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Published September 15, 2019 | Supplemental Material
Journal Article Open

Both differential and equatorial heating contributed to African monsoon variations during the mid-Holocene

Abstract

The Sahara was significantly greener 11-5 kya and during multiple earlier interglacial periods. But the mechanisms related to the greening of the Sahara remain uncertain as most climate models severely underestimate past wet conditions over north Africa. The variations in the African monsoon related to the greening of the Sahara are thought to be associated with the variations in the inter-hemispheric differential heating of Earth, caused by orbital variations. However, how orbital variations affect regional climate is not well understood. Using recent theory that relates the position of the tropical rain belt to the atmospheric energy budget, we study the effect of orbital forcing during the mid-Holocene on the African monsoon in simulations provided by the third phase of the Paleo Model Intercomparison Project (PMIP3). We find that energy fluxes in the African sector are related to orbital forcing in a complex manner. Contrary to generally accepted theory, orbital modulation of seasonal differential heating alone is shown to be a weak driver of African monsoon variations. Instead, net atmospheric heating near the equator, which modulates the intensity and extent of seasonal migrations of the tropical rain belt, is an important but overlooked driver of African monsoon variations. A conceptual framework that relates African monsoon variations to both equatorial and inter-hemispheric differential solar heating is presented.

Additional Information

© 2019 Elsevier B.V. Received 28 January 2019, Revised 15 May 2019, Accepted 17 June 2019, Available online 1 July 2019. The PMIP3 data was downloaded from Earth System Grid Federation (ESGF). Ori Adam acknowledges support by the Israel Science Foundation grant 1185/17.

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