摘要
1998年 7月 2 0～ 2 3日 (简称“98.7”)发生在武汉周边地区的特大暴雨过程与沿低涡切变线相继生成和强烈发展的MαCS及MβCS直接关联。利用MM5模拟提供的高空间分辨 (2 0km)输出资料 ,对这次突发性特大暴雨中尺度切变线低涡发展的动力学机制进行了诊断。涡度分析指出 ,高、低空正涡度中心在武汉周边地区上空的叠加和耦合是该低涡切变线持续发展的主要物理机制之一。总涡源的诊断揭示 ,在突发性暴雨强烈发生发展期 ,武汉周边地区上空从低层到高层有一近乎垂直的涡源高值区生成和维持 ,其垂直结构的发展演变与涡度场垂直结构的发展演变相一致。这一结果表明 ,大气总涡源对该中尺度低涡切变线的生成和发展起着决定性作用 ,也是该暴雨中尺度系统持续发展的重要动力学机制。对贡献于总涡源的诸分量计算表明 ,在 6 5 0hPa以下 ,散度项对大气总涡源的正贡献最大 ,但在此层以上至 2 0 0hPa之间 ,垂直涡度平流项的贡献要比散度项大 ,同时水平平流项也为正贡献 ;在整个对流层 ,扭转项对总涡源为负贡献 ,散度项只在 4 5 0～ 2 5 0hPa之间为负贡献。在近地层 ,垂直涡度平流项和水平平流项基本对总涡源不作任何贡献。时间平均涡源和纯扰动涡源对低涡切变线的生成很重要 ;在强烈发展期 ,相互作用涡源作用最大 。
During the period of 20～23 July 1998 ('98.7' ), an extraordinary heavy rainstorm event occurred in Wuhan surrounding which was direct relationship with the successive generating and intensive developing MαCSand MβCS.The dynamic mechanism of the development of the mesoscale low vortex with shear line in association with an abruptly extraordinary heavy rainstorm was diagnosed byusing the MM5(V2.12)successfully simulated high spatial resolution (20 km) output data. The analyses of vorticity indicated that one of the mainly physical mechanism of the persistent development of the low vortex withshear line was the superposition and coupling of positive vortivty centers over the upper and lowerlevelsof the regions of Wuhan surrounding; diagnoses of the total vorticity sources revealed that there was an almost vertical columnof high positive vorticity sources value generating and maintaining from low to upper levelsover Wuhan surrounding during the intensive genesis and development of the abrupt heavy rainfall. The vertical structure and evolution of the positive vorticity sourcecenters were basically consistent with that of the positive vorticity centers of the vorticitiyfield. This result showed the total vorticity sources played dominantrole in the genesis and development of the mesoscale low vortexwith shear line, which was also an important mechanic of the persistent development of the mesoscale system of the heavy rainfall. The computed componentsof contribution to the total vorticity source indicatedthe divergence term possesses the most contributionbelow 650 hPa, but the contribution of the vertical vorticity advection term is bigger than divergence termbetween650 hPa and200 hPa; whilethe horizontal advection is also positive. The divergence term was negative contribution between 450～250 hPa, the twisting term was negative contribution throughout thetroposphere. Inthe surface layer, there was almost no contribution to the vorticity source concerning the advection terms of thevertical vorticity and horizontal vorticity. The time-averagedand pure perturbation vorticity sourcesplayed important roles forthe genesis of the low vortex with shear line; During the intensive development of the low vortex, the effectof the nonlinear interactive vorticity sourceis the most, the pure perturbation vorticity source is next; The low vortex moveeastward and weakening when the nonlinear interactive vorticity source was decreased, in spite ofthe time-averagedand pure perturbation vorticity sourcewere still positive.
出处
《高原气象》
CSCD
北大核心
2002年第5期447-456,共10页
Plateau Meteorology
基金
国家重点基础研究发展规划项目 (G19980 40 90 7)资助
关键词
切变线低涡
涡度
总涡源
论断
1998年
7月
Low vortex with shear line
Vorticity
Total vorticity source
Diagnoses
