Numerical Simulation Of Hail Clouds In The Southern Mountains Of Ningxia

Based on the conventional observation data,C-band Doppler radar data,and precipitation fusion products,using MY double moment scheme and the Thompson scheme of the mesoscale numerical model(WRFv3.7.1)respectively,the hailfall processes in the southern mountainous area of Ningxia from 2013 to 2018 were analyzed and numerically simulated with ERA-interim data.Comparing the simulation results of the two microphysical schemes and analyzing macro-and micro-evolution characteristics of hail process under different weather background.Using these simulations to analyze the cloud microphysical structure and microphysical transformation characteristics in the hailfall process in the semi-arid area and changing the CCN concentration to analyze the impact of the CCN concentration on the hailfall process in the semi-arid area.The results show that:By comparing MY double moment physical scheme and Thompson scheme simulations,we can find that the reflectivity of the two schemes exhibit different characteristics.The convective cloud anvil simulated by the MY double moment microphysical scheme is larger,and the strong reflectivity center is concentrated into a block,which has a large area;Thompson scheme simulated strong reflectance center is concentrated into a point,and the area is small,and it is easy to deviate from the radar observation position.In both schemes,the simulated strong reflectance center intensity is weaker than the actual observed value.The rain belts simulated by Thompson scheme are relatively narrow and long,and there are deviations from the observations.The simulated precipitation center area is easy to deviate.However,the precipitation center area of the MY scheme is generally better simulated and slightly deviates from the observed precipitation area.There are significant differences between MY double moment microphysics scheme and Thompson scheme for simulating convective clouds.The Thompson scheme pays attention to the warm phase process of convective clouds,and the MY double moment scheme pays attention to the ice phase process,resulting in different distribution of simulated raindrops in the cloud body.The hail processes in southern mountains occurred in two weather background.The first type was behind low-pressure trough in high altitude,and the second type was affected by surrounding cyclones and anti-cyclones.Therefore,cases of 2017,2018 as the first type and 2014 as the second type were selected to compare and analyze the cloud microphysical structure and microphysical transformation characteristics in the hailfall process,which indicated that the formation of hail clouds in this area mainly depends on the unstable stratification of "upper dry and lower wet" and local heating in the afternoon.By comparison,it is found that the physical structure of hail clouds is unique due to its special climatic background.Relatively speaking,the process of autoconversion from cloudwater to rain in the Ningxia mountainous area is relatively weak.The height of the hail forming is relatively low.After the hail is formed,it mainly grows by collecting supercooled cloud water.In addition to the increase by collecting supercooled cloudwater,the condensation of supersaturated water vapor on the ice surface is also an important way for ice phase particle(ice crystals,snow particles and graupel)mass growth.The rainwater is mainly formed by the snow,graupel,and hail particles melting during the falling process,and the evaporation of the rainwater is significant during the falling process.As the concentration of CCN increases,the number of cloud droplets and ice crystals also increase.The large amount of ice crystals makes it difficult to transform them into snow particles and reduce the amount of snow particals.However,the number concentration of graupel particles still increased.As the number concentration increases,the weighted-mass average particle diameter of the graupel decreases,and smaller graupel appear at heights near the 0-degree layer.At the same time,the effect of CCN concentration on the average diameter of hail is not obvious.Furthermore,with the increase of CCN concentration,the diameter of raindrops decreased significantly.Smaller raindrops evaporate faster during falling,resulting in smaller raindrops reaching on the ground.As a result,precipitation on the ground is reduced by increasing CCN concentrations.