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2023年冬季华东地区降雪微物理特征及其相关性分析

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

  • 摘要: 本文针对2023年12月—2024年2月南京地区三次大范围冰冻雨雪天气过程,利用激光雨滴谱仪PARSIVEL2和称重式降水传感器等获取的分钟分辨率观测资料,分析了降雪粒子微物理量演变特征和相关性,并建立雪密度(ρs)和降雪率(SR)估算关系。结果表明:雪花微物理特征差异与温湿层结存在密切关联,大尺度雪花的形成主要归因于逆温层和暖层引发的融化碰并机制。随着降雪率等级的增加,降雪粒子谱峰值直径、峰值数密度以及谱宽均值皆增大,这与Gamma函数拟合的形状参数μ和斜率参数Λ均值逐步减小表现一致。不同类型降雪μ-Λ拟合关系分布相对集中,尤其在Λ < 20 mm-1时与科罗拉多地区的研究结果相近;干雪的μ、Λ均值虽低于湿雪,但两者μ-Λ拟合关系较为一致。其次,为了分析微物理量(归一化截距参数Nw、中值体积直径D0和冰水含量IWC)对不同降雪率的贡献,分别拟合了ρs-D0关系(ρs = 0.36D0-1.34)和IWC-SR关系(SR = 4.23IWC)。由降雪率等值线可知,在相同降雪率条件下,雪的微物理性质存在显著差异,降雪率主要由低浓度的大颗粒降雪或高浓度的小颗粒降雪构成。最后,建立等效雷达反射率因子(Ze)和降雪率关系:Ze = 173SR1.54,分析其前因子azs的变化,并给出了理论表达式。对比结果表明,较低的雪花下落末速Vt和较小的截距参数N0值会造成azs增大。

     

    Abstract: 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.

     

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