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WANG Na, ZHAO Junhu, LOU Panxing. 2023. Analysis of the Circulation Characteristics and Driving Factors of the Super Strong Autumn Flood in Shaanxi Province in 2021 [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 47(4): 1283−1294. DOI: 10.3878/j.issn.1006-9895.2305.22241
Citation: WANG Na, ZHAO Junhu, LOU Panxing. 2023. Analysis of the Circulation Characteristics and Driving Factors of the Super Strong Autumn Flood in Shaanxi Province in 2021 [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 47(4): 1283−1294. DOI: 10.3878/j.issn.1006-9895.2305.22241

Analysis of the Circulation Characteristics and Driving Factors of the Super Strong Autumn Flood in Shaanxi Province in 2021

  • In September–October 2021, Shaanxi Province experienced record-breaking rainfalls, resulting in severe floods and disasters. This study analyzed the extreme characteristics of the super strong autumn flood that occurred in 2021 over Shaanxi Province and demonstrated the interannual variations in its associated circulation and the driving factors behind the flood using observational and reanalysis data. The results showed that: (1) The cumulative rainfall over Shaanxi Province during the 2021 flood had been the heaviest since 1961. Moreover, this flood was closely related to the extremely strong anomalous anticyclone developed over the western North Pacific (WNPAC), the development of high pressure in Bohai Bay, and the formation of a significantly low trough over Lake Balkhash. As a result of these phenomena, cold/warm air converged over Shaanxi Province, resulting in the formation of a strong autumn flood that sustained for a long time. (2) The strengthening of the cold east equatorial Pacific sea surface temperature (SST) during the periods of September and October 2021 and the development of a second La Niña event led to an intensification of the downdraft in the troposphere and Central Pacific. This resulted in the strengthening of the WNPAC, BSH (Bohai Sea High), and BLT (Balkhash Lake trough) and the formation of a type of “west–low and east–high” circulation anomaly in the middle–high latitude East Asia regions. (3) The WNPAC was stimulated by the zonal reversing circulation of the tropical North Atlantic–Central Pacific Ocean, which was enhanced by the abnormally warm tropical Atlantic SST in summer and autumn. Thus, this work reveals that the synergy between the development of La Niña and abnormally warm SSTA (SST anomaly) in the tropical North Atlantic caused the super strong autumn flood in Shaanxi Province in 2021.
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