Statistical analysis of extreme thunderstorm gusts in central and eastern China under the background of Northeast China Cold Vortex

The Northeast China Cold Vortex (NCCV) is one of the main synoptic-scale systems causing extreme thunderstorm gusts (ETGs) in the central and eastern parts of China. Environmental conditions are known to be distinctly different in the four quadrants of NCCV, rendering prediction of the ETGs related to NCCV more challenging. Based on 8-yr observations from 17677 automatic weather stations and ERA5 reanalysis data, 1717 ETGs events were identified and divided into four quadrant groups according to their relative position to the center of the NCCV (CVC). The observation characteristics and environmental conditions of ETGs in different quadrants of NCCV were analyzed in this paper. The results show that the frequencies of ETGs in the different quadrants are, in descending order, as follows: southeast, southwest, northeast and northwest. Heilongjian Province experiences the highest frequency of ETGs. The percentages of ETGs in the Northeast and North China regions is the highest in the southeast quadrant, while is the highest in the southwest quadrant in other provinces. The ETGs occur frequently in July and afternoon. All the ETGs show a seasonal northward movement with a peak in midsummer and a much weaker secondary peak in spring. The favorable conditions for the occurrence of ETGs in different quadrants vary with seasons. All ETGs samples are analyzed by establishing a new coordinate system with CVC as the origin and the radius of the northeast cold vortex (rCV) as the unit distance. The results show that the proportion of ETGs first increases and then decreases with the increase of the distance from CVC. Up to 41.4% of ETGs occur in the area about 1.2 to 2.5 rCV away from CVC and at an angle of 120—210°. This is the region where ETGs are most concentrated relative to the NCCV with favorable conditions such as abundant water vapor, strong dry air in the middle layer and moderate intensity 0-6 km wind vector difference. In the southwest quadrant, there is also a relatively smaller high-value area at an angle of 235–245° and 1.5–2 rCV away from CVC, which corresponds to the strong convergence zone formed by the dryline convergence characteristics and has favorable conditions such as the temperature difference between 850hPa and 500hPa exceeding 29℃. The insights gained from this study on the ETGs in different quadrants of NCCV can serve as valuable references for enhancing the forecasting accuracy of ETGs.