根据雷暴云电场特征,结合雷达等观测资料,本文提出一个利用电场幅值阈值和差分阈值方法,为进行电场测站的首次地闪的雷电临近预报方法。该方法首先判断电场是否达到设定的幅值阈值或者差分阈值。如果电场达设定阈值,认为此时测站周围云中电荷量较大,发生闪电的概率也较大,进而判断该时刻之前的雷达资料是否达到设定的阈值。如果雷达资料达到设定的阈值则发出预警;如果未达要求则继续查看下一体扫的雷达情况,直到发出预警或者电场阈值取消为止。利用此方法对2009年南京周边观测区7个站点数据进行预警检验,得到其探测概率约为80%,平均预警时间约为14min。同时,本文尝试用该预报方法对雷暴云移过测区的整个过程进行区域性雷电临近预报。结果发现区域雷电预警可以直观呈现雷暴云和闪电发生发展情况,对发生闪电潜在区域也能够直观判断,并收到较好的预警效果。区域预警不仅能实现对一个地区的监测预警,而且能对雷暴云的整个过程进行监测预警,具有单站电场所没有的优势。

The amplitude and differential threshold have been used to describe the characteristics of atmospheric electric fields in thundercloud in this paper. With these two electric field threshold and combined with radar data, a method for the first Cloud-Ground (CG) lightning forecasting in a certain range of electric field station have been put forward. First, judging electric field which reflects the charge of thundercloud whether reach amplitude threshold or differential threshold, if electric field threshold is satisfied, it is considered that the total charge of cloud is large and the probability of occurring CG lightning is also large, and then the radar data whose scan is end before the electric field threshold is detected will be judged. If radar reach the set radar threshold, the warning will occurred, otherwise judging the radar data of next scan whether reach, until warning occur or electric field indexes is canceled. The electric field data of 7 stations in summer of 2009 in Nanjing surrounding observation area were analyzed and the result showed that the probability of detection was about 80% and the average warning time was about 14min. A typical thunderstorm which moved across observation area was analyzed with the local lightning forecasting method proposed and found that it had a good warning effect. With the local lightning forecasting method, the development of thunderstorm and lightning in observation region will be presented visually and the lightning potential areas can be judged intuitively. In the meanwhile, this local lightning forecasting method can not only monitor and warn a big region, but also can monitor and warn the whole thundercloud. So it has the advantage which single-station electric field have not got.