气候变化领域集成服务门户(CCPortal): Low-level stratiform clouds and dynamical features observed within the southern West African monsoon

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DOI	10.5194/acp-19-8979-2019
	Low-level stratiform clouds and dynamical features observed within the southern West African monsoon
	Dione C.; Lohou F.; Lothon M.; Adler B.; Babić K.; Kalthoff N.; Pedruzo-Bagazgoitia X.; Bezombes Y.; Gabella O.
发表日期	2019
ISSN	16807316
起始页码	8979
结束页码	8997
卷号	19 期号:13
英文摘要	During the boreal summer, the monsoon season that takes place in West Africa is accompanied by low stratus clouds over land that stretch from the Guinean coast several hundred kilometers inland. Numerical climate and weather models need finer description and knowledge of cloud macrophysical characteristics and of the dynamical and thermodynamical structures occupying the lowest troposphere, in order to be properly evaluated in this region. The Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa (DACCIWA) field experiment, which took place in summer 2016, addresses this knowledge gap. Low-level atmospheric dynamics and stratiform low-level cloud macrophysical properties are analyzed using in situ and remote sensing measurements continuously collected from 20 June to 30 July at Savè, Benin, roughly 180 km from the coast. The macrophysical characteristics of the stratus clouds are deduced from a ceilometer, an infrared cloud camera, and cloud radar. Onset times, evolution, dissipation times, base heights, and thickness are evaluated. The data from an ultra-high-frequency (UHF) wind profiler, a microwave radiometer, and an energy balance station are used to quantify the occurrence and characteristics of the monsoon flow, the nocturnal low-level jet, and the cold air mass inflow propagating northward from the coast of the Gulf of Guinea. The results show that these dynamical structures are very regularly observed during the entire 41 d documented period. Monsoon flow is observed every day during our study period. The so-called "maritime inflow" and the nocturnal low-level jet are also systematic features in this area. According to synoptic atmospheric conditions, the maritime inflow reaches Savè around 18:00-19:00 UTC on average. This timing is correlated with the strength of the monsoon flow. This time of arrival is close to the time range of the nocturnal low-level jet settlement. As a result, these phenomena are difficult to distinguish at the Savè site. The low-level jet occurs every night, except during rain events, and is associated 65 % of the time with low stratus clouds. Stratus clouds form between 22:00 and 06:00 UTC at an elevation close to the nocturnal low-level jet core height. The cloud base height, 310±30 m above ground level (a.g.l.), is rather stationary during the night and remains below the jet core height. The cloud top height, at 640±100 m a.g.l., is typically found above the jet core. The nocturnal low-level jet, low-level stratiform clouds, monsoon flow, and maritime inflow reveal significant day-to-day and intra-seasonal variability during the summer given the importance of the different monsoon phases and synoptic atmospheric conditions. Distributions of strength, depth, onset time, breakup time, etc. are quantified here. These results contribute to satisfy the main goals of DACCIWA and allow a conceptual model of the dynamical structures in the lowest troposphere over the southern part of West Africa. © 2019. This work is distributed under the Creative Commons Attribution 4.0 License.
语种	英语
scopus关键词	aerosol composition; cloud microphysics; monsoon; numerical model; remote sensing; seasonal variation; stratiform cloud; volcanic cloud; Atlantic Ocean; Gulf of Guinea
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/144281
作者单位	Laboratoire d'Aérologie, Université de Toulouse, CNRS, UPS, Toulouse, France; Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany; Wageningen University and Research, Netherlands; African Centre for Meteorological Applications for Development, Niamey, Niger
推荐引用方式 GB/T 7714	Dione C.,Lohou F.,Lothon M.,et al. Low-level stratiform clouds and dynamical features observed within the southern West African monsoon[J],2019,19(13).
APA	Dione C..,Lohou F..,Lothon M..,Adler B..,Babić K..,...&Gabella O..(2019).Low-level stratiform clouds and dynamical features observed within the southern West African monsoon.Atmospheric Chemistry and Physics,19(13).
MLA	Dione C.,et al."Low-level stratiform clouds and dynamical features observed within the southern West African monsoon".Atmospheric Chemistry and Physics 19.13(2019).