A comparison is made between the high-speed photography data of two rocket-triggered negative lightning flashes. The analysis shows: the initial propagation velocity of upward positive leader (UPL) in altitude-triggered negative lightning (ATNL) is about one order of magnitude lower than that in classical-triggered negative lightning (CTNL), while the triggering height of ATNL is higher than that of CTNL; the afterglow time of metal-vaporized part of the lightning channel can endure about 160~170ms. According to the different characteristics of the luminosity change of the lightning channel, together with the observation of the electric field changes, the processes after return-stroke (RS) can be distinguished into three types. Statistically, the interval of RS with M component is longer than that of RS without M component. The distinction between the relative luminosity of the lightning channel before RS and that before M component is obvious. The former is very weak or even invisible, while the latter is still considerable luminous.
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