Measurements of Visual Range and Radiation-Fog (Haze) Microphysics

Meyer, M.; Jiusto, James E.; Lala, G. Garland

doi:10.1175/1520-0469(1980)037<0622:movrar>2.0.co;2

Cited by 52 publications

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“…4), on 14 occasions, when fog usually formed or dissipated. Consistently, Meyer et al (1980) observed that droplets were formed at 1-2 km visibility range, and Jiusto (1981) defined light fog by visibility between 1 and 5 km. Such visibility was caused by few rather large droplets that contributed more to LWC and less to the extinction coefficient: the droplet effective diameter was larger than the monthly average of 15 ± 3 µm, similar to Wendisch et al (1998), and droplet number concentration was smaller (8-45 cm −3 ) than the monthly average of 100 ± 50 cm −3 .…”

Section: Fogmentioning

confidence: 56%

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Enhanced extinction of visible radiation due to hydrated aerosols in mist and fog

Elías¹,

Dupont

Hammer

et al. 2015

Atmos. Chem. Phys.

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Abstract. The study assesses the contribution of aerosols to the extinction of visible radiation in the mist-fog-mist cycle. Relative humidity is large in the mist-fog-mist cycle, and aerosols most efficient in interacting with visible radiation are hydrated and compose the accumulation mode. Measurements of the microphysical and optical properties of these hydrated aerosols with diameters larger than 0.4 µm were carried out near Paris, during November 2011, under ambient conditions. Eleven mist-fog-mist cycles were observed, with a cumulated fog duration of 96 h, and a cumulated mist-fogmist cycle duration of 240 h.In mist, aerosols grew by taking up water at relative humidities larger than 93 %, causing a visibility decrease below 5 km. While visibility decreased down from 5 to a few kilometres, the mean size of the hydrated aerosols increased, and their number concentration (N ha ) increased from approximately 160 to approximately 600 cm −3 . When fog formed, droplets became the strongest contributors to visible radiation extinction, and liquid water content (LWC) increased beyond 7 mg m −3 . Hydrated aerosols of the accumulation mode co-existed with droplets, as interstitial non-activated aerosols. Their size continued to increase, and some aerosols achieved diameters larger than 2.5 µm. The mean transition diameter between the aerosol accumulation mode and the small droplet mode was 4.0 ± 1.1 µm. N ha also increased on average by 60 % after fog formation. Consequently, the mean contribution to extinction in fog was 20 ± 15 % from hydrated aerosols smaller than 2.5 µm and 6 ± 7 % from larger aerosols. The standard deviation was large because of the large variability of N ha in fog, which could be smaller than in mist or 3 times larger.The particle extinction coefficient in fog can be computed as the sum of a droplet component and an aerosol component, which can be approximated by 3.5 N ha (N ha in cm −3 and particle extinction coefficient in Mm −1 ). We observed an influence of the main formation process on N ha , but not on the contribution to fog extinction by aerosols. Indeed, in fogs formed by stratus lowering (STL), the mean N ha was 360 ± 140 cm −3 , close to the value observed in mist, while in fogs formed by nocturnal radiative cooling (RAD) under cloud-free sky, the mean N ha was 600 ± 350 cm −3 . But because visibility (extinction) in fog was also lower (larger) in RAD than in STL fogs, the contribution by aerosols to extinction depended little on the fog formation process. Similarly, the proportion of hydrated aerosols over all aerosols (dry and hydrated) did not depend on the fog formation process.Measurements showed that visibility in RAD fogs was smaller than in STL fogs due to three factors: (1) LWC was larger in RAD than in STL fogs, (2) droplets were smaller, (3) hydrated aerosols composing the accumulation mode were more numerous.

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Section: Fogmentioning

confidence: 56%

“…Considering that hydrated aerosols are potential condensation nuclei for the formation of fog droplets (Meyer et al, 1980), a large reservoir of nuclei was usually available. Compared to the accumulation mode number, 23 ± 18 % of droplets were observed in fog.…”

Section: Influence Of the Fog Formation Processesmentioning

confidence: 99%

Enhanced extinction of visible radiation due to hydrated aerosols in mist and fog

Elías¹,

Dupont

Hammer

et al. 2015

Atmos. Chem. Phys.

