The Southern Indian Ocean Dipole and its effects on Precipitation in China

Abstract

Abstract This study analyzes and discusses the characteristics of sea surface temperature (SST) in the Southern Indian Ocean, the changes in the location of the Indian Ocean Intertropical Convergence Zone (ITCZ), and their impact on precipitation in China from 1979 to 2021. Results show that the Southern Indian Ocean Dipole (SIOD), an SST southwest-northeast dipole distribution between the subtropics and extratropics, is the dominant mode of interannual variability in the Southern Indian Ocean in observations. The SIOD displays an apparent seasonal phase-locking, with the anomaly pattern developing in boreal autumn, peaking in winter, and decaying in the ensuing spring and summer. Wavelet analysis shows that the SIOD mode has an interdecadal variation period of 6–7 years over the study period. Moreover, the SIOD has a strong correlation with the El Niño–Southern Oscillation (ENSO), and it is found that after separating ENSO signals, the Indian Ocean ITCZ positions (averaged over 35°–75°E) in boreal winter (DJF) of the same year and the spring (MAM) of the next year are significantly influenced by pure SIOD events, with a southward (northward) shift in the Indian Ocean ITCZ under pure positive SIOD (pure negative SIOD) events during DJF. In MAM, the Indian Ocean ITCZ moves in the opposite direction to that in DJF under pure positive and negative SIOD events, and the position changes are greater than those in DJF. Additionally, in boreal winter and spring, precipitation in China is associated with the position of the Indian Ocean ITCZ, which is positively (negatively) connected with precipitation in DJF (MAM) in the middle and lower reaches of the Yangtze River. In DJF and MAM, the precipitation in the middle and lower reaches of the Yangtze River decreases (increases) under pure positive SIOD (pure negative SIOD) events. That is, the position of the ITCZ in the Indian Ocean may be one of the intermediaries by which the SIOD affects precipitation in the middle and lower reaches of the Yangtze River.