Analysis on characteristics of the hail in Hohhot under a background of cold vortex

Based on Doppler radar, satellite and the NCEP 1°×1° 6 h interval reanalysis data, a hail weather event is analyzed, which occurred in the rear of the cold vortex on July 29, 2015 in Hohhot. The results indicate that in the rear of the cold vortex, the convective instability of atmosphere increased with cold advection in upper level and warm advection in lower level. Especially, the warm advection in the lower level is more conductive to the accumulation of unstable energy in the hail area and to the formation of large CAPE. Water vapor transportation of middle and lower atmosphere, strong clockwise rotation in low-level winds (0~6 km) and the moderate vertical wind shears are advantageous to the development of convective storms. The surface convergence line, cold air and dry line are the main triggering factors of the hail. The hail was generated in the lower atmosphere with high-energy area and is close to the moist area of the dry line. The characteristics of "hook echo"and"bow echo"were presented in the basic reflectivity factor figure, and there was a weak echo area in the vertical section of basic reflectivity factor figure, while great than or equal to 45 dBz echo reached above the height of -20 ℃ level. Cyclonic rotation convergence and upwind section can be seen in the radial velocity figure. VIL reached great than or equal to 64 kg·m^-2, and it jumped significantly before the hail occurred.