Microphysical Characteristics of Snowfall and the Correlation Analysis in East China During the Winter of 2023

In this paper, for the three widespread freezing rain and snow weather processes in the Nanjing area from December 2023 to February 2024, we analysed the evolution characteristics and correlations of the microphysical quantities of snowfall particles and established the relationship between the snow density (ρs) and the snowfall rate (SR) estimation by using the minute-resolution observations of PARSIVEL2 distrometer and the weighing precipitation gauge. The results show that the differences in the microphysical characteristics of snowflakes were closely related to the temperature and humidity junctions, and the formation of large snowflakes was mainly attributed to the melting and merging mechanism triggered by the inversion and warm layer. The peak diameters, peak number concentrations, and mean spectral width of the snowfall particle spectrum increased with increasing snowfall rate level, which were consistent with gradual decrease in the mean values of the shape parameter μ and the slope parameter Λ fitted by the Gamma function. The distribution of the μ-Λ fitting relationship for different types of snowfall was relatively concentrated, especially at Λ < 20 mm-1 which was similar to the results of the study in the Colorado region; the mean values of μ and Λ for dry snow were lower than those for wet snow, but the two μ-Λ fits were consistent. Secondly, to analyse the contribution of microphysical quantities (normalised intercept parameter Nw, median volume diameter D0 and ice-water content IWC) to the different snowfall rate, the ρs-D0 relationship (ρs = 0.36D0-1.34) and the IWC-SR relationship (SR = 4.23IWC) were fitted. From the snowfall rate contours, it can be seen that there were significant differences in the microphysical properties of snow under the same snowfall rate conditions, with snowfall rate consisting mainly of low concentrations of large-particle snowfall or high concentrations of small-particle snowfall. Finally, the equivalent radar reflectivity factor (Ze) and snowfall rate relationship was established: Ze = 173SR1.54, the variation of its prefactor azs was analysed, and a theoretical expression was given. Comparison results showed that lower snowflake terminal velocities Vt and smaller values of the intercept parameter N0 caused azs to increase.