Impact of Southern Indian ocean dipole via the ITCZ on winter and spring precipitation in China

Abstract

This study analyzes the characteristics of sea surface temperature (SST) in the southern Indian Ocean, the changes in location of the Indian Ocean intertropical convergence zone (ITCZ), and their impacts on winter and spring precipitation in China from 1979 to 2021. The Southern Indian Ocean Dipole (SIOD) displays a southwest–northeast inverse phase distribution of SST. After separating El Niño–Southern Oscillation (ENSO) signals, the Indian Ocean ITCZ positions (averaged over 35°–75°E) in boreal winter (December–February, DJF) of the same year and in the spring (March–May, MAM) of the next year are influenced by pure SIOD events, with a southward (northward) shift under pure positive SIOD (pure negative SIOD, i.e., the opposite to positive events) events during DJF. Meanwhile, the Indian Ocean ITCZ moves in the opposite direction in MAM and position variations are more obvious. DJF (MAM) precipitation in the middle and lower reaches of the Yangtze River (MLYR) is positively (negatively) correlated with the Indian Ocean ITCZ position. In addition, the DJF (MAM) precipitation in the MLYR decreases (increases) under pure positive SIOD (pure negative SIOD) events. That is, the Indian Ocean ITCZ position may be one of the mediators by which SIOD affects winter and spring precipitation in the MLYR. 摘要 本文分析了1979–2021年南印度洋冬季海表面温度特征, 印度洋热带辐合带 (ITCZ) 位置变化及其对中国冬春季降水的影响. EOF分析第一模态表明南印度洋冬季海表面温度异常显示西南-东北反相分布, 即南印度洋偶极子模态 (SIOD). 分离厄尔尼诺-南方涛动 (ENSO) 信号后, 纯SIOD事件对同年冬季和次年春季的印度洋ITCZ位置 (35°–75°E平均) 均有影响, 冬季, 纯正 (负) SIOD事件使印度洋ITCZ往南 (北) 移动. 春季, SIOD则使印度洋ITCZ移动方向与冬季相反, 且移动幅度更大. 冬,春季长江中下游地区 (MLYR) 的降水量与印度洋ITCZ位置分别呈正, 负相关. 同时, 在纯正 (负) SIOD事件下, 冬, 春季MLYR的降水分别减少, 增加, 可见印度洋ITCZ位置变化可能是SIOD影响MLYR冬, 春季降水的媒介之一.