强风暴中反极性电荷结构研究进展

反极性电荷结构是强风暴系统中一种常见的电荷结构配置,它是强风暴中正地闪大量发生的重要原因之一,同时也往往与灾害性天气相联系。人们对云内电荷结构的认识随电场探空、多种地面观测手段的发展而深入。反极性电荷结构并非在强风暴的起始阶段就出现,而存在一个演变过程,出现在风暴发展的特定阶段。宽广强烈的上升气流被认为在反极性电荷结构的形成中起关键作用,它使得上升气流区液态水含量等微物理条件发生改变,进而影响大小粒子碰撞的起电过程,使风暴内主要起电区霰粒子荷正电,冰晶等粒子荷负电,从而形成反极性电荷结构。强风暴中气流的动力输送、风切变等也被认为是反极性电荷结构形成的可能原因。利用数值模式,在真实的气象背景场下再现强风暴的反极性电荷结构演变特征和闪电活动特征,也是研究反极性结构形成的有效途径之一。针对正地闪大量发生的强风暴开展大规模外场观测试验,并将观测结果与数值模拟相结合,将有利于理解强风暴中反极性电荷结构的形成及其与闪电活动特征的关系。

Review on Inverted Charge Structure of Severe Storms

The charge structure in storms is regarded as a bridge linking lightning activity with dynamic and microphysical conditions. An inverted charge structure is always seen in severe storms, which attracts much attention in recent years.Although the charge structure in thundercloud is complicated, the tripole charge structure could be used to describe the main discharging region. In general, the tripole charge structure is characterized by a negative charge region between levels of -10 ℃ and -25 ℃, accompanied by a respective positive charge region below and above the negative charge region. In 2000, lightning mapping array and electric field sounding are carried out in the experiment of Severe Thunderstorm Electrification and Precipitation Study (STEPS) organized by USA. Most case studies in this experiment indicate that the charge structure in severe storms is opposite to the normal charge structure, when original positive charge changes into negative charge, and vice versa. This new structure is called inverted charge structure.Related studies on the inverted charge structure are reviewed, focusing on the discovery, formation, relevant numerical simulation and the detection method. The inverted charge structure appears in the severe storms, resulting in the substantial positive cloud-to-ground lightning. Moreover, it is always associated with disastrous weather. The inverted charge structure doesn't appear in the beginning of storms, but in the special developing stage of storms.The inverted charge structure formation is associated with the strong ascending motion in severe storms, which makes the liquid water content change and influences the electrification process during the collision among different kinds of particles in the main electrification region. It will result in graupel charged positively and ice crystal charged negatively, implying the formation of the inverted charge structure. One view focuses on microphysical conditions, by which the charge separation is influenced during the collision of particles, and this physical process is defined as microphysically-inverted. Another view is, the inverted charge structure could be formed through the dynamic transport and wind shear in severe storms when the graupel is still charged negatively in the main electrification region, and this is defined as dynamically-inverted. The research on the latter is relatively scarce compared to the former.