A comparison of the parameterization schemes of fog visibility using the in-situ measurements in the North China Plain

This study investigates the parameterization of fog visibility and its relationship with microphysical properties. Fog visibility and droplet spectra are observed for four fog cases in the North China Plain from November to December in 2009. The calculated visibility using droplet spectra is similar to the observed visibility for the dense fogs, but is higher than the observed visibility during the relatively light fogs. Two parameterization schemes of fog visibility from previous studies are applied to the four fog cases. The parameterization considering only liquid water content (LWC) has an overestimation of about 70%, while the parameterization using both LWC and Nd has relative errors within 40%, compared to the calculated visibility. However, much larger relative errors are found between the parameterized and the observed visibilities, especially in the relatively light fogs. By slightly changing the coefficients in the parameterization schemes, we found that the scheme considering only LWC fits the calculated visibility with relative errors within 20%, and that the scheme considering both LWC and Nd with relative errors within 5%. Much larger changes of the coefficients are needed in order to best-fit the observed visibility, but still with relative errors larger than 20%. Detailed analyses of the inconsistencies between the calculated, observed and parameterized visibility suggest that the effect of aerosol extinction should be considered in the visibility parameterizations of fogs in the North China plain and other polluted areas. (C) 2014 Elsevier Ltd. All rights reserved.Environmental SciencesMeteorology & Atmospheric SciencesSCI(E)EI0ARTICLEhxue@pku.edu.cn44-509