The Concurrent Record-breaking Rainfall over Northwest India and North China in September 2021

Abstract

Extremely heavy rainfall occurred over both Northwest India and North China in September 2021. The precipitation anomalies were 4.1 and 6.2 times interannual standard deviation over the two regions, respectively, and broke the record since the observational data were available, i.e., 1901 for India and 1951 for China. In this month, the Asian upper-tropospheric westerly jet was greatly displaced poleward over West Asia, and correspondingly, an anomalous cyclone appeared over India. The anomalous cyclone transported abundant water vapor into Northwest India, leading to the heavy rainfall there. In addition, the Silk Road pattern, a teleconnection pattern of upper-level meridional wind over the Eurasian continent and fueled by the heavy rainfall in Northwest India, contributed to the heavy rainfall in North China. Our study emphasizes the roles of atmospheric teleconnection patterns in concurrent rainfall extremes in the two regions far away from each other, and the occurrence of rainfall extremes during the post- or pre-monsoon period in the northern margins of monsoon regions.

摘要

2021年9月, 在印度西北部和中国华北地区出现极端强降水。印度西北部的降水异常达到4.1倍的年际标准差, 打破自1901年有观测以来的历史记录；同时, 华北降水异常达到6.2倍的年际标准差, 破1951年以来记录。在该月, 西亚地区上对流层西风急流位置显著偏北, 相应地, 印度地区出现气旋式环流异常。异常的气旋式环流输送大量水汽至印度西北部, 导致该地区出现极端降水。此外, 欧亚陆地上空的丝绸之路遥相关型, 在印度西北部降水的加强下, 对华北极端降水起到重要贡献。研究结果强调大气遥相关对两地同时出现极端降水的作用, 揭示季风北边缘区在季风盛行前、后时期发生极端降水的成因。