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El Niño events detected from the ERS Altimeter instrument

El Niño observed by ERS-2 RADAR ALTIMETRY

This is an image from the first set of ERS-2 RADAR ALTIMETER 'pictures' (Sea level anomalies averaged over 7 days; this one around 26/10/97) of the Tropical Pacific in a well established El Niño situation.

The 'normal' state of the Pacific Ocean is such that the sea level on the western side is higher than on the eastern side. This difference is namely due to the constantly blowing Trade Winds from east to west, which causes the water to pile up on the western side of the ocean. Also due to the Trade Winds, the surface water on the eastern side is constantly transported westward, and replaced by cold nutritious water that comes from deeper layers. This vertical movement is called upwelling. So, normally, cold and nutritious water prevails along the South American coast, while on the western side the surface water is warm. The warm water favors evaporation and rainfall on Australia and South-East Asia which allows productive farming.

During an El Niño event, the Trade Winds relax and become weak (they may even reverse). This causes the warm surface waters to flow back eastward causing the sea level to drop on the western side (in deep blue) and rise on the eastern side (in red) by up to 30 centimeters. Consequently, the upwelling of cold water on the eastern side vanishes and the nutrient-rich water is replaced by warm nutrient-poor water. The fish stock migrates to higher latitudes or dies, impacting the ones that feed on fish: humans (economical disruption, unemployment, pauperisation), pelicans (death), etc. Moreover, The evaporation and rainfall patterns are displaced to the eastern side of the Pacific Ocean, producing drastic floods and mud-slides in the West coast of South-America and drought in Australia and South-East Asia.

The data used to make this 'picture' are used by scientists worldwide to develop our understanding of the physical processes, in the ocean and atmosphere, involved in the El Niño event.


The ERS2.ALT.OPR1 data product was used. The OPR1 data is processed at French-PAF (Processing and Archiving Facility) in less than a month. The image has been produced in cooperation with DEOS, Delft University (Netherlands). DEOS orbits have been used in constructing the sea level anomalies.

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Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry