Synchronized Two‐Station Optical and Electric Field Observations of Multiple Upward Lightning Flashes Triggered by a 310‐kA +CG Flash.

A positive cloud‐to‐ground (+CG) lightning flash containing a single stroke with a peak current of approximately +310 kA followed by a long continuing current triggered seven upward lightning flashes from tall structures. The flashes were observed on 4 June 2016 at the Tall Object Lightning Observatory in Guangzhou, Guangdong Province, China. The optical and electric field characteristics of these flashes were analyzed using synchronized two‐station data from two high‐speed video cameras, one total‐sky lightning channel imager, two lightning channel imagers, and two sets of slow and fast electric field measuring systems. Three upward flashes were initiated sequentially in the field of view of high‐speed video cameras. One of them was initiated approximately 0.35 ms after the return stroke of +CG flash from the Canton Tower, the tallest structure within a 12‐km radius of the +CG flash, while the other two upward flashes were initiated from two other, more distant tall objects, approximately 18 ms after the +CG flash stroke. The initiation of the latter two upward flashes could be caused by the combined effect of the return stroke of +CG flash, its associated continuing current, and K process in the cloud. Each of these three upward flashes contained multiple downward leader/upward return stroke sequences, with the first leader/return stroke sequence of the second and third flashes occurring only after the completion of the last leader/return stroke sequence of the preceding flash. The total number of strokes in the three upward flashes was 13, and they occurred over approximately 1.5 s. Key Points: Seven upward lightning flashes were triggered by a 310‐kA +CG flashThree upward flashes, each containing downward leader/upward return stroke sequences, were studied in detailThe first leader/return stroke sequence of the second and third flashes occurred only after the completion of the last leader/return stroke sequence of the preceding flash [ABSTRACT FROM AUTHOR]