Characteristics of unconnected upward leaders initiated from tall structures observed in Guangzhou

Forty‐five unconnected upward leaders (UULs) occurred in 19 downward negative flashes are analyzed. Each observed UUL is initiated by a downward stepped leader before a new strike point is struck. For each UUL, several parameters are determined when possible mainly by using high‐speed images: inception height, inception time prior to return stroke (RS), horizontal distance from the flash's strike point, two‐dimensional (2D) distance between the nearest downward leader branch tip and the UUL's inception point at its inception time, 2D length, and 2D average propagation velocity. Their values range from 40 to 503 m (number of samples: 45),