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两次夏季暴雨期间高低空急流相互作用的诊断分析

Diagnostic analysis for interaction of upper and lower level jet streams during two heavy rainfall events in the summer

  • 摘要: 利用ERA-Interim数据,计算扰动能量方程,分析了2012年7月21日北京暴雨和2010年7月12日江苏暴雨期间高低空急流相互作用的能量特性。结果表明,与高层急流有关的扰动动能的产生主要由斜压过程和非地转风位势通量散度决定,而低空急流的扰动动能主要由后者决定。当中低空对流层扰动位势为负时,高层急流引起的次级环流的下支通过非地转位势通量矢量将高层的扰动动能输送到低空急流附近,使低空急流增强。上述两次暴雨过程中,能量通过直接(间接)环流自高层向低层的输送方式存在明显不同。

     

    Abstract: The energetics of the interaction between the tropospheric upper and lower level jet streaks during the development of summer severe convective storms developed in Beijing on 21 July 2012 and in Jiangsu on 12 July 2010 were analyzed using ERA-Interim six-hourly data and energy equations. It revealed that eddy kinetic energy (EKE) generation associated with the upper jet stream was mainly determined by the baroclinic processes and the convergence of ageostrophic geopotential fluxes, while in the lower level jet the latter plays an important role in the EKE generation. The descending motion induced by upper level jet streaks transported the EKE downward from upper level jet to low level to enhance lower level jet streak by vertical ageostrophic geopotential fluxes when the eddy geopotential was negative in middle and lower troposphere, which provides favorable conditions for the development of the summer storm. The transport of energy from upper to lower level by direct (indirect) circulation was significantly different during the two heavy rain events.

     

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