Synoptic-scale controls of fog and low-cloud  variability in the Namib Desert

Andersen, Hendrik; Čermák, Jan; Fuchs, Julia; Knippertz, Peter; Gaetani, Marco; Quinting, Julian; Sippel, Sebastian; Vogt, Roland

doi:10.5194/acp-20-3415-2020

Cited by 24 publications

(15 citation statements)

References 76 publications

(134 reference statements)

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“…A study found that the formation of advection fog is attributed to. Synoptic-scale circulation (South Atlantic high and lower mean sea level pressure on land) circulation in Namib desert causes alteration in the moisture transport and intensified cooling of the marine boundary layer, helping in the formation of sustenance of advection fog (Andersen et al 2020 ). Similarly, Koran Western peninsula experiences fog when there is the formation of a high-pressure zone in the Yellow sea, during night time the moisture-laden south-westerly winds flow towards the land where it meets offshore land breeze and Katabatic easterly winds, together with nocturnal cooling the air becomes saturated leading to the formation of advection fog near the coast (Choi and Speer 2006 ).…”

Section: Factors Influencing Fog Formationmentioning

confidence: 99%

A review on factors influencing fog formation, classification, forecasting, detection and impacts

Lakra

Avishek

2022

Rend. Fis. Acc. Lincei

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With the changing climate and environment, the nature of fog has also changed and because of its impact on humans and other systems, study of fog becomes essential. Hence, the study of its controlling factors such as the characteristics of condensation nuclei, microphysics, air–surface interaction, moisture, heat fluxes and synoptic conditions also become crucial, along with research in the field of prediction and detection. The current review expands for the period between 1976 to 2021, however, especially focused on the research articles published in the last two decades. It considers 250 research papers/research letters, 24 review papers, four book chapters/manuals, five news articles, 15 reports, six conference papers and five other online readings. This review is a compilation of the pros and cons of the techniques used to determine the factors influencing fog formation, its classification, tools and techniques available for its detection and forecast. Some recent advanced are also discussed in this review: role of soil properties on fogs, application of microwave communication links in the detection of fog, new class of smog, and how the cognitive abilities of humans are affected by fog. Recently India and China are facing an emergence and repetitions of fog haze/smog and thus their policies initiatives are also briefly discussed. It is concluded that the complexity in fog forecasting is high due to multiple factors playing a role at multiple levels. Most of the researchers have worked upon the role of humidity, temperature, wind, and boundary layer to predict fogs. However, the role of global wind circulations, soil properties, and anthropogenic heat requires further investigations. Literature shows that fog is being harnessed to address water insecurity in various countries, however, coastal areas of Angola, Namibia and South Africa, Kenya, Eastern Yemen, Oman, China, India, Sri Lanka, Mexico, along with the mountainous regions of Peru, Chile, and Ecuador, are some of the potential sites that can benefit from the installation of fog water harvesting systems.

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Section: Factors Influencing Fog Formationmentioning

confidence: 99%

A review on factors influencing fog formation, classification, forecasting, detection and impacts

Lakra

Avishek

2022

Rend. Fis. Acc. Lincei

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“…Therefore, the diurnal cycle of the coastal circulation is likely a main driver of the observed patterns in FLS formation and dissipation times at the Mediterranean coast. At the Atlantic coast of northern Spain, blocking of FLS by the Cantabrian mountains (Egli et al ., 2017) and upwelling (Alvarez et al ., 2010) might be important for FLS formation, as the latter plays an important role in other FLS‐prone regions such as at the southwestern African coast (Olivier and Stockton, 1989; Cermak, 2012; Andersen et al ., 2020). Close to the French Atlantic coast over the Landes forest south of 45°N, FLS forms earlier over the forest (around midnight) than over its surroundings (FLS formation in the morning), particularly in spring and summer.…”

Section: Discussionmentioning

confidence: 99%

A satellite‐based climatology of fog and low stratus formation and dissipation times in central Europe

