青藏高原东北部地区夏季雷电特征的观测研究

Observation on the Summer Lightning Discharge in the Northeastern Verge of Qinghai-Xizang Plateau

介绍了2002年夏季在海拔2650m的青海东部地区所进行的雷电综合观测实验及初步研究结果。实验中采用了GPS同步的6个站闪电快、慢电场变化和平均电场的同步观测,配合1ms的高速摄像对该地的雷暴电荷结构、闪电放电特征等进行了研究。初步研究结果表明,青海东部的雷暴云当顶时,地面电场既可受云内的负电荷所控制,也可能受正电荷所控制,揭示了雷暴电荷结构的复杂性。同时,闪电特征也存在一定的特殊性,所发生的地闪先导常以多分叉的形式慢速向地面行进,并在地面形成两个或两个以上的接地点;梯级先导的发展速度约为0.8～1.18×105m·s-1。同时在地闪发生之前和之后常有持续时间较长、闪道清晰的云内放电过程发生。高速摄像观测首次发现,在一次云内正电荷控制地面电场的雷暴条件下,云内放电过程呈现出双层结构特征。放电首先从上部负电荷区和下部正电荷之间的地方激发,然后上、下同时发展。在开始阶段只能看到向下的负流光通道,当上、下发展的通道分别到达负、正电荷区时,明亮的的主通道形成。之后放电在下部正电荷区以多分叉的形式水平扩展,下部的水平扩展停止后,主通道上部的放电开始水平扩展,是一种反极性的云内放电过程。

In the summer of 2002, a comprehensive observation on natural lightningdischarges was conducted in the northeasternverge of Qinghai\|XizangPlateau. The average altitude on the observation area is about 2650 m. During the experiment, field mill, fast and slow antenna systems were employed in 6 sites synchronized by GPS with 0.4 μs time resolution. Meanwhile, high speed video camera with 1 ms resolution was used in the observation.The preliminary study shows that the polarity of electric field underneath thunderstorm could be positive or negative with positive is more often, indicating the complexityof the thunderstorm charge structure in this area. The lightning discharge shows some special characteristics with corresponding to the complex of charge structure andspecial topography. The stepped leader usually develops downward to ground with multi\|branches with a 2\|D velocity of about 0.8～1.2×105m·s\+\{-1\}. Because of the multi\|branches of the stepped leader, more than one striking point on the ground was often observed as a result. Long intracloud (IC) discharges will occurnot onlyjust before the ground discharge but also after the ground discharge. The pictures from high videocamera confirmed the bi\|level structure of IC discharge, as observed by interferometerand TOA observation.The IC discharge initiates excitation between upper negative charge region and lower positive charge region, and developed downward and upward to the lower positive and upper negative region, respectively. After the main vertical channel setup, the discharge developshorizontally in the lower positive charge region with more branches. In the final stage, the discharge in the upper channel developshorizontally in the negative charge region.