气候变化领域集成服务门户(CCPortal): Breakup of nocturnal low-level stratiform clouds during the southern West African monsoon season

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DOI	10.5194/acp-21-2027-2021
	Breakup of nocturnal low-level stratiform clouds during the southern West African monsoon season
	Zouzoua M.; Lohou F.; Assamoi P.; Lothon M.; Yoboue V.; Dione C.; Kalthoff N.; Adler B.; Babić K.; Pedruzo-Bagazgoitia X.; Derrien S.
发表日期	2021
ISSN	1680-7316
起始页码	2027
结束页码	2051
卷号	21 期号:3
英文摘要	Within the framework of the DACCIWA (Dynamics Aerosol Chemistry Cloud Interactions in West Africa) project and based on a field experiment conducted in June and July 2016, we analyze the daytime breakup of continental low-level stratiform clouds in southern West Africa. We use the observational data gathered during 22 precipitation-free occurrences at Savè, Benin. Our analysis, which starts from the stratiform cloud formation usually at night, focuses on the role played by the coupling between cloud and surface in the transition towards shallow convective clouds during daytime. It is based on several diagnostics, including the Richardson number and various cloud macrophysical properties. The distance between the cloud base height and lifting condensation level is used as a criterion of coupling. We also make an attempt to estimate the most predominant terms of the liquid water path budget in the early morning. When the nocturnal low-level stratiform cloud forms, it is decoupled from the surface except in one case. In the early morning, the cloud is found coupled with the surface in 9 cases and remains decoupled in the 13 other cases. The coupling, which occurs within the 4 h after cloud formation, is accompanied by cloud base lowering and near-neutral thermal stability in the subcloud layer. Further, at the initial stage of the transition, the stratiform cloud base is slightly cooler, wetter and more homogeneous in coupled cases. The moisture jump at the cloud top is usually found to be lower than 2 g kg-1 and the temperature jump within 1 5 K, which is significantly smaller than typical marine stratocumulus and explained by the monsoon flow environment in which the stratiform cloud develops over West Africa. No significant difference in liquid water path budget terms was found between coupled and decoupled cases. In agreement with previous numerical studies, we found that the stratiform cloud maintenance before sunrise results from the interplay between the predominant radiative cooling, entrainment and large-scale subsidence at its top. Three transition scenarios were observed depending on the state of coupling at the initial stage. In coupled cases, the low-level stratiform cloud remains coupled until its breakup. In five of the decoupled cases, the cloud couples with the surface as the lifting condensation level rises. In the eight remaining cases, the stratiform cloud remains hypothetically decoupled from the surface throughout its life cycle since the height of its base remains separated from the condensation level. In cases of coupling during the transition, the stratiform cloud base lifts with the growing convective boundary layer roughly between 06:30 and 08:00 UTC. The cloud deck breakup, occurring at 11:00 UTC or later, leads to the formation of shallow convective clouds. When the decoupling subsists, shallow cumulus clouds form below the stratiform cloud deck between 06:30 and 09:00 UTC. The breakup time in this scenario has a stronger variability and occurs before 11:00 UTC in most cases. Thus, we argue that the coupling with the surface during daytime hours has a crucial role in the low-level stratiform cloud maintenance and its transition towards shallow convective clouds. © 2021 Copernicus GmbH. All rights reserved.
语种	英语
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/168766
作者单位	Laboratoire des Sciences de la Matière, De l'Environnement et de l'Energie Solaire (LASMES), Université Félix Houphouët Boigny, Abidjan, Cote d'Ivoire; Laboratoire d'Aérologie, Université de Toulouse, CNRS, Ups, Toulouse, France; African Centre of Meteorological Applications for Development, Niamey, Niger; Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT, Karlsruhe, Germany; Meteorology and Air Quality Group, Wageningen University and Research, Wageningen, Netherlands
推荐引用方式 GB/T 7714	Zouzoua M.,Lohou F.,Assamoi P.,et al. Breakup of nocturnal low-level stratiform clouds during the southern West African monsoon season[J],2021,21(3).
APA	Zouzoua M..,Lohou F..,Assamoi P..,Lothon M..,Yoboue V..,...&Derrien S..(2021).Breakup of nocturnal low-level stratiform clouds during the southern West African monsoon season.Atmospheric Chemistry and Physics,21(3).
MLA	Zouzoua M.,et al."Breakup of nocturnal low-level stratiform clouds during the southern West African monsoon season".Atmospheric Chemistry and Physics 21.3(2021).