of North Atlantic low-frequency SST variability. J. Climate, 9 , 20832092.

  • Macdonald, A. M., and C. Wunsch, 1996: An estimate of global ocean circulation and heat fluxes. Nature, 382 , 436439.

  • Marshall, J., H. Johnson, and J. Goodman, 2001: A study of the interaction of the North Atlantic oscillation with ocean circulation. J. Climate, 14 , 13991421.

    • Search Google Scholar
    • Export Citation
  • Mehta, V., M. Suarez, J. Manganello, and T. Delworth, 2000: Oceanic influence on the North Atlantic Oscillation and associated Northern Hemisphere climate variations: 1959–1993. Geophys. Res. Lett., 27 , 121124.

    • Search Google Scholar
    • Export Citation
  • Palmer, T. N., and Z. Sun, 1985: A modelling and observational study of the relationship between sea surface temperature in the north-west Atlantic and the atmospheric general circulation. Quart. J. Roy. Meteor. Soc., 111 , 947975.

    • Search Google Scholar
    • Export Citation
  • Pope, V. D., M. L. Gallani, P. R. Rowntree, and R. A. Stratton, 2000: The impact of new physical parametrizations in the Hadley Centre climate model: HadAM3. Climate Dyn., 16 , 123146.

    • Search Google Scholar
    • Export Citation
  • Rayner, N. A., D. E. Parker, P. Frich, E. B. Horton, C. K. Folland, and L. V. Alexander, 2000: SST and sea-ice fields for ERA40. Proc. Second WCRP Int. Conf. on Reanalyses, Wokefield Park, Reading, United Kingdom, WCRP/WMO, WCRP-109, WMO/TD-985, 23–27.

    • Search Google Scholar
    • Export Citation
  • Rodwell, M. J., and C. K. Folland, 2002: Atlantic air–sea interaction and seasonal predictability. Quart. J. Roy. Meteor. Soc., in press.

    • Search Google Scholar
    • Export Citation
  • Rodwell, M. J., D. P. Rowell, and C. K. Folland, 1999: Oceanic forcing of the wintertime North Atlantic Oscillation and European climate. Nature, 398 , 320323.

    • Search Google Scholar
    • Export Citation
  • Seager, R., Y. Kushnir, M. Visbeck, N. Naik, J. Miller, G. Krahmann, and H. Cullen, 2000: Causes of Atlantic Ocean climate variability between 1958 and 1998. J. Climate, 13 , 28452862.

    • Search Google Scholar
    • Export Citation
  • Semtner, A. J., 1976: A model for the thermodynamic growth of sea ice in numerical investigations of climate. J. Phys. Oceanogr., 6 , 379389.

    • Search Google Scholar
    • Export Citation
  • Sutton, R. T., and M. R. Allen, 1997: Decadal predictability in North Atlantic sea surface temperature and climate. Nature, 388 , 563567.

    • Search Google Scholar
    • Export Citation
  • Visbeck, M., H. Cullen, G. Krahmann, and N. Naik, 1998: An ocean model's response to North Atlantic Oscillation–like wind forcing. Geophys. Res. Lett., 25 , 45214524.

    • Search Google Scholar
    • Export Citation
  • Watanabe, M., and M. Kimoto, 2000: On the persistence of decadal SST anomalies in the North Atlantic. J. Climate, 13 , 30173028.

  • Wood, R. A., A. B. Keen, J. F. B. Mitchell, and J. M. Gregory, 1999: Changing spatial structure of the thermohaline circulation in response to atmospheric CO2 forcing in a climate model. Nature, 399 , 572575.

    • Search Google Scholar
    • Export Citation
  • Wright, D. K., and C. Gordon, 1997: The positioning of the North Atlantic current. Ocean Applications Tech. Note 14, Met Office, Bracknell, Berkshire, United Kingdom, 34 pp.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 245 48 4
PDF Downloads 83 19 2