• Adler, R. F., and Coauthors, 2003: The version 2 Global Precipitation Climatology Project (GPCP) monthly precipitation analysis (1979–present). J. Hydrometeor., 4 , 11471167.

    • Search Google Scholar
    • Export Citation
  • Back, L. E., and C. S. Bretherton, 2009a: A simple model of climatological rainfall and vertical motion patterns over the tropical oceans. J. Climate, 22 , 64776497.

    • Search Google Scholar
    • Export Citation
  • Back, L. E., and C. S. Bretherton, 2009b: On the relationship between SST gradients, boundary layer winds, and convergence over the tropical oceans. J. Climate, 22 , 41824196.

    • Search Google Scholar
    • Export Citation
  • Bader, J., and M. Latif, 2011: The 1983 drought in the West Sahel: A case study. Climate Dyn., 36 , 463472. doi:10.1007/s00382-009-0700-y.

    • Search Google Scholar
    • Export Citation
  • Behera, S. K., S. Krishnan, and T. Yamagata, 1999: Unusual ocean–atmosphere conditions in the tropical Indian Ocean during 1994. Geophys. Res. Lett., 26 , 30013004.

    • Search Google Scholar
    • Export Citation
  • Feng, J., J. Li, and Y. Li, 2010: A monsoon-like southwest Australian circulation and its relation with rainfall in southwest Western Australia. J. Climate, 23 , 13341353.

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

  • Fontaine, B., and S. Bigot, 1993: West African rainfall deficits and sea surface temperatures. Int. J. Climatol., 13 , 271285.

  • Fontaine, B., and S. Janicot, 1996: Sea surface temperature fields associated with West African rainfall anomaly types. J. Climate, 9 , 29352940.

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

    • Search Google Scholar
    • Export Citation
  • Hannachi, A., I. T. Jolliffe, and D. B. Stephenson, 2007: Empirical orthogonal functions and related techniques in atmospheric science: A review. Int. J. Climatol., 27 , 11191152.

    • Search Google Scholar
    • Export Citation
  • Janicot, S., A. Harzallah, B. Fontaine, and V. Moron, 1998: West African monsoon dynamics and eastern equatorial Atlantic and Pacific SSTA (1970–88). 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
  • Joly, M., and A. Voldoire, 2010: Role of the Gulf of Guinea in the interannual variability of the West African monsoon: What do we learn from CMIP3 coupled simulations? Int. J. Climatol., 30 , 18431856.

    • Search Google Scholar
    • Export Citation
  • Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77 , 437470.

  • Kucharski, F., A. Bracco, J. H. Yoo, A. M. Tompkins, L. Feudale, P. Ruti, and A. Dell’Aquila, 2009: A Gill–Matsuno-type mechanism explains the tropical Atlantic influence on African and Indian monsoon rainfall. Quart. J. Roy. Meteor. Soc., 135 , 569579.

    • Search Google Scholar
    • Export Citation
  • Lamb, P. J., 1978: Case studies of tropical Atlantic surface circulation patterns during recent sub-Saharan weather anomalies: 1967 and 1968. Mon. Wea. Rev., 106 , 482491.

    • Search Google Scholar
    • Export Citation
  • Latif, M., and A. Grötzner, 2000: The equatorial Atlantic oscillation and its response to ENSO. Climate Dyn., 16 , 213218.

  • Li, J., and Q. Zeng, 2000: Significance of the normalized seasonality of wind field and its rationality for characterizing the monsoon. Sci. China, 43D , 646653.

    • Search Google Scholar
    • Export Citation
  • Li, J., and Q. Zeng, 2002: A unified monsoon index. Geophys. Res. Lett., 29 , 1274. doi:10.1029/2001GL013874.

  • Li, J., and Q. Zeng, 2003: A new monsoon index and the geographical distribution of the global monsoons. Adv. Atmos. Sci., 20 , 299302.

    • Search Google Scholar
    • Export Citation
  • Lindzen, R. S., and S. Nigam, 1987: On the role of sea surface temperature gradients in forcing low-level winds and convergence in the Tropics. J. Atmos. Sci., 44 , 24182436.

    • 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
  • Mitchell, T. D., and P. D. Jones, 2005: An improved method of constructing a database of monthly climate observations and associated high-resolution grids. Int. J. Climatol., 25 , 693712.

