• Annamalai, H., , J. M. Slingo, , K. R. Sperber, , and K. Hodges, 1999: The mean evolution and variability of the Asian summer monsoon: Comparison of ECMWF and NCEP–NCAR reanalyses. Mon. Wea. Rev., 127, 11571186.

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

    • Search Google Scholar
    • Export Citation
  • Bretherton, C. S., , C. Smith, , and J. M. Wallace, 1992: An intercomparison of methods for finding coupled patterns in climate data. J. Climate, 5, 541560.

    • Search Google Scholar
    • Export Citation
  • Camberlin, P., , S. Janicot, , and I. Poccard, 2001: Seasonality and atmospheric dynamics of the teleconnection between African rainfall and tropical sea-surface temperature: Atlantic vs. ENSO. Int. J. Climatol., 21, 9731005, doi:10.1002/joc.673.

    • Search Google Scholar
    • Export Citation
  • Caminade, C., , and L. Terray, 2010: Twentieth century Sahel rainfall variability as simulated by the ARPEGE AGCM, and future changes. Climate Dyn., 35, 7594, doi:10.1007/s00382-009-0545-4.

    • Search Google Scholar
    • Export Citation
  • Chan, S. C., , and S. Nigam, 2009: Residual diagnosis of diabatic heating from ERA-40 and NCEP reanalyses: Intercomparisons with TRMM. J. Climate, 22, 414428.

    • Search Google Scholar
    • Export Citation
  • Charney, J. G., 1975: Dynamics of deserts and drought in the Sahel. Quart. J. Roy. Meteor. Soc., 101, 193202.

  • Dai, A., , P. J. Lamb, , K. E. Trenberth, , M. Hulme, , P. D. Jones, , and P. Xie, 2004: The recent Sahel drought is real. Int. J. Climatol., 24, 13231331, doi:10.1002/joc.1083.

    • Search Google Scholar
    • Export Citation
  • Déqué, M., , C. Dreveton, , A. Braun, , and D. Cariolle, 1994: The ARPEGE/IFS atmosphere model: A contribution to the French community climate modeling. Climate Dyn., 10, 249266.

    • Search Google Scholar
    • Export Citation
  • Folland, C. K., , T. N. Palmer, , and D. E. Parker, 1986: Sahel rainfall and worldwide sea temperatures, 1901-85. Nature, 320, 602607.

  • Frankignoul, C., , and E. Kestenare, 2005: Observed Atlantic SST anomaly impact on the NAO: An update. J. Climate, 18, 40894094.

  • Giannini, A., , J. C. H. Chiang, , M. A. Cane, , Y. Kushnir, , and R. Seager, 2001: The ENSO teleconnection to the tropical Atlantic Ocean: Contributions of the remote and local SSTs to rainfall variability in the tropical Americas. J. Climate, 14, 45304544.

    • Search Google Scholar
    • Export Citation
  • Giannini, A., , R. Saravannan, , and P. Chang, 2003: Oceanic forcing of Sahel rainfall on interannual to interdecadal time scales. Science, 302, 10271030.

    • Search Google Scholar
    • Export Citation
  • Gill, A. E., 1980: Some simple solutions for heat-induced tropical circulation. Quart. J. Roy. Meteor. Soc., 106, 447462.

  • Hoerling, M., , J. W. Hurrell, , J. Eischeid, , and A. S. Phillips, 2006: Detection and attribution of twentieth-century northern and southern African rainfall change. J. Climate, 19, 39894008.

    • Search Google Scholar
    • Export Citation
  • Hourdin, F., and Coauthors, 2006: The LMDZ4 general circulation model: Climate performance and sensitivity to parametrized physics with emphasis on tropical convection. Climate Dyn., 27, 787813.

    • Search Google Scholar
    • Export Citation
  • Janicot, S., , V. Moron, , and B. Fontaine, 1996: ENSO dynamics and Sahel droughts. Geophys. Res. Lett., 23, 515518.

  • Janicot, S., , A. Harzallah, , B. Fontaine, , and V. Moron, 1998: West African monsoon dynamics and eastern equatorial Atlantic and Pacific SST anomalies (1970–1988). J. Climate, 11, 18741882.

    • 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, 303320.

    • Search Google Scholar
    • Export Citation
  • Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77, 437471.

  • Krishnamurti, T. N., , C. M. Kishtawal, , D. W. Shin, , and C. E. Williford, 2000a: Improving tropical precipitation forecasts from a multianalysis superensemble. J. Climate, 13, 42174227.

