Analysis of the characteristics of a hail event with multi-source data

To understand the evolution characteristics of radar echo, microphysical parameters, and thermal dynamics of the convective systems during different stages of hailstorms, observations from Doppler weather radar, laser raindrop spectrometer, microwave radiometer, and automatic meteorological stations were used to investigate the radar echo characteristics, raindrop spectrum difference, temperature, humidity and water vapor variation characteristics of a hailstorm occurred in Tianjin on July 9, 2017. The results are as follows. (1) The warm and wet air on the east side of the shear line at 850 hPa is superimposed with the cold air at 500 hPa, which is conducive to the accumulation of unstable energy and triggering of convective weather. With hail approaching, the instability of the ambient atmosphere increased significantly. (2) During the evolution stage of the hail cloud, two hailfall events were observed, both of which occurred during the strengthening and merging processes of the convective cells. (3) During the hailfall stage, the maximum diameter, mass-weighted mean diameter, and median volume diameter of the precipitation particles reached their peak values. The contribution rate of medium and large droplets to precipitation intensity reached 94.56%, and the average spectral width during the hailfall stage was the largest. While after hailfall, the contribution rate of particles with a diameter less than 1.0 mm increased. The mean spectrum of particles within the range of less than 1.0 mm showed a bimodal pattern, with the first peak and the second peak occurring near 0.3 mm and 0.6 mm, respectively. (4) Before the hailfall, the water vapor accumulated slowly but continuously. The integrated water vapor and liquid water content showed an obvious increase in 1 h before hailfall. Due to the existence of temperature inversion, the upper layers were dryer and colder, while the lower layers were warmer and wetter. Note that the water vapor content in the whole atmosphere started to decrease after the hailfall.