超强台风“威马逊”(1409)强度和降水特征及其近海急剧加强原因

Characteristics on intensity and precipitation of super typhoon Rammasun(1409) and reason why it rapidly intensified offshore

利用常规观测资料以及海南省中尺度自动站资料、海口多普勒雷达产品、FY系列卫星云图和NECP 1°×1°再分析资料,分析了2014年第9号超强台风"威马逊"(1409)在海南岛登陆前后其强度和降水特征及其近海急剧加强的原因。结果表明:"威马逊"登陆海南省文昌市翁田镇时强度维持或略有减弱,登陆前其中心附近极大风速超过74 m·s-1,最低海平面气压899.2 h Pa,为1949年建国以来登陆我国大陆最强台风;"威马逊"从7月18日10时到当日15时登陆文昌前的5 h内,其中心附近最大风速增大了5 m·s-1,最低气压下降了20 h Pa,其超强台风量级从18日11时开始维持时间达17 h;"威马逊"眼壁回波造成的海南北部地区强降水具有降水效率高、对流发展不够强盛的混合性降水特征,而其螺旋雨带"列车效应"造成的海南西部地区极值降水则具有典型的对流性降水特征;西太平洋副热带高压、低空急流、西风槽和南亚高压是"威马逊"近海持续加强的主要影响系统;低层辐合与高层辐散、弱的环境风垂直切变和适宜的海面温度、深厚的暖涡是"威马逊"近海急剧加强的原因。

Using conventional observation data, observations from automatic weather station at Hainan, Doppler radar products at Haikou, FY satellite cloud images and NCEP/NCAR reanalysis data with 1° × 1° resolution, we discuss the characteristics of intensity and precipitation of super typhoon Rammasun （1409） before and after landfall in Hainan Island and, the reason of its rapidly intensification offshore. The results indicate that before landfall in Wengtian town of Wenchang in Hainan, the maximum wind speed near the center of Rammasun exceeded 74 m· s-1 and the minimum sea-level pressure reached to 899.2 hPa. At landfall in Wengtian, Rammasun＇ s intensity was maintained or slightly decreased, for which it became to the strongest typhoon at landfall in China mainland since 1949. Near the center of Rammasun, the maximum wind speed increased by 5 m·s-1 and the minimum sea-level pressure decreased by 20 hPa form 10：00 BT to 15：00 BT 18 July 2014; its super typhoon grade has been maintained for 17 hours from 11：00 BT the same day. In the north of Hainan the heavy precipitation caused by eyewall echoes of Rammasun is characterized by mixed precipitation with high precipitation efficiency and convective activity being not very strong. However, in the west of Hainan extreme precipitation caused by spiral rain bands around Rammasun is characterized by typical convective precipitation. Rammasun continuously strengthens offshore under the influence of a wide variety of systems such as Western Pacific subtropical high, low level jet, westerly trough and South Asia high. It rapidly intensifies offshore due to the convergence in the low level and divergence in the upper level, weak vertical shear of environment wind, appropriate sea surface temperature and deep warm vortex.