Abstract:
Using multi-source meteorological observation data and ERA5 reanalysis data, combined with CMA-MESO high-resolution numerical simulation results, the main weather systems, spatio-temporal evolution and three-dimensional structure characteristics affecting the process of rare winter hail in 2024 are analyzed in detail. There were two precipitation stages from 08:00 on January 1st to 08:00 on January 2nd. From 19:00 on January 1st to 00:00 on January 2nd, the hail was the main convective activity in the west and south of the central part of Guizhou. From 00:00 to 08:00 on January 2nd, the precipitation was the main convective activity in the east and south of the central part of Guizhou. The research object was the first stage. The results indicate: (1) Before the hail process occurred (14:00 and 18:00 on January 1st), there was a thermal low pressure development in eastern Yunnan and western Guizhou, whose thermal effect strengthened the ground convergence and the accumulation of unstable energy in the west and south of the central part of Guizhou. (2) In terms of the configuration of high and low circulation field in the troposphere, the divergence in the upper troposphere, the eastward disturbance of the short-wave trough in the middle troposphere, the obvious southerly warm and wet airflow and warm shear in the middle and lower troposphere, as well as the superposition of the dry and wet regions in the middle and lower layers provided favorable dynamic, water vapor and unstable stratification background conditions for the hail process. The stable maintenance of the ground stationary front was the main synoptic scale system for the hail process, providing triggering conditions for this process. The upward motion of the surface prefrontal overlapped with the updraft of upper-level westerly jet, which enhanced the occurrence and development of the hail process. (3) The strongest hail process occurred in Changshun around 21:30, which companied with the peak activity of the strong echo cell activity of the squall line, forming an echo overhanging structure in the middle and lower troposphere. Under the background of the lower 0℃ layer and −20 ℃ layer, strong updraft circulated to lift the hail embryo, making the surface of the hail condensation continuously, providing the necessary conditions for the formation of heavy hail. (4) The CMA-MESO high-resolution numerical model clearly revealed that during the occurrence and development of heavy hail process in Changshun, a significant θ
se front region was formed in the region of the strongest rising velocity due to the intrusion of cold air in the mid-upper troposphere, which not only increased the instability of the atmosphere, but also provided a triggering mechanism for the occurrence of convective weather. The change characteristics of environmental field, which included the high CAPE value was released continuously, wind vertical shear was strengthened continuously, warm advection was strengthened continuously in the lower troposphere, and the dry invasion of cold air was from strong to weak in the mid-upper troposphere, had good indicative significance for the prediction of hail region.