Transient phenomena in positive cloud-to-ground lightning discharges

Positive lightning discharges to ground (+CGs) are relatively rare and considerably less studied than negative ones (-CGs). We present observations of unusual transient phenomena occurring in +CGs and discuss their mechanisms. One of them is a brief electric coupling to a concurrent -CG initiated from a 257-m tall tower located 11 km from the +CG channel. A transient process (stroke) in the -CG flash appears to cause a transient luminosity enhancement (M-component) in the +CG channel. In the course of these essentially simultaneous transients, positive charge is in effect taken from the ground at the position of the tower and injected into the ground at the position of the +CG channel. Recoil leaders reactivating decayed +CG branches near the cloud base are each observed to cause a transient luminosity decrease (dip), as opposed to the expected luminosity increase, in the +CG main channel.