The West African monsoon response to aerosols from past, present and potential future emitting regions
Abstract
West Africa has one of the fastest growing populations in the world and depends heavily on the summer monsoon to supply annual rainfall. However, future predictions of the West African monsoon under a changing climate contain some of the largest uncertainties. Aerosols play a critical role in the hydrological cycle by modifying large-scale atmospheric dynamics and thermodynamics as well as microphysical cloud processes. While most studies of aerosol-induced precipitation changes in Africa have focused on locally sourced aerosols, such as Saharan dust or biomass burning emissions, here we focus on the relative control of the West African monsoon by remote aerosol sources. Using a coupled atmospheric and mixed-layer ocean model, we isolate the impact of emissions from the largest past (United States and Europe), present (China and India) and future projected (Brazil and Indonesia) emitters of anthropogenic aerosols, relative to aerosol emissions on the African continent (East Africa and South Africa). We fix the aerosol composition and amount for each emitting region, allowing us to directly compare the impact of the aerosol emissions' geographic location. Our initial results show that, per unit of emissions, aerosols from the northern hemisphere mid-latitudes induce stronger reductions in West African precipitation than emissions from the African continent. The identified effect of these northern hemisphere emissions agrees with studies of the effect of historical emissions (which have largely been from the northern hemisphere) on observed changes in West African precipitation and the southward shift of the intertropical front over the 20th century. However, the climate impact of future aerosol emissions remains relatively unexplored. Our results also show that emissions from the southern hemisphere mid-latitudes and the tropics, where emissions are projected to increase, induce the weakest precipitation response and appear to do so through a different dynamical process. The findings from this study suggest a reduced sensitivity of the West African monsoon to future aerosol emissions as the dominant geographic location of emissions change.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A51S2882L
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0320 Cloud physics and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0321 Cloud/radiation interaction;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES;
- 3354 Precipitation;
- ATMOSPHERIC PROCESSES