A Comparative Study On Microphysical Characteristics And Visibility Parameterization Schemes Of Urban Fog,Alpine Fog And Sea Fog

In this paper,we use the data of urban fog observed in Nanjing,Mountain fog in Lushan and sea fog in Shenzhen by the team and the fog drop spectrum,aerosol,visibility and conventional meteorological data are analyzed.Combined with the results of other regions,the microphysical structure and regional characteristics of visibility parameterization scheme of dense fog in city,mountain and seaside are compared and analyzed.The results show that:(1)The radiation urban Fog produced by night cold advection and long wave radiation cooling has the characteristics of explosive growth: the short-term liquid water content and the number concentration of fog drops increase by three orders of magnitude,the visibility suddenly reduces to below 50 m,and the fog drop spectrum is obviously widened.In the intermittent supercooled alpine fog,the droplet number concentration,average diameter and LWC fluctuate greatly.The advection sea fog is formed by the change of wind direction and the discontinuous transportation of air mass.During the fog period,the microphysical quantity is unstable.(2)Characteristics of droplet spectrum evolution: under the background of high concentration aerosol,more than 80% of D<10?m droplets are formed in urban fog.The quality of alpine fog mass is not stable enough,10<D<20?m droplets account for more than 50%.D< 10?m in sea fog is more than 70%.The Gamma fit spectrum of three kinds of fog is as follows: D<10?m: urban fog(Nanjing)>sea fog(Shenzhen)>alpine fog(Lushan),D>10?m: urban fog(Nanjing)>alpine fog(Lushan)>sea fog(Shenzhen).(3)The results of the three visibility schemes show that the slope of land fog is larger than that of sea fog,which is mainly related to the water content and fog droplets number concentration in the fog process.With the increase of years,the slope and intercept of urban fog become larger,which is related to the decrease of droplet size caused by the increase of pollutant types.Gultepe scheme can be used in Nanjing urban fog mode(e=0.0389,f=0.3041),Kunkel scheme can be used in Lushan alpine fog mode(a=0.0768,b=0.2663),and Gultepe scheme can be used in Shenzhen sea fog mode(e=0.1757,f=0.2489).(4)It is assumed that the extinction of dense fog mainly comes from two parts: pure water droplets and aerosols.The extinction efficiency of urban droplets is the largest in the small droplet section;the extinction efficiency of alpine fog and sea droplets is mostly concentrated below 20?m.The phenomenon of decreased extinction of aerosol exists in the process of fog,which is more obvious in areas with large background aerosol concentration.It shows that extinction of fog can not only consider the extinction of fog droplets,but also the extinction effect of aerosol is important.