Raindrop spectral characteristics and Z-R relationship of different rainstorm types in Huaibei region

Based on observations of summer raindrop spectra in Huaibei region from 2017 to 2020, the raindrop spectrum distributions of four rainstorm types, i.e., the trough type, the subtropical high edge type, the cold vortex type and the typhoon type, are analyzed. Results show that the occurrence frequency of precipitation in Huaibei area is dominated by stratiform precipitation, while convective precipitation is the main contributor to total precipitation. The microphysical parameters of different types of rainstorms are also different. The number concentration of low trough type and typhoon type is larger than that of other types, and the characteristic diameters of subtropical high edge type and cold vortex type are larger than those of the other two types. The relationship between raindrop particles and rain intensity at different scales is analyzed. It is found that small raindrops account for more than 60% of the number concentration, yet medium raindrops make a major contribution to rain intensity. The differences between different types of rainstorm are mainly caused by differences in the contribution rates of small raindrops and heavy raindrops to rainfall intensity. And with the increase of precipitation intensity, the contribution rate of small raindrops decreases, while that of large raindrops increases. The distribution of raindrop spectrum under different rain intensity classes is basically unimodal. With the increase of rain intensity, the number concentrations of various particles increase, the spectral width increases and the slope decreases. When the rain intensity increases, the mass-weighted mean diameter (D_m)-normalized intercept parameter (lgN_W) distribution tends to be concentrated, and the mean values of D_m and lgN_W are 1.15 mm and 3.79 mm⁻¹m⁻³, respectively. Through Gamma distribution fitting, it is found that the mean values and standard deviations of spectral distribution parameters of low trough type and typhoon type are greater than those of the other two types. The skewness of all parameters is positive except that of the parameters (lgN_W), which is negative. The shape parameter-slope parameter (µ-Λ) and radar reflectivity factor-radar reflectivity factor (Z-R) are slightly different between different types of rainstorm. In this paper, total precipitation in Huaibei area is calculated by Z=164.4R^1.42. In contrast, the standard relationship adopted by radar system at present underestimates rainstorm precipitation in Huaibei area, especially for low trough type rainstorms and typhoon type rainstorms.