梅雨锋云系内对流回波与层状回波的研究

本文利用1998年“淮河流域能量与水分循环试验（HUBEX）”所获得的大量雷达资料及遥测雨量计计资料，细致分析了淮河流域梅雨锋云系的结构，根据层状云和对流云在雷达回波图中的不同特征，本文提出用松散系数D（反映云系结构疏松程度）来区分大范围云带中的降水云类型，同529张PPI资料统计表明，若D＞0．17则说明该区结构松散，降水属于层状云降水，D≤0．17时，云区是对流性降水，由于梅雨锋水具有明显的不均匀结构特征，其中锋面对流云带和强下挂回波带是造成强降水的主要原因，在用地面雨量资料和雷达资料对地面降水进行短时（3小时以内）校正时，针对不同的降水类型采用不同的Z－R关系比用同一种Z－R关系的校正精度大约提高4％。

A STUDY ON THE CONVECTIVE AND STRATIFORM CLOUDS OF MEI-YU FRONT BY USE OF RADAR FIELD DATA

We analyze the structure of precipitation cloud system in Mei-yu front,and we propose an identification factors for distinguishing strait form and convective precipitation among the stratiform cloud system of the large area precipitation. The identification factor is Looseness coefficient D,statistics show that it is a convective precipitation when D>0. 17, otherwise it's strait form. Research of radar data and associated raingauge data from June 29 to July 2 shows that the contributions of convective and hang down echo precipitation varies from 60% on 1 July to 73% on 29 June,but the echo area coverage was less than 40%. For this reason,the con- vective and hang down echo precipitation are the main contributions for Mei-yu front precipi- tation. Considering in the calculation of surface radar-based rainfall accumulation within the three hours,a distinct Z-R relationship is required for the different precipitation type, the accuracy on the calibrated radar rainfall estimation raises about 4% than using single Z-R relation.