Luminosity characteristics of leaders in natural cloud-to-ground lightning flashes

Using high-speed cameras, we have recorded the leaders contained in four natural negative cloud-to-ground (CG) lightning flashes in the summers of 2006 and 2007 at Conghua, Guangdong, China. It was found that the downward negative leaders preceding the first return stroke could propagate at quite different speeds. In one flash, the average speed of the downward negative stepped leader with no branches is about 2.2 × 106 m s− 1, while that of the other 3 flashes are all of the order of 105 m s− 1 with multilevel branches. The luminosity of the leaders shows an increasing tendency in propagating downward to the ground. For the leaders preceding the subsequent strokes, although all of them exhibit high speeds as reported previously. One subsequent leader exhibits an increasing speed from 5.2 × 105 m s− 1 to 1.7 × 106 m s− 1 during its propagation from about 1.26 to 0.36 km above the ground, and its luminosity also increased. The speed and luminosity of a leader between subsequent strokes of a natural lightning appear to decrease as it developed downward. Its speed ranges from 1.1 × 106 to 1.1 × 105 m s− 1, with a height between 1.15 and 0.81 km above the ground.