气候变化领域集成服务门户(CCPortal): The role of low-level clouds in the West African monsoon system

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DOI	10.5194/acp-19-1623-2019
	The role of low-level clouds in the West African monsoon system
	Kniffka A.; Knippertz P.; Fink A.H.
发表日期	2019
ISSN	16807316
起始页码	1623
结束页码	1647
卷号	19 期号:3
英文摘要	Realistically simulating the West African monsoon system still poses a substantial challenge to state-of-the-art weather and climate models. One particular issue is the representation of the extensive and persistent low-level clouds over southern West Africa (SWA) during boreal summer. These clouds are important in regulating the amount of solar radiation reaching the surface, but their role in the local energy balance and the overall monsoon system has never been assessed. Based on sensitivity experiments using the ICON model for July 2006, we show for the first time that rainfall over SWA depends logarithmically on the optical thickness of low clouds, as these control the diurnal evolution of the planetary boundary layer, vertical stability and finally convection. In our experiments, the increased precipitation over SWA has a small direct effect on the downstream Sahel, as higher temperatures due to increased surface radiation are accompanied by decreases in low-level moisture due to changes in advection, leading to almost unchanged equivalent potential temperatures in the Sahel. A systematic comparison of simulations with and without convective parameterization reveals agreement in the direction of the precipitation signal but larger sensitivity for explicit convection. For parameterized convection the main rainband is too far south and the diurnal cycle shows signs of unrealistic vertical mixing, leading to a positive feedback on low clouds. The results demonstrate that relatively minor errors, variations or trends in low-level cloudiness over SWA can have substantial impacts on precipitation. Similarly, they suggest that the dimming likely associated with an increase in anthropogenic emissions in the future would lead to a decrease in summer rainfall in the densely populated Guinea coastal area. Future work should investigate longer-term effects of the misrepresentation of low clouds in climate models, e.g. moderated through effects on rainfall, soil moisture and evaporation. © 2019 Author(s).
语种	英语
scopus关键词	atmospheric moisture; climate modeling; cloud cover; energy balance; monsoon; rainband; rainfall; solar radiation; summer; Sahel [Sub-Saharan Africa]
来源期刊	Atmospheric Chemistry and Physics
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/144664
作者单位	Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Karlsruhe, Germany
推荐引用方式 GB/T 7714	Kniffka A.,Knippertz P.,Fink A.H.. The role of low-level clouds in the West African monsoon system[J],2019,19(3).
APA	Kniffka A.,Knippertz P.,&Fink A.H..(2019).The role of low-level clouds in the West African monsoon system.Atmospheric Chemistry and Physics,19(3).
MLA	Kniffka A.,et al."The role of low-level clouds in the West African monsoon system".Atmospheric Chemistry and Physics 19.3(2019).