The Three-parameter Gamma Spectrum Is Used To Simulate And Study The Collision And Growth Process Of The Raindrop Spectrum

The mesoscale cloud resolution mode is very uncertain in the prediction of rainstorm area and rainfall.One of the important reasons is that the cloud patterns that describe the cloud microphysics process have defects.It is an important way to improve the forecast level of the rainstorm by establishing and improving the cloud model,especially the research on the parameterized scheme of the warm rain,which can describe the cloud microphysical process more accurately.Warm rain is caused by cloud droplets through random collisions.It is necessary to calculate the cloud rain conversion rate in the parameterization scheme.It can determine the evolution of the cloud droplet spectrum and the raindrop spectrum.At present,the parameterization scheme is not based on random collision theory to determine the conversion rate of cloud.The reason is that the use of gamma function analytic representation cannot find random collisions of cloud droplets and raindrops spectrum evolution solution.Therefore,the same spectrum of conditions in the cloud,the cloud of different conversion scheme,the simulation results can differ by three orders of magnitude.The single-moment parameterization scheme is simple,and the disadvantage is that it can only reflect the spectral changes by the change of the slope.The double-moment parameterization scheme can reflect the spectral changes by adjusting the changes of the two parameters.In this paper,we use the third parameter,shape parameter,to describe the coalescence process.We hope to describe the change of raindrop spectrum in the process of collision based on shape parameter,slope and intercept three variable parameter Gamma function spectrum,and get more similar raindrop spectrum of natural change.Therefore,the calculation method adopted in this paper is directly using polynomial approximation to represent the efficiency of collision.We use the three quantities of number concentration,mass concentration and radar reflectivity factor to solve the analytic solution of three parameter Gamma function.The new three-moment parameterization scheme for coalescence uses quasi-random collision theory,by calculating the autoconversion rate,the accretion rate and self-colletion rate of the analytical solution,determine the new spectrum of cloud droplet and raindrop spectrum after coalescence.In this paper,we discuss the coalescence process.The simulation results show that in the collision process,the cloud droplet number concentration gradually decreased with time,and the number concentration reduction rate in the simulationtime consistent.With the passage of time,the cloud droplets through collision gradually generate greater scale of cloud droplets and raindrops.The cloud droplets spectrum become narrower and the raindrop spectra become wider.And the raindrop size increases gradually.In the coalescence process,not the larger the raindrop and the higher the efficiency.The shape parameter increases will lead to the initial droplet spectrum narrowed.And the raindrop spectrum by the development of coalescence also narrowed.If the shape parameter increases,the number concentration reduction rate of cloud droplet will decreases,and the increase rate of the number concentration of raindrops is also smaller.The increasing of initial total mass concentration of cloud droplets can make the initial cloud droplet mean diameter increases,the number concentration of cloud droplet decreased faster.The increase of initial total mass concentration of cloud droplet can make more cloud transformation process happen.The raindrop spectrum is broadened to a large scale.