台风“桑美”(0608)登陆前后降水结构的时空演变特征

Temporal and Spatial Variations in Precipitation of Typhoon Saomai (0608) before and after Its Landfall

利用雷达雨量计联合测量降水技术得到的1小时雨量分布资料,分析了台风"桑美"登陆前后距台风中心111km以内的降水结构及其时空演变特征,尤其是登陆前双眼墙循环过程中,降水结构的变化特征。研究发现:在登陆前"桑美"经历了双眼墙循环过程,在此期间,其内、外眼墙和雨带降水均以强降水为主,内、外眼墙平均降水率均随时间增强,而外眼墙增长幅度更大,且平均降水率始终大于内眼墙,但并没有伴随外眼半径减小的过程。而雨带平均降水率随时间变化很小,略有下降。在登陆后,"桑美"内核和外围区仍是以强降水为主,登陆前三小时左右内核区平均降水率有一个迅速增长的趋势,登陆后随着台风强度的减弱,其平均降水率迅速下降。"桑美"降水的空间分布特征显示,其登陆前后降水结构有明显的非对称性,在登陆前内、外眼墙和雨带最大降水均出现在台风移动路径的右侧,且雨带的最大降水率始终位于内、外眼墙的右方;登陆后,内核区和外围降水更多地出现在移动路径的后方,而不是登陆前的右侧。

A new hourly rainfall dataset is formed using variational method, based on raingauge and radar-rctrieved rainfall intensity. The new data are used to investigate temporal and spatial variations of precipitation structure within lll-km radius centered the typhoon, especially the evolution of rainfall structure during the concentric eyewalls cycle before Saomai landfall. The authors find that typhoon Saomai had concentric eyewalls before it landed, and the mean radii of the inner and outer eyewalls were 24 km and 59 km, respectively. The radius of the outer eyewall did not minish due to the rapid landfall of typhoon Saomai after the concentric eyewalls combination. During concentric eyewalls circulation, the precipitation in the inner and outer eyewalls and rainband regions was very heavy. In the outer eyewall region, the time series of mean rainfall rate was more variable than that in the inner eyewall and rainband regions. And in the inner and outer eyewalls regions, the mean rainfall rate increased with time, but in the rainband region it decreased. The precipitation in the inner-core and outer regions was also heavy, and the mean rainfall rate in the inner-core region increased abruptly about the three hours before Saomai landed, and then it decreased, accompanied with the reduction of the typhoon intensity after Saomai landed. The distribution of precipitation of typhoon Saomai was asymmetric. Before Saomai landfall, the maximum rainfall rates in the inner eyewall, outer eyewall, and rainband regions occurred in the right quadrant relative to the storm moving track, and the azimuth in the rainband region was always to the right of those in the inner and outer eyewalls regions. The azimuth of the maximum precipitation in outer eyewall and rainband regions varied with time during the concentric circulation. After typhoon Saomai landfall more precipitation in the inner-core and outer regions appeared in the back quadrant relative to the storm track.