    • Search Google Scholar
    • Export Citation
  • Krishnamurti, T. N., , C. M. Kishtawal, , Z. Zhang, , T. LaRow, , D. Bachiochi, , E. Williford, , S. Gadgil, , and S. Surendran, 2000b: Multimodel ensemble forecasts for weather and seasonal climate. J. Climate, 13, 41964216.

    • Search Google Scholar
    • Export Citation
  • Lamb, P. J., , and R. A. Peppler, 1992: Further case studies of tropical Atlantic surface atmospheric and oceanic patterns associated with sub-Saharan drought. J. Climate, 5, 476488.

    • Search Google Scholar
    • Export Citation
  • Losada, T., , B. Rodriguez-Fonseca, , S. Janicot, , S. Gervois, , F. Chauvin, , and P. Ruti, 2010: A multi-model approach to the Atlantic Equatorial mode. Impact on the West African monsoon. Climate Dyn., 35, 2943.

    • Search Google Scholar
    • Export Citation
  • Matsuno, T., 1966: Quasigeostrophic motions in the equatorial area. J. Meteor. Soc. Japan, 44, 2542.

  • Mechoso, C. R., , S. W. Lyons, , and J. A. Spahr, 1990: The impact of sea surface temperature anomalies on the rainfall over northeast Brazil. J. Climate, 3, 812826.

    • Search Google Scholar
    • Export Citation
  • Mechoso, C. R., , J. Y. Yu, , and A. Arakawa, 2000: A coupled GCM pilgrimage: From climate catastrophe to ENSO simulations. General Circulation Model Development, D. A. Randall, Ed., International Geophysics Series, Vol. 70, Academic Press, 539–575.

    • Search Google Scholar
    • Export Citation
  • Meehl, G. A., and Coauthors, 2007: Global climate projections. Climate Change 2007: The Physical Science Basis, S. Solomon et al., Eds., Cambridge University Press, 747–845.

    • Search Google Scholar
    • Export Citation
  • Meehl, G. A., , A. Hu, , and B. D. Santer, 2009: The mid-1970s climate shift in the Pacific and the relative roles of forced versus inherent decadal variability. J. Climate, 22, 780792.

    • Search Google Scholar
    • Export Citation
  • Misra, V., , P. A. Dirmeyer, , and B. P. Kirtman, 2003: Dynamic downscaling of seasonal simulations over South America. J. Climate, 16, 103117.

    • Search Google Scholar
    • Export Citation
  • Mohino, E., , S. Janicot, , and J. Bader, 2011a: Sahel rainfall and decadal to multi-decadal sea surface temperature variability. Climate Dyn., doi:10.1007/s00382-010-0867-2, in press.

    • Search Google Scholar
    • Export Citation
  • Mohino, E., , B. Rodriguez-Fonseca, , T. Losada, , S. Gervois, , S. Janicot, , J. Bader, , P. Ruti, , and F. Chauvin, 2011b: Changes in the interannual SST-forced signals on West African rainfall: AGCM intercomparison. Climate Dyn., in press.

    • Search Google Scholar
    • Export Citation
  • Moron, V., , N. Philippon, , and B. Fontaine, 2003: Skill of Sahel rainfall variability in four atmospheric GCMs forced by prescribed SST. Geophys. Res. Lett., 30, 2221, doi:10.1029/2003GL018006.

    • Search Google Scholar
    • Export Citation
  • Moron, V., , N. Philippon, , and B. Fontaine, 2004: Simulation of West African monsoon circulation in four atmospheric general circulation models forced by prescribed sea surface temperature. J. Geophys. Res., 109, D24105, doi:10.1029/2004JD004760.

    • Search Google Scholar
    • Export Citation
  • Neelin, J. D., , C. Chou, , and H. Su, 2003: Tropical drought regions in global warming and El Niño teleconnections. Geophys. Res. Lett., 30, 2275, doi:10.1029/2003GL018625.

    • Search Google Scholar
    • Export Citation
  • Nicholson, S. E., 2000: Land surface processes and Sahel climate. Rev. Geophys., 38, 117139.

  • Nicholson, S. E., , and J. Kim, 1997: The relationship of the El Niño-Southern Oscillation to African rainfall. Int. J. Climate, 17, 117135.

    • Search Google Scholar
    • Export Citation
  • Paeth, H., , and P. Friederichs, 2004: Seasonality and time scales in the relationship between global SST and African rainfall. Climate Dyn., 23, 815837.

    • Search Google Scholar
    • Export Citation
  • Palmer, T. N., 1986: Influence of the Atlantic, Pacific, and Indian Oceans on Sahel rainfall. Nature, 322, 251253.

