超强台风威马逊快速增强及大尺度环流特征

Rapid Intensification and Associated Large-scale Circulation of Super Typhoon Rammasun in 2014

超强台风威马逊(1409)登陆前发生快速增强现象,并成为我国有气象记录以来的最强登陆台风。该文利用中国气象局台风最佳路径资料、NCEP FNL分析资料、NOAA高分辨率逐日最优插值海表温度融合分析资料和天气学、动力学诊断分析方法,分析这次罕见的台风快速增强过程。研究结果表明:威马逊(1409)快速增强与持续有利背景场有关,如海温异常偏暖、低空急流和越赤道气流的增强、环境风垂直切变维持较小、高层维持较强流出气流等。尤其是台风下游大气处于热力不稳定,在其他有利因子的共同作用下,台风移入热力不稳定环境场中,有利于台风环流内部对流活动的增强和对流凝结潜热效率的增加,从而有利于台风强度增加。动能诊断方程表明:威马逊(1409)快速增强期间低层动能主要来源于风穿越等压线所作的功,这与台风环流内强降雨释放的对流凝结潜热驱动台风中心附近上升、外围下沉的垂直环流圈的加强紧密联系。

Most offshore tropical cyclones（TCs） would be weaken because of energy decay due to land surface friction, while a small part of them intensify instead. There is an average of 0.8 TCs per year which intensifies abruptly in offshore waters of South China. Statistical, diagnostic and numerical work reveal that sea surface temperature （SST）, TC inner structure and characteristics of atmospheric circulation are the most important factors. And for the latter, strength or strengthening of a low-level jet linking with TC and weak environmental wind vertical shear are significant, and widely applied in operation to judge the TC in- tensity change trend. The mechanism of TC abrupt intensification in offshore waters is still not fully re- vealed, and therefore it is still very difficult to give an accurate forecast for these phenomena in the route operation. Wrong judge and forecast for TC abrupt intensification in offshore waters would lead to under- estimation and insufficient defense of TC disasters. Super typhoon Rammasun is intensifying continuously for over 24 h before it makes landfall at Wenchang of Hainan at 0730 UTC 18 July 2014, with 40 m · s^-1 of maximal central wind speed, 960 hPa of minimal central sea level pressure at central part of South China Sea at 0000 UTC 17 Jul 2014, 72 m · s^-1 888 hPa at 0600 BT 18 Jul 2014. And Rammasun becomes the strongest landfalling TC on national record. Based on CMA TC track data, satellite and radar images, NCEP reanalysis data, NOAA high-resolu- tion blended analysis of daily optimum interpolation SST and synoptic analysis and kinetic energy budget, study is carried out on the characteristic of abrupt intensity change of Rammasun and its cause. Synoptic analysis show that the continuous abrupt intensification of Rammasun is concerned with the favorable atmospheric background circulation, the anomalous warm SST in central and northern part of South China Sea during the middle ten days of July 2014, intensification of the southwestern low level jet and cross-equatorial flow linking with Rammasun, and the maintenance of upper level outflow especially the unstable atmosphere in the downstream region. Its moving into the unstable circumstance is advanta- geous to the convective activities and the efficiency of convective condensation latent heat release within the cyclone circulation, and leads to the maintenance or intensification of the TC. Kinetic energy budget output reveals, main kinetic energy source at low level is from the wind cross- ing through the isobar, and this is connected with vertical circulation of ascending in the central area and descending in the outer region forced by convective condensation latent head. To consider in view of con- vective activities and condensation latent heat release is helpful for understanding of TC intensity change and forecast in operation.