选取2013年5月20日发生在广东三水的一次飑线过程作为研究对象,首先结合飑线回波带移经三水及其上空雷达回波的时间-高度分布特征将降水过程划分为3个阶段,然后通过计算各时刻的粒子总数密度、中值体积直径和峰值数分析降水过程雨滴谱的变化,再对Z-R关系(Z=aRb)进行分析,根据雨滴谱实测资料分别统计整体Z-R关系和3个降水阶段的Z-R关系,在此基础上讨论雨滴谱的变化和雷达观测的回波强度对降水估计的影响。结果表明:中值体积直径在对流云降水阶段和层状云降水阶段基本一致,但对流云降水阶段的粒子总数密度远大于层状云降水阶段;对流云降水阶段以双峰型为主,当降水向层状云类型发展时,多峰谱比例增加;雷达观测的回波强度常低于雨滴谱计算的反射率因子,离地面越近两者的相关性越好;根据3个降水阶段分别进行Z-R关系拟合,即分型Z-R关系,通过相对误差分析可知,利用分型Z-R关系反演雨强的效果明显优于整体Z-R关系反演效果,雨滴谱在层化降水阶段估计的相对误差最小、对流云降水阶段反演精度稍低于层状云降水阶段,这与对流云降水中雨强和雨滴谱谱型变化大且快有关;在雷达观测方面,利用分型Z-R关系反演雨强的相对误差较小而雷达观测的误差在对流云降水阶段较小,当降水向层状云降水转化时,雷达观测引起的相对误差增大,这主要是由于对流云降水阶段中雨滴谱仪和雷达对应的回波强度误差最小,也与雷达观测精度、两种仪器采样的时空差异和雨滴谱特征变化等因素有关。
A squall line process as the research object which occurs on 20 May 2013,at Sanshui in Guangdong has been selected.Firstly,the precipitation process is divided into three stages by the distribution of radar echo over time and height and the characteristics when the squall line moving towards Sanshui.Secondly,analyzing the change of the raindrop spectrum in this precipitation by calculating the number density of total particles、the median diameter and peak number.Thirdly,stating the relationships between echo and precipitation intensity in the whole process and the grading process respectively according to the data of raindrop spectrum,then discussing the influence of raindrop spectrum's change and radar echo on the rainfall estimation.The following conclusions have been given:The median diameter in stages of convective cloud precipitation is basically in line with stratiform cloud precipitation stages,but its number density is much greater.Convective cloud precipitation phase is given priority to two peaks,and when the precipitation reaches to a stratiform one,the ratio of multi-peak spectrum is increasing.Radar echo is often less than the reflectivity calculated by HSC-OTT Parsivel,their correlation increases with descent height.Between the relationship of echo and precipitation intensity,b fluctuates within the range of 1~2,however,a has major fluctuation,especially when the convective cloud precipitation stages progressing towards stratiform clouds,a value increases and b value decreases;Then a segmented relationship between echo and precipitation intensity is defined according to the characteristics of three stages,the precipitation's inversion of segmented relationship is much better,the relative error given by raindrop spectrum is minimal in the period of transition,but the inversion accuracy in stratiform cloud precipitation stages is higher than convective clouds,which bears on the rapid and dramatic changes of convective clouds raindrop spectrum and its rainfall intensity;In the aspect of radar observations,the precipitation inversion of segmented relationship is better,the deviation caused by radar is smaller in convective clouds,but this value will be higher when the type of precipitation transits to stratiform clouds,which is mainly due to the the minimum error between the distrometer and radar in the phase of convection,the differences of two instruments on time and height,the precision of radar observation and the changes of raindrops spectrum also have important influence on rainfall estimation.
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