卫星观测到的青藏高原雷电活动特征

Lightning Activities on Qinghai-Xizang Plateau as Observed by Satellite-Based Lightning Imaging Sensor

利用TRMM卫星上携带的闪电探测系统获取的闪电定位资料首次对青藏高原上的闪电活动进行了研究。研究发现,青藏高原上的闪电活动呈现出大陆性气候特征,但是受其特殊地形的热力和动力特征所调制,高于93%的闪电活动发生于5～9月之间,并在夏季出现单一闪电活动峰值。随着地表加热和湿度的增加,闪电活动在5月份开始明显增加。较高的闪电密度发生在高原的中部,揭示了闪电活动与地形特征的相关性。63%的闪电活动发生于14:00～18:00(地方时,下同)之间,而只有<3%的闪电发生于00:00～10:00之间。闪电光辐射能的时平均值也呈现出明显的日变化,随着太阳的升起,闪电光辐射能在08:00开始增加,并在10:00达到稳定的极大值,直到02:00开始明显减小。闪电的光辐射能在高原北部呈现最大值,高原西部呈现最小值。青藏高原上的闪电放电强度比其它地区弱得多,其差别归因于高原上较低的对流不稳定能量。

The lightning flash activities on Qinghai\|Xizang Plateau are being studied, for the first time, by using Lightning Imaging Sensor (LIS) database. The flash activity is found to exhibit a continental type climate behavior and is a sensitive indicator of solar heating on the Plateau. Over 93% of the flashes are found to occur during May to September with a single peak in the summer. The monthly variation clearly shows a flash activity in May with the increase of surface heating and moisture. The high flash density on the Central Plateau reveals the affinity of lightning activity with the topography. The diurnal variation of the flash activity shows a peak activity from 14:00 to 18:00 LT with 63% of all flash activities occuring in this period. Less than 3% of all lightning flashes are observed between 00:00～10:00 LT. There is also a diurnal variation in the meanflash radiance with a sharp drop at around 02:00 LT, and increases rapidly from 08:00 LTwith the sunrise. The optical radiance of flashes onthe Plateau can be fitted well to a lognormal distribution with energetic flashes on the Northern Plateau and weak flashes on the Western Plateau. The lower flash discharge energy on Qinghai\|Xizang Plateau could be attibuted to the lower convective available potential energy and the lower cloud top.