Tropical Atlantic Impacts on the Recent Trends over the Tropical Ocean and Atmosphere

During the last three decades, tropical sea surface temperature (SST) has shown zonal asymmetry trends, with warming over the tropical Atlantic and Indo-Western Pacific but cooling over the Eastern Pacific. This cooling has recently been identified as a driver of the global warming hiatus. Previous studies revealed atmospheric bridges between the tropical Pacific, Atlantic, and Indian Ocean, which have the potential to explain this zonal asymmetry SST pattern. However, the mechanisms and the interactions between these teleconnections remain unclear.

To investigate these questions, we first performed a ‘pacemaker’ simulation by restoring the tropical Atlantic SST changes in a state-of-the-art climate model – the CESM1. Results show that the Atlantic plays a key role in initiating the tropical-wide teleconnections, and the Atlantic-induced anomalies contribute ~55%-75% of the tropical SST and circulation changes during the satellite era. We further investigate the physical mechanisms of these teleconnections using a hierarchy of oceanic and atmospheric models: the Atlantic warming drives easterly wind anomalies over the Indo-Western Pacific through the Kelvin wave, and westerly anomalies over the eastern Pacific as Rossby waves, in line with Gill’s solution. The wind changes induce an Indo-Western Pacific warming via the wind-evaporation-SST effect, and this warming intensifies the La Niña-type response in the tropical Pacific by enhancing the easterly trade winds and through the Bjerknes ocean-dynamical processes. The teleconnection finally develops into a tropical-wide SST dipole pattern, with an enhanced trade wind and Walker circulation.

This mechanism, supported by observations and a hierarchy of climate models, reveals that the tropical ocean basins are more tightly connected than previously thought, and the Atlantic plays a key role in the tropical pattern formation and further the global warming hiatus.