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焦宝峰, 冉令坤, 李舒文, 等. 2022. 一次暴雨中尺度涡旋发展机制诊断分析研究[J]. 大气科学, 46(3): 762−774. DOI: 10.3878/j.issn.1006-9895.2202.21247
引用本文: 焦宝峰, 冉令坤, 李舒文, 等. 2022. 一次暴雨中尺度涡旋发展机制诊断分析研究[J]. 大气科学, 46(3): 762−774. DOI: 10.3878/j.issn.1006-9895.2202.21247
JIAO Baofeng, RAN Lingkun, LI Shuwen, et al. 2022. Diagnosis of the Mesoscale Vortex Development Mechanism in a Heavy Rain Event [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 46(3): 762−774. DOI: 10.3878/j.issn.1006-9895.2202.21247
Citation: JIAO Baofeng, RAN Lingkun, LI Shuwen, et al. 2022. Diagnosis of the Mesoscale Vortex Development Mechanism in a Heavy Rain Event [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 46(3): 762−774. DOI: 10.3878/j.issn.1006-9895.2202.21247

一次暴雨中尺度涡旋发展机制诊断分析研究

Diagnosis of the Mesoscale Vortex Development Mechanism in a Heavy Rain Event

  • 摘要: 中尺度涡旋可以持续激发新对流,是造成局地持续性降水的重要系统。基于经典涡度方程的诊断无法描述热力信息对于涡旋发展的贡献。本文采用Boussinesq近似对涡度方程进行整理,将方程唯一强迫项定义为垂直速度位涡,其形式与位涡类似,利用垂直速度替换位温。进一步在垂直速度位涡倾向方程中,以气压水平梯度的形式引入热力过程的间接作用,定量描述动热力配置的贡献。以2021年6月15日发生在南疆的一次极端暴雨为例,利用高分辨率数值模拟资料,初步分析了低层动热力强迫作用向垂直涡度的传递。结果表明,垂直速度位涡的局地变化主要来自热力强迫项中低层垂直风切变与低层冷池的耦合作用,两者在降水区前侧产生大范围的正值区。该区域与垂直速度位涡的正值区重叠,促进垂直速度位涡的增长,进而维持降水前缘的正涡度,有利于产生较强的上升运动,触发新对流并造成持续性降水。

     

    Abstract: Mesoscale vortex usually stimulates local convection, which is an important system for persistent precipitation. The solution to the classical vorticity equation cannot directly describe and quantify the contribution of thermodynamic information to the development of vortices. In this study, the Boussinesq approximation is adopted to rewrite the vorticity equation, and the only forcing term employed is the vertical velocity potential vorticity. The form of this forcing term is similar to that of potential vorticity; however, vertical velocity is used instead of the potential temperature. Furthermore, the indirect effect of the thermodynamic process is introduced in the form of the horizontal pressure gradient to quantitatively describe the contribution of the dynamic and thermodynamic configurations to the vertical velocity potential vorticity equation. A heavy rain event, which occurred in southern Xinjiang on June 15, 2021, was selected as a case to analyze the transfer of low-level thermodynamic forcing to vertical vorticity using high-resolution numerical simulation data. The results showed that the local variation of the vertical velocity potential vorticity mainly originates from the coupling effect of the low-level vertical wind shear and low-level cold pool in the thermodynamic term, which contributed to a wide region of positive values ahead of the rainband. This pattern promotes the growth of vertical velocity potential vorticity in the corresponding region. The distribution and tendency of vertical velocity potential vorticity help maintain the positive vorticity ahead of the rainband, thereby making it conducive to the generation of strong ascending motion and new convection, directly leading to continuous precipitation.

     

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