Advances in fog microphysics research in China

Liu, Duanyang; Li, Zihua; Yan, Wenlian; Li, Yi

doi:10.1007/s13143-016-0028-6

Cited by 13 publications

(5 citation statements)

References 18 publications

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“…In our study, droplet concentrations are rather low for semiurban conditions, with a maximum value of 150 cm −3 . For instance, Liu et al (2017) reported values in China as high as 1000 cm −3 . Moreover, our values of critical diameter are large, with a median value of 3.8 µm.…”

Section: Discussionmentioning

confidence: 99%

“…As a general rule in cloud physics, increase in aerosols causes an increase in the droplet number concentration for a given cloud type (Gultepe and Isaac, 1996;Ramanathan et al, 2001). Hudson (1980) and Liu et al (2017) found systematic differences in the fog microstructure between fogs formed in maritime, continental and urban air masses with a simultaneous increase of fog condensation nuclei and aerosol concentration. Recent numerical simulations exhibit a strong positive correlation between aerosol and droplet concentrations (Zhang et al, 2014;Stolaki et al, 2015;Maalick et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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Experimental study of the aerosol impact on fog microphysics

et al. 2019

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Abstract. Comprehensive field campaigns dedicated to fog life cycle observation were conducted during the winters of 2010–2013 at the Instrumented Site for Atmospheric Remote Sensing Research (SIRTA) observatory in a suburb of Paris. In order to document their properties, in situ microphysical measurements collected during 23 fog events induced by both radiative cooling and stratus lowering are examined here. They reveal large variability in number, concentration and size of both aerosol background before the fog onset and fog droplets according to the different cases. The objective of this paper is to evaluate the impact of aerosol particles on the fog microphysics. To derive an accurate estimation of the actual activated fog droplet number concentration Nact, we determine the hygroscopicity parameter κ, the dry and the wet critical diameter and the critical supersaturation for each case by using an iterative procedure based on the κ-Köhler theory that combines cloud condensation nuclei (CCN), dry particle and droplet size distribution measurements. Our study reveals low values of the derived critical supersaturation occurring in fog with a median of 0.043 %. Consequently, the median dry and wet activation diameters are 0.39 and 3.79 µm, respectively, leading to a minor fraction of the aerosol population activated into droplets. The corresponding Nact values are low, with median concentrations of 53.5 and 111 cm−3 within the 75th percentile. The activated fraction of aerosols exhibits remarkably low correlation with κ values, which reflects the chemical composition of the aerosols. On the contrary, the activated fraction exhibits a strong correlation with the inferred critical diameter throughout the field campaigns. This suggests that the variability in the activated fraction is mostly driven by particle size, while variations in aerosol composition are of secondary importance. Moreover, our analysis suggests that the supersaturation reached in fog could be lowered by the aerosol number concentration, which could contribute to the sink term of water vapor during the radiative cooling. Although radiative fogs are usually associated with higher aerosol loading than stratus-lowering events, our analysis also reveals that the activated fraction at the beginning of the event is similar for both types of fog. However, the evolution of the droplet concentration during the fog life cycle shows significant differences between both types of fog. This work demonstrates that an accurate calculation of supersaturation is required to provide a realistic representation of fog microphysical properties in numerical models.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental study of the aerosol impact on fog microphysics

et al. 2019

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“…It is referred to as fog burst reinforcement, which was firstly raised by Korb and Zdunkowski (1970) and systematically reviewed by Liu et al (2012) and Li et al (2019). Fog burst reinforcement is accompanied by the drastic formation of fog droplets, sudden increase of fog liquid water and broadening of droplet spectrum (D. Liu et al, 2017;Q. Liu et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

Effect of the boundary layer low-level jet on fast fog spatial propagation

Yan,

Wang,

Liu

et al. 2023

Atmos. Chem. Phys.

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Abstract. The spatiotemporal variation of fog reflects the complex interactions among fog, boundary layer thermodynamics and synoptic systems. Previous studies revealed that fog can present a fast spatial propagation feature and attribute it to the boundary layer low-level jet (BLLJ), but the effect of the BLLJ on fog propagation is not quantitatively understood. Here we analyze a large-scale fog event in Jiangsu, China, from 20 to 21 January 2020. Satellite retrievals show that fog propagates from the southeast coastal area to the northwest inland area with a speed of 9.6 m s−1, which is 3 times larger than the ground wind speeds. The ground meteorologies are insufficient to explain the fast fog propagation, which is further investigated by Weather Research and Forecasting model (WRF) simulations. The fast fog propagation could be attributed to the BLLJ occurring between 50 and 500 m, because the wind speeds (10 m s−1) and directions (southeast) of the BLLJ core are consistent with fog propagation. Through sensitive experiments and process analysis, three possible mechanisms of the BLLJ are revealed: (1) the abundant oceanic moisture is transported inland, increasing the humidity of the boundary layer and promoting condensation; (2) the oceanic warm air is transported inland, enhancing the inversion layer and favoring moisture accumulation; and (3) the moisture advection probably promotes low-stratus formation, and later it subsides to become ground fog by turbulent mixing of fog droplets. The fog propagation speed would decrease notably by 6.4 m s−1 (66 %) in the model if the BLLJ-related moisture and warm advections were turned off.

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“…As a mountain city, its extremely undulating terrain influences the dispersion of ozone. About one-third days per year are foggy; Chongqing is also known as the "Fog City," and it is always covered by thick clouds [3]. The harsh weather conditions furthermore complicate the studies in Chongqing.…”

Section: Introductionmentioning

confidence: 99%

An Optimization Approach for Hourly Ozone Simulation: A Case Study in Chongqing, China

Zhu

Zeng

Zhu³

et al. 2021

IEEE Geosci. Remote Sensing Lett.

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Continuous spatial knowledge is required to control the regional ozone pollution. Measurements from ground-level sites are beneficial to this goal, but their number is limited due to the huge expenses of site establishment, operation, and maintenance. Remote sensing seems a promising data source, but its application is challenged by bad weather conditions. Always covered by thick clouds, Chongqing, a populated industrial city in west China, is facing serious ozone pollution, but relevant studies here are relatively insufficient. Another alternative is estimating ozone by models. Well-performed models degrade in Chongqing partially due to the very complex terrain. Modeled hourly ozone does not agree with ground-level measurements. Therefore, an optimization approach is proposed to improve model estimates for such regions. This approach integrates the ground-level information (e.g., measured ozone and meteorology) through the employment of ResNet (Residual Network). ResNet overcomes the notorious vanishing gradient issue in classic neural networks, and the ability of learning complex systems is largely boosted. Ozone distribution is like a gray image that varies every second, which is not the case usually learned by ResNet. A color-image alike data structure is raised to address this "nonstill image" problem; according to the Taylor Expansion, polynomials can describe a complex system, and the errors are acceptable. To facilitate the usage in business operations, this approach is designed to be robust, inexpensive, and easy to use. The scheme of control site selection is discussed in detail. In crossvalidations, this approach performs well, averaged R 2 is higher than 0.9 and the error is less than 5 µg/m 3 .

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Advances in fog microphysics research in China

Cited by 13 publications

References 18 publications

Experimental study of the aerosol impact on fog microphysics

Experimental study of the aerosol impact on fog microphysics

Effect of the boundary layer low-level jet on fast fog spatial propagation

An Optimization Approach for Hourly Ozone Simulation: A Case Study in Chongqing, China

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