青藏高原那曲地区冰雹天气系统中的大气电场

THE CHARACTERISTICS OF ELECTRIC FIELD OF HAILSTORM WEATHER IN NAGQU AREA OF QINGHAI-XIZANG PLATEAU

利用 1 998年 4～ 9月间进行的GAME TIBET青藏高原云和降水的多普勒雷达及大气平均电场加强期观测实验资料 ,对青藏高原那曲地区的冰雹天气系统中的大气电场作了定量观测和研究。结果表明 :在降雹过程中大气电场强度基本上均为负值 ,其峰值也均强于- 2 2kVm- 1;在降雹过程中随着降雹时间的临近 ,大气电场强度不断增强 ,但降雹开始时大气电场强度并未达到其峰值 ,峰值出现的时刻比开始降雹的时刻略有滞后 ;在各降雹日中 ,较强的大气电场强度基本上对应着各冰雹谱分布段较多的冰雹数目 ,而这种较好的相关在各谱分布段上都表现出来 ;随着降雹时间的临近 ,每 5min闪电频数不断增强。在开始降雹时每 5min闪电频数平均达到 43,峰值的出现时刻略滞后于开始降雹的时刻 ,这一滞后时间一般平均在 3min左右 ;在降雹过程中 ,单位面积中的冰雹数目与对应时段内总闪电数有着较好的对数关系 ,相关系数R为 0 .9540。在降雹过程的时间序列上 ,冰雹云成熟期过后 ,总闪电次数与冰雹降雹率成反相关。

The characteristics of electric field of hailstorm weather in Nagqu area of Qinghai Xizang Plateau are analyzed. The results show that the lightning is observed in the central and strongest convective cell, all eletrical fields of hailstorm weather are almost minus, the strongest electric fields in all the hailstone weather are stronger than -22 kV·m -1 and weaker than -48 kV·m -1 . In the hailstone weather, with the eletric field getting weaker, the number of all sizes of hailstones is decreasing. The coherence between the electric field and the number of all sizes of hailstones in different diameter scope is very good. In the proceedings of hailstone weather, with the time of hailstone falling getting near, the electric field is getting stronger and stronger at first, and then getting weaker. At same time, with hailstone falling time getting near, the number of the lightning per 5 minutes is increasing, and the peak value almost appear at the hailstone falling time, it appears about 3 minutes later than the hailstone falling time. The average peak value is 43. After the peak value appears, the value begins to decrease, but the decreasing speed is slower than the one of increasing speed. The non inductive charging mechanism is the major electrification processes in the hailstone weather. So the electric field and the number of lightning per 5 minutes can be used as indicator of hailstone weather. In the proceeding of hail falling, especially in the latter mature stage of hailstorm cloud, hail rate and lightning number appear to be anticorrelated.