基于Ka波段云雷达观测的中国西天山降雨云宏微观物理特征研究

Macro–Micro Physical Characteristics of Rainfall Clouds in the West Tianshan Mountains Based on Ka-Band Cloud Radar

利用Ka毫米波云雷达与自动气象站降雨资料,研究了西天山地区2019年和2020年5~8月的降雨云宏微观特性。结果表明:(1)降雨主要发生在夜间,累积降雨量集中在21:00(北京时间,下同)至次日07:00,降雨频次和累积降雨量相关系数为0.71。大雨强频次虽最少,但对总累积降雨量贡献较显著。(2)小雨强、中雨强、大雨强平均反射率因子最大值分别为30 dBZ、35.8 dBZ和39.5 dBZ,最大平均液态水含量分别为1.5 g m^(-3)、4.2 g m^(-3)和7.3 g m^(-3)。(3)不同降雨强度对应的反射率因子都有两个集中区域,2.0~4.4 km反射率因子集中在15~26 dBZ,地面附近的小雨强、中雨强、大雨强对应的反射率因子分别集中在24~32 dBZ、29~38 dBZ和31~42 dBZ。1.75 km以下中雨强和大雨强液态含水量小于1gm^(-3)的频率明显少于小雨强,降雨强度的越大降雨粒子径向速度越集中。

This study analyzed the physical characteristics of rainfall clouds in the West Tianshan Mountains,from May 2019 to August 2020,based on the Ka-band millimeter-wave cloud radar and rainfall data from automatic weather stations.The findings demonstrate that:(1)Rainfall occurs primarily at night.The cumulative rainfall was concentrated from 2100 BJT to 0700 BJT the next day.There was a significant beneficial correlation between rainfall frequency and accumulated precipitation.The frequency of heavy rainfall was the lowest,but its contribution to total accumulated rainfall was significant.(2)The maximum average reflectivity of light,moderate,and heavy rainfall intensities were 30,35.8,and 39.5 dBZ,respectively,and the maximum average liquid water content was 1.5,4.2,and 7.3 g m^(-3),respectively.(3)There are two concentrated areas for the reflectivity of various rainfall intensities.The reflectivity of 2.0–4.4 km was concentrated in 15–26 dBZ,and the reflectivity of light,moderate,and heavy rainfall intensities near the surface was respectively concentrated in 24–32 dBZ,29–38,and 31–42 dBZ.The frequency of moderate and heavy rain intensity below 1.75 km,where the liquid water content is less than 1 g m^(-3),is significantly lower than light rain intensity.The greater the intensity of rainfall,the more concentrated the radial velocity of rainfall particles.