How ocean subsurface heat could help predict El Niño and future forecast challenges

  • 13 December 2016
  • Number of views: 1014
How ocean subsurface heat could help predict El Niño and future forecast challenges

Two new NOAA Research- funded studies provide insight into a potential new source of El Niño predictability and future research and forecast challenges for these ocean warming events. El Niño is one phase of the El Niño-Southern Oscillation (or ENSO) characterized by unusually warm ocean surface temperatures in the central and eastern tropical Pacific Ocean. La Niña, the opposite phase, features abnormally cool ocean surface temperatures. ENSO is one of the most important climate phenomena in the world due to its ability to impact atmospheric circulation, which in turn, influences temperature and precipitation across the earth.

A predictability problem known as the spring barrier, model forecasts issued in the spring or earlier are typically unable to predict whether an El Niño or a La Niña event will occur at the end of that year. However, changes below the ocean’s surface may foreshadow the onset and strength of El Niño several seasons in advance and help compensate for the spring barrier problem. Past research has shown that a buildup in heat content below the ocean’s surface has preceded all of the major El Niño events since 1980, and that the event’s magnitude is usually proportional to the heat’s magnitude 2 to 3 seasons in advance. Given this relationship, research led by Joan Ballester (California Institute of Technology), recently published in Nature Scientific Reports, assessed El Niño’s sensitivity to the magnitude of ocean subsurface heat buildup at longer lead times, 21 months in advance. The authors found that a large increase in heat content can cause equatorial Pacific warming the winter before a very strong El Niño event, and that the relationship between subsurface heat content and the strength of the subsequent El Niño is directly proportional. These findings have the potential to provide the public with more advanced warning of significant El Niño events and associated impacts.

 

Though El Niño forecasts continue to progress, the growth in communication platforms to disseminate this information presents its own challenges for the future. Occurring almost two decades after the last major El Niño of 1997-98, the 2015-16 El Niño was one of the strongest since 1950. A new study in the Bulletin of the American Meteorological Society summarizes scientists’ challenges and experiences in tracking this historic event’s evolution. The scientists noted that the 2015-16 El Niño differed from previous major events in 1997-98 and 1982-83 in several ways: the west-central Pacific Ocean temperatures were much warmer while the eastern Pacific was comparatively cooler, and the trade winds were not as week as compared to previous significant events. Additionally, mobile devices, social media, and blogs caused a demand for real-time updates at a faster pace than forecast centers could provide. The authors suggested that future research should try to clarify communication issues with the public and develop climate services that provide easy-to-navigate webpages and an authoritative social media presence.

Both studies  were funded, in part, by the NOAA Office of Oceanic and Atmospheric Research Climate Program Office’s Modeling, Analysis, Predictions, and Projections Program.

 

Joan Ballester and coauthors: http://www.nature.com/articles/srep36344

Michelle L’Heureux and coauthors: http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-16-0009.1

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