Study on the macro and micro characteristics of a large-scale freezing rain weather event in Hubei Province

In February 2024, two rounds of low temperature,rainfall/snowfall and freezing weather occurred in the middle and lower reaches of the Yangtze River.The first round of the event from February 1 to 6.Showed characteristics such as a large amount of freezing rain,wide range,long duration,and severe hazard.Based on the observation data of laser raindrop spectrometers from 80 national meteorological stations in Hubei Province,and combined with meteorological element observation data,this study quantitatively identified frozen rain and analyzed its macro and micro characteristics.The results are as follows.(1) During this rainfall/snowfall and freezing weather process,frozen rain mainly occurred in areas such as the Jianghan Plain and the Wuhan urban area,characterized by long-term maintenance of liquid precipitation.(2) The distribution characteristics of freezing rain hours and freezing rain amounts were consistent,with high-value areas positioned along the northwest-southeast direction.The duration of freezing rain was generally longer than 15 hours,while the freezing rain amount exceeded 24 mm.The peak period for freezing rain appeared from February 2 to 3 in 2024, with the proportion of numerical concentration,liquid water content,rain intensity,and particle size station hours in each interval significantly higher than in other periods.(3) The average spectrum of frozen rain droplets in various regions showed an unimodal distribution,with the peak number density around 200 mm^-3mm^-1.(4) The constructed Z-R relationship was different from short-term,regional frozen rain processes.It could effectively estimate the quantitative precipitation estimation (Quantitative Precipitation Estimation,QPE) of such frozen rain.The average values of D_m and log₁₀N_w throughout the entire process were 1.07 mm and 3.03 mm,respectively.(5) This freezing rain process was mainly influenced by the combined effects of water vapor condensation,clustering,and glaze attachment mechanisms,and formed by the melting and formation of dense graupel particles and ice crystal polymers.