冰晶异质核化对雷暴云电过程影响的数值模拟

引入一种新型冰晶异质核化方案, 基于二维雷暴云模式, 探讨雷暴云电过程对三种异质核化的响应。结果表明: 浸润核化是冰晶生成的最重要异质核化过程, 较高数浓度的冰晶消耗雷暴云内液态水含量, 抑制淞附过程, 导致霰粒子比含水量低, 表现为较强的负极性非感应起电率; 接触核化生成的冰晶量最少, 仅对雷暴云中下层3~5 km处的冰晶有贡献, 同时霰粒子数浓度较低, 导致该方案下的起电过程最弱; 沉积核化主要影响云砧处的冰晶, 有利于提高霰收集云滴的效率, 表现为极高的霰比含水量, 促进低温区非感应起电过程的发生。总体上来看, 三个方案下的电荷结构均由较复杂的多极性发展为偶极性。其中浸润方案中主正电荷区的抬升最明显, 而接触方案过低的冰晶分布高度与沉积方案过高的冰晶分布高度, 都直接导致了次正电荷区更快消散。 

NUMERICAL SIMULATION OF EFFECTS OF HETEROGENEOUS NUCLEATION ON MICROPHYSICAL PROCESS AND ELECTRIFICATION IN THUNDERSTORMS

A two-dimensional cumulus model with electrification and lightning process was carried out to investigate the effect of heterogeneous nucleation on microphysical process, electrification and charge structure in thunderstorms. Simulation showed that immersion freezing played a leading role. The high content of ice crystals consumed cloud water, inhibited the growth of graupel, so the mixing ratio of graupel was low and the non-inductive electric rate was the highest. The contact case showed 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 be more efficient, which resulted in a high mixing ratio of graupel. The charge structure of all cases developed from multipole to dipole, and the secondary positive charge region disappeared quickly with too much or less ice crystals contents at high-temperature regions.