Observations of very unusual behavior of lightning discharges.

• M-component incident wave in the +CG channel coupled with the first stroke of a distant –CG. • A branched positive leader intermittently extended via bidirectional transients separated by inactive intervals of about 5 ms. • The bidirectional transients, moving negative charge in the backward direction, triggered a downward negative leader, resulting in a three-stroke –CG. • A subsequent-stroke negative leader, moving through virgin air, entered the lower part of residual (non-luminous) first-stroke channel, in addition to creating a new ground termination about 950 m away. • Ultraviolet images of lightning are presented for a negative cloud-to-ground lightning flash with two ground terminations. Based on recent observations at the Lightning Observatory in Gainesville (LOG), Florida, we present three examples of very unusual behavior of cloud-to-ground (CG) lightning flashes: (a) One +CG and one tower-terminated -CG separated by 11 km, were briefly coupled, so that positive charge was in effect drawn from the ground at the position of –CG and injected into the ground at the position of +CG. That unusual interaction was accomplished by the initiation of M-component incident wave in the +CG channel by the leader of the first stroke of the –CG. (b) A branched positive leader intermittently extended via bidirectional transients separated by inactive intervals of about 5 ms, on average. One of the bidirectional transients, moving negative charge in the backward direction, triggered a downward negative leader, resulting in a three-stroke –CG. (c) A subsequent-stroke negative leader, moving through virgin air, entered the lower part of residual (non-luminous) first-stroke channel, in addition to creating a new ground termination about 950 m away. Studying unusual lightning behavior helps to improve our understanding of the variability of basic lightning processes and to identify new potential lightning hazards to various objects and systems. [ABSTRACT FROM AUTHOR]