气候变化领域集成服务门户(CCPortal): Synoptic-scale controls of fog and low-cloud variability in the Namib Desert

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DOI	10.5194/acp-20-3415-2020
	Synoptic-scale controls of fog and low-cloud variability in the Namib Desert
	Andersen H.; Cermak J.; Fuchs J.; Knippertz P.; Gaetani M.; Quinting J.; Sippel S.; Vogt R.
发表日期	2020
ISSN	1680-7316
起始页码	3415
结束页码	3438
卷号	20 期号:6
英文摘要	Fog is a defining characteristic of the climate of the Namib Desert, and its water and nutrient input are important for local ecosystems. In part due to sparse observation data, the local mechanisms that lead to fog occurrence in the Namib are not yet fully understood, and to date, potential synoptic-scale controls have not been investigated. In this study, a recently established 14-year data set of satellite observations of fog and low clouds in the central Namib is analyzed in conjunction with reanalysis data in order to identify synoptic-scale patterns associated with fog and low-cloud variability in the central Namib during two seasons with different spatial fog occurrence patterns. It is found that during both seasons, mean sea level pressure and geopotential height at 500 hPa differ markedly between fog/low-cloud and clear days, with patterns indicating the presence of synoptic-scale disturbances on fog and low-cloud days. These regularly occurring disturbances increase the probability of fog and low-cloud occurrence in the central Namib in two main ways: (1) an anomalously dry free troposphere in the coastal region of the Namib leads to stronger longwave cooling of the marine boundary layer, increasing low-cloud cover, especially over the ocean where the anomaly is strongest; (2) local wind systems are modulated, leading to an onshore anomaly of marine boundary-layer air masses. This is consistent with air mass back trajectories and a principal component analysis of spatial wind patterns that point to advected marine boundary-layer air masses on fog and low-cloud days, whereas subsiding continental air masses dominate on clear days. Large-scale free-tropospheric moisture transport into southern Africa seems to be a key factor modulating the onshore advection of marine boundary-layer air masses during April, May, and June, as the associated increase in greenhouse gas warming and thus surface heating are observed to contribute to a continental heat low anomaly. A statistical model is trained to discriminate between fog/low-cloud and clear days based on information on large-scale dynamics. The model accurately predicts fog and low-cloud days, illustrating the importance of large-scale pressure modulation and advective processes. It can be concluded that regional fog in the Namib is predominantly of an advective nature and that fog and low-cloud cover is effectively maintained by increased cloud-top radiative cooling. Seasonally different manifestations of synoptic-scale disturbances act to modify its day-to-day variability and the balance of mechanisms leading to its formation and maintenance. The results are the basis for a new conceptual model of the synoptic-scale mechanisms that control fog and low-cloud variability in the Namib Desert and will guide future studies of coastal fog regimes.. © 2020 BMJ Publishing Group. All rights reserved.
语种	英语
scopus关键词	air mass; atmospheric moisture; boundary layer; cloud cover; data set; fog; geopotential; satellite imagery; synoptic meteorology; troposphere; Namib Desert; Namibia
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/141461
作者单位	Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany; Institute of Photogrammetry and Remote Sensing, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany; IPSL LISA, CNRS, Université Paris-Est Créteil_aor4 Université Paris, Créteil, France; IPSL LATMOS, CNRS, Sorbonne Université_aor4 Université Paris-Saclay, Paris, France; Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland; Norwegian Institute of Bioeconomy Research, Ås, Norway; Department of Environmental Sciences, University of Basel, Basel, Switzerland
推荐引用方式 GB/T 7714	Andersen H.,Cermak J.,Fuchs J.,et al. Synoptic-scale controls of fog and low-cloud variability in the Namib Desert[J],2020,20(6).
APA	Andersen H..,Cermak J..,Fuchs J..,Knippertz P..,Gaetani M..,...&Vogt R..(2020).Synoptic-scale controls of fog and low-cloud variability in the Namib Desert.Atmospheric Chemistry and Physics,20(6).
MLA	Andersen H.,et al."Synoptic-scale controls of fog and low-cloud variability in the Namib Desert".Atmospheric Chemistry and Physics 20.6(2020).