98.7"特大暴雨低涡的螺旋度和动能诊断分析

Diagnostic Analysis of the Helicity and Kinetic Energy for a Low Vortex of "98.7" Extraordinary Heavy Rainfall

"98.7"特大暴雨过程与700hPa低涡切变线的强烈发展以及丰沛的水汽和强垂直运动密切相关。螺旋度的诊断结果揭示,与强暴雨区和切变线低涡相应的是一对符号相反而又紧邻的螺旋度带,它们的垂直结构是一对符号相反而又互伴的螺旋度柱;螺旋度及其诸分量的量级是相同的。这表明,垂直运动的水平切变和水平速度的垂直切变以及水平速度的水平切变对螺旋度有相同大小的贡献,也意味着强垂直运动和低空急流对暴雨的发生和发展极其重要。动能的诊断结果显示,强动能区与暴雨区和低涡切变线有很好的对应关系,在中、低空的强动能中心也正是强降雨中心;动能最强的700hPa也是低涡切变线发展最强的层面。强动能及其强梯度区和强螺旋度区基本一致。表明强动能及其强梯度对螺旋度变率及其通量有重要贡献。

The '98.7' extraordinary heavy rainfall event was in close relationship with the intensive development of a low vortex with shear line on 700 hPa and the abundant moisture as well as strong vertical motion. The diagnostic results of the helicity revealed that there was a pair of close neighboring helicity bands with opposite sigh, which corresponding to both the heavy rainfall area and the low vortex with shear line, their vertical structure was a pair of intercompanying columns of helicity with opposite sigh. The order of magnitudeof the helicity and its each component were the same, which showed the horizontal shear of vertical velocity and the vertical shear of horizontal velocity as well as the horizontal shear of horizontal velocity were possessed of the same contribution to the helicity, which also mean that both intensive vertical motion and the lower level jet were very important to the genesis and development of the heavy rainfall. The diagnostic results of the kinetic energy showed that the area of the kinetic energy with high value was well correspondingto that of both the rainfall band and the low vortex with shear line, the centers of the high energy on the middle\| and lower\|level were also the center of heavy precipitation; the 700 hPa with the strongest kinetic energy was also the level of the intensive development of the low vortex with shear line. The area of the high value kinetic energy with strong gradient and the area of the strong helicity was basically consistent, which showed that the high value kinetic energy with strong gradient was possessed of important contribution to the rate of change of helicity and its fluxes.