A better representation of the equatorial Atlantic variability in summer and its lagged connection mechanism with the Pacific relates to enhanced capacity in predicting autumn/winter ENSO (El Niño–Southern Oscillation). BSC researchers Eleftheria Exarchou and Pablo Ortega, from the Climate prediction group, along with the TROPA UCM group in Madrid and a researcher formerly at BSC and now at Meteo-France, were able to demonstrate, for the first time, this relation by using a multi-model ensemble of seasonal forecast systems. The research “Impact of equatorial Atlantic variability on ENSO predictive skill” has been published today in Nature Communications.
El Niño–Southern Oscillation (ENSO) is a climate phenomenon that takes place when sea surface temperatures and winds across the tropical Pacific behave anomalously. It oscillates between warm events (El Niños) and cold events (La Niñas) with a period between two and seven years. ENSO generates perturbations in temperature, precipitation and winds that alter the large-scale atmospheric circulation and trigger a cascade of weather patterns affecting the weather and climate throughout the world. Given the widespread impacts of ENSO, its skillful prediction at seasonal timescales has paramount importance in accurately predicting temperature and precipitation at different regions of the world. Despite the recent progress in predicting ENSO, successful predictions remain a challenge, as demonstrated by the large spread in ENSO predictions across climate models.
There is important potential for improving seasonal predictions of ENSO through increased understanding of the dynamical connections among the tropical basins. While the effects of ENSO on other tropical basins, like the Tropical Atlantic and Indian Oceans, are well studied, the feedbacks of other tropical basins back onto the Pacific are less known and under an ongoing debate. A center of such an interbasin connection is the equatorial Atlantic, where a variability similar to ENSO takes place in the boreal summer. The equatorial Atlantic variability is expressed with sea surface temperature anomaly fluctuations between warm and cold events, also known as Atlantic Niños and Niñas. Recent studies based on observations demonstrate that summer Atlantic Niños (Niñas) favor the development of Pacific Niñas (Niños) the following winter, through a modification of the equatorial atmospheric circulation (named Walker circulation).
Despite the recent evidence for the Atlantic/Pacific connection, it remained unclear whether current seasonal prediction systems capture this connection, and what is its role in their ability to accurately predict ENSO.
Unfortunately, the tropical Atlantic is a region of key uncertainty in the climate system: state-of-the-art climate models exhibit large systematic error. Correcting these errors improves the forecast skill in the autumn/winter ENSO, as the authors further demonstrated with an additional sensitivity study performed with the European Consortium global climate model EC-Earth.
The study, therefore, implies that improving the representation of the equatorial Atlantic in climate models offers the potential to increase their ability to predict ENSO, and through it to better predict ENSO’s most important widespread climate impacts.
DOI: 10.1038/s41467-021-21857-2
https://www.nature.com/articles/s41467-021-21857-2
- Caption: Atlantic Niño influence on summer surface temperatures and winds. Correlation pattern between summer Atlantic Niño and summer sea surface temperatures (in shaded colors) and surface winds (in vectors).