青岛地区短时强降水雷达回波特征与中小尺度系统分析

Radar Echo Characteristics and Meso-Microscale Systems of Short-Term Strong Rainfall in Qingdao

利用青岛地区2011-2015年间32次短时强降水个例的雷达反射率因子、地面雨量站数据和FNL再分析资料对产生短时强降水的中小尺度系统和雷达回波特征进行分析,结果表明:造成短时强降水的中小尺度系统主要为与低空切变(槽)、台风倒槽或在偏南(北)气流中局地发展的对流相联系的辐合区或中小尺度辐合线;雷达回波多表现为中尺度强回波带,其移向与回波带长轴的夹角较小,或为局地发展少动的强对流单体;雷达回波剖面显示回波按质心高度可分为大陆强对流型和热带海洋型,大陆强对流型强降水的平均反射率因子垂直廓线强度总体明显强于热带海洋型,对流发展更加旺盛,热带海洋型强回波集中在低层,在近地面最强,而大陆强对流型回波悬垂明显,最强回波位于2km左右;针对大陆强对流型和热带海洋型两种不同类型的短时强降水,采用分型Z-I关系法进行定量降水估测能够较好地反映强降水的落区和极值,相比于固定Z-I关系法,20mm·h^-1以上雨强的相对误差由70%左右下降到30%左右。

The meso-microscale systems and radar echo characteristics during 32 short-term strong rainfall cases in Qingdao from 2011 to 2015 are analyzed based on the CINRAD/SA radar reflectivity factor,automatic rain-gauge and FNL re-analysis data.The results show that the meso-microscale systems that led to short-term strong rainfall are the mesoscale convergence areas or lines related to the low-level shear line(trough),inverted typhoon trough or local convections in Southerly(Northerly).The radar echoes mostly show as a mesoscale strong echo band or local strong convective cells,and the angle between moving direction and long axis of the echo band is small,and otherwise the moving speed of local cells is slow.The short-term strong rainfall can be divided into the continental convection type and tropical marine type by the centroid height of radar reflectivity.The average vertical profile of reflectivity of the continental convection type is generally stronger than that of the tropical marine type,which brings much stronger convective activity.The strongest reflectivity of the tropical marine type occurs in the low level with the maximum near the land surface;however,the continental convection type has clear hanging echoes with the maximum at 2 km altitude.Two different Z-I relations corresponding to the two rainfall types are used for quantitative precipitation estimation.Compared with the fixed Z-I relation,the result from the categorical relations shows better performance for the displacement and value of short-term strong rainfall,and the relative error is reduced from 70% to 30% when the rainfall intensity is greater than 20 mm·h-1.