Abstract
An extreme torrential rain (ETR) event occurred in Henan Province, China, during 18–21 July 2021. Based on hourly rain-gauge observations and ERA5 reanalysis data, the ETR was studied from the perspective of kinetic energy (K), which can be divided into rotational wind (VR) kinetic energy (KR), divergent wind kinetic energy (KD), and the kinetic energy of the interaction between the divergent and rotational winds (KRD). According to the hourly precipitation intensity variability, the ETR process was divided into an initial stage, a rapid increase stage, and maintenance stage. Results showed that the intensification and maintenance of ETR were closely related to the upper-level K, and most closely related to the upper-level KR, with a correlation coefficient of up to 0.9. In particular, the peak value of hourly rainfall intensity lagged behind the KR by 8 h. Furthermore, diagnosis showed that K transformation from unresolvable to resolvable scales made the ETR increase slowly. The meridional rotational wind (uR) and meridional gradient of the geopotential (φ) jointly determined the conversion of available potential energy (APE) to KR through the barotropic process, which dominated the rapid enhancement of KR and then caused the rapid increase in ETR. The transportation of K by rotational wind consumed KR, and basically offset the KR produced by the barotropic process, which basically kept KR stable at a high value, thus maintaining the ETR.
摘 要
2021年7月18日至21日, 中国河南发生一次极端暴雨事件(下称“21·7”暴雨). 本文利用地面逐小时降水资料和ERA5再分析资料, 从动能角度对“21·7”暴雨进行研究, 其中动能可被分解为旋转风动能、 辐散风动能、 辐散风旋转风相互作用动能; 根据暴雨区小时雨强变率, “21·7”暴雨被划分为初始阶段、 急剧增强阶段和维持阶段. 结果表明, 暴雨的增强、 维持与高层动能密切相关, 并且与高层旋转风动能关系最为密切, 两者相关系数高达0.9. 特别地, 暴雨小时雨强的峰值滞后于旋转风动能8小时. 旋转风动能方程诊断表明, 次网格尺度向网格尺度的动能转换使暴雨缓慢发展; 经向旋转风与经向位势梯度的共同作用决定着有效位能通过正压过程转换为旋转风动能, 进而主导了旋转风动能的急剧增强, 有利于暴雨的急剧增强; 旋转风对动能的输送消耗了旋转风动能, 基本抵消了正压过程制造的旋转风动能, 使旋转风动能基本稳定维持在高值, 使得暴雨维持.
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Acknowledgements
This study was jointly supported by the National Natural Science Foundation of China (Grant Nos. 42275013, 42030611 and 42175008) and the Open Grants of the State Key Laboratory of Severe Weather (Grant No. 2021LASW-B17).
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• The intensification and maintenance of ETR were closely related to the upper-level K and most closely related to the upper-level KR.
• The uR and meridional gradient of φ jointly determined the conversion of APE to KR, which dominated the rapid enhancement of KR and ETR.
• Transportation of K by VR consumed KR and cancelled the KR produced by the barotropic process, which maintained both the KR and ETR.
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Yao, X., Li, R., Bao, X. et al. Diagnosis of the Kinetic Energy of the “21·7” Extreme Torrential Rainfall Event in Henan Province, China. Adv. Atmos. Sci. 41, 73–83 (2024). https://doi.org/10.1007/s00376-023-3025-6
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DOI: https://doi.org/10.1007/s00376-023-3025-6
Key words
- extreme torrential rain
- rotational kinetic energy
- kinetic energy generation and transport
- barotropic process