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West African monsoon response to greenhouse gas and sulphate aerosol forcing under two emission scenarios

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Abstract

The impact of increased greenhouse gases (GHG) and aerosols concentrations upon the West African monsoon (WAM) is investigated for the late twenty-first century period using the Météo-France ARPEGE-IFS high-resolution atmospheric model. Perturbed (2070–2100) and current (1961–2000) climates are compared using the model in time-slice mode. The model is forced by global sea surface temperatures provided by two transient scenarios performed with low-resolution coupled models and by two GHG evolution scenarios, SRES-A2 and SRES-B2. Comparing to reanalysis and observed data sets, the model is able to reproduce a realistic seasonal cycle of WAM despite a clear underestimation of the African Easterly Jet (AEJ) during the boreal summer. Mean temperature change indicates a global warming over the continent (stronger over North and South Africa). Simulated precipitation change at the end of the twenty-first century shows an increase in precipitation over Sudan-Sahel linked to a strong positive feedback with surface evaporation. Along Guinea Gulf coast, rainfall regimes are driven by large-scale moisture advection. Moreover, results show a mean precipitation decrease (increase) in the most (less) enhanced GHG atmosphere over this region. Modification of the seasonal hydrological cycle consists in a rain increase during the monsoon onset. There is a significant increase in rainfall variance over the Sahel, which extends over the Guinea coast region in the moderate emission scenario. Enhanced precipitation over Sahel is linked to large-scale circulation changes, namely a weakening of the AEJ and an intensification of the Tropical Easterly Jet.

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  1. CERFACS, 42 Avenue G. Coriolis, 31057, Toulouse-Cedex, France

    C. Caminade, L. Terray & E. Maisonnave

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  1. C. Caminade
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  2. L. Terray
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  3. E. Maisonnave
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Correspondence to C. Caminade.

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Caminade, C., Terray, L. & Maisonnave, E. West African monsoon response to greenhouse gas and sulphate aerosol forcing under two emission scenarios. Clim Dyn 26, 531–547 (2006). https://doi.org/10.1007/s00382-005-0083-7

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  • DOI: https://doi.org/10.1007/s00382-005-0083-7

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