Analysis And Observation Of CG Lightning Flashes

A field experiment on artificially rocket-triggered lightning and observing natural lightning was conducted in summer of 2006 and 2007 in Conghua, Guangdong province, by Lightning Physics and Protection Engineering Laboratory of Chinese Academy of Meteorological Sciences. Using a Redlake MotionPro HS-4 high-speed camera which consists of 512×512 sensor pixels, each 16×16μm2 in size, with the lens of 3.5 mm focal length, we have recorded the leaders contained in two natural cloud-to-ground (CG) lightning flashes, one altitude-triggered lightning and four rocket-triggered lightning by ground-base activity with a sampling rate of 5000 frames per second (fps). Combined with other electrical data at the same time, we analyzed the characteristics of the C-G lightning in this lightning, and calculated the characteristic parameters for positive upward leaders in four artificial triggering of lightning by ground-base activity in this dissertation. The results are summarized as following.In a C-G lightning with several return strokes, we observedβ-typed leader with the average speed of 2.23×106m/s. The speed of the attempted leader exhibits to decrease as it develops down toward the ground. The speed of a dart leader appears to increase as it approaches to the ground.In artificial triggered lightning experiments, the speed of positive upward leaders should be of the order of 105m/s. As the leader tip reached a higher height, the channel showed greater degree of luminosity. But in our observations, the upward leader may not propagate into the cloud at the time lightning channel shown the peak luminance in the initial stage of negative rocket-triggered lightning.We have observed bidirectional leader both in a natural C-G lightning and an altitude-triggered lightning. The bidirectional leader propagated continuously with a speed at the order of 105 m/s, and branched in whether the natural C-G lightning or the altitude-triggered lightning.In a C-G lightning with 13 return strokes and a negative rocket-triggered lightning with 12 return strokes, it is found that the cut-off time before one subsequent return stroke exhibited a consistent trend with the total luminosity of this subsequent return stroke and the continuing current (CC) followed, but there was no fixed proportionality between them, especially there was a proportionality relationship between them after the 9th return stroke.The geometric average of 17 M-components'lasting time and intervals between the consecutive M-components in a C-G lightning with 13 return strokes were larger than that of the M-components in the initial stage of negative rocket-triggered lightning.It was calculated that the line charge density along the leader channel was from 76.43 to 466.83μC/m, and the leader current was 0.0133～0.0835kA in a negative rocket-triggered lightning. The electric field change rate at 100m distance to the lightning channel were 4128,3793,1722(V/m)/ms separately in three rocket-triggered lightning by ground-base activity.