山东半岛一次典型冷流暴雪的粒子谱特征分析

Analysis on Snow Particle Spectrum Characteristics of a Typical Cold-flow Blizzard in Shandong Peninsula

为深入研究山东半岛冷流暴雪微物理特征及变化,利用激光降水现象仪(OTT Parsivel)、多普勒天气雷达和常规气象观测资料,对2020年初冬山东半岛一次东北冷涡后强冷空气造成的暴雪过程的雪粒子谱特征进行了分析。结果表明:(1)本次暴雪过程中,渤海上空850 hPa温度为-16℃,大连到山东半岛为北风与偏西风的辐合,强降雪发生在对流不稳定的大气层结中。(2)降雪粒子谱呈多峰分布,强降雪过程的初始发展、稳定和消散阶段,及一个强降雪对流系统的生成发展、成熟和消散阶段,雪粒子谱均有不同。雪粒子Gamma谱三参数特征:形状因子μ在零线附近波动,斜率参数λ小于1.0 mm^(-1),lgN0为3 m-3·mm^(-1-μ)左右。(3)强降雪时,多个数浓度中心对应的雪粒子下落末速度均在1.0 m·s^(-1)以下,最大雪粒子数浓度的峰值下落末速度为0.55 m·s^(-1)。在直径1.0 mm左右时,浓度大的雪粒子的下落末速度存在峰值,其贴近未结霜雪粒子速度曲线,说明冷流降雪的多数雪粒子不易结霜,以干雪为主。雪粒子以密凇附的枝状和聚并的板状两种类型为主,两种类型雪粒子下落末速度V和粒子直径D的关系系数和指数分别为0.62和0.33及0.69和0.41,拟合关系分别为V=0.62D^(0.33)和V=0.69D^(0.41)。

In order to study microphysical characteristics and changes of cold-flow snowstorms in Shandong Peninsula,the snow particle spectrum characteristics of a blizzard process caused by strong cold airflow after northeast cold vortex in Shandong Peninsula in the early winter of 2020 are analyzed based on the data of precipitation distrometer measurements(OTT Parsivel),new generation Doppler radar and conventional observation.The results show that:(1)The 850 hPa temperature over the Bohai Sea was^(-1)6℃during the blizzard process.The surface winds were characterized by the convergence of northerly wind and westerly wind from Dalian to Shandong Peninsula,and the snowstorm occurred in the atmospheric stratification with convective instability.(2)The snow particle spectrum of the blizzard was distributed in a multi-peak pattern and differed in the stages of beginning,development and dissipation,i.e.the periods of development,maturation and weakening of a convective system of severe snowfall.The three-parameter characteristics of Gamma function of snow particles are that the shape factorμis positive or negative near the zero,the slopeλis less than 1.0 mm^(-1),and the lg N 0 is about 3 m-3·mm^(-1-μ).(3)During the blizzard process,the falling terminal velocities of snow particles corresponding to multiple number concentration centers were all below 1.0 m·s^(-1),and the peak falling velocity of maximum number concentration of snow particles was 0.55 m·s^(-1).When the diameter of snow particle was about 1.0 mm,the falling velocity spectrum of snow particles with large total concentration had a peak value,which was close to the velocity curve of non-frosting snow particles,indicating that the most snow particles of the cold-flow blizzard were dry and not easy to frost.The snow snowflake types were mainly the densely rimed dendrites and the assemblages of coalesced plates.The coefficient and exponents for the relationship between the terminal falling velocity V and particle diameter D of the two different snowfall types are 0.62 and 0.33 for dendrites,and 0.69 and 0.41 for coalesced plates,respectively.The fitting velocity-diameter relationships for dendrites and coalesced plates are V=0.62 ^(0.33) and V=0.69D^(0.41),respectively.