    • Search Google Scholar
    • Export Citation
  • Monahan, A. H., J. C. Fyfe, M. H. P. Ambaum, D. B. Stephenson, and G. R. North, 2009: Empirical orthogonal functions: The medium is the message. J. Climate, 22 , 65016514.

    • Search Google Scholar
    • Export Citation
  • Motha, R. P., S. K. Ludic, L. T. Steyaert, C. M. Sakamota, and N. D. Strommen, 1980: Precipitation patterns in West Africa. Mon. Wea. Rev., 108 , 15671578.

    • Search Google Scholar
    • Export Citation
  • New, M., M. Hulme, and P. D. Jones, 2000: Representing twentieth-century space–time climate variability. Part 2: Development of 1901–96 monthly grids of terrestrial surface climate. J. Climate, 13 , 22172238.

    • Search Google Scholar
    • Export Citation
  • Nicholson, S. E., and P. J. Webster, 2007: A physical basis for the interannual variability of rainfall in the Sahel. Quart. J. Roy. Meteor. Soc., 133 , 20652084.

    • Search Google Scholar
    • Export Citation
  • Okumura, Y., and S.-P. Xie, 2006: Some overlooked features of tropical Atlantic climate leading to a new Niño-like phenomenon. J. Climate, 19 , 58595874.

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

  • Polo, I., B. Rodriguez-Fonseca, T. Losada, and J. Garcia-Serrano, 2008: Tropical Atlantic variability modes (1979–2002). Part I: Time-evolving SST modes related to West African rainfall. J. Climate, 21 , 64576475.

    • Search Google Scholar
    • Export Citation
  • Rayner, N. A., D. E. Parker, E. B. Horton, C. K. Folland, L. V. Alexander, D. P. Rowell, E. C. Kent, and A. Kaplan, 2003: Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res., 108 , 4407. doi:10.1029/2002JD002670.

    • Search Google Scholar
    • Export Citation
  • Rayner, N. A., P. Brohan, D. E. Parker, C. K. Folland, J. J. Kennedy, M. Vanicek, T. Ansell, and S. F. B. Tett, 2006: Improved analyses of changes and uncertainties in sea surface temperature measured in situ since the mid-nineteenth century: The HadSST2 dataset. J. Climate, 19 , 446469.

    • Search Google Scholar
    • Export Citation
  • Rowell, D. P., C. K. Folland, K. Maskell, and M. N. 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
  • Schneider, U., T. Fuchs, A. Meyer-Christoffer, and B. Rudolf, 2008: Global precipitation analysis products of the GPCC. Global Precipitation Climatology Centre, 12 pp.

    • Search Google Scholar
    • Export Citation
  • Smith, T. M., R. W. Reynolds, T. C. Peterson, and J. Lawrimore, 2008: Improvements to NOAA’s historical merged land–ocean surface temperature analysis (1880–2006). J. Climate, 21 , 22832296.

    • Search Google Scholar
    • Export Citation
  • Stevens, B., J. J. Duan, J. C. McWilliams, M. Munnich, and J. D. Neelin, 2002: Entrainment, Rayleigh friction, and boundary layer winds over the tropical Pacific. J. Climate, 15 , 3044.

    • Search Google Scholar
    • Export Citation
  • Sultan, B., and S. Janicot, 2003: The West African monsoon dynamics. Part II: The “preonset” and “onset” of the summer monsoon. J. Climate, 16 , 34073427.

    • Search Google Scholar
    • Export Citation
  • Trzaska, S., A. W. Robertson, J. Farrara, and C. R. Mechoso, 2007: South Atlantic variability arising from air–sea coupling: Local mechanisms and tropical–subtropical interactions. J. Climate, 20 , 33453365.

    • Search Google Scholar
    • Export Citation
  • Venegas, S. A., L. A. Mysak, and D. N. Straub, 1996: Evidence for interannual and interdecadal climate variability in the South Atlantic. Geophys. Res. Lett., 23 , 26732676.

    • Search Google Scholar
    • Export Citation
  • Venegas, S. A., L. A. Mysak, and D. N. Straub, 1997: Atmosphere–ocean coupled variability in the South Atlantic. J. Climate, 10 , 29042920.

    • Search Google Scholar
    • Export Citation
  • Vigaud, N., Y. Richard, M. Rouault, and N. Fauchereau, 2009: Moisture transport between the South Atlantic Ocean and southern Africa: Relationships with summer rainfall and associated dynamics. Climate Dyn., 32 , 113123.

