An M component with a concurrent dart leader traveling along different paths during a lightning flash
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abstract
2015. American Geophysical Union. All Rights Reserved. Utilizing time-correlated high-speed video and electric field change data, a seven-stroke lightning flash is described in which the fifth return stroke (RS) occurs 0.80 ms after the fourth RS connects to a different ground location 3.3 km away. The fifth RS is 0.34 ms after an M component starts down the different channel. The fifth stroke involves a dart leader traveling concurrently, though slower than the M component, in a prior channel to ground. There was no indication of leader advance along this path earlier during the fourth RS. The fourth stroke involves a stepped leader that started from the end of an observed prior dart leader branch which did not previously propagate to ground. The concurrent M component and dart leader are preceded by an in-cloud event evidenced by a large-amplitude, fast electric field change pulse, at 6.1 km estimated altitude, inferred as the connection to the channel for the M component. The M component current apparently initiates the dart leader about 40 s later. A visible channel length of 10,400 m allows for the 2-D propagation speed of the M component luminosity to be estimated in the range of 1.0 to 1.2 108 ms1. The concurrent dart leader travels a visible length of 3445 m with 2-D speed of 1.7 107 ms1, similar to other dart leaders in this flash. Luminosity evolution along the channel through the RS and M component is also described. Estimated optical risetimes of three separate M components are 80200 s at 520 m above ground.
