气候变化领域集成服务门户(CCPortal): The diurnal stratocumulus-to-cumulus transition over land in southern West Africa

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DOI	10.5194/acp-20-2735-2020
	The diurnal stratocumulus-to-cumulus transition over land in southern West Africa
	Pedruzo-Bagazgoitia X.; De Roode S.R.; Adler B.; Babić K.; Dione C.; Kalthoff N.; Lohou F.; Lothon M.; Vilà-Guerau De Arellano J.
发表日期	2020
ISSN	1680-7316
起始页码	2735
结束页码	2754
卷号	20 期号:5
英文摘要	The misrepresentation of the diurnal cycle of boundary layer clouds by large-scale models strongly impacts the modeled regional energy balance in southern West Africa. In particular, recognizing the processes involved in the maintenance and transition of the nighttime stratocumulus to diurnal shallow cumulus over land remains a challenge. This is due to the fact that over vegetation, surface fluxes exhibit a much larger magnitude and variability than on the more researched marine stratocumulus transitions. An improved understanding of the interactions between surface and atmosphere is thus necessary to improve its representation. To this end, the Dynamics-aerosol-chemistry-cloud interactions in West Africa (DACCIWA) measurement campaign gathered a unique dataset of observations of the frequent stratocumulus-to-cumulus transition in southern West Africa. Inspired and constrained by these observations, we perform a series of numerical experiments using large eddy simulation. The experiments include interactive radiation and surface schemes where we explicitly resolve, quantify and describe the physical processes driving such transition. Focusing on the local processes, we quantify the transition in terms of dynamics, radiation, cloud properties, surface processes and the evolution of dynamically relevant layers such as subcloud layer, cloud layer and inversion layer. We further quantify the processes driving the stratocumulus thinning and the subsequent transition initiation by using a liquid water path budget. Finally, we study the impact of mean wind and wind shear at the cloud top through two additional numerical experiments. We find that the sequence starts with a nighttime well-mixed layer from the surface to the cloud top, in terms of temperature and humidity, and transitions to a prototypical convective boundary layer by the afternoon. We identify radiative cooling as the largest factor for the maintenance leading to a net thickening of the cloud layer of about 18 g m-2 h-1 before sunrise. Four hours after sunrise, the cloud layer decouples from the surface through a growing negative buoyancy flux at the cloud base. After sunrise, the increasing impact of entrainment leads to a progressive thinning of the cloud layer. While the effect of wind on the stratocumulus layer during nighttime is limited, after sunrise we find shear at the cloud top to have the largest impact: the local turbulence generated by shear enhances the boundary layer growth and entrainment aided by the increased surface fluxes. As a consequence, wind shear at the cloud top accelerates the breakup and transition by about 2 h. The quantification of the transition and its driving factors presented here sets the path for an improved representation by larger-scale models. © 2020 Authors.
语种	英语
scopus关键词	aerosol; atmospheric chemistry; atmospheric dynamics; boundary layer; cloud microphysics; diurnal variation; stratocumulus; West 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/247938
作者单位	Meteorology and Air Quality Group, Wageningen University and Research, Wageningen, Netherlands; Department of Geoscience and Remote Sensing, Delft University of Technology, Delft, Netherlands; Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany; Laboratoire d'Aérologie, Université de Toulouse, CNRS, UPS, Toulouse, France
推荐引用方式 GB/T 7714	Pedruzo-Bagazgoitia X.,De Roode S.R.,Adler B.,et al. The diurnal stratocumulus-to-cumulus transition over land in southern West Africa[J],2020,20(5).
APA	Pedruzo-Bagazgoitia X..,De Roode S.R..,Adler B..,Babić K..,Dione C..,...&Vilà-Guerau De Arellano J..(2020).The diurnal stratocumulus-to-cumulus transition over land in southern West Africa.ATMOSPHERIC CHEMISTRY AND PHYSICS,20(5).
MLA	Pedruzo-Bagazgoitia X.,et al."The diurnal stratocumulus-to-cumulus transition over land in southern West Africa".ATMOSPHERIC CHEMISTRY AND PHYSICS 20.5(2020).