Optimization And Validation Of A Cloud Microphysical Scheme Based On CMA-MESO Model

Floods,landslides,mudslides,and other disasters caused by heavy rainfall often bring serious damage to the national economy and the safety of people’s lives and properties.The CMA-MESO(GRAPES-MESO)model is widely used in storm forecasting and research,and currently uses a single-moment cloud microphysical scheme for operational purposes.As the resolution and power of numerical forecasting models gradually increase,and the models need to gradually shift to double-moment schemes that can more reasonably describe actual atmospheric cloud microphysical processes,while improving the cloud microphysics scheme.In this paper,we use the CMA-MESO 5.1 model to study the simulation of precipitation,total cloud amount,black body temperature,radar reflectivity,and horizontal and vertical distribution of hydrometeor using multiple data such as regional automatic observation stations,FY satellites,mosaic radar,and ERA5 reanalysis data,evaluate the performance of the scheme for precipitation and cloud macro-microphysics feature and diagnose the strengths and weaknesses of the scheme.In addition,the parameterization method and empirical parameters of the Thompson scheme are modified to improve the simulation performance of the precipitation and ice particle distribution.An in-depth analysis of the microphysical mechanism of the effect of the modifications on the simulated hydrometeor is carried out,and precipitation evaluation metrics are used to diagnose the effect of the improved scheme on the simulated precipitation.The main conclusions of this paper are as follows:The WSM6,Liu-Ma and Thompson schemes in the CMA-MESO model can effective simulate the 24 h cumulative precipitation fall area,central location,intensity,and hourly precipitation trends,but the simulated precipitation is more dispersed.The model simulated cloud location and black body temperature distribution are consistent with the satellite detection,but there are shortcomings in that the simulated range of cloud area is large and the total cloud amount is high.The simulate radar’s strong echo area center intensity is low,the position is northward,and the echo system moves to lag.The simulated range and intensity of hydrometeor are large.And the center of hydrometeor,except for cloud water,is located southward.The Thompson scheme simulates the most total cloud amounts,the distribution of black body temperature lowvalue areas is too large and the magnitude is lower,and the forecast echo intensity is greater than that of WSM6.Compared with the observed data,the Thompson scheme does not simulate all cloud features and precipitation as well as the other two schemes.The typical features and shortcomings of the Thompson scheme are discussed,and the following modifications are made: optimize the snow particle riming growth equation to improve the conversion process from snow to graupel;optimize the terminal velocity parameters of cloud ice,rain,and graupel;optimize the parameters in the massdiameter distribution of snow and graupel;set the capture efficiency of snow to cloud ice as a function of temperature;and reset the distribution of graupel particles to a generalized gamma distribution.It is found that using the modified riming parameterization method for snow particles can significantly reduce the simulated highaltitude snow content and increase the graupel content,but the intensity of the strong graupel particle center in eastern Guangxi Province is reduced.Also,the simulation effect is not optimal after modifying the terminal velocity parameters of cloud ice,rain,graupel,and snow particle.And reset the particle spectra of both cloud ice,raindrops,snow,and graupel to generalized gamma distribution cannot further improve the precipitation simulation effectively while reducing the graupel particle size distribution alone can improve the TS scores of heavy rain and below level precipitation and ensure the computational efficiency.Optimizing the parameters in the mass-diameter relationship between snow and graupel can optimize the simulation effect of ice phase particle distribution.The improved Thompson scheme simulates more precipitation and can better simulate the precipitation centers in northern Anhui and eastern Guangxi,but still fails to simulate the precipitation center in northern Hunan Province.The modified scheme effective simulates stronger echoes,reduces the errors of the original scheme of the lagging movement of the echo system and the lack of east-west development,and can better simulate the echo centers in central Guangdong Province and eastern Guangxi Province.After the scheme modification,the increase of the melting rate of snow and graupel particles increases the rain content within the precipitation center,and the increase of the rime process significantly reduces the high altitude snow content and increases the graupel content within the rain area.The TS score of the modified scheme is higher than that of the original scheme,and the forecast effect of light rain,moderate rain,heavy rain,and above is significantly improved.The BS score of the simulated precipitation at all levels is greater than that of the original scheme,which can compensate the deficiency of low forecast precipitation of the original scheme to a certain extent,but it will increase the error of high forecast precipitation.In a comprehensive analysis,the optimized and improved Thompson cloud microphysical scheme in this paper is significantly better than the original one for precipitation simulation forecasting.The research results of this paper can provide a certain basis and reference for further improvement of the cloud microphysical scheme in the CMA-MESO model.