    • Search Google Scholar
    • Export Citation
  • Vizy, E. K., and K. H. Cook, 2001: Mechanisms by which Gulf of Guinea and eastern North Atlantic sea surface temperature anomalies can influence African rainfall. J. Climate, 14 , 795821.

    • Search Google Scholar
    • Export Citation
  • Wagner, R. G., and A. M. Da Silva, 1994: Surface conditions associated with anomalous rainfall in the Guinea coastal region. Int. J. Climatol., 14 , 179199.

    • Search Google Scholar
    • Export Citation
  • Wang, B., and Coauthors, 2008: How to measure the strength of the East Asian summer monsoon. J. Climate, 21 , 44494462.

  • Ward, M. N., 1992: Provisionally corrected surface wind data, worldwide ocean–atmosphere surface fields, and Sahelian rainfall variability. J. Climate, 5 , 454475.

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

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

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 542 243 12
PDF Downloads 425 215 8

Influence of the South Atlantic Ocean Dipole on West African Summer Precipitation

View More View Less
  • 1 State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China, and Department of Geography, University of Nigeria, Nsukka, Nigeria
  • | 2 State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
Restricted access

Abstract

This paper demonstrates a causal link between the air–sea phenomenon referred to as the South Atlantic Ocean (SAO) dipole (SAOD) and the interannual variability of precipitation over West Africa during the boreal summer monsoon rainy season in which most of the annual rainfall is recorded using an array of observational datasets. Analyses show that positive precipitation anomalies exceeding 40 mm month−1 over most locations at the Guinea Coast are associated with the positive phase of the SAOD, which is characterized by warm sea surface temperature anomalies (SSTAs) in the northeastern part of the SAO or the northeast pole (NEP)—that is, the Atlantic Niño sector—and cool SSTA in the southwestern part [southwest pole (SWP)] off the Argentina–Uruguay–Brazil coast. On the other hand, interannual variability in the Sahel is closely connected to the West African summer monsoon and the Atlantic Niño.

The results of this study reveal that the well-known influence of the Atlantic Niño on Guinea Coast precipitation in the literature represents only a component of the ocean–atmosphere interactions in the SAO causing the precipitation anomalies. Indeed, correlation and composite analyses using Guinea Coast precipitation indices consistently yield significant links to both the NEP and SWP centers of action. The hypothesized physical mechanism through which the SAOD-type SST gradients could induce Guinea Coast precipitation anomalies is the Lindzen–Nigam process. During the positive phase of the SAOD, the imprint of SST gradients gives rise to divergence over the SWP linked to convergence and vigorous upward motion over the NEP thereby leading to enhancement of precipitation over the Guinea Coast.

Corresponding author address: Dr. Jianping Li, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China. Email: ljp@lasg.iap.ac.cn

Abstract

This paper demonstrates a causal link between the air–sea phenomenon referred to as the South Atlantic Ocean (SAO) dipole (SAOD) and the interannual variability of precipitation over West Africa during the boreal summer monsoon rainy season in which most of the annual rainfall is recorded using an array of observational datasets. Analyses show that positive precipitation anomalies exceeding 40 mm month−1 over most locations at the Guinea Coast are associated with the positive phase of the SAOD, which is characterized by warm sea surface temperature anomalies (SSTAs) in the northeastern part of the SAO or the northeast pole (NEP)—that is, the Atlantic Niño sector—and cool SSTA in the southwestern part [southwest pole (SWP)] off the Argentina–Uruguay–Brazil coast. On the other hand, interannual variability in the Sahel is closely connected to the West African summer monsoon and the Atlantic Niño.

The results of this study reveal that the well-known influence of the Atlantic Niño on Guinea Coast precipitation in the literature represents only a component of the ocean–atmosphere interactions in the SAO causing the precipitation anomalies. Indeed, correlation and composite analyses using Guinea Coast precipitation indices consistently yield significant links to both the NEP and SWP centers of action. The hypothesized physical mechanism through which the SAOD-type SST gradients could induce Guinea Coast precipitation anomalies is the Lindzen–Nigam process. During the positive phase of the SAOD, the imprint of SST gradients gives rise to divergence over the SWP linked to convergence and vigorous upward motion over the NEP thereby leading to enhancement of precipitation over the Guinea Coast.

Corresponding author address: Dr. Jianping Li, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China. Email: ljp@lasg.iap.ac.cn

Save