暴雨中尺度涡旋系统发生发展的诊断

Diagnostic Analysis on the Formation and Development of Meso-scale Vortex Systems

从位涡方程出发,导出描述三维涡度强度变化方程,分析大气层结及其变化等对三维涡度强度变化的影响。在此基础上,通过对垂直涡度变化的分析,揭示了大气层结变化、水平能量锋演化、垂直风切变等有利于涡旋系统发展的动力机制。针对湿中性层结特征(θse/p≈0),讨论了降水反馈对中尺度系统发展的影响,并揭示湿中性层结下凝结潜热的垂直非均匀分布与垂直涡度的耦合强迫作用可能是暴雨中尺度系统发展的动力机制。

Abstract： Torrential rain and flood are the main disasters of meteorology in summer in China. So meteorology workers pay close attention to the cause of torrential rain and the forecast of it. Our level of understanding heavy rain process is low because of the complex nature of heavy rainfall formation. It is imperative to enhance research on occurrence mechanism of heavy rainfall. In this paper, the intensity temporal variation equation of three-dimension vorticity vector was deduced from the moist potential vorticity equation. The effects of atmospheric stratification structure and its variation on the intensity of three-dimension vorticity vector was analysed with this equation. Vertical voticity temporal variation equation was obtained on the basis of this equation. The dynamic mechanism of atmospheric stratification structure variation and horizontal energy front variation etc. favorable to formation and development of the mesoscale vortex systems was revealed through analysis on vertical voticity temporal variation. To counter moist neutral stratification, the feedback effect of precipitation on meso-scale vortex systems development was discussed. The main results are as follows： （1） The intensity temporal variation equation of three-dimension vorticity vector dζ/dt=ζa·↓ΔQ/r1·r2｜↓Δθe｜-ζ↓Δ·V-ζ/｜↓Δθc｜d/dt｜↓Δθc｜-ζ/r1·r2 d/dt（r1·r2） can serve as a useful tool for the diagnosis of mesoscale vortex systems development. （2） The formation and development of mesoscale systems are mainly influenced by the variation of potential equivalent temperature gradient d｜↓Δθe｜/dt and temporal variation of vertical wind shear [d（δu/δz）/dt.d（δv/δz）/dt] in the formation stage of mesoscale systems. （3） The contributing factors on development of mesoscale system are the coupling forces between vertical variation of diabatic heating and vertical component of vorticity [ζz（δQ/δz）] and the coupling forces between three-dimensional divergence and vertical component of vorticity （-ζz↓Δ·V ） and the coupling forces between horizontal frontogenesis and vertical component of vorticity ζz（d｜↓Δsθc｜/dt） in the development stage of mesoscale systems. （4） For a case of southwest vortex occurring in Sichuan basin in July 7-10, 1989, results of diagnostic analysis is not different with theoretical analysis.