Climate phenomenon in the Indian Ocean warns about El Niño

Long-term forecast possible thanks to Indian Ocean Dipole

Temperature anomalies during a positive Indian Ocean dipole: In Indonesia it is colder (blue), but warmer (red) than normal in front of the African coast. © NASA
Read out

A climate phenomenon in the Indian Ocean indicates when the next El Niño in the Pacific threatens. A model now presented by Japanese researchers in Nature Geoscience takes advantage of this newly discovered context, enabling a longer-term and safer El Niño prediction than before. The affected regions would thus have more time to prepare for the weather extremes that are accumulating during this period.

{1l}

Every few years comes "El Niño" - the "Christ Child". In this climatic phenomenon, a tongue of abnormally warm water forms in the Eastern Pacific Ocean, causing not only local but also climatic changes worldwide, such as more frequent rains and storms, or greater drought. For the regions affected by these weather extremes, it is extremely important to know as soon as possible when an El Niño or its cold "sister", the La Niña, threatens. So far, however, the current models only allow a prediction several months in advance. Forecasts over a year into the future are very unreliable. That could change now.

Climate dipole in the Indian Ocean

Takeshi Izumo and his colleagues at the Japanese research center JAMSTEC developed a simple predictive model that does not take sea-level changes and water temperatures in the Pacific as the basis, but looks further west to the Indian Ocean. Here also exists a cyclically recurring climate phenomenon, the so-called "Indian Ocean Dipole". If this dipole is in a positive phase, water temperatures and precipitation are higher in the west of the Indian Ocean and lower in the east than normal. Conversely, the negative phase gives the coasts from Indonesia to Australia warm water and humid climates, while the East African coast dryness.

Negative dipole precedes El Niño

The Japanese researchers have now found that the climate phenomena in the Indian Ocean and the Pacific seem to be interlinked: Whenever there is a negative dipole in the Indian Ocean, an El Niño will follow in the Pacific Ocean a good year later. After a positive dipole a La Niña follows. This relationship between the two phenomena can be exploited with the help of the new model to predict an imminent El Niño more than a year in advance and safer than before. display

Connection via atmospheric circulation

According to the scientists, an atmospheric circulation pattern influenced by the climate over the Indian Ocean and in turn to the air currents and wind directions over the Pacific could be responsible for the connection acts. In an accompanying commentary, climate scientist Peter Webster of the Georgia Institute of Technology in Atlanta concludes: "If the forecasting horizon of El Ni o and La Ni a is expanded, then both the Indian and the Chinese Pacific ocean basins are included in the empirical and dynamic predictive models

(Nature, 23.02.2010 - NPO)