赵坤,周仲岛,潘玉洁,葛文忠. 2008. 台湾海峡中气旋结构特征的单多普勒雷达分析[J]. 气象学报, 66(4):637-651, doi:10.11676/qxxb2008.060
台湾海峡中气旋结构特征的单多普勒雷达分析
Single-Doppler radar analysis of a mesocyclone in the Taiwan Strait.
  
DOI:10.11676/qxxb2008.060
中文关键词:  多普勒雷达, 钩状回波, 中气旋, 地基雷达,风速轨迹,显示法
英文关键词:Doppler radar, Hook echo, Mesocyclone, GBVTD
基金项目:国家自然科学基金(40505004和40333025)项目、国家重点机理研究发展项目(973:2004CB18301)、上海台风研究基金(2006STA01-2)
作者单位
赵坤 教育部国家中尺度灾害性天气重点实验室南京大学大气科学系南京210093 
周仲岛 台湾大学大气科学系台北 
潘玉洁 教育部国家中尺度灾害性天气重点实验室南京大学大气科学系南京210093 
葛文忠 教育部国家中尺度灾害性天气重点实验室南京大学大气科学系南京210093 
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中文摘要:
      2004年9月10日傍晚,在台湾北部海面大范围中尺度对流雨带中有一钩状回波并伴随中气旋。受台湾东北部和西南部海面两个热带低压系统的环流影响,海峡北部海面有一大尺度的风切辐合带,为中气旋发展提供了有利环境。文中利用台湾地区北部民用航空局中正机场多普勒雷达资料,分析中气旋特征,结果显示此中气旋由低层形成随后向上发展,最高可达8 km以上,内核直径先是低层大中层小,随后中层扩大与低层接近成圆柱状,之后快速减弱,整个过程约2 h。进一步用地基雷达风速轨迹显示法(GBVTD)反演中气旋成熟期间的环流结构变化,结果显示在分析期间,最大风半径维持在5—6 km,且随时间在高度分布由向内倾斜转化为无明显倾斜再到向外倾斜。轴对称径向风先在低层最大风速半径以内有外流,以外有内流,在最大风速半径处为上升运动区并伴随强回波,而在气旋中心附近为下沉运动区。随后气旋中心回波和下沉运动均逐渐增强,同时低层外流增强并扩散至最大风速半径外,相应的上升运动和强回波也移至最大风速半径外。切向风先呈现波数1的非对称结构,最大风速区位于气旋移动的左侧,且随高度有沿逆时针方向旋转的现象,随后显著增强,分布趋于对称,最大轴对称切向风达20 m/s位于约1 km高度。此后切向风速逐渐减弱,同时波数1非对称结构又有加强的趋势,最大风速区位于移动方向左前侧。中气旋发展过程和结构同其他地区观测的非超级单体微气旋非常相似,其成熟期环流特征同台风结构也非常类似,不同之处在于其中心下沉运动及低层外流为降水所造成,且尺度和生命期均远小于台风。
英文摘要:
      The kinematic and precipitation structure of a mesocyclone associated with a hook echo was analyzed by single Doppler radar, located in northern Taiwan. The mesocyclone was embedded in a mesoscale convective rainband near northern Taiwan coast on 10 September 2004. The synoptic environment was characterized by a moderate CAPE and weak ambient vertical shear from surface to 5 km. In addition, a pronounced low-level mesoscale shear/convergence zone, which might result from the interaction of two tropical depressions, was also identified in the northwest coast of Taiwan, providing a favorable dynamic condition for the development of the mesocyclone. The mesocyclone was firstly documented by analyzing the dipole signature revealed from the single Doppler radar radial velocity data. The analysis shows that this mesocyclone formed initially at low level, then deepened and strengthened rapidly into mature stage with the vertical depth deeper than 8 km and later decayed rapidly. Correspondingly, the couplet diameter of mesocyclone decreased with the height at the time of vortexgenesis, and then evolved into columnar structure accompanied with the broader diameter in middle layer. The mesocyclone lasted for about 2 hour. The Ground Based Velocity Track Display (GBVTD) method proposed by Lee et al. (1999) was further applied to retrieve the axisymmetric circulation of the mesocyclone. The GBVTD-derived primary circulation shows the radius of maximum wind (RMW) of the mesocyclone was about 5-6 km and varied from inward tilting to outward tilting with time. The axisymmetric radial wind field was initially characterized with a low level outflow inside RMW and inflow outside RMW, respectively. The strongest reflectivity was associated with stronger updraft near RMW, and weak downdraft was located at the center of the cyclone. Subsequently the downdraft and reflectivity near the mesocyclone center strengthened obviously, accompanied with the low-level outflow, strong updraft as well as high reflectivity extending outside RMW. The relative tangential wind initially exhibited a wavenumber 1 asymmetric structure with the maximum wind region at the left portion of the cyclone and shifted counterclockwise with height. The axisymmetric tangential wind strengthened and reached its maximum intensity with a value about 20 m/s at z=1 km. After that the axisymmetric tangential wind decreased rapidly, meanwhile the wave-1 asymmetric structure redeveloped with the maximum wind at the left front of motion. In summary, the evolution and structure of the mesocyclone is similar to that observed within a non-supercell misocyclone. It is worth to mention that the axisymmetric circulation characteristics of the mesocyclone at its mature stage are very similar to those observed in a mature typhoon. However, there are significant differences, i.e., the size is much smaller, the life time is much shorter, and the downdraft in the center is produced by precipitation instead of compensating subsidence.
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