Researchers from the Institute of Atmospheric Physics of the Chinese Academy of Sciences and University of Colorado have revealed that warmer-than-usual sea surface temperature over western tropical Atlantic triggers La Niña events.

Their study was published in Climate Dynamics.

Unusual sea surface temperature over the tropical Atlantic can influence the following El Niño–Southern Oscillation (ENSO) --- an irregular periodic variation in winds and sea surface temperatures over the tropical Pacific Ocean, affecting the climate of much of the tropics and subtropics.

Previous studies have pointed out that the sea surface temperature anomalies over each of the north tropical Atlantic, the Atlantic Niño region and the Atlantic warm pool are able to regulate the air–sea coupling over the tropical Pacific and trigger ENSO events. However, it is still unclear that in which region over the Atlantic Ocean the sea surface temperature anomalies has the predominant impact on ENSO variability.

In this study, the researchers identified that the sea surface temperature anomalies over the western tropical Atlantic exhibited a more permanent connection with the following ENSO variability during the observational record. Different SST datasets recognized that ENSO had stronger correlation with the previous spring sea surface temperature anomalies over the western tropical Atlantic than that with the sea surface temperature anomalies over each of the Atlantic Niño region, the north tropical Atlantic or the Atlantic warm pool.

Further analysis suggested that the modulation of the sea surface temperature anomalies over the western tropical Atlantic to the following ENSO was intensified after the mid-1980s. This exhibited as that the warmer-than-usual sea surface temperature over the western tropical Atlantic induced significant precipitation anomalies in situ, and generated atmospheric teleconnection that affected the anomalous zonal wind over the equatorial Pacific, and in turn triggered La Niña events.

"Both observations and CMIP model historical runs imply that this intensified modulation tends to be attributed to the decadal enhancement in climatological mean SST over the western tropical Atlantic," said Dr. CHEN Wei, first author of the study.

Sayram Lake, located in the northern Tianshan Mountains in Xinjiang, China. As the last place to feel the warm air current of the Atlantic Ocean, the lake is nicknamed the "last tear of the Atlantic". (Image by DONG Junjie)