![]() Ein Studium seiner Gegenwart und seiner Zukunft wiederum hilft uns dabei, die global bedeutende Artenvielfalt und die ökosystemaren Dienstleistungen Ostafrikas zu schützen. Ostafrika ist ein natürliches Labor: Durch ein Studium seiner einzigartigen geologischen und biologischen Geschichte lassen sich unsere Theorien und Modelle überprüfen und verbessern. A conceptual framework that relates African monsoon variations to both equatorial and inter-hemispheric differential solar heating is presented. 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. Contrary to generally accepted theory, orbital modulation of seasonal differential heating alone is shown to be a weak driver of African monsoon variations. ![]() We find that energy fluxes in the African sector are related to orbital forcing in a complex manner. ![]() 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). ![]() However, how orbital variations affect regional climate is not well understood. 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. 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 Sahara was significantly greener 11-5 kya and during multiple earlier interglacial periods. 1b i.e., assuming the changes in precipitation are caused primarily by changes in the position of the ITCZ, not its intensity or the duration of the wet season). Similarly, the simulated mean position of the African ITCZ during boreal summer is shifted by about 1 degree, compared with a minimal shift of about 5 degrees required to maintain a Saharan steppe ( Fig. 1b Jolly et al., 1998 Joussaume et al., 1999) or lacustrine environments (Lézine et al., 2011). However, all models severely underestimate reconstructions of the minimal increase in precipitation required to sustain a Saharan steppe: simulated changes do not exceed 100 mm yr −1 in the mid Sahara, in disagreement with evidence of widespread grasslands that require an increase of at least 200-300 mm yr −1 (Fig. 1a see Harrison et al., 2015 Chevalier et al., 2017 for a detailed analysis). As expected, a clear northward shift of the annual-mean precipitation over Africa is captured in the ensemble mean of PMIP3 models ( Fig. ![]()
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January 2023
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