Simulated changes in the relationship between tropical ocean temperatures and the western African monsoon during the mid-Holocene |
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| Authors: | Y Zhao P Braconnot S P Harrison P Yiou O Marti |
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| Institution: | (1) IPSL/Laboratoire de Sciences du climat et de l’environnement, Unité mixte CEA-CNRS, Orme des Merisiers, bat. 709, 91191 Gif-sur-Yvette, France;(2) School of Geographical Sciences, University of Bristol, Bristol, BS8 1SS, UK |
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| Abstract: | Results from nine coupled ocean-atmosphere simulations have been used to investigate changes in the relationship between the
variability of monsoon precipitation over western Africa and tropical sea surface temperatures (SSTs) between the mid-Holocene
and the present day. Although the influence of tropical SSTs on the African monsoon is generally overestimated in the control
simulations, the models reproduce aspects of the observed modes of variability. Thus, most models reproduce the observed negative
correlation between western Sahelian precipitation and SST anomalies in the eastern tropical Pacific, and many of them capture
the positive correlation between SST anomalies in the eastern tropical Atlantic and precipitation over the Guinea coastal
region. Although the response of individual model to the change in orbital forcing between 6 ka and present differs somewhat,
eight of the models show that the strength of the teleconnection between SSTs in the eastern tropical Pacific and Sahelian
precipitation is weaker in the mid-Holocene. Some of the models imply that this weakening was associated with a shift towards
longer time periods (from 3–5 years in the control simulations toward 4–10 years in the mid-Holocene simulations). The simulated
reduction in the teleconnection between eastern tropical Pacific SSTs and Sahelian precipitation appears to be primarily related
to a reduction in the atmospheric circulation bridge between the Pacific and West Africa but, depending on the model, other
mechanisms such as increased importance of other modes of tropical ocean variability or increased local recycling of monsoonal
precipitation can also play a role. |
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