Definitions for "Stepped leader"
The initial streamer of a lightning discharge; an intermittently advancing column of high ion-density which establishes the channel for subsequent return streamers and dart leaders. The peculiar characteristic of this type of leader is its step-wise growth at intervals of about fifty to one hundred microseconds. The velocity of growth during the brief intervals of advance, each only about one microsecond in duration, is quite high (about 5 x 109 cm/s), but the long stationary phases reduce its effective speed to only about 5 x 107 cm/s (roughly 1/1000th the speed of light). Stepped leaders typically exhibit some degree of branching because they tend to grow in an exploratory manner, seeking out the optimal path through the air.
The initial, invisible, streamer of a lightning discharge.
A stream of electrons emanating from the negative portion of a thundercloud. The stepped leader travels 100-200 feet, in 50msec and then abruptly changes direction.