Prof. Zheng Xiaotong’s team at the Frontiers Science Center for Deep Ocean Multispheres and Earth System and the College of Oceanic and Atmospheric Sciences, in collaboration with international scholars, made important progress in the research of tropical ocean-atmosphere interactions and climate change, and proposed that wind-driven ocean circulation changes have important contributions to the spatial structure of tropical Pacific warming. The research outcome, titled “Historical changes in wind-driven ocean circulation drive pattern of Pacific warming”, was published in Nature Communications.

The sea surface temperature (SST) of the tropical Pacific Ocean plays an important role in regulating regional and global climate. The research shows that the vast majority of climate models consistently simulate SST warming in the Eastern Equatorial Pacific (EP), showing an El Niño-like warming pattern, while the observed SST trend shows cooling in the Central Equatorial Pacific (CP), sometimes referred to as a La Niña-like warming pattern. In particular, the recent tropical Pacific SST trends since 1958 show a more complex spatial structure than the typical El Niño-like or La Niña-like patterns, and the warming modes in the equatorial tropical Pacific have a warm-cold-warm tripolar substructure whose formation mechanism remains unclear.

In the study, the complex warming structure observed in the tropical Pacific since 1958 is the result of multiple physical processes. Historical radiative forcing can cause warming in the subtropical northeast Pacific and extend into the equatorial western Pacific without causing wind-driven changes in ocean circulation. In contrast, changes in wind-driven ocean circulation lead to warming in the eastern equatorial Pacific Ocean. The warming in the eastern equatorial Pacific is mainly dominated by the ocean-dynamic processes of the wind-driven ocean circulation, while the atmospheric adjusting processes are weaker. Through further analysis of the ocean dynamic process, it is found that the eastern Pacific warming is driven by anomalous trans-equatorial winds, the main mechanism of which is the southward Ekman transport caused by the westerly wind anomaly at about 5°N north of the equator, and the further diffusion of the warm signals to the poles and western Pacific through the mean zonal and meridional circulation, rather than the adjustment of the ocean vertical progradation. 

The findings of this research not only provide a new dynamic mechanism for understanding the spatial pattern of tropical Pacific warming in history, but also provide an important reference for predicting future climate change. It also highlights the shortcomings of existing climate models in capturing cooling signals in the central equatorial Pacific, pointing out the urgent need to improve simulations of equatorial ocean processes and ocean thermal structures.