不同水汽条件下气溶胶对雷暴云电过程影响的数值模拟研究

A numerical study of aerosol impacts on thunderstorm electrification under different water vapor conditions

中文关键词:  水汽含量  气溶胶  起电率  电荷结构  数值模拟

英文关键词:Water vapor  Aerosol  Charging rate  Charge structure  Numerical simulation

中文摘要:

      为全面了解水汽在气溶胶影响雷暴云电过程中的作用，本研究在已有的二维雷暴云起、放电模式基础上，通过改变相对湿度和气溶胶初始浓度（文中气溶胶浓度均指气溶胶数浓度）进行敏感性数值模拟试验。结果表明：（1）随着气溶胶浓度升高，雷暴云产生更多的小云滴，降水过程受到抑制。而当水汽含量升高时，云滴数浓度的增长速度更快，雨滴数浓度升高，缓解了降水变弱的趋势。（2）水汽含量较低时，随着气溶胶浓度升高，更多小云滴被带入冻结层形成大量小冰晶，霰粒含量升高，雷暴云起电过程增强。气溶胶浓度升高至一定的量级（3000 cm^-3）时，冰晶尺度减小和雨滴浓度降低抑制霰粒生长，雷暴云起电过程受到削弱。感应起电和非感应起电过程随气溶胶浓度升高呈先增强后减弱的趋势。水汽含量的升高促进了冰相粒子的增长，起电过程呈现持续增强的趋势，气溶胶浓度为3000 cm^-3时起电率达到极值，电荷密度的增幅扩大。（3）水汽含量较低时，雷暴云难以发展成深厚的系统，气溶胶浓度变化对其影响不明显，电荷结构由三极性发展，在消散期演变为偶极性电荷结构；水汽含量较高时，雷暴云迅速发展成深厚的系统，随着气溶胶浓度升高，在雷暴发展旺盛阶段电荷分布表现为多层复杂结构。研究显示水汽含量在气溶胶浓度变化对雷暴云微物理、起电过程及电荷结构的作用中扮演重要角色。

英文摘要:

      Numerical simulations are carried out to investigate the impacts of varying the cloud condensation nuclei (CNN) on dynamic and microphysical processes as well as electrification and charge structure in thunderstorm clouds under different water vapor conditions by changing the relative humidity and aerosol initial concentration. The results are as follows: (1) The thunderstorm clouds will produce more small cloud droplets and precipitation process is restrained as the aerosol concentration increases. When water vapor increases, the increase in cloud drop content is faster, the content of raindrops increase, and the trend of precipitation weakening is relieved. (2) When water vapor content is relatively low, more small cloud droplets are brought into the frozen layer to form abundant ice crystal particles as the aerosol concentration increases. The content of graupel increases, and thus the electrification is enhanced. When the aerosol concentration increases to a certain level (3000 cm^-3), the decrease in ice crystal size and raindrop content restrain the growth of graupel particles, and the electrification is restrained. Therefore, the occurrence of inductive electrification and non-inductive electrification increases first and then decreases as the aerosol concentration increases. The increase in water vapor promotes the growth of ice particles, and the electrification presents a continuous increasing trend, the charging rate reaches the maximum value at 3000 cm^-3 aerosol concentration, and the amplification of charge density increases. (3) When water vapor content is relatively low, thunderstorm clouds are difficult to develop into a deep system and the change in aerosol concentration has little influence. The charge structure develops from tripolar to dipole in the dissipation period. When the water vapor content is relatively high, thunderstorm clouds can rapidly develop into a deep system. The charge distribution of thunderstorm shows a multi-layer complex structure as the aerosol concentration increases. Therefore, water vapor content plays an important role in the aerosol concentration impacts on the microphysics, electrification and charge structure of thunderstorm clouds.