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“…It has been shown [55,56] that for more adequate visibility parameterization, particularly under warm-fog conditions, it is necessary that the droplet number concentration N d be also taken into account as an independent variable along with the LWC. According to the experimental relation of Jiusto [57], the visibility is directly related to the average cloud droplet radius (and hence to the number concentration) and is indirectly related to the LWC.…”

Section: Fog Modeling and Forecastingmentioning

confidence: 99%

Fogs: Physical Basis, Characteristic Properties, and Impacts on the Environment and Human Health

Pérez-Díaz

Ivanov

Peshev

et al. 2017

Water

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This work presents a selective overview of natural fogs in terms of fog types, forms and states of occurrence, physical, micro-physical, chemical and dynamic properties, basic characterizing parameters, etc. In focus are related achievements and contributions reported mainly during the last decade and a half, as a result of both laboratory studies and field observations. Processes of homogeneous and heterogeneous nucleation are analyzed in the aspects of condensation, nuclei diversity and specifics, as related to the activation, growth and deposition of fog droplets. The effect is highlighted of the water vapor's partial pressure on the surface tension of the liquid water-air interface and the freezing point of the water droplets. Some problems and aspects of fog modeling, parameterization, and forecasting are outlined and discussed on the examples of newly developed relevant 1D/3D theoretical models. Important issues of fog impacts on the air quality, ecosystems, water basins, societal life, and human health are also addressed and discussed, particularly in cases of anthropogenically modified (chemical, radioactive, etc.) fogs. In view of reducing the possible negative effects of fogs, conclusions are drawn concerning the new demands and challenges to fog characterization imposed by the changing natural and social environment and the needs for new data on and approaches to more adequate observations of fog-related events.

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“…In the last 30 years, fog droplet size distributions and microphysical characteristics were investigated in many field experiments, e.g., in Albany, New York (MEYER et al, 1980), and in two field campaigns (in 1989 and 1994) in the Po Valley, Italy (FUZZI et al, 1992HEINTZENBERG et al, 1998;LAJ et al, 1998;RICCI et al, 1998), during which bimodal drop-size distribution and quasi-periodic oscillations with a period between 10 and 15 min were discussed . During the recent 10 years, Paris Fog Field Experiment (ELIAS et al, 2009;HAEFFELIN et al, 2010) and Fog Remote Sensing and Modeling (FRAM) project (GULTEPE et al, , 2009GULTEPE and MILBRANDT, 2010) were conducted in Paris, France and in Canada, respectively.…”

Section: Introductionmentioning

confidence: 99%

Summary of a 4-Year Fog Field Study in Northern Nanjing, Part 2: Fog Microphysics

Niu

Liu

Zhao

et al. 2011

Pure Appl. Geophys.

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Comprehensive field observations of fog were conducted during the winters of 2006-2009 at the Nanjing University of Information Science & Technology, in order to study macro-and micro-physical structures and physical-chemical processes of dense fogs in northern Nanjing. The fog boundary-layer structures of different types and their corresponding characteristics are presented in Part I of these twin papers. In this second part, microphysical characteristics and droplet spectrum distributions of different types of fogs, microphysical relationships (among fog droplet concentration, liquid water content, and mean diameter), and microphysics of atmospheric aerosols during haze/fog events are discussed. The results show that there are large differences in microphysical parameters among four types of haze/fog. Many interesting phenomena, including fog burst reinforcement, fog droplet spectrum broadening, fog bimodal or multi-modal drop-size distributions, and critical triggering maxD value of fog coagulation growth, were captured during the 4-year field study.

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Measurements of Visual Range and Radiation-Fog (Haze) Microphysics

Cited by 52 publications

References 0 publications

Enhanced extinction of visible radiation due to hydrated aerosols in mist and fog

Enhanced extinction of visible radiation due to hydrated aerosols in mist and fog

Fogs: Physical Basis, Characteristic Properties, and Impacts on the Environment and Human Health

Summary of a 4-Year Fog Field Study in Northern Nanjing, Part 2: Fog Microphysics

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