Comparison of Spatiotemporal Distribution and Occurrence Conditions of Large and Small Hail Events in the Beijing–Tianjin–Hebei Region

Abstract

Abstract Using hail records at national meteorological stations for 2014–18, ERA-Interim reanalysis data, and Doppler weather radar data, the spatiotemporal distribution of hail events (HEs) in the Beijing–Tianjin–Hebei region is revealed, and the environmental conditions and hailstorm structures corresponding to large hail (diameter ≥ 20 mm) events (LHEs) and small hail (2 ≤ diameter < 20 mm) events (SHEs) are compared. It is found that, although HEs may be more frequent in mountainous areas, most LHEs occur in the plains and near the foot of the mountains. The HE frequency peaks in June, and the average hailstone size is larger during May and June. According to daytime records, the HEs predominantly occur in the afternoon and evening, whereas LHE tends to be more in the evening. Comparison of environmental parameters suggests that, relative to SHEs, LHEs tend to correspond to higher 2-m temperature, a wetter lower layer, a larger difference in relative humidity between 925 and 500 hPa, greater unstable energy, and stronger wind shear. Hailstorms associated with LHEs tend to feature greater mesoscale rotation velocity than those associated with SHEs. Hailstorms usually show rapid increase (RI) in vertically integrated liquid (VIL) before hailstones are observed. A significant difference between the hailstorms associated with LHEs and SHEs is that the former has an obviously longer time interval between the end of VIL RI and the occurrence of hailfall, indicating that the large hail size benefits from the constant supply of liquid water and the hail can be lifted by updrafts for a long time. Significance Statement Whereas previous studies have predominantly focused on large hail (diameter ≥ 20 mm) events (LHEs) and their yielding conditions, this study was devoted to examining the difference between the LHEs and small hail (2 ≤ diameter < 20 mm) events in their associated atmospheric environments and storm structures. The interesting new insight is that the hailstorms yielding LHEs tend to feature a significantly longer time interval after the rapid increase of vertically integrated liquid and before hailfall. This study can provide a reference for the early warning of the scale of hail, which is one of the difficulties of weather services.