北上台风“杜苏芮”登陆后河北中南部的雨滴谱特征分析

Analysis of Raindrop Size Distribution Characteristics in the Central and Southern Hebei Province after Typhoon Doksuri Landing

利用雨滴谱仪观测资料,分析了2023年7月29日至8月1日的河北中南部极端降水的雨滴谱特征,研究降水的微物理特征变化。结果表明,降雨强度R小于50 mm/h时,雨滴直径随着R的增加明显增大,R超过50 mm/h时,随着R的继续增大,雨滴的质量加权平均直径不再继续增长,趋于平衡,稳定在2 mm。此次降水位于海洋性对流特征区域的点较多,而位于大陆性的点较少,仍有很多点位于两种形态的过渡区间内,表明地面降水的微物理过程具有显著的时空变化。利用K-means聚类算法,将降水样本按照滴谱特征分为5类,发现不同强度滴谱特征具有明显差异,当降水强度高于50 mm/h时,降水的滴谱性质体现为较大的加权平均直径和较大的粒子数浓度,正是因为有持续稳定的大直径粒子和高数浓度的特征,雨滴谱的突变加上台风输送源源不断的水汽,才能在短时间内产生强降水。利用滴谱数据进行雷达降水估测关系拟合,得到雷达反射率Z、差分反射率KDP和R的拟合公式Z=224R1.44和R=45.8KDP0.77,使用R-KDP定量降水估测关系,结果要优于使用Z-R关系,尤其是超过40 mm/h的降水,估计误差明显好于使用Z-R关系。

The raindrop size distribution characteristics for extreme precipitation in central and southern Hebei from 29 Jul to 1 Aug 2023,were analyzed by using the raindrop spectrometer observation data.Results show that when the precipitation intensity R value is less than 50 mm/h,the raindrop diameter increases significantly with an increase in the value of R.However,as the R value increases,the raindrop diameter reaches a plateau,stabilizing at 2 mm without further increase.There are more data points where precipitation occurred in the oceanic convection characteristic area,whereas there are fewer data points where precipitation occurred in the continent characteristic area;however,there are still many data points in the transition interval between the two areas.Using the K-means clustering algorithm,precipitation samples were divided into five categories according to their droplet spectral characteristics,revealing obvious differences across various intensities.When the precipitation intensity is higher than 50 mm/h,the droplet spectral properties for precipitation exhibit large values.Because of the sustained stability of large particle diameters and high number concentrations,a sudden change in the raindrop spectrum and the continuous flow of water vapor transported by typhoons can produce heavy precipitation over a short period.Using the droplet spectral data to fit the radar precipitation estimation relationship,the authors obtain fitting formulas for radar reflectivity Z,differential reflectivity KDP,and precipitation intensity R,Z=224R1.44 and R=45.8KDP0.77.Results obtained using R–KDP for quantifying the precipitation estimation relationship are better than those yielded using the Z–R relationship,especially over 40 mm/h precipitation,and the estimation error for the former is significantly better than that for the latter.