La Niña—a climate phenomenon characterized by unusually cool sea surface temperatures in the central and eastern tropical Pacific Ocean—can persist for multiple years, with significant worldwide climate impacts. In recent decades, such prolonged La Niña events have become more frequent. However, the mechanisms that sustain these multiyear cooling episodes have remained unclear.
To address this challenge, a research team from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) has uncovered a critical feedback loop involving rainfall and ocean salinity that helps sustain multiyear La Niña conditions. Their findings were published in Nature Communications on January 14.
In the vast western equatorial Pacific, sustained reduction in rainfall driven by multiyear La Niña leads to a steady increase in upper-ocean salinity. This rise in salinity destabilizes the upper layers of the ocean, which in turn triggers a series of ocean wave processes—ultimately causing cooling in the eastern equatorial Pacific, over 10,000 kilometers away. When this positive salinity anomaly persists for two years, slower ocean circulation kicks in, promoting cooling across the entire tropical Pacific.
Quantitative analysis shows that this rainfall-linked cooling boosts the intensity of multiyear La Niña by 14% in the first year and a further 32% in the second year. This effect enables reduced rainfall to play a key role in maintaining the sustained cooling of multiyear La Niña events.
"We have demonstrated, for the first time, that multiyear rainfall and salinity feedbacks regulate the persistence of La Niña, reshaping our understanding of ocean-atmosphere interactions during these prolonged events", said Dr. TIAN Feng, the study's first author.
The role of salinity feedback caused by reduced rainfall in sustaining multi-year La Niña events (the background image shows the sea surface temperature anomaly during the 2020-2023 triple La Niña period). (Image by IOCAS)
(Text by TIAN feng)
Media Contact:
ZHANG Yiyi
Institute of Oceanology
E-mail: zhangyiyi@qdio.ac.cn
(Editor: ZHANG Yiyi)