The Role of the Sahara Low in Summertime Sahel Rainfall Variability and Change in the CMIP3 Models

M. Biasutti Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York

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A. H. Sobel Columbia University, New York, New York

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Suzana J. Camargo Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York

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Abstract

Projections for twenty-first-century changes in summertime Sahel precipitation differ greatly across models in the third Coupled Model Intercomparison Project (CMIP3) dataset and cannot be explained solely in terms of discrepancies in the projected anomalies in global SST.

This study shows that an index describing the low-level circulation in the North Atlantic–African region, namely, the strength of the low-level Saharan low, correlates with Sahel rainfall in all models and at the time scales of both interannual and interdecadal natural variability and of the forced centennial trend.

An analysis of Sahel interannual variability provides evidence that variations in the Sahara low can be a cause, not just a consequence, of variations in Sahel rainfall and suggests that a better understanding of the sources of model discrepancy in Sahel rainfall predictions might be gained from an analysis of the mechanisms influencing changes in the Sahara low.

Corresponding author address: Michela Biasutti, Lamont-Doherty Earth Observatory, Columbia University, Department of Oceanography, 61 Route 9W, P.O. Box 1000, Palisades, NY 10968-8000. Email: biasutti@ldeo.columbia.edu

This article included in the U.S. CLIVAR Drought special collection.

Abstract

Projections for twenty-first-century changes in summertime Sahel precipitation differ greatly across models in the third Coupled Model Intercomparison Project (CMIP3) dataset and cannot be explained solely in terms of discrepancies in the projected anomalies in global SST.

This study shows that an index describing the low-level circulation in the North Atlantic–African region, namely, the strength of the low-level Saharan low, correlates with Sahel rainfall in all models and at the time scales of both interannual and interdecadal natural variability and of the forced centennial trend.

An analysis of Sahel interannual variability provides evidence that variations in the Sahara low can be a cause, not just a consequence, of variations in Sahel rainfall and suggests that a better understanding of the sources of model discrepancy in Sahel rainfall predictions might be gained from an analysis of the mechanisms influencing changes in the Sahara low.

Corresponding author address: Michela Biasutti, Lamont-Doherty Earth Observatory, Columbia University, Department of Oceanography, 61 Route 9W, P.O. Box 1000, Palisades, NY 10968-8000. Email: biasutti@ldeo.columbia.edu

This article included in the U.S. CLIVAR Drought special collection.

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  • Allan, R. J., and T. J. Ansell, 2006: A new globally complete monthly historical mean sea level pressure data set (HadSLP2): 1850–2004. J. Climate, 19 , 5816–5842.

    • Search Google Scholar
    • Export Citation
  • Bader, J., and M. Latif, 2003: The impact of decadal-scale Indian Ocean sea surface temperature anomalies on Sahelian rainfall and the North Atlantic Oscillation. Geophys. Res. Lett., 30 , 2169. doi:10.1029/2003GL018426.

    • Search Google Scholar
    • Export Citation
  • Biasutti, M., and A. Giannini, 2006: Robust Sahel drying in response to late 20th century forcings. Geophys. Res. Lett., 33 , L11706. doi:10.1029/2006GL026067.

    • Search Google Scholar
    • Export Citation
  • Biasutti, M., D. S. Battisti, and E. S. Sarachik, 2003: The annual cycle over the tropical Atlantic, South America, and Africa. J. Climate, 16 , 2491–2508.

    • Search Google Scholar
    • Export Citation
  • Biasutti, M., I. M. Held, A. H. Sobel, and A. Giannini, 2008: SST forcings and Sahel rainfall variability in simulations of the twentieth and twenty-first centuries. J. Climate, 21 , 3471–3486.

    • Search Google Scholar
    • Export Citation
  • Bretherton, C. S., and A. H. Sobel, 2003: The Gill model and the weak temperature gradient approximation. J. Atmos. Sci., 60 , 451–460.

    • Search Google Scholar
    • Export Citation
  • Christensen, J. H., and Coauthors, 2007: Regional climate projections. Climate Change 2007: The Physical Science Basis, S. Solomon et al., Eds., Cambridge University Press, 847–940.

    • Search Google Scholar
    • Export Citation
  • Cook, K. H., 2008: Climate science: The mysteries of Sahel droughts. Nat. Geosci., 1 , 647–648.

  • Cook, K. H., and E. K. Vizy, 2006: Coupled model simulations of the West African monsoon system: Twentieth- and twenty-first-century simulations. J. Climate, 19 , 3681–3703.

    • Search Google Scholar
    • Export Citation
  • Eltahir, E. A. B., and C. Gong, 1996: Dynamics of wet and dry years in West Africa. J. Climate, 9 , 1030–1042.

  • Emanuel, K. A., 1995: On thermally direct circulations in moist atmospheres. J. Atmos. Sci., 52 , 1529–1534.

  • Giannini, A., M. Biasutti, I. M. Held, and A. H. Sobel, 2008: A global perspective on African climate. Climatic Change, 90 , 359–383.

