一次飑线过程的动力和微物理结构及滴谱变化对降水估测的影响研究  

DYNAMIC AND MICROPHYSICAL STRUCTURES OF A SQUALL LINE SYSTEM AND EFFECTS OF RAIN DROP SIZE DISTRIBUTION ON PRECIPITATION

作　　者：刘黎平[1] 牟容[1] 许小永[1] 胡志群[1] 

机构地区：[1]中国气象科学研究院灾害天气国家重点实验室,北京100081

出　　处：《气象学报》2007年第4期601-611,共11页Acta Meteorologica Sinica

基　　金：国家科技部科研院所技术开发研究专项资金项目"双线偏振雷达气象产品生成软件系统研制"项目;国家重大基础研究项目(2004CB418305)

摘　　要：雨滴谱的变化和回波强度的垂直变化是影响雷达估测降水的重要原因。文章利用美国KOUN双线偏振雷达观测的一次飑线过程资料,用模糊逻辑的方法、β方法和约束条件下的Λ方法,分析了飑线过程降水粒子相态和雨区雨滴谱分布及其相态混合区冰雹融化过程,结合四维变分方法风场反演方法,研究了雨滴谱变化与飑线过程风场中尺度结构的关系,及其对双线偏振雷达不同估测降水方法的影响。结果表明:处在气旋中的飑线存在中低层辐合线,低层辐合带及强烈上升形成强回波,飑线后部的层状云中存在下沉气流,而飑线的前部存在下沉气流形成的边界层辐合线。飑线中对流单体组成的强回波带和后侧的层状云降水的雨滴谱分布有明显的变化,大雨滴区往往在飑线前部,在东南气流中新生的对流单体也常常有大雨滴区存在。ZH、ZDR随高度变化比较明显,而KDP基本不随高度变化,高度的选取对传统的Z-R关系方法、(ZH,ZDR)方法估测降水量影响很大,但KDP方法几乎不受高度变化的影响。本次过程雨滴谱变化非常明显,这对Z-R关系估测降水将产生重要影响,(ZH、ZDR)方法和KDP方法估测的降水比较接近,而Z-R关系方法在对流中心降水估测值偏大。小于30 dBz回波的KDP脉动很大,出现的不正常值对降水估测有一定影响,采用综合降水估测方法是必要的。Changes of rain drop size distribution and vertical variations of reflectivity are main factors in precipitation estimation with radar. The KOUN dual linear polarization radar data of a squall line case in USA are used to analyze horizontal and vertical variations of ZH, ZDR, KDP, wind field , hydrometeor phase distributions, rain drop size distributions（DSD） and hail melting processes, and their effects on precipitation estimations by five retrieval algorithms. The retrieval algorithms used in this paper include the ＂beta＂ （fl） method and the ＂constrained-gamma＂ method for rain drop size distribution, the fuzzy logical phase distinguish, and the 4DVAR wind retrieval. The results show that the squall line lay in the mid-lower level convergence zone of northwest and southeast winds within a cyclone. There were downdrafts in the stratiform clouds of the rear part of the squall line, and a boundary layer convergence line induced by downdrafts in front of the squall line. The DSDs were different in the strong echo band of convective cells and in the stratiform cloud precipitation area rear of the squall line, and large drops often occurred in the new echo in front of the squall line. Variations of ZH, ZDR with altitude were obvious, but KDP almost did not change with altitude. Correspondingly, the selection of radar data level has larger influence on precipitation values estimated by the Z-R relation and the R （ZH, ZDR） estimator. The DSD distinctively varied in the convective precipitation process, which has important effect on precipitation estimations by the Z-R relation. Precipitations estimations by the R （ZH, ZDR） and R （KDp） methods are similar, but the Z-R relation overestimated the precipitation at convective centers. The KDp method had larger errors of precipitation estimation in cases of weak echo （less than 30 dBz）. Therefore, it is necessary to use a ＂hybrid＂ approach to estimate precipitation.

关 键 词：双线偏振雷达 雨滴谱 降水估测 

分 类 号：P406[天文地球—大气科学及气象学]