Unraveling Physical Processes Driving the Atlantic El Niño

Year-to-year temperature fluctuations in the tropical Atlantic are strongly influenced by a phenomenon known as the Atlantic Niño, which involves irregular variations in sea surface temperatures (SST) in the eastern part of the basin, and significantly influences regional climate patterns—affecting rainfall, hurricanes, and food security in tropical regions.Althouhg understanding the Atlantic Niño physical drivers is key to improving seasonal forecasts and anticipating changes under global warming, the exact physical drivers behind its variability remain under discussion. Some explanations—labeled as dynamical—point to the role of internal ocean wave activity, while others—referred to as thermodynamic—emphasize surface heat fluxes and the redistribution of heat via ocean currents.An analysis of SST records from 1940 to 2022 reveals two dominant spatial patterns: one centered over the central tropical Atlantic and another located in the eastern portion. However, during the more recent period from 1993 to 2022, these patterns display differing behaviors. From 1993 to 2009, they jointly contribute to SST variability in the eastern tropical Atlantic, whereas from 2010 to 2022, they tend to act in opposition.To disentangle these influences, we examine sea surface height data and assess heat transport by ocean currents. Our results show that from 1993 to 2010, the sea surface temperature anomalies in the eastern tropical Atlantic were mainly driven by horizontal advection of heat from the south. In contrast, between 2010 and 2022, wave-driven dynamics appear to play the dominant role.These findings suggest that the two spatial SST modes affecting the eastern tropical Atlantic stem from distinct physical processes, each governed by a separate set of mechanisms.