Multiscale Causes of Persistent Heavy Rainfall in the Meiyu Period over the Middle and Lower Reaches of the Yangtze River

Yicong Xia,Tianle Sun,Suxiang Yao,Qian Huang

doi:10.3389/feart.2021.700878

Yicong Xia, Tianle Sun + Show 2 more

Open Access

https://doi.org/10.3389/feart.2021.700878

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Abstract

Based on observation data supplied by the Chinese Meteorological Administration (CMA) and reanalysis datasets provided by the ECMWF, the multiscale causes of persistent heavy rainfall events (PHREs) that occurred from 1979 to 2018 during Meiyu periods over the middle and lower reaches of the Yangtze River (MLYR) are investigated. During Meiyu periods, precipitation shows obvious interannual variabilities. In PHRE years, the contribution rate of persistent heavy rainfall to the total precipitation is approximately 57%. Precipitation also shows significant synoptic-scale (less than 10 days) characteristics. Through the quantitative diagnosis of interactions among background-scale (greater than 30 days), quasi-biweekly-scale (10–30-days), and synoptic-scale variables, the possible causes of PHREs are explored. The results reveal that the difference in precipitation intensity between PHRE years and non-PHRE years is determined by the background water vapor, background wind and synoptic-scale wind conditions. In PHRE years, the prevailing background southwesterly winds from lower latitudes provide more background water vapor, and more mean kinetic energy is converted to perturbation energy. Moreover, the active synoptic-scale oscillations from higher latitudes and the convergence of Rossby wave disturbance energy over the MLYR could also cause the occurrence and maintenance of PHREs during Meiyu periods. The multiscale causes and corresponding circulation patterns in 2020 PHREs are similar to PHREs years.

Highlights

Persistent heavy rainfall events (PHREs) and the subsequent associated disasters tend to cause catastrophic losses of property, agriculture and human lives
Based on the definition provided in Definition of persistent heavy rainfall events (PHREs) during the Meiyu Period, 37PHREs that occurred during Meiyu periods were selected, with an average duration of 4.35 days
The results indicate that the −∇ · qV and −∇ · qV′′ items are the main contributors of PHREs in the 2020 Meiyu period, which is consistent with the conclusions on the climatic characteristics of PHREs in Multiscale Analysis of Interannual Variations in PHREs

Summary

INTRODUCTION

Persistent heavy rainfall events (PHREs) and the subsequent associated disasters tend to cause catastrophic losses of property, agriculture and human lives. Further studies have shown that, during a PHRE, water vapor transport is controlled by the Somali cross-equatorial jet, by the cross-equatorial flow near the Bay of Bengal and the Indonesian archipelago, and by the Northwest Pacific Subtropical high (Chow et al, 2008; Sun et al, 2016) It has been documented extensively in the literature that the precipitation that occurs during Meiyu periods over the MLYR is modulated by low-frequency circulation oscillations, which have significant intraseasonal oscillation (ISO) characteristics (Lau and Li, 1984; Yang and Li, 2003; Ding and Wang, 2008; Mao et al, 2010; Yang et al, 2010; Yao et al, 2012). When the WAF vectors converge, the wave energy accumulates, and this condition is conducive to enhancing the disturbance; the wave energy disperses when the WAF vectors diverge

RESULTS

CONCLUSION AND DISCUSSION

DATA AVAILABILITY STATEMENT