基于RAMS V6.0的非感应起电机制评估和雷暴初期电荷结构模拟

数值模式是研究雷暴内起电和电荷结构的重要工具. 本文将Takahashi (1978) 和Saunders (1991) 两种主流非感应起电机制加入最新版本的中尺度模式RAMS(Version 6.0), 建立了一个区域大气-电耦合中尺度雷暴云模式, 据此对发生于北京的一次雷暴过程首次放电前的电荷结构和水成物粒子起电情况进行了较成功的模拟. 结果表明, Takahashi (1978) 和Saunders (1991)方案模拟的雷暴电荷结构在电场达到击穿阈值时均呈现三极性特征, 但Takahashi和Saunders方案模拟的雷暴电荷结构演变过程有一定的差异, Takahashi方案的电荷结构从起电到放电都是三极性特征, Saunders方案的电荷结构从反偶极性演变为三极性. 此外, 两种方案的模拟结果均表明雨滴是雷暴云低层的正电荷载体, 聚合物和霰是高层的主要电荷载体, 霰的电荷中心分布形态与雷暴云的总电荷分布形态相似.

Evaluation of noninductive charging mechanisms and simulation of charge characteristic structure in the early thunderstorm based on RAMS V6.0

A new regional thunderstorm model, coupled with two primary non-inductive electrification mechanisms, namely Takahashi (1978) and Saunders (1991) schemes, is developed based on the newest version of RAMS V6.0. Based on the simulation on a thunderstorm in its early stage which occurred in Beijing, the results show that the total charge distribution is tripolar in both schemes when the electric field reaches breakdown value. The results are in agreement with some observations and results of other model. However, the evolution processes and shapes of cloud charge distribution in the two schemes are different. The result of Takahashi's (1978) scheme produces a tripolar charge distribution in the cloud before the first lightning. The Saunders' (1991) scheme produces a transform from inverted dipole distribution to tripolar charge distribution. This is because they used different experimental conditions: different factors lead to different results. The results from both schemes show that the positive charge carrier at a low level of thunderstorm is rain droplet, the aggregates and graupels are located in high level of thunderstorm, and the charge center distribution of graupels is similar to the distribution of total charge in thunderstorm cloud.