Climatic characteristics of cloud-to-ground lightning activities in convective weather asssociated with the Northeast China cold vortex

In this paper, the ERA5 atmospheric reanalysis data provided by ECMWF and the lightning data observed by the Chinese meteorological lightning detection system are applied to conduct a statistical analysis of the lightning activities of 103 Northeast China cold vortex (NCCV) events from May to September during 2017-2023. The results show that both the proportion of positive cloud-to-ground (CG) lightning and the lightning current intensity under the background of the NCCV are higher than the annual average. The high proportion of positive CG lightning is mainly located in the Northeast Plain and the northern part of the North China Plain. The diurnal variation distribution of lightning activities under the background of the NCCV generally presents the characteristics of one peak and one valley, with the maximum and minimum values occurring at 16:00 and 09:00 (Beijing time), respectively. Based on the hourly position of the center of the NCCV, the spatial distribution of all lightning flashes with the center of the cold vortex as the origin is obtained through dynamic synthesis. The results indicate that lightning flashes mainly occur in the southern and eastern parts of the cold vortex. Specifically, the fourth and third quadrants of the cold vortex account for 48.4% and 38.7%, respectively, while the first and second quadrants combined account for 12.9%. Through the comparative analysis of the lightning data of 18 thunderstorm wind gust, 9 heavy precipitation and 8 hybrid type processes associated with NCCV, it is found that the ratios of positive CG lightning in thunderstorm wind gust processes and heavy precipitation processes are 39.2% and 12.2%, respectively. The proportion of positive CG lightning in thunderstorm wind gust processes is more than three times higher than that in heavy precipitation events. Although the current intensities of negative CG lightning flashes in thunderstorm wind gust processes and heavy precipitation processes are nearly the same, the average current intensity of positive CG lightning in thunderstorm wind gust processes is 72.3 kA, which is significantly higher than that in heavy precipitation ones. The CG flashes in thunderstorm wind gust events mainly occur within 1000 km in the southeastern region of NCCV, while the CG lightning in heavy precipitation mainly occurs in the southeastern region of NCCV within 1000 km and in its southwestern region outside 1000 km away. The area with high CG density in heavy precipitation events usually corresponds to the low positive CG ratio, while the regions with high proportion of positive CG are generally consistent with areas of high positive CG density. The above analysis preliminarily reveals the spatiotemporal distribution characteristics of CG lightning under the background of the cold vortex and explores the physical reasons for the influence of environmental conditions on the polarity distribution of CG lightning, which is conducive to the understanding of the lightning activity characteristics of different types of severe weather under the cold vortex situation.