Pauli

Čermák

Andersen

2022

Quart J Royal Meteoro Soc

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Knowledge of fog and low stratus (FLS) cloud patterns and life cycles is important for traffic safety, for the production of solar energy and for the analysis of cloud processes in the climate system. While meteorological stations provide information on FLS, a data set describing FLS formation and dissipation times on large spatial and temporal scales does not yet exist. In this study, we use logistic regression to extract FLS formation and dissipation times from a satellite-based 10-year FLS data set covering central Europe. The resulting data set is the first to provide a geographic perspective on FLS formation and dissipation at a continental scale. The patterns found show a clear dependency of FLS formation and dissipation times on topography. In mountainous areas, FLS forms in the night and dissipates in the morning. In river valleys, the typical FLS life cycle shifts to formation after sunrise and dissipation in the afternoon. Seasonal patterns of FLS formation and dissipation show similar FLS formation and dissipation times in winter and autumn, and in spring and summer, with longer events in the former two seasons.

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“…9g). This circulation pattern advects moist, warm air along the coast of Namibia, encouraging an inland fog (Andersen et al, 2020). Perhaps this produces enough precipitation to reduce N d near the shore, although that remains speculation.…”

Section: October: Increased Cloud Cover On Smokier Daysmentioning

confidence: 98%

Sunlight-absorbing aerosol amplifies the seasonal cycle in low cloud fraction over the southeast Atlantic

Zhang¹,

Zuidema²

2021

Preprint

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Abstract. Many studies examining shortwave-absorbing aerosol-cloud interactions over the southeast Atlantic apply a seasonal averaging. This disregards a meteorology that raises the mean altitude of the smoke layer from July to October. This study details the month-by-month changes in cloud properties and the large-scale environment as a function of the biomass-burning aerosol loading at Ascension Island from July to October, based on measurements from Ascension Island (8º S, 14.5º W), satellite retrievals and reanalysis. In July and August, variability in the smoke loading predominantly occurs in the boundary layer. During both months, the low-cloud fraction is less and is increasingly cumuliform when more smoke is present, with the exception of a late morning boundary layer deepening that encourages a short-lived cloud development. The meteorology varies little, suggesting aerosol-cloud interactions consistent with a boundary-layer semi-direct effect can explain the cloudiness changes. September marks a transition month during which mid-latitude disturbances can intrude into the Atlantic subtropics, constraining the land-based anticyclonic circulation transporting free-tropospheric aerosol to closer to the coast. Stronger boundary layer winds help deepen, dry, and cool the boundary layer near the main stratocumulus deck compared to that on days with high smoke loadings, with stratocumulus reducing everywhere but at the northern deck edge. Longwave cooling rates generated by a sharp water vapor gradient at the aerosol layer top facilitates small-scale vertical mixing, and could help to maintain a better-mixed September free troposphere. The October meteorology is more singularly dependent on the strength of the free-tropospheric winds advecting aerosol offshore. Free-tropospheric aerosol is less, and moisture variability more, compared to September. Low-level clouds increase and are more stratiform, when the smoke loadings are higher. The increased free-tropospheric moisture can help sustain the clouds through reducing evaporative drying during cloud-top entrainment. Enhanced subsidence above the coastal upwelling region increasing cloud droplet number concentrations may further prolong cloud lifetime through microphysical interactions. Reduced subsidence underneath stronger free-tropospheric winds at Ascension supports slightly higher cloud tops during smokier conditions. Overall the monthly changes in the large-scale aerosol and moisture vertical structure act to amplify the seasonal cycle in low-cloud amount and morphology, raising a climate importance as cloudiness changes dominate changes in the top-of-atmosphere radiation budget.

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Synoptic-scale controls of fog and low-cloud variability in the Namib Desert

Cited by 24 publications

References 76 publications

A review on factors influencing fog formation, classification, forecasting, detection and impacts

A review on factors influencing fog formation, classification, forecasting, detection and impacts

A satellite‐based climatology of fog and low stratus formation and dissipation times in central Europe

Sunlight-absorbing aerosol amplifies the seasonal cycle in low cloud fraction over the southeast Atlantic

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