Analysis Of Particle Size Distribution And Scattering Characteristics Of Water Cloud With Growing Droplet

Cloud is the important part of the atmosphere.It covers half of the earth's surface all the year round.The middle and low clouds in the atmosphere are generally water cloud,which have a very important impact on human production and life.Numerical simulation is an important means to study the scattering characteristics of water cloud.However,most of the existing studies are aimed at water cloud in certain state,which is not conducive to the study of the dynamic change process of water cloud.In view of this,the PSD(particle size distribution)in the process of cloud droplet growth is analyzed based on Atmospheric Physics.On this basis,the scattering characteristics of water cloud during cloud droplet growth are analyzed according to the Mie theory.Finally,the influence of multiple scattering on the scattering characteristics of water cloud is studied by Monte Carlo method.The research results are of great significance for remote sensing data inversion,earth-atmosphere radiation balance and weather modification.Firstly,the dynamic change process of PSD in the process of cloud droplet growth is studied.The results show that condensation growth make the FWHM,effective radius and mode radius of water cloud' PSD increase continuously.The coalescence growth will result in the multi peak distribution in water cloud' PSD and increase the effective radius of cloud droplets.The average growth rate of the effective radius of cloud droplets is 8nm/s in the condensation and coalescence growth,and there will be a multi peak distribution in the late growth of water cloud.The scattering characteristics at 1.064?m,2.2?m,3.7pm,12?m,22?m,200?m and 3.2mm of the growing water cloud droplet are obtained based on Mie theory.The results show that the extinction coefficient and scattering coefficient of water cloud increase with the cloud droplet growth.The extinction coefficients of water cloud at 1.064?m,2.2?m,3.7?m,12?m are relatively close.Because of the refractive index the anomalous dispersion phenomenon occurs at 22?m.After 2500s,the growth rate of extinction coefficient and scattering coefficient of water cloud at 200?m increased significantly.The extinction coefficient at 3.2mm is very small,and its range of variation is also small.Except for 22?m,the single scattering albedo decreases with the increase of wavelength.After 1500s,the asymmetric factor of water cloud tends to be stable,and its value is between 0.8?1,when the wavelength is less than 22?m.The asymmetric factor at 200?m increased continuously.The asymmetric factor of 3.2mm is close to 0.The lidar ratio fluctuates near 20sr at 1.064?m and 2.2?m,and the lidar ratio fluctuates greatly at 3.7?m.The Angstrom exponent can be positive or negative,with the growth of cloud droplets finally approach to zero.Finally,the influence of multiple scattering on the scattering characteristics of water cloud is studied by Monte Carlo method.The results show that the extinction coefficient obtained by Mie theory is larger than that obtained by Monte Carlo method.The influence of multiple scattering on the scattering characteristics of water clouds is more significant when the receiving field is increased.The multiple scattering factors gradually decrease with the increase of effective radius.At 1.064?m,2.2?m,3.7?m,12?m and 22?m,when the effective radius of the water cloud is less than 6?m;at 200?m and 3.2mm,when the effective radius is less than 13?m the multiple scattering factor is close to 1,and the effect of multiple scattering can be negligible.