AE001-0010
Natural Upward Negative Leaders Triggered by In-cloud Activity of a Nearby Negative Cloud-to-ground Flash
Tuesday, 8 December 2020
Poster
Fanchao Lyu, Chinese Academy of Meteorological Sciences, Nanjing Joint Institute for Atmospheric Sciences, Nanjing, China, Steven A Cummer, Duke University, Electrical and Computer Engineering, Durham, NC, United States, Zilong Qin, The Hong Kong Polytechnic University, Department of Building Services Engineering, Hong Kong, China, Mingli Chen, Hong Kong Polytechnic University, Department of Building Services Engineering, Hong Kong, China and Weitao Lyu, State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China
Abstract:
Lightning imaging/mapping from both optical cameras and radio frequency location systems play important roles in understanding the mechanisms and the dynamic development of the lightning discharges during thunderstorms. The low-frequency (LF) interferometric-TOA mapping array demonstrated to be a useful tool to image the lightning discharge processes inside the thunderclouds. Here we report on the electromagnetic field measurements and LF 3D mapping of two coincident flashes. One is a normal downward negative cloud-to-ground flash, which started with extensive intracloud activity and consisted of three return strokes. And another upward positive flash started with an upward negative leader (UNL) initiated from the ground.
The LF 3D mapping clearly showed the existence of preceding in-cloud activities, which probably moved negative charges away from the initiation position of the UNL, which then favor the initiation of the UNL. The whole UNL developed for ~10 km horizontally at the altitude of ~ 2 km above the ground, with a total of more than 3C positive charge transferring from the cloud to ground during this negative leader process. With the 3D map on the progression of the UNL and the measured electric field change at Duke forest site, the line charge density during the progression of the UNL was estimated with a mean value of 3.46 mC/m. It can be inferred that the preceding in-cloud activities could be responsible for the triggering of the UNL, while the existence of the potential wells of positive charge at the lower level of the thundercloud might facilitate and maintain the long horizontal propagation of the negative leaders inside the thundercloud before the positive return stroke.
