风廓线雷达对降水相态变化的观测分析

Analysis on Observations of Precipitation Phase Changes Using Wind Profile Radar Data

利用北京延庆风廓线雷达资料对2012年11月3日地面由降雨转为降雪的过程进行宏观和微观结构分析。结果显示:风廓线雷达的强度和速度产品能够很好地监测、诊断降雨到降雪相态变化的持续时间。降雨发生前,风廓线雷达反射率、信噪比、谱宽等因子均表现为不连续特征;地面降雨发生时,800~1000 m高度上出现明显的反射亮带;随着亮带的消失,地面降雨转变为降雪。地面降雨阶段,回波功率密度谱图呈现分层结构,1300 m以上表现为固态粒子特征,700 m以下为液态粒子,分层的高度与温度存在密切的关系,一般在274~275 K的环境内为融化层,融化层功率谱密度变化最为明显。另外,北京近3年层状云降水条件下.降雨和降雪阶段的垂直径向速度和信噪比数据统计表明,降雨发生时径向速度的范围一般在3~6 m·s^(-1)之间,信噪比在15~25 dB;而降雪发生时垂直径向速度值较小,在0~1.5 m·s^(-1),信噪比在3~15 dB之间。

The macro and micro structures of the weather process in which surface rain turns into snow are analyzed in this paper by using the data obtained from wind profile radar on 3 November 2012 in Yanqing of Beijing.The results show that the products of intensity and velocity field of wind profile radar are good for diagnosing and distinguishing the evolution of precipitation phase change from rainfall into snowfall.Fea-tures of reflectivity,signal to noise ratio (SNR),spectral width and other factors are discontinuous before raining,bright band appears in the 800-1000 m height when surface rainfall is seen,but with bright band disappearing,rainfall turns into snow.In the surface rainfall stage,the figure of the echo intensity spectra has a clear hierarchical structure,showing solid particles above 1300 m height and liquid below 700 m height,respectively.So,close relations are found between stratification height and temperature.General-ly,there is a melting layer with temperature of 274-275 K,and with the most significant change of echo intensity spectra.In addition,statistics of radial velocity and SNR of the stratus precipitation in the recent 3 years show that,radial velocity ranges within 3-6 m·s-1 and SNR is in 15-25 dB when raining;but in the process of snowing they are 0-1.5 m·s-1 and 3-15 dB respectively.