On the Mechanism of North Atlantic Decadal Variability

F. M. Selten Royal Netherlands Meteorological Institute, De Bilt, the Netherlands

Search for other papers by F. M. Selten in
Current site
Google Scholar
PubMed
Close
,
R. J. Haarsma Royal Netherlands Meteorological Institute, De Bilt, the Netherlands

Search for other papers by R. J. Haarsma in
Current site
Google Scholar
PubMed
Close
, and
J. D. Opsteegh Royal Netherlands Meteorological Institute, De Bilt, the Netherlands

Search for other papers by J. D. Opsteegh in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

North Atlantic decadal climate variability is studied with a coupled atmosphere–ocean–sea ice model (ECBILT). After having reached an approximate statistical equilibrium in coupled mode without applying flux corrections, a subsequent 1000-yr integration is performed and analyzed. Compared to the current climate, the surface temperatures are 2°C warmer in the Tropics to almost 8°C warmer in the polar regions.

The covariability between the atmosphere and ocean is explored by performing a singular value decomposition (SVD) of boreal winter SST anomalies and 800-hPa geopotential height anomalies. The first SVD pair shows a red variance spectrum in SST and a white spectrum in 800-hPa height. The second mode shows a peak in both spectra at a timescale of about 16–18 yr. The geopotential height pattern is the model’s equivalent of the North Atlantic oscillation (NAO) pattern; the SST anomaly pattern is a north–south oriented dipole.

Additional experiments have revealed that the decadal oscillation in ECBILT is basically an oscillation in the subsurface of the ocean. The oscillation is excited by anomalies in the atmospheric NAO pattern, both through anomalous surface heat fluxes and anomalous Ekman transports. The atmospheric response to the SST anomaly enhances the oscillation and slightly modifies it, but is not essential. The atmospheric response consists primarily of a local surface air temperature adjustment to the SST anomaly. An important element in the physical mechanism of the oscillation is the geostrophic response of the ocean circulation to the forced temperature anomalies creating surface salinity anomalies through anomalous horizontal advection. These salinity anomalies influence the convective activity in the area of the temperature anomaly such as to break down the subsurface temperature anomaly. Both temperature and salinity anomalies slowly propagate eastward at a rate consistent with the mean current.

Corresponding author address: Frank M. Selten, Royal Netherlands Meteorological Institute, P.O. Box 201, 3730 AE De Bilt, the Netherlands.

Email: selten@knmi.nl

Abstract

North Atlantic decadal climate variability is studied with a coupled atmosphere–ocean–sea ice model (ECBILT). After having reached an approximate statistical equilibrium in coupled mode without applying flux corrections, a subsequent 1000-yr integration is performed and analyzed. Compared to the current climate, the surface temperatures are 2°C warmer in the Tropics to almost 8°C warmer in the polar regions.

The covariability between the atmosphere and ocean is explored by performing a singular value decomposition (SVD) of boreal winter SST anomalies and 800-hPa geopotential height anomalies. The first SVD pair shows a red variance spectrum in SST and a white spectrum in 800-hPa height. The second mode shows a peak in both spectra at a timescale of about 16–18 yr. The geopotential height pattern is the model’s equivalent of the North Atlantic oscillation (NAO) pattern; the SST anomaly pattern is a north–south oriented dipole.

Additional experiments have revealed that the decadal oscillation in ECBILT is basically an oscillation in the subsurface of the ocean. The oscillation is excited by anomalies in the atmospheric NAO pattern, both through anomalous surface heat fluxes and anomalous Ekman transports. The atmospheric response to the SST anomaly enhances the oscillation and slightly modifies it, but is not essential. The atmospheric response consists primarily of a local surface air temperature adjustment to the SST anomaly. An important element in the physical mechanism of the oscillation is the geostrophic response of the ocean circulation to the forced temperature anomalies creating surface salinity anomalies through anomalous horizontal advection. These salinity anomalies influence the convective activity in the area of the temperature anomaly such as to break down the subsurface temperature anomaly. Both temperature and salinity anomalies slowly propagate eastward at a rate consistent with the mean current.

Corresponding author address: Frank M. Selten, Royal Netherlands Meteorological Institute, P.O. Box 201, 3730 AE De Bilt, the Netherlands.

Email: selten@knmi.nl

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

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

  • Bretherton, C. S., C. Smith, and J. M. Wallace, 1992: An intercomparison of methods for finding coupled patterns in climate data. J. Climate,5, 541–560.

  • Delworth, T. L., 1996: North Atlantic interannual variability in a coupled ocean–atmosphere model. J. Climate,9, 2356–2375.

  • ——, S. Manabe, and R. J. Stouffer, 1993: Interdecadal variations of the thermohaline circulation in a coupled ocean–atmosphere model. J. Climate,6, 1993–2011.

  • Deser, C., and M. L. Blackmon, 1993: Surface climate variations over the North Atlantic Ocean during winter 1900–1989. J. Climate,6, 1743–1753.

  • Ferranti, L., F. Molteni, and T. N. Palmer, 1994: Impact of localized tropical and extratropical SST anomalies in ensembles of seasonal GCM integrations. Quart. J. Roy. Meteor. Soc.,120, 1613–1645.

  • Grötzner, A., M. Latif, and T. P. Barnett, 1998: A decadal climate cycle in the North Atlantic ocean as simulated by the ECHO Coupled GCM. J. Climate,11, 831–847.