    • Search Google Scholar
    • Export Citation
  • Gill, A. E., 1980: Some simple solutions for heat-induced tropical circulation. Quart. J. Roy. Meteor. Soc., 106 , 447–462.

  • Gleckler, P. J., K. E. Taylor, and C. Doutriaux, 2008: Performance metrics for climate models. J. Geophys. Res., 113 , D06104. doi:10.1029/2007JD008972.

    • Search Google Scholar
    • Export Citation
  • Grist, J. P., and S. E. Nicholson, 2001: A study of the dynamic factors influencing the rainfall variability in the West African Sahel. J. Climate, 14 , 1337–1359.

    • Search Google Scholar
    • Export Citation
  • Haarsma, R. J., F. M. Selten, S. L. Weber, and M. Kliphuis, 2005: Sahel rainfall variability and response to greenhouse warming. Geophys. Res. Lett., 32 , L17702. doi:10.1029/2005GL023232.

    • Search Google Scholar
    • Export Citation
  • Held, I. M., T. L. Delworth, J. Lu, K. L. Findell, and T. R. Knutson, 2005: Simulation of Sahel drought in the 20th and 21st centuries. Proc. Natl. Acad. Sci. USA, 102 , 17891–17896.

    • Search Google Scholar
    • Export Citation
  • Herceg, D., A. Sobel, and L. Sun, 2007: Regional modeling of decadal rainfall variability over the Sahel. Climate Dyn., 29 , 89–99.

    • Search Google Scholar
    • Export Citation
  • Hoerling, M., J. Hurrell, J. Eischeid, and A. Phillips, 2006: Detection and attribution of twentieth-century northern and southern African rainfall change. J. Climate, 19 , 3989–4008.

    • Search Google Scholar
    • Export Citation
  • Houghton, J. T., L. G. Meira Filho, B. A. Callander, N. Harris, A. Kattenberg, and K. Maskell, Eds.,. 1996: Climate Change 1995: The Science of Climate Change. Cambridge University Press, 572 pp.

    • Search Google Scholar
    • Export Citation
  • Hulme, M., 1992: A 1951–80 global land precipitation climatology for the evaluation of general circulation models. Climate Dyn., 7 , 57–72.

    • Search Google Scholar
    • Export Citation
  • Janicot, S., S. Trzaska, and I. Poccard, 2001: Summer Sahel–ENSO teleconnection and decadal time scale SST variations. Climate Dyn., 18 , 303–320.

    • Search Google Scholar
    • Export Citation
  • Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77 , 437–471.

  • Kaplan, A., M. Cane, Y. Kushnir, A. Clement, M. Blumenthal, and B. Rajagopalan, 1998: Analyses of global sea surface temperature 1856–1991. J. Geophys. Res., 103 , 18567–18589.

    • Search Google Scholar
    • Export Citation
  • Lau, K. M., S. S. P. Shen, K-M. Kim, and H. Wang, 2006: A multimodel study of the twentieth-century simulations of Sahel drought from the 1970s to 1990s. J. Geophys. Res., 111 , D07111. doi:10.1029/2005JD006281.

    • Search Google Scholar
    • Export Citation
  • Matsuno, T., 1966: Quasi-geostrophic motions in the equatorial area. J. Meteor. Soc. Japan, 44 , 25–43.

  • Meehl, G., C. Covey, T. Delworth, M. Latif, B. McAvaney, J. Mitchell, R. Stouffer, and K. Taylor, 2007a: The WCRP CMIP3 Multimodel Dataset: A new era in climate change research. Bull. Amer. Meteor. Soc., 88 , 1383–1394.

    • Search Google Scholar
    • Export Citation
  • Meehl, G., and Coauthors, 2007b: Global climate projections. Climate Change 2007: The Physical Science Basis, S. Solomon et al., Eds., Cambridge University Press, 747–846.

    • Search Google Scholar
    • Export Citation
  • Neelin, J. D., M. Munnich, H. Su, J. Meyerson, and C. Holloway, 2006: Tropical drying trends in global warming models and observations. Proc. Natl. Acad. Sci. USA, 103 , 6110–6115.

    • Search Google Scholar
    • Export Citation
  • Nicholson, S., and P. Webster, 2007: A physical basis for the interannual variability of rainfall in the Sahel. Quart. J. Roy. Meteor. Soc., 133 , 2065–2084.

    • Search Google Scholar
    • Export Citation
  • Reichler, T., and J. Kim, 2008: How well do coupled models simulate today’s climate? Bull. Amer. Meteor. Soc., 89 , 303–311.

    • Search Google Scholar
    • Export Citation
  • Sutton, R. T., B. Dong, and J. M. Gregory, 2007: Land/sea warming ratio in response to climate change: IPCC AR4 model results and comparison with observations. Geophys. Res. Lett., 34 , L02701. doi:10.1029/2006GL028164.

    • Search Google Scholar
    • Export Citation
  • Webster, P., 1972: Response of the tropical atmosphere to local, steady forcing. Mon. Wea. Rev., 100 , 518–541.

  • Webster, P., 1987: The elementary monsoon. Monsoons, J. S. Fein and P. L. Stephens, Eds., Wiley, 3–32.

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