First Documented Downward Positive Cloud-To-Ground Lightning Initiated By An Upward Negative Lightning

An interesting downward positive cloud-to-ground lightning (DPCG) initiated by an upward negative cloud-to-ground lightning (UNCG) was recorded by the instruments installed at the Tall-Object Lightning Observatory in Guangzhou. The characteristics of the discharges before and after the DPCG return stroke were investigated in detail using both optical and electric field change data. The UNCG was triggered from the tip of the Canton Tower (600 m high) by a distant +CG lightning. A sequence of intracloud (IC) discharges developed toward and connected to several pre-existing channels of the UNCG. As a result, some positive charge was pumped from remote thundercloud regions to the region around the intersection of the pre-existing and new channels. A branch of one IC channel developed from the intersection point toward the ground, transformed into a downward positive leader, terminated on the ground, and resulted in a positive return stroke. After that, the discharge processes in the cloud continued to neutralize the remaining positive charge. The UNCG served to facilitate the IC discharges that supplied positive charges for the DPCG. Most of the charge involved in the UNCG-initiated DPCG originated from remote positively charged regions in the cloud. These observations constitute evidence for a new scenario of the initiation of +CG lightning.Key PointsA downward +CG initiated by an upward tall-object -CG was recorded for the first timeThe characteristics of the discharges before and after the +CG were investigated using optical and electric field change dataThe observed sequence of events constitutes evidence for a new scenario of the initiation of downward +CG