Intracloud to Cloud-to-Ground Lightning Ratio over China and Its Relationship with Thunderstorm Structure

The intracloud (IC) to cloud-to-ground (CG) lightning ratio (IC:CG ratio) provides not only essential information for extrapolating IC flashes from the continuously monitored CG activities but also implications for the kinematic and microphysical structures of thunderstorms. This study examines the IC:CG ratio and the corresponding thundercloud structure over China, using satellite-based total lightning flashes from OTD and LIS and CG lightning detected by the China Lightning Detection Network (CLDN). Climatological IC:CG ratios are first derived from full records of OTD/LIS (1995-2014) and CLDN (2009-2018) data, and coincident IC:CG ratios are further determined by using coincident observations of LIS and CLDN in 2009-2014. Results show that climatological IC:CG ratios and coincident ratios share similar magnitude and spatiotemporal variability, verifying the reliability of the climatological IC:CG ratios. In general, most lightning-prone areas in China have regular IC:CG ratios (2-5), except the North China Plain where IC:CG ratios are abnormally high (> 10). Interestingly, the high IC:CG ratios in the North China Plain coincide with a maximum positive CG fraction (+CG:CG), which may indicate the exceptional intensity of these thunderstorms. IC:CG ratios in China also show significant seasonal variability. IC:CG ratios in the two maximum lightning regions including southern China and Sichuan Basin maximize in April and substantially reduce after the onset of the summer monsoon. In contrast, high IC:CG ratios in the North China Plain persists through May to August, mainly due to the lack of CG flashes in the summer. We further investigates the convective characteristics and vertical structures of thunderstorms with regular and abnormally high IC:CG ratios using spaceborne and ground-based radar observations.