青藏高原雷暴的闪电特征及其成因探讨

The Lightning Characteristics of Thunderstorm over Tibetan Plateau and Its Origin Discussion

通过对2003—2004年夏季青藏高原那曲地区30次雷暴过程的地面电场及闪电电场变化的分析,发现高原雷暴具有三极性电荷结构特征,其中73%(22次)的雷暴过程在其成熟阶段地面电场呈正极性,表明在雷暴云下部存在较常规雷暴范围广、电荷量大的正电荷区(LPCC),其余27%(8次)的雷暴同样具有三极性电荷结构特征,但LPCC相对要小得多。高原雷暴平均闪电频数一般只有1 fl.min-1,相对其它地区要小几十倍。对雷暴云闪电特征的进一步分析发现,具有较大LPCC的雷暴按照闪电特征可分为以云闪(IC)、负地闪(-CG)和正地闪(+CG)为主的三类雷暴。结合气象参量分析发现IC型雷暴对应较高的地气温差和地表温度,相对湿度较小,而+CG型雷暴发生在傍晚,因此对应的地气温差偏小。

Ground-based observation of thunderstorm and lightning flash was carried out over central Tibetan Plateau in the summer of 2003 and 2004. 30 cases of thunderstorm were analyzed in this article. The results showed that the thunderstorm over Tibetan Plateau has a triple charge structure. Among them 73% have a large-than-usual lower positive charge center （LPCC）, and 27% have a normal triple charge structure, i. e. , the LPCC is weaker than the former. The flash frequency of thunderstorm over Tibetan Plateau is tens times smaller than other lower altitude regions with similar latitude, and the average value is usually about 1 fl · min^-1. Due to the different characteristics of lightning flash, the thunderstorm with a large-than-usual LPCC can be classified into three types and defined them IC-dominated type, --CG-- dominated type, ＋CG-dominated type, respectively. Finally, after investigating of meteorological parameters of the three type thunderstorms, we found that there is a high difference between surface and air temperature and a low relative humidity just before IC-dominated type thunderstorms, while the difference between surface and air temperature is small for the ＋CG-dominated type thunderstorm because they occurred in the evenfall time.