Abstract:
Using conventional meteorological observation data,hail observation data,and the European Centre for Medium-Range Weather Forecasts ERA5 reanalysis dataset,the K-means clustering method was applied to classify the synoptic patterns of 53 hail events in the Longdong Loess Plateau from 2012 to 2023.Meanwhile,the characteristic features and threshold values of key physical parameters for different hail types were summarized. The results show that:(1)The large-scale circulation associated with hail events in Longdong can be categorized into three types:low-trough type (20 .8%),low-vortex type (22 .6%),and northwest airflow type (56 .6%).The
700 hPa shear line and surface convergence line correspond well with the hail occurrence areas for all types.(2)The low-trough type mainly occurs in late spring and early summer (May-June);the low-vortex type mainly occurs in summer (June-August);and the northwest airflow type occurs from April to October,with the highest frequency in June (37%).(3)Diagnostic analysis of physical parameters indicates significant differences in environmental field characteristics among the three hail types.The low-trough type is characterized by strong stratifi
cation instability and weak shear,with a large K-index and a low special-layer height.The low-vortex type is characterized by high energy and moderate shear,with large Convective Available Potential Energy,abundant low-level moisture,and a high special-layer height.The northwest airflow type is characterized by low energy and strong shear,with dry stratification in the middle and lower levels,an average 0-6 km vertical wind shear>12 m ·s-1,and thin thickness of the 0 ℃ and −20 ℃ layers.(4)Nine parameters were selected to establish forecast thresholds for hail in Longdong.Validation results indicate that these thresholds have practical reference value
and can provide quantitative reference indicators for hail potential forecasting in the region.
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