El Niño means child in Spanish (meaning Jesus, because it is usually in full swing around Christmas) and is one of the strongest environmental disruptions. It is also during this phenomenon that the climate-ocean interactions are most evident.
Approximately every two to seven years, a trade wind weakening, or even a reversal, can be observed in the Tropical Pacific. So the ocean reacts: the hot water which is normally pushed towards Indonesia by these winds is in fact moving eastwards, towards the coasts of South America. Since the hot water which is normally surrounding Indonesia is absent, the humidity it usually brings to the atmosphere is absent too and that explains why the Pacific West coasts is so drought. On the contrary, the quite dry air on the Peruvian coasts becomes hot and damp. Torrential rains appear and cause flooding and landslides. The anchovies which feed the fishermen leave because of the water heat. However, the consequences are not that catastrophic everywhere, especially if the situation can be forecasted in advance: the climate in some areas become milder during this period.
After the particularly strong El Niño event of 1982-1983, it has been decided to perform a sustained monitoring of the area would be carried out. Not only at sea but also airborne and space means were implemented to observe and quickly alert the authorities. In particular, the Topex/Poseidon mission (NASA/CNES), launched in 1992, showed that accurate space altimetry enabled the general characteristics of such phenomenon to be recognized several months in advance. It enabled the whole science community to analyse and understand this complex phenomenon during which the ocean and atmosphere are closely linked.
The past Topex/Poseidon and Jason-1 (CNES/NASA) and current Jason-2 (CNES/Eumetsat/NASA/NOAA) space altimetry missions have been ensuring a sustained monitoring of all the oceans (among which the Pacific) by precisely measuring the surface and oceanic current variations.
From winter 2002 (and with greater certainty in June 2002), the red flag were all up for El Niño in 2002-2003. Since then, other events succeeded (2004-2005; 2006-2007; 2009-2010) jointly with the increase in atypical events ("Modoki"), during which the hot waters remained stuck in the middle of the Pacific instead of reaching the coasts of South America. The altimetry enabled these examples to be detected and studied.
The observation networks offer the possibility to test and refine the scientific knowledge and so design climate digital models and oceanic and atmospheric motion mathematical representations. Moreover, using all the observations enable the initial conditions to be adjusted in real-time and force the forecasting models to remain close to the observations. If the climatic whims of El Niño cannot be prevented, the adverse effects have to be reduced using better forecasting methods.
- CNES oceanography program scientist: Juliette Lambin