A decadal Twin Dipole mode in the Southern Atlantic and Indian Oceans

Abstract

Abstract Our analysis of observed sea surface temperature (SST) data robustly detects dipole-pattern decadal anomalies in the southern Atlantic and Indian Oceans (SAIOs) which co-occur like twins. This trans-basin mode on decadal timescales, termed as the Atlantic-Indian Twin Dipoles (AITDs), is effective in promoting synchronized regional SST extremes in both basins such as the Benguela Niño/Niña and Ningaloo Niño/Niña and thereby exerts notable climatic and socioeconomic impacts. Further, the mechanism of the AITDs is investigated using observational data, ocean model experiments, and climate models. A positive phase of the AITDs – with warm and cold SSTs in the southwestern and northeastern sectors of the SAIOs, respectively – is coupled with alterations in subtropical highs that involve a variety of regional air-sea processes. Specifically, wind-driven coastal ocean dynamics and cloud-controlled radiative heating play key roles in the South Atlantic, while the perturbed turbulent heat flux by air temperature advection is more important in the Indian Ocean. Both the Interdecadal Pacific Oscillation (IPO) and the Southern Annular Mode (SAM) are conducive to the AITDs by modulating the subtropical highs. By highlighting the trans-basin linkage between the SAIOs, our results have important implications for the decadal prediction of the Southern-Hemisphere climate and regional extremes.