A study on lightning discharge precursor by taking advantages of simple structure and observation easiness of Tibetan thunderstorms

我们于2005年和2006年夏季在中国西藏高原地区拉萨市进行了一次闪电观测活动。我们found1。几乎所有的西藏闪电都发生在中午晚些时候到午夜。雷暴的闪电活动差别很大，有些雷暴在一分钟内产生20次闪电，有些雷暴在整个生命周期内只产生几次闪电。许多雷暴在地面表现出正的主导电场，并倾向于产生较小的云对地（CG）放电比例。在记录的CG放电中，近90%为负放电。在一般的夏季雷暴中，触发CG放电的最佳条件可能是在主电荷区下方存在相反极性的口袋电荷。对于西藏雷暴，负口袋电荷可能不存在于产生主导正电场的主正电荷下方。这可能是导致CG排放量少的原因。闪电放电主要发生在两个高度：一个高度约为2公里，另一个高度约为4公里。这些结果强烈表明，云内放电的初始优势leader根据其初始高度可以是负leader或正leader。通常在云内放电的初始阶段观察到的大微秒级脉冲似乎是在负先导在正电荷区域内传播时产生的。在雷暴的不同阶段，重心比差异很大，这表明存在产生重心的有利电荷结构。

We have performed a lightning observation campaign in Lhasa city, Tibet plateau region of China in the summers of 2005 and 2006. We found1. Almost all Tibetan lightning occurred from late after noon to mid night. Thunderstorms differ greatly in lightning activity with some thunderstorms producing 20 flashes within one minute and some only a few even during their whole life period.2. Many of the thunderstorms exhibit positive dominant electric fields at the ground and tend to produce smaller ratio of cloud-to-ground (CG) discharges. Among the CG discharges recorded, nearly 90% of them are negative ones. In general summer thunderstorms, the favorite condition for triggering a CG discharge may be the presence of the opposite polarity of pocket charge beneath a main charge region. For Tibeuan thunderstorms, a negative pocket charge may not exist just beneath the main positive charge which produced the dominant positive electric fields. This may account for the small number of CG discharges.3. The lightning discharges are found to be initiated mainly at two heights : one is roughly 2 km and the other is 4 km above the ground. These results strongly suggest that the initial dominant leader of an intracloud discharge could be either a negative leader or a positive leader depending on its initial height. The large microsecond scale pulses usually observed at the initial stage of an intracloud discharge appeared to be generated when a negative leader is propagating within a positive charge region.4. The CG ratio differs much during different stages of thunderstorms which suggest that favorite electrical charge structures for producing CG exist.