贵州东部一次冻雨过程的微物理特征及相关性分析OA

Freezing rain is a high-impact winter weather hazard that poses substantial threats to transportation,power transmission,and agriculture.The Guizhou Plateau in southwestern China,characterized by complex terrain and frequent quasi-stationary frontal activity during winter,is one of the regions most prone to freezing rain in China.Although considerable research has focused on the climatological characteristics and synoptic conditions of freezing rain in central and western Guizhou,the microphysical properties of freezing raindrops in the mountainous eastern part of the province remain poorly understood.In particular,quantitative differences in rain-drop size distribution characteristics among stations at different elevations and their implications for radar-based quantitative precipitation estimation have not been systematically investigated.Improved understanding of freezing-rain microphysics is essential for refining the parameterization of ice-phase processes in numerical weather predic-tion models and enhancing operational forecasting over complex terrain. This study investigated a regional freezing rain event that occurred in eastern Guizhou in January 2022 using laser disdrometer observations,conventional meteorological data,and radiosonde profiles.The microphysical char-acteristics and their relationships were analyzed at three stations with different elevations(Cengong,Bijiang,and Wanshan).The main findings are summarized as follows: Under the influence of a strong cold-air outbreak,the mean precipitation microphysical characteristics were generally similar among the three stations,with maximum spectral widths below 4 mm.The freezing rain occurred predominantly at the higher-elevation Wanshan station.Compared with the other stations,Wanshan exhibited the highest mean drop concentration and the smallest mean and raindrop diameter,primarily because of the dominant contribution of small drops with diameters between 0.5 and 0.8 mm.The shorter sub-cloud fall distance and wea-ker collision-coalescence processes at higher elevations may also have contributed to these characteristics. The freezing rain formed through an ice-phase melting mechanism characterized by a three-layer vertical structure consisting of an ice-crystal layer,a melting layer,and a near-surface refreezing layer.This structure differs substantially from the warm-rain mechanism commonly observed in central and western Guizhou.A deep melting layer extending from approximately 800 to 650 hPa allowed snowflakes descending from the ice-crystal layer to melt completely into relatively large raindrops.These drops subsequently passed through a near-surface re-freezing layer approximately 900 m thick,with temperatures ranging from-1 to-3℃,where they became super-cooled before reaching the surface as freezing rain. The melting signature was significantly stronger than the refreezing signature,indicating that most raindrops originated from melted snowflakes rather than small ice pellets.The freezing raindrops were relatively large,with mean values of lgNw and Dm of 3.91 and 0.87 mm,respectively,comparable to observations reported for the Jianghan Plain.Furthermore,Dm exerted a significant constraint on the μ-Λ relationship of the Gamma-fitted drop size distribution. The Z=ARb relationships for the three stations were optimized for the freezing rain period.The exponent b re-mained relatively stable at approximately 1.4,whereas the prefactor A varied over as much wider range and was strongly correlated with raindrop size.Furthermore,a positive linear relationship between A and Dm was estab-lished,providing insight into regional differences in radar-based quantitative precipitation estimation for freezing rain. Because this study focused on a single freezing rain event in a relatively high-elevation mountainous region of eastern Guizhou,future work will expand the observational network and incorporate long-term drop size obser-vations from diverse topographic regions across Guizhou to further investigate the influence of terrain on freezing-rain microphysics.Enhanced vertical observations of hydrometeors and thermodynamic structures will also be con-ducted to improve the parameterization of ice-phase processes in numerical weather prediction models,particularly the simulation of vertical structures associated with freezing rain formation over complex terrain.These efforts will provide a more robust microphysical basis for operational forecasting and quantitative precipitation estimation of freezing rain.