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Simulated impacts of the South Atlantic Ocean Dipole on summer precipitation at the Guinea Coast

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Abstract

An intermediate complexity atmospheric general circulation model has been used to investigate the influence of the South Atlantic Ocean (SAO) dipole (SAOD) on summer precipitation over the Guinea Coast of West Africa. Two ensemble integrations in which idealized but realistic SAOD-type sea surface temperature (SST) anomaly is prescribed only in the SAO, and then globally are performed and inter-compared. Consistently, above (below) the average precipitation is simulated over the Guinea Coast during the positive (negative) phase of the SAOD. Comparison of the two set of experiments reveal that in its active years, the SAOD is a dominant mechanism that shapes the spatial character of summer precipitation at the Guinea coast, the global SST variability merely slightly moderate its effects. During the SAOD, cool SST anomaly in the extra-tropical SAO off the Brazil–Uruguay–Argentina coast gives rise to suppressed convection and mass divergence. In turn, the subsidence tends to amplify the sub-tropical arm of anomalous Hadley-type circulation and consequently large scale convection and mass flux convergence in the equatorial Atlantic Ocean/Gulf of Guinea region bordering on the coastal fringes of West Africa. Precipitation is therefore increased at the Guinea Coast.

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Notes

  1. Two summertime precipitation regions are often identified over West Africa; the Guinea Coast in the south and the Sahel to the north. The boundary between these two regions lies at about 10°–12°N.

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Acknowledgments

Support for this work has been provided by the China 973 Program (2010CB950400) and NSFC Key Project (41030961). The first author is also supported by the Abdus Salam International Centre for Theoretical Physics, Trieste, Italy through the Junior Associateship visit during which part of the work was completed. With thank the anonymous reviewers for thorough criticisms of an earlier draft of this paper.

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Authors and Affiliations

  1. State Key Laboratory of Numerical Modelling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

    Hyacinth C. Nnamchi & Jianping Li

  2. Graduate University of the Chinese Academy of Sciences, Beijing, China

    Hyacinth C. Nnamchi

  3. School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea

    In-Sik Kang

  4. Earth System Physics Section, Abdus Salam International Center for Theoretical Physics, Trieste, Italy

    Fred Kucharski

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  1. Hyacinth C. Nnamchi
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Correspondence to Jianping Li.

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Nnamchi, H.C., Li, J., Kang, IS. et al. Simulated impacts of the South Atlantic Ocean Dipole on summer precipitation at the Guinea Coast. Clim Dyn 41, 677–694 (2013). https://doi.org/10.1007/s00382-012-1629-0

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