A Decadal Climate Mode in the Indian Ocean

While considerable progress has been made in understanding the decadal climate variability in the Pacific and Atlantic Oceans, our knowledge of the Indian Ocean (IO) natural internal decadal variability remains limited. Through observational analysis, we have identified an IO Decadal Oscillation mode (IDO) in sea surface temperature (SST), with maximum amplitudes occurring in the subtropical South IO and dominant period of 8–15 years, which is associated with prominent atmospheric signals in surface wind and sea level pressure. Through observational analysis combined with numerical experiments using a coupled global climate model and a simple ocean-atmosphere coupled model for midlatitude region, we found that the IDO is generated by the IO internal processes, involving ocean dynamics (e.g., oceanic Rossby wave) and air-sea coupling. While the maximum IDO signals concentrate in the subtropical basin, its atmosphere-ocean signatures extend to the tropical basin. The IDO can exert active influences on the Antarctic climate through Rossby wave train and tropical climate, and it can operate independently of forcings from the Pacific and Atlantic. Our finding may provide an additional source of decadal climate predictability.