Sea Surface Temperature Anomalies in the Western Indian Ocean as a Trigger for Atlantic Nino Events

Pacific El Nino and Atlantic Nino events represent prominent interannual climate fluctuations in tropical regions. Both of them have considerable impacts on the climate system and human livelihoods. The interaction between the Pacific El Nino and Atlantic Nino has received wide attention. Here, we use observations and numerical model experiments to show a new trigger from the western Indian Ocean (WIO) that can serve as a predictor for Atlantic Nino events. The warm sea surface temperature (SST) anomalies in the WIO alter the Walker circulation in the boreal winter, weaken the surface trade winds over the tropical Atlantic and favor an Atlantic Nino in the subsequent summer. These inter-basin processes also affect the interaction between the Pacific El Nino and Atlantic Nino. The results imply that a better simulation of the WIO SST and its teleconnection may help to forecast Atlantic Nino events. Plain Language Summary The Atlantic Nino is a prominent mode of climate variability in the equatorial Atlantic. It not only influences climate over the surrounding continents but also has an important contribution to variabilities in other tropical oceans. The ability to forecast the Atlantic Nino accurately is important to human livelihoods and requires a thorough understanding of the relevant physical mechanisms. Surface wind anomalies are important in the evolution of Atlantic Nino events, which can trigger the Atlantic Nino through the Bjerknes feedback. However, part of these surface wind anomalies can be induced remotely from Pacific El Nino events. In this study, we find the surface wind anomalies can also be induced by warm sea surface temperature (SST) anomalies in the western Indian Ocean (WIO). The warm WIO SST anomalies alter the Walker circulation in the boreal winter, weaken the surface trade winds over the tropical Atlantic and favor an Atlantic Nino in the subsequent summer. The WIO SST anomalies can also modulate the interaction between the Pacific El Nino and Atlantic Nino. A better simulation of the WIO SST may provide a predictor for Atlantic Nino events and may even provide deeper insights into tropical climate variability.

Automated summary

The Pacific El Nino and Atlantic Nino events have significant impacts on tropical climate systems and human livelihoods. Research shows that warm sea surface temperature anomalies in the western Indian Ocean can serve as a predictor for Atlantic Nino events, influencing the Walker circulation and surface trade winds, ultimately affecting the interaction between the Pacific El Nino and Atlantic Nino. Studying these inter-basin processes may provide insights for better forecasting of Atlantic Nino events and understanding tropical climate variability.