  • Haarsma, R. J., F. M. Selten, J. D. Opsteegh, G. Lenderink, and Q. Liu, 1997: ECBILT: A coupled atmosphere ocean sea-ice model for climate predictability studies. KNMI Tech. Rep. TR-195, De Bilt, the Netherlands, 32 pp. [Available from KNMI, P.O. Box 201, 3730 AE De Bilt, the Netherlands.].

  • Hansen, D. V., and H. F. Bezdek, 1996: On the nature of decadal anomalies in North Atlantic sea surface temperature. J. Geophys. Res.,101, 8749–8758.

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

  • Held, I. M., and M. J. Suarez, 1978: A two level primitive equation atmosphere model designed for climate sensitivity experiments. J. Atmos. Sci.,35, 206–229.

  • Hurrell, J. W., 1995: Decadal trends in the North Atlantic Oscillation regional temperatures and precipitation. Science,269, 676–679.

  • Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-year reanalysis project. Bull. Amer. Meteor. Soc.,77, 437–471.

  • Kushnir, Y., 1994: Interdecadal variations in North Atlantic sea surface temperature and associated atmospheric conditions. J. Climate,7, 141–157.

  • Latif, M., and T. P. Barnett, 1994: Causes of decadal variability over the North Pacific and North America. Science,266, 634–637.

  • Lau, N.-C., and M. J. Nath, 1990: A general circulation model study of the atmospheric response to extratropical SST anomalies observed in 1950–79. J. Climate,3, 713–725.

  • Lenderink, G., and R. J. Haarsma, 1994: Variability and multiple equilibria of the thermohaline circulation associated with deep water convection. J. Phys. Oceanogr.,24, 1480–1493.

  • ——, and ——, 1996: Rapid convective transitions in the presence of sea-ice. J. Phys. Oceanogr.,26, 1448–1467.

  • Levitus, S., A. M. Da Silva, and C. C. Young, 1994a: Anomalies of Directly Observed Quantities. Atlas of Surface Marine Data 1994. Vol. 2, NOAA/NESDIS 7, 416 pp. [Available from National Oceanographic Data Center, User Services Branch, NOAA/NESDIS E/OC21, 1825 Connecticut Avenue, NW Washington, DC 20235.].

  • ——, R. Burgett, and T. P. Boyer, 1994b: Salinity. Atlas of Surface Marine Data 1994. Vol. 3, NOAA/NESDIS, 99 pp. [Available from National Oceanographic Data Center, User Services Branch, NOAA/NESDIS 3 E/OC21, 1825 Connecticut Avenue, NW Washington, DC 20235.].

  • 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, 702–708.

  • Mann, M. E., J. Park, and R. S. Bradley, 1995: Global interdecadal and century-scale climate oscillations during the past five centuries. Nature,378, 266–270.

  • Marshall, J., and F. Molteni, 1993: Toward a dynamic understanding of planetary-scale flow regimes. J. Atmos. Sci.,50, 1792–1818.

  • Oortwijn, J., 1998: Predictability of the onset of blocking and strong zonal flow regimes. J. Atmos. Sci.,55, 973–994.

  • Opsteegh, J. D., R. J. Haarsma, and F. M. Selten, 1998: ECBILT: A dynamic alternative to mixed boundary conditions in ocean models. Tellus,50A, 348–367.

  • Palmer, T. N., 1993: A nonlinear dynamical perspective on climate change. Weather,48, 313–348.

  • ——, 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, 947–975.

  • Reverdin, G., D. Cayan, and Y. Kushnir, 1997: Decadal variability of hydrography in the upper North Atlantic 1948–1990. J. Geophys. Res.,102, 8505–8531.

  • Saravanan, R., 1998: Atmospheric low-frequency variability and its relationship to midlatitude SST variability: Studies using the NCAR climate system model. J. Climate,11, 1386–1404.

  • ——, and J. C. McWilliams, 1998: Advective ocean–atmosphere interaction: An analytical stochastic model with implications for decadal variability. J. Climate,11, 165–188.

  • Schlesinger, M. E., and N. Ramankutty, 1994: An oscillation in the global climate system of period 65–70 years. Nature,367, 723–726.

  • Sutton, R. T., and M. R. Allen, 1997: Decadal predictability of North Atlantic sea surface temperature and climate. Nature,388, 563–567.

  • Timmermann, A., M. Latif, R. Voss, and A. Grötzner, 1998: Northern hemispheric interdecadal variability: A coupled air–sea mode. J. Climate,11, 1906–1931.

  • Verbeek, J., 1997: Windstress and SST variability in the North Atlantic area: Observations and five coupled GCM’s in concert. Mon. Wea. Rev.,125, 942–957.

  • von Storch, H., G. Brger, R. Schnur, and J. von Storch, 1995: Principal oscillation pattern: A review. J. Climate,8, 377–400.

  • Wallace, J. M., and D. S. Gutzler, 1981: Teleconnections in the geopotential height field during the Northern Hemisphere winter. Mon. Wea. Rev.,109, 784–812.

  • Zorita, E., V. Kharin, and H. von Storch, 1992: The atmospheric circulation and sea surface temperature in the North Atlantic area in winter: Their interaction and relevance for Iberian precipitation. J. Climate,5, 1097–1108.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 220 43 2
PDF Downloads 56 12 0