Day-night ocean warming reveals why El Niño prevails over La Niña in climate models

On July 7, 2026, research published in Geophysical Research Letters highlights how day-night ocean warming aids in understanding why El Niño events are more pronounced than La Niña events in climate models. This study, led by Xiaodan Yang and his team, examines the role of diurnal sea surface temperature variations in affecting the El Niño-Southern Oscillation (ENSO) asymmetry.

Understanding ENSO Asymmetry

Researchers have long noted an asymmetry between El Niño and La Niña within the ENSO framework, where warm events consistently outpace cooler ones. The study reveals that many large-scale climate models fail to accurately represent this asymmetry due to unaccounted variables. Yang and colleagues focused on how fluctuations in sea surface temperature from day to night contribute to this phenomenon.

By comparing 35 models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), they found that models exhibiting larger diurnal amplitudes (DA) for temperature were better at capturing the ENSO asymmetry. This indicates that daily temperature shifts significantly impact long-term ocean warming trends.

Key Findings on Diurnal Temperature Variations

The study identifies a crucial mechanism behind the ENSO asymmetry: opposing daily mean sea surface temperature anomaly responses in the central and eastern Pacific. This east-west temperature gradient results in uneven ocean warming over extended periods, leading to the conclusion that El Niño events warm the ocean more than La Niña events cool it.

Yang's team emphasizes that incorporating larger DA values in climate models can improve ENSO simulation accuracy by up to 38.5%. This enhancement underscores the necessity of factoring in daily changes in sea surface temperature when modeling significant climatic events like El Niño.

Implications for Future Climate Models

The implications of these findings extend beyond just understanding ENSO. By improving the modeling of ENSO asymmetry, climate scientists can gain insights into broader climatic patterns and improve predictions of future climate scenarios. Yang and his team suggest that implementing a larger DA could influence various aspects of ENSO simulations, including phase locking, asymmetry, and amplitude.

This research not only sheds light on the mechanics of El Niño and La Niña but also provides valuable guidance for the development of future climate models, ultimately contributing to a more accurate understanding of global climate dynamics.