Numerical Simulation Study Of The Influence Of Different Ice Nuclei On The Electrical Process Of Thunderstorm Clouds

Based on a two-dimensional cumulus model with different parametrization of ice nucleation and the case of mountain thundercloud,this study discusses the effect of ice nuclei on microphysical development,electrification,and charge structure.Simulation results show that homogeneous freezing maintains so much small ice crystals near cloud tops that the non-inductive charge separation rate is high,leading to a steady upper positive charge region.While heterogeneous freezing contributes to the main negative regions,the charge structure depends on the freezing nucleation process that is the major contributor of ice production.And the large ice particles produced from heterogeneous freezing lead to the enhancement of the coagulation of rain with cloud ice,leaving a stronger charge separation rate around-15 °C.Thus,the heterogeneous freezing process presents a dipole structure with a strong main charge region in dissipation stage.When both immersion and homogeneous freezing processes are considered,the competition between water vapor and liquid water results in a lighter mean ice particle mass,smaller ice particle size and faster convection.Thereafter the available cloud water content contributes to stronger and widespread graupel particle production.However,since the melting of precipitating particles reduce the electrification processes and total negative charge,the charge structure tends to be normal dipole.In addition,new particle-dependent parameterizations of heterogeneous freezing are carried out to investigate the effect of those freezing processes on microphysical process,electrification and charge structure in thunderstorms.The scheme is based on adiabatic air parcel model with entrainment and includes three heterogeneous freezing processes,numbers types of ice nuclei and particle-type-dependent description.Simulation shows that the immersion freezing play a leading role.In this case,the high content of ice crystals consumed cloud water,inhibited the growth of graupel,so that the mixing ratio of graupel is low and the negative non-inductive charging rate is the highest.The contact case shows the least amount of ice crystals,which contributed to the middle and lower layers of thunderstorm clouds and low non-inductive charging rate.Besides,the deposition freezing mainly affected the ice crystals at cloud top.In this way,the process of graupel collecting cloud droplets can more efficient,which results in a high mixing ratio of graupel.The charge structure of all cases has developed from multipole to dipole,and the secondary positive charge region can disappear quickly with too much or less ice crystals contents at high-temperature regions.