Luminosity characteristics of initial continuous current pulses in upward lightning flashes

The luminosity characteristics of initial continuous current pulses (ICC pulse) in upward negative lightning flashes were observed using the automatic lightning progressing observation system (ALPS) at the 200 m chimney in the Fukui thermal power plant. Furthermore, the current waveforms of upward negative lightning flashes were measured with two shunt resistors. As a result, we obtained 81 current waveforms and 20 image files using ALPS from 1989 to 2008. From our observation results, we analyzed the luminosity variation of the lighting channel involving ICC pulses in the upward lightning flash. 13 of the 20 ICC pulses were accompanied by upward progressing luminous phenomena. From the obtained analysis results, we found that the average speed of the luminous channel was about 7×10⁷m/s, which is close to return stroke speed.