Detection Results of Guangdong-Hongkong-Macao Lightning Location System for Tall-object Lightning

Abstract

Tall-object lightning is one hot topic in the field of atmospheric electricity. In order to explore the application of Guangdong-Hong Kong-Macao Lightning Location System (GHMLLS) data on tall-object lightning, the performance of GHMLLS is evaluated based on the observation obtained at the Tall-Object Lightning Observatory in Guangzhou (TOLOG) during 2016 to 2017, and a preliminary comparative analysis on characteristics of lightning activities in the tall-object area in Guangzhou are made. Results show that the flash detection and the stroke detection of GHMLLS is about 93% (214/229) and 93% (449/481). The arithmetic mean (median) value of the location error is about 361 m(188 m), 252 m(167 m) and 294 m(173 m) for downward first negative strokes, downward subsequent negative strokes and upward negative strokes respectively. It is found that the cloud-to-ground (CG) lightning with higher grounding points are more likely to be misidentified as intro-cloud (IC) lightning by the GHMLLS. When the grounding point is (is not) lower than 200 m, the identification accuracy of the IC/CG classification is 99% (80%) and 93% (35%), respectively, for downward first negative strokes and the subsequent negative strokes. The accuracy of the IC/CG classification for upward negative strokes is found to be only 17%. According to statistical results of GHMLLS dataset from 2014 to 2018, negative IC records in tall-object area in Guangzhou are found to be more prominently gathered near buildings with height over 300 m than CG records, indicating that most negative IC records are actually tall-object strokes but just misjudged by GHMLLS. Mean shift algorithm is used to identify the lightning density centers of three relatively isolated tall buildings, namely the Canton Tower (600 m), the CITIC Plaza (390 m) and the GF Securities Headquarters (308 m). It's found that the number of strokes within the radius of 200 m in the lightning density center of the Canton Tower is about 5 times as much as that of the CITIC Plaza or the GF Securities Headquarters. It is speculated that most lightning occurred on the Canton Tower belonging to upward type, while those hitting the CITIC Plaza and the GF Securities Headquarters are mainly downward type.

Keywords

• tall-object
• return stroke
• performance evaluation