In‐Cloud Discharge of Positive Cloud‐To‐Ground Lightning and Its Influence on the Initiation of Tower‐Initiated Upward Lightning. Issue 24 (26th December 2021)

• Record Type: Journal Article
• Authors: Yuan, Shanfeng; Qie, Xiushu; Jiang, Rubin; Wang, Dongfang; Wang, Yu; Wang, Caixia; Srivastava, Abhay; Tian, Ye
• Is Part Of: Journal of geophysical research. Volume 126:Issue 24(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-12-26
• Subjects: upward lightning -- positive cloud‐to‐ground lightning -- in‐cloud discharge -- lightning mapping; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2021JD035600
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: We conducted a comprehensive observation of tower‐initiated upward lightning (UL) during the summer season from 2012 to 2020, using high‐speed video and the Beijing Broadband Lightning Network (BLNET). A total of 25 UL flashes were observed, and 21 of them were triggered by nearby positive cloud‐to‐ground (CG) lightning. It is interesting to note that eight (38%) of the parent +CG lightning flashes have more than one return stroke (RS). The distance between the UL and the grounding point of its parent +CG lightning was 4–38 km, where nine (43%) of the UL were triggered less than 2 ms after the positive RS, and 11 (52%) of them were triggered after a long time delay of 5–187 ms. Based on high‐speed video and mapping results, the short time delay was associated with the reactivation of the decayed established leader above the tower. The long time delay was associated with the negative leader extending to the region above the tower during the long continuing current. The positive E‐field change during RS or continuing current period favored the inception of an upward leader. Although both preliminary breakdown (PB) and RS in a +CG flash produced positive E‐field changes, an upward positive leader induced by PB aborted its sustained propagation after +RS. Plain Language Summary: In favorable conditions, an upward leader could initiate from the top of high constructions and develop toward the cloud base, named upward lightning (UL). Observation revealed that most UL transfer negative charge into the ground from the cloud and, quite often, such negative UL tends to be triggered by nearby positive cloud‐to‐ground (CG) lightning. So far, the in‐cloud channel structure that favors the initiation of UL remains unclear. This paper shows how nearby +CG flashes triggered upward leaders based on 21 cases from two tall towers in Beijing based on multi‐band detection of E‐field change, lightning mapping results, and high‐speed video observations. Nearly all UL was initiated after the occurrence of +RS, and UL can be initiated immediately (<2 ms) after +RS or after a long delay (5–187 ms) following +RS. There are two interesting findings: first, eight (38%) of the parent +CG have multiple strokes with different terminations; second, one attempted upward leader aborted its development after the occurrence of +RS, although lightning activities before or after +RS both produced positive electric field changes. Thus, we suggested two types of in‐cloud structures of +CG lightning and compared the effects of their leader propagation on UL initiation. Key Points: Eight (38%) of 21 positive cloud‐to‐ground lightning flashes that triggered upward lightning (UL) have more than one return stroke (RS) Propagating in‐cloud negative leaders after positive RS were the most efficient triggering component for UL Approaching positive leaders at lower altitudes above the tower prevented the sustained propagation of an upward positive leader