An 8-yr (i.e., 2008–15) climatology of the spatiotemporal characteristics of hail events in China and their associated environmental conditions are examined using hail observations, L-band rawinsondes, and global reanalysis data. A total of 1003 hail events with maximum hail diameter (MHD) of greater than 5 mm are selected and then sorted into three hail-size bins. Hail events with the largest MHD bin correspond to the median vertical wind shear in the lowest 6-km layer (SHR6) of 21.6 m s⁻¹, precipitable water (PW) of 34.8 mm, and convective available potential energy (CAPE) of 2192 J kg⁻¹. Hail with different MHD bins share similar freezing-level heights (FLHs) of about 4000 m. The thickness of the hail growth zone is thinner for hail events with the largest MHD bin. Hail events with different MHD bins display seasonal variations associated with the summer monsoon; that is, the hail season starts in South China in spring and then shifts to North China in summer. Larger hail is mainly observed during the spring in South China before monsoon onset in the presence of an upper-level jet and a low-level southwesterly flow accounting for large SHR6 and PW. In contrast, smaller-MHD hailstorms occur mainly during the summer in North China when surface heating is high and the low-level southerly flow shifts northward with pronounced baroclinicity providing large CAPE and PW, moderate SHR6, and low FLH. Environmental CAPE and SHR6 for large hailstones in China are comparable in magnitude to those in the United States but larger than those in some European countries.

Mesoscale convective vortices (MCVs) often cause rainstorms. To deepen our understanding of MCV formation mechanisms, reanalysis data from the National Centers for Environmental Prediction and the Weather Research and Forecasting model were used to simulate MCV activity in East China in August 2009. The simulations could reproduce the MCV and associated convective activities well. The vorticity budget and MCV formation mechanisms were then analyzed. The results show that the planetary vorticity advection is much smaller than other terms of the vorticity equation. The MCV initiates in the convective precipitation region and below 800 hPa. When the MCV initiates, there are vorticity-variation couplets within the vortex, and the MCV moves towards the positive vorticity-variation direction. In positive vorticity-variation areas, the divergence term and the tilting term are the vorticity source. The equilibrium response to diabatic heating is one of the forming mechanisms of this MCV. The latent-heating level is relatively low in this MCV case, and the MCV-forming level is also relatively low. Another forming mechanism of this MCV is the tilting of the horizontal vortex tube caused by the upward motion. At the MCV initiation, the perturbation scale of the vortex is found to be larger than the Rossby deformation radius, and thus the MCV could have a long duration.