ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Archive > Volume 47 Issue 11 > 2021,47(11):1347-1358. DOI:10.7519/j.issn.1000-0526.2021.11.004 Prev Next
Analysis of Abnormal Characteristics and Causes of Meiyu over the Yangtze-Huaihe River Basin in 2019
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Abstract:
Based on the Meiyu monitoring data, precipitation observation, NCEP reanalysis data and sea surface temperature data, the abnormal characteristics of Meiyu over the Yangtze-Huaihe River Basin (YHRB) in 2019 and its causes of large-scale circulation are analyzed. The results are as follows. The abnormal characteristics of the 2019 Meiyu obviously showed that the Meiyu onset date was later than normal with a shorter duration. The Meiyu rain was generally less than normal, presenting a distribution pattern of the more in the south and the less in the north of the Yangtze River over YHRB. Since 1951, the 2019 Meiyu belt stagnated the longest time in the south of the Yangtze River. Among the three subareas, the Meiyu period in the middle and lower reaches of Yangtze River was almost simultaneous with that in the south of Yangtze River, and the Yangtze-Huaihe River Subarea did not receive Meiyu obviously. Due to the periodical enhancement of the cold air from 8 to 15 June, the seasonal northward of East Asian summer monsoon was impeded and delayed, leading to the late conversion of the circulation pattern in East Asian from winter to early summer and also the late onset of Meiyu over YHRB. It can be regarded as the precursory signals of Meiyu onset date later over YHRB in 2019 that the sea surface temperature in Indian Ocean was warmer than normal in May-June and the reverse date of meridional temperature gradient of the middle-upper troposphere， was later over 60°-80°E of South Asia. Compared with climate mean state, the eastern ridge of South Asian high and East Asia westerly jet were southward in upper air, the circulation meridionality in the middle-high latitude in Eurasia was stronger and the western ridge of Northwest Pacific subtropical high was southward and the geopotential height east of Australia was higher at middle level, the strength of the low-level East Asia summer monsoon was weaker and the northernmost of the monsoon was southward. As a result of the combined influence of the above-mentioned abnormal characteristics, the south of the Yangtze River over YHRB was under the control of the strong divergence at high level and the strong meridional gradient convergence of vapor flux at low level, which is greatly conducive to the development of vertical upward movement and the occurrence of heavy rainfall, contributing to the distribution of the Meiyu precipitation in 2019 with the more in the south and the less in the north of the Yangtze River over YHRB.
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