Jason is monitoring El Niño and La Niña

A bad or a sunny summer, a harsh or a mild winter? The El Niño and La Niña phenomena, situated in the Pacific Ocean, have a say in the matter...

 

Jason-2 in orbit (illustration). Associating NASA, the CNES, EUMETSAT (European organisation that manages weather satellites) and NOAA (American agency tasked with studying the atmosphere and the oceans), this satellite measures the height of the surface of the sea. Credit: CNES/D. Ducros

The Earth’s climate is known to be a delicately balanced “machine”, the numerous parameters of which are all interlinked. In the centre of this gigantic puzzle, the height of the waters of the Pacific Ocean off the coasts of Peru in South America acts as an essential indicator.

Hot and cold in the Pacific Ocean
Why height? Well, because it reveals the temperature of the waters and, in this region of the world, shows the intensity of an El Niño or La Niña phase. Recently, on 11 June, the French-American satellite Jason-2 noted a drop in the level of the Pacific Ocean on the equator, equalling up to 18 centimetres in relation to the reference value. Consequently, scientists believe that a phase known as La Niña could follow an El Niño phase. It is worthy of note that a cold sea-surface current (the Humboldt Current) usually flows up from Antarctica and along the coastlines of Chile and Peru. With temperatures of 7 to 8°C below the average of the waters in the latitudes it crosses and a higher concentration of carbon dioxide, it stimulates the growth of plankton, which attracts fish and therefore aids fishing. According to a poorly understood cycle, roughly once or twice a decade, a phenomenon dubbed El Niño (the small boy, but also the baby Jesus, as it often begins just after Christmas) is characterised by an interruption of the cold current: the Pacific Ocean is therefore warmer around the equator off the Peruvian coasts and fishermen have trouble filling their nets such that it can cause serious economic consequences in the region. And that’s not all.

The height of the level of the sea measured by Jason-2 from its orbit at an altitude of 1,336 km. Green indicates a height equal to the reference value. Red coloured areas show raised heights of up to 10 cm which correspond to regions where the water is warmer. Blue is the opposite, it represents lower ocean levels (up to 18 centimetres less for the darkest blue) and therefore the coldest waters. The blue band around the Earth’s equator could indicate the occurrence of a so-called La Niña phase. Credit: NASA/JPL Ocean Surface Topography Team

El Niño and La Niña: a duo that bring rain and good weather
The effects of an El Niño phase (which usually lasts 18 months) go far beyond the fishing industry and are able to drastically disturb the weather. First of all, the north of Peru experiences heavy rain and, as the saying goes one man’s sorrow is another man’s joy, the farmers appear favoured. But depending on its intensity, an El Niño phase can, above all, prove catastrophic by giving rise to heavy rain, leading to flooding with dramatic consequences in certain regions whilst conversely causing drought elsewhere. Today, climatologists have shown the worldwide effect of this phenomenon originating in the Pacific Ocean. The 1982-83 El Niño phase caused, amongst other things, diluvian rain in Ecuador and Peru whilst affecting the prevailing west winds and diverting the typhoons to Hawaii and Tahiti, not to mention an exceptional drought in Southern Africa and Australia. Europe does not escape the influence of this phenomenon which is why the CNES, the French Space Agency, became associated with NASA to launch the TOPEX-Poseidon satellite in 1992. Equipped with a radar altimeter capable of measuring the height of the oceans with an accuracy of 2 cm, one of its main objectives was to monitor El Niño. The importance of this mission is such that the satellite was replaced by Jason-1 and 2 which still unite NASA with the CNES. And on 11 June, it was this Jason-2 that showed the drop in the level of the Pacific Ocean over the equator mentioned at the beginning of the article. A press release from NASA’s JPL on 22 June explains that scientists fear that this drop is a precursor of what is known as La Niña (the small girl in Spanish), which in a manner of speaking is El Niño’s mirror image. The problem is that this inverse situation is more like an over-reaction than a return to normal where cold waters resume their usual course. Hurricanes in the Atlantic Ocean could worsen as it has been noted that the 1988-89, 1995-96 and 1997-98 phases of La Niña coincided with the occurrence of particularly powerful and devastating tropical cyclones. In North America, the winter should be colder with heavy snow whereas Europe and Indonesia could experience heavier rain falls. Contrarily, however, Peru and Ecuador will have drier weather (as with El Niño, this list of possible consequences is far from exhaustive).
Obviously, the measuring of the height of the oceans from space is of capital importance as it keeps us informed of the occurrence of weather and climate phenomena with worldwide repercussions. Moreover, it has already been announced that Jason-3, a successor to Jason-1 and 2, is to be launched in 2013.

Published on 24 June 2010