  • Palmer, T. N., , C. Branković, , P. Viterbo, , and J. Miller, 1992: Modeling interannual variations of summer monsoons. J. Climate, 5, 399417.

    • Search Google Scholar
    • Export Citation
  • Polo, I., , B. Rodríguez-Fonseca, , T. Losada, , and J. García-Serrano, 2008: Tropical Atlantic variability modes (1979–2001). Part I: Time-evolving SST models related to West African rainfall. J. Climate, 21, 64576475.

    • Search Google Scholar
    • Export Citation
  • Reason, C. J. C., , R. J. Allan, , J. A. Lindesay, , and T. J. Ansell, 2000: ENSO and climatic signals across the Indian Ocean basin in the global context: Part I, interannual composite patterns. Int. J. Climatol., 20, 12851327.

    • Search Google Scholar
    • Export Citation
  • Rodriguez-Fonseca, B., , I. Polo, , J. Garcia-Serrano, , L. Losada, , E. Mohino, , C. R. Mechoso, , and F. Kucharski, 2009: Is the Atlantic Niño dynamically affecting the Pacific ENSO in recent decades? Geophys. Res. Lett., 36, L20705, doi:10.1029/2009GL040048.

    • Search Google Scholar
    • Export Citation
  • Rodriguez-Fonseca, B., and Coauthors, 2010: Interannual and decadal SST-forced responses of the West African monsoon. Atmos. Sci. Lett., 12, 6774, doi:10.1002/asl.308.

    • Search Google Scholar
    • Export Citation
  • Roeckner, E., and Coauthors, 1996: The atmospheric general circulation model ECHAM-4: Model description and simulation of present-day climate. Max-Planck Institute for Meteorology Rep. 218, 94 pp.

    • Search Google Scholar
    • Export Citation
  • Rowell, D. P., 2001: Teleconnections between the tropical Pacific and the Sahel. Quart. J. Roy. Meteor. Soc., 127, 16831706.

  • Rowell, D. P., , C. K. Folland, , K. Maskell, , J. A. Owen, , and N. M. Ward, 1992: Modelling the influence of global sea surface temperatures on the variability and predictability of seasonal Sahel rainfall. Geophys. Res. Lett., 19, 905908.

    • Search Google Scholar
    • Export Citation
  • Rowell, D. P., , C. K. Folland, , K. Maskell, , and N. M. Ward, 1995: Variability of summer rainfall over tropical north Africa (1906-92): Observations and modelling. Quart. J. Roy. Meteor. Soc., 121, 669704.

    • Search Google Scholar
    • Export Citation
  • Smith, T. M., , and R. W. Reynolds, 2004: Improved extended reconstruction of SST (1854–1997). J. Climate, 17, 24662477.

  • Trenberth, K. E., and Coauthors, 2007: Observations: Surface and atmospheric climate change. Climate Change 2007: The Physical Science Basis, S. Solomon et al., Eds., Cambridge University Press, 235–336.

    • Search Google Scholar
    • Export Citation
  • Trzaska, S., , V. Moron, , and B. Fontaine, 1996: Global atmospheric response to specific linear combinations of the main SST modes. Part I: Numerical experiments and preliminary results. Ann. Geophys., 14, 10661077.

    • Search Google Scholar
    • Export Citation
  • Uppala, S. M., and Coauthors, 2005: The ERA-40 Re-Analysis. Quart. J. Roy. Meteor. Soc., 131, 29613012.

  • Ward, M. N., 1998: Diagnosis and short–lead time prediction of summer rainfall in tropical North Africa at interannual and multidecadal time scales. J. Climate, 11, 31673191.

    • Search Google Scholar
    • Export Citation
  • Xie, P., , and P. A. Arkin, 1997: Global precipitation: A 17-year monthly analysis based on gauge observations, satellite estimates, and numerical model outputs. Bull. Amer. Meteor. Soc., 78, 25392558.

    • Search Google Scholar
    • Export Citation
  • Yoshioka, M., , N. M. Mahowald, , A. J. Conley, , W. D. Collins, , D. W. Fillmore, , C. S. Zender, , and D. B. Coleman, 2007: Impact of desert dust radiative forcing on Sahel precipitation: Relative importance of dust compared to sea surface temperature variations, vegetation changes, and greenhouse gas warming. J. Climate, 20, 14451467.

    • Search Google Scholar
    • Export Citation
  • Zebiak, S. E., 1993: Air–sea interaction in the equatorial Atlantic region. J. Climate, 6, 15671586.

  • Zeng, N., , J. D. Neelin, , K. M. Lau, , and C. J. Tucker, 1999: Enhancement of interdecadal climate variability in the Sahel by vegetation interaction. Science, 286, 15371540.

