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WANG Qing, FAN Mingyue, LI Ji, et al. 2021. The Microphysical Characteristics of Winter Fog in Jinan and Its Effect on Visibility [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 45(2): 333−354. doi: 10.3878/j.issn.1006-9895.2011.19248
Citation: WANG Qing, FAN Mingyue, LI Ji, et al. 2021. The Microphysical Characteristics of Winter Fog in Jinan and Its Effect on Visibility [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 45(2): 333−354. doi: 10.3878/j.issn.1006-9895.2011.19248

The Microphysical Characteristics of Winter Fog in Jinan and Its Effect on Visibility

  • As affected by stable atmosphere, there had been ten fog events in Jinan from 19 December 2016 to 9 January 2017, during which the minimum value of visibility was below 50 m. The low visibility caused by the continuous fog events brought serious negative impacts to industrial and agricultural activities as well as to people’s daily live. In this paper, based on the measurements from fog drop spectrometers, automatic weather stations, and conventional meteorological instruments during the 10 fog events, the fogs’ microphysical characteristics were analyzed, microphysical processes and intensity were deduced, and their effects on visibility were discussed. The results were as follows: (1) The droplet spectrum distribution was different with different thicknesses of the winter fogs, changing from mono-modal to multi-modal as fog became thicker. (2) The droplet number concentration (Nc) had a close inverse correlation with visibility (V), while the liquid water content (LWC) and relative dispersion of the droplet size distribution (S) did not have a definite inverse relationship with V. (3) The temperature of air had an impact on the microphysical processes. The activation and condensational growth (or droplet evaporation) processes played leading roles in the whole winter fog lifecycle. (4) The collection processes arose in the development and maturation stages of the fogs, but not or very infrequently in the formation and weakening stages of the fogs. (5) The results from the autoconversion rate show that the collection rarely occurred in the fogs with V>200 m, while it was very weak or intermittent in the heavy fogs with 100 m≤V<200 m. The collection mainly occurred in the extremely dense fogs with V<50 m and heavy fogs with 50 m≤V<100 m, while it was more frequent and stronger in the heavy fogs with 50 m≤V<100 m than in the extremely dense fog with V<50 m. A larger number of small fog droplets led to poorer visibility in the extremely dense fog with V<50 m, however the maximum values of the droplet properties such as Nc, LWC appeared in the heavy fogs with 50 m≤V<100 m, in which these quantities showed the biggest variations as well. (6) The variations may be related to the more frequent and stronger collection in the heavy fogs with 50 m≤V<100 m, in which collision–coalescence and collision-fragmentation played a role in the biggest variations of microphysical quantities. (7) The trend values of calculated visibility based on the observational data from fog drop spectrometers agreed well with the actual trend values, however the calculated visibility values themselves were much greater than the actual ones, mainly caused by the large amount of aerosol particles in the fogs. In polluted fogs, observational data from fog drop spectrometers are not enough to estimate the visibility of fogs. The influence of aerosol particles on visibility must be considered at the same time.
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