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Changes in the interannual SST-forced signals on West African rainfall. AGCM intercomparison

Abstract

Rainfall over West Africa shows strong interannual variability related to changes in Sea Surface Temperature (SST). Nevertheless, this relationship seem to be non-stationary. A particular turning point is the decade of the 1970s, which witnessed a number of changes in the climatic system, including the climate shift of the late 1970s. The first aim of this study is to explore the change in the interannual variability of West African rainfall after this shift. The analysis indicates that the dipolar features of the rainfall variability over this region, related to changes in the Atlantic SST, disappear after this period. Also, the Pacific SST variability has a higher correlation with Guinean rainfall in the recent period. The results suggest that the current relationship between the Atlantic and Pacific El Niño phenomena is the principal responsible for these changes. A fundamental goal of climate research is the development of models simulating a realistic current climate. For this reason, the second aim of this work is to test the performance of Atmospheric General Circulation models in simulating rainfall variability over West Africa. The models have been run with observed SSTs for the common period 1957–1998 as part of an intercomparison exercise. The results show that the models are able to reproduce Guinean interannual variability, which is strongly related to SST variability in the Equatorial Atlantic. Nevertheless, problems in the simulation of the Sahelian interannual variability appear: not all models are able to reproduce the observed negative link between rainfall over the Sahel and El Niño-like anomalies in the Pacific, neither the positive correlation between Mediterranean SSTs and Sahelian rainfall.

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Acknowledgments

We would like to thank the anonymous reviewers for their comments and suggestions that helped improved the manuscript. This project has been funded by the EU-AMMA project. Based on French initiative, AMMA was built by an international scientific group and is currently funded by a large number of agencies, especially from France, UK, US and Africa. It has been the beneficiary of a major financial contribution from the European Community’s Sixth Framework Research Programme. Detailed information on scientific coordination and funding is available on the AMMA International website http://www.amma-international.org. EM would like to thank the support from the programme POSDEXT-MEC of the Spanish Ministry for Science and Innovation. JB would also want to thank the support from the COMPAS project funded by the research council of Norway. This study was supported also by the Spanish projects: MEC CGL2006-04471, MEC CGL2009-10285 and MMA MOVAC:200800050084028. GR58/08 program (supported by BSCH and UCM) has also partially financed this work through the Research Group “Micrometeorology and Climate Variability” (no. 910437).

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Correspondence to Elsa Mohino.

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Mohino, E., Rodríguez-Fonseca, B., Losada, T. et al. Changes in the interannual SST-forced signals on West African rainfall. AGCM intercomparison. Clim Dyn 37, 1707–1725 (2011). https://doi.org/10.1007/s00382-011-1093-2

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Keywords

  • Interannual climate variability
  • West African Monsoon
  • Atmospheric general circulation models