    • Search Google Scholar
    • Export Citation
  • Zhong, A., , H. H. Hendon, , and O. Alves, 2005: Indian Ocean variability and its association with ENSO in a global coupled model. J. Climate, 18, 36343649.

    • Search Google Scholar
    • Export Citation
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Impacts of the Tropical Pacific/Indian Oceans on the Seasonal Cycle of the West African Monsoon

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  • 1 LOCEAN/IPSL, Université Pierre et Marie Curie, Paris, France
  • | 2 Universidad de Sevilla, Seville, Spain
  • | 3 Universidad Complutense de Madrid, Madrid, Spain
  • | 4 Instituto de Geosciencias, Consejo Superior de Investigaciones Cientificas and Universidad Complutense de Madrid, Madrid, Spain
  • | 5 Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, California
  • | 6 Progetto Speciale Clima Globale, Ente Nazionale per le Nuove Tecnologie, l’Energia e l’Ambiente, Rome, Italy
  • | 7 GAME/CNRM, Météo-France/CNRS, Toulouse, France
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Abstract

The current consensus is that drought has developed in the Sahel during the second half of the twentieth century as a result of remote effects of oceanic anomalies amplified by local land–atmosphere interactions. This paper focuses on the impacts of oceanic anomalies upon West African climate and specifically aims to identify those from SST anomalies in the Pacific/Indian Oceans during spring and summer seasons, when they were significant. Idealized sensitivity experiments are performed with four atmospheric general circulation models (AGCMs). The prescribed SST patterns used in the AGCMs are based on the leading mode of covariability between SST anomalies over the Pacific/Indian Oceans and summer rainfall over West Africa. The results show that such oceanic anomalies in the Pacific/Indian Ocean lead to a northward shift of an anomalous dry belt from the Gulf of Guinea to the Sahel as the season advances. In the Sahel, the magnitude of rainfall anomalies is comparable to that obtained by other authors using SST anomalies confined to the proximity of the Atlantic Ocean. The mechanism connecting the Pacific/Indian SST anomalies with West African rainfall has a strong seasonal cycle. In spring (May and June), anomalous subsidence develops over both the Maritime Continent and the equatorial Atlantic in response to the enhanced equatorial heating. Precipitation increases over continental West Africa in association with stronger zonal convergence of moisture. In addition, precipitation decreases over the Gulf of Guinea. During the monsoon peak (July and August), the SST anomalies move westward over the equatorial Pacific and the two regions where subsidence occurred earlier in the seasons merge over West Africa. The monsoon weakens and rainfall decreases over the Sahel, especially in August.

Corresponding author address: E. Mohino, LOCEAN/IPSL, Université Pierre et Marie Curie-Tour 45-55-4eme étage 4, place Jussieu, 75252 Paris CEDEX 05, France. E-mail: emohino@fis.ucm.es

Abstract

The current consensus is that drought has developed in the Sahel during the second half of the twentieth century as a result of remote effects of oceanic anomalies amplified by local land–atmosphere interactions. This paper focuses on the impacts of oceanic anomalies upon West African climate and specifically aims to identify those from SST anomalies in the Pacific/Indian Oceans during spring and summer seasons, when they were significant. Idealized sensitivity experiments are performed with four atmospheric general circulation models (AGCMs). The prescribed SST patterns used in the AGCMs are based on the leading mode of covariability between SST anomalies over the Pacific/Indian Oceans and summer rainfall over West Africa. The results show that such oceanic anomalies in the Pacific/Indian Ocean lead to a northward shift of an anomalous dry belt from the Gulf of Guinea to the Sahel as the season advances. In the Sahel, the magnitude of rainfall anomalies is comparable to that obtained by other authors using SST anomalies confined to the proximity of the Atlantic Ocean. The mechanism connecting the Pacific/Indian SST anomalies with West African rainfall has a strong seasonal cycle. In spring (May and June), anomalous subsidence develops over both the Maritime Continent and the equatorial Atlantic in response to the enhanced equatorial heating. Precipitation increases over continental West Africa in association with stronger zonal convergence of moisture. In addition, precipitation decreases over the Gulf of Guinea. During the monsoon peak (July and August), the SST anomalies move westward over the equatorial Pacific and the two regions where subsidence occurred earlier in the seasons merge over West Africa. The monsoon weakens and rainfall decreases over the Sahel, especially in August.

Corresponding author address: E. Mohino, LOCEAN/IPSL, Université Pierre et Marie Curie-Tour 45-55-4eme étage 4, place Jussieu, 75252 Paris CEDEX 05, France. E-mail: emohino@fis.ucm.es
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