Cause Analysis of a Post-frontal Extreme Rainstorm on the Northeast Side of Qinghai-Xizang Plateau

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  • 1. Lanzhou Central Meteorological ObservatoryLanzhou 730020GansuChina
    2. Northwestern Regional Center of Numerical Weather Prediction/Key Laboratory of Arid Climate Change and Disaster Reduction of China Meteorological Administration and Gansu ProvinceInstitute of Arid Meteorology of China Meteorological AdministrationLanzhou 730020GansuChina
    3. Heavy Rain and Drought - Flood Disasters in Plateau and Basin Key Laboratory of Sichuan ProvinceChengdu 610072SichuanChina

Online published: 2025-02-24

Abstract

On August 13-142022an extreme rainstorm event occurred in Yuzhong region of Gansu Provincenortheast of the Qinghai-Xizang Plateau. Accumulated daily precipitation reached 130. 6 mm and the maximum hourly precipitation was 36. 6 mmbreaking the heaviest daily precipitation records of the region and causing serious social impact and economic losses. Based on the data of surface minute observation and high altitude observationLanzhou Doppler radar and ECMWF Reanalysis v5ERA5),by analyzing the observation characteristicsenvironmental conditionstopographic effects and instability mechanism of the two heavy precipitation stages in this extreme rainstormthe results show that:(1The rainstorm was caused by the convergence of weak cold air brought by the shortwave trough in the westerlies and warm and humid air outside the subtropical high in the Longzhong area. The 700 hPa shear line provided the dynamic lifting conditionsand the surface cold front provided the triggering conditions.2The radar reflectance factor in the rainstorm process was characterized by persistent strong echoes accompanied by "backward propagation"low-level jets and obvious convergence. In the second stagethe echo top height behind the cold front was similar to that in the first stagebut the scope was larger and the structure was more compactand the convective cloud development was more vigorous. 3The water vapor conditions of the rainstorm were abundant. In the first stagethere was significant convective instability due to strong convergence and upward movement at the lower level and high convective effective potential energy. In the second stagethe upward movement was weakenedthe convective effective potential energy was 0and the dynamic and convective instability conditions were weak.4The release of unstable energy triggered by cold front baroclinic frontogenesis was the main triggering mechanism of precipitation in the first stage. After the transit of the cold frontthe precipitation in the second stage was formed by the combination of terrainfrontogenic secondary circulation and instability. Since the heavy precipitation after the summer cold front was not common in the northeast part of the Qinghai-Xizang Plateauforecasters tended to ignore such kind of rainstorms. Thereforewe need to strengthen monitoring and early warning of such rainstorm events.

 

Cite this article

FU Jing, DUAN Haixia, FU Zhao, LI Chenrui, SHA Honge, SONG Xingyu . Cause Analysis of a Post-frontal Extreme Rainstorm on the Northeast Side of Qinghai-Xizang Plateau[J]. Plateau Meteorology, 0 : 1 . DOI: 10. 7522/j. issn. 1000-0534. 2024. 00117

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