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| Subject keyword(s) | Astronomy, Atmospheric science, Climate, Climatology, Earth's water, Earth and space science, Earth science, Geoscience, Meteorology, Oceanography, Oceans, Physical oceanography, Physical sciences, Science, Space Science, Space sciences, Thermocline |
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NASA Earth Observatory Home Images Global Maps Features News & Notes by Jason Starr The oceans and the atmosphere are eternally intertwined in a game ofgive-and-take. Each reacts to changes in the other. These reactions andcounter-reactions can snowball until the system builds to a point where everydaypeople notice the effects. (Image courtesy of Jet Propulsion Laboratory) Pacific Ocean temperaturesat their peak on December 10, 1997. (Image courtesy of Jet Propulsion Laboratory) Milder El Niñocharacteristics, on May 3, 1998. The objective of theTOPEX/Poseidon mission, launched in August 1992, is to determine oceantopography with a sea surface height measurement precision of three centimetersand a sea level measurement accuracy of 13 centimeters. TOPEX/Poseidon dataproducts are available from the Jet Propulsion Laboratory (JPL) PhysicalOceanography DAAC. For more information, visit the Jet Propulsion Laboratory DAAC (now named the Physical OceanographyDAAC). (A new browser window will open.) In the fall of 1996, easterly winds raced across the Pacific Ocean,keeping warm water bottled up near Indonesia. Waters off the coast of Peruremained cool. In December, however, a quick burst of wind shot eastward towardPeru, against the normal flow of the trade winds. In retrospect, this windreversal was the first sign of the devastatingly strong 1997/1998 El Niñothat would later be blamed for destroying homes, taking lives and consuming vastacres of normally damp forest. The December westerly wind burst set the stage for a second wind spurt inMarch 1997. This westerly wind cleared a path eastward for a wave of warm water a "Kelvin Wave." When this warm water pulse reached South America, itdisrupted the normal easterly trade winds, diminishing them enough to allow evenmore warm water to migrate eastward. By May of 1997, the trade winds hadceased, and a pool of warm water continued to build in the eastern equatorialPacific. El Niño was underway. Scientists monitoring the ocean were announcing El Niño in May. TOPEX/Poseidon, the Jet Propulsion Lab's satellite launched in 1992 to measuresea level rise, had seen the gradual build-up of warm water in the easternequatorial Pacific. According to JPL research oceanographer Victor Zlotnicki, a change in sealevel is directly correlated to a change in thermocline depth. "Near theequator, when sea level rises one inch, the thermocline goes down 200 inches,"he said. The thermocline is a sharp separation of warm upper water from colddeeper water in the ocean. The lower the thermocline, the more heat stored inthe water. So, by measuring the amount of sea level rise in the Eastern Pacific,TOPEX/Poseidon allows scientists to determine the amount of heat stored in thewater. In 1997, using TOPEX/Poseidon, scientists saw as much as a 16 inch rise insea level in the eastern equatorial Pacific and nearly a 350 foot dip in thethermocline, both unmistakable signs of El Niño. Plans for a follow-up mission are already set, said TOPEX/Poseidon ChiefScientist, Lee Fu. "We want to understand many cycles of El Niño, so wewant to extend the data stream by launching a sequence of missions likeTOPEX/Poseidon," he said. The next mission, called Jason-1, is, like TOPEX/Poseidon, a joint effortof the United States and France. It is planned for launch in 2000 and will alsocollect sea level data, but with perhaps greater accuracy. "The goal is toreach one centimeter accuracy," Fu said. The need for an ocean monitoring system became apparent when the 1982/1983El Niño, the strongest of the century, arrived undetected by the sciencecommunity. In response, under the auspices of the Tropical Ocean GlobalAtmosphere program, scientists developed a collection of buoys to measurelarge-scale changes in the ocean and to help detect El Niño events asthey develop. These 70 buoys, called the Tropical Atmosphere Ocean Array, sitstationary in the tropical Pacific giving scientists a daily record of oceanchanges. Because each buoy in the array only measures the water in which it sits,the system gives a dotted view of the ocean, unlike the full ocean viewTOPEX/Poseidon provides. "The buoys occupy a very narrow strip along theequator in the Pacific," Fu said. "El Niño is a very large-scalephenomenon. Just knowing the information along the equator is not enough. TheTopex/Poseidon data give a global view of the Pacific." Still, the buoys are amajor piece in the El Niño monitoring system.Because of TOPEX/Poseidon's global monitoring capabilities, the 1997/1998 ElNiño was the earliest detected El Niño event ever. "This is thefirst time we saw it right from its beginning," said William Patzert, researchoceanographer at JPL. Ants Leetma at the National Oceanic and Atmospheric Administration usedTOPEX/Poseidon data in a prediction model that enabled him to detect ElNiño in March of 1997, months before the rest of the scientificcommunity. For the first time, preparations were made in the summer before an ElNiño winter. "This forecast was distributed early, and it was takenseriously," Patzert said. "There was so much information available thatpreparations were made all across the country at a local, state and nationallevel. The loss of life and property in this particular event definitely couldhave been much worse than it was."Although Leetma's model was the first to detect El Niño in March, a trueprediction of the event would have come in the fall, before the appearance ofthe first Kelvin Wave. But scientists are not yet able to predict ElNiño before its first signs show in the ocean, according to Patzert. "There will be no prediction unless there is a major revolution in our thinkingand major advances in the way we model these events," he said. "The presentgeneration of models is primitive. I think we are ten years away (from aprediction of El Niño)." If these predictions come to fruition, we will be talking about ElNiño for more than a year before we feel its atmospheric effects. In thewinter of 1997/1998, the talk began six months before the weather. Although the current detection abilities provide a six-month warning forthe continental United States, science does not benefit the Southern Hemisphereas much. In these areas, El Niño's effects come in June, directly on theheels of a detection in May. Therefore, South America and Indonesia have themost to gain from long-term El Niño predictions. The 1997/1998 El Niño has been called the most destructive inrecent history in tropical latitudes. The Brazilian government has spenthundreds of millions of dollars fighting fires that have destroyed hundreds ofthousands of acres of forest and savanna. In Indonesia, farmers continued theirnormal agricultural burning practices expecting the seasonal rains to extinguishthe fires. The rains never came, and the forests burned out of control. Ecuador and Peru saw months of almost non-stop torrential rain starting in June 1997 that destroyed more than 30 percent of the countries' infrastructure, according to Patzert. The 1997/1998 El Niño was so devastating in these regions because the May warning did not allow enough preparation time. The accumulation of TOPEX/Poseidon data from one El Niño to thenext gives scientists the best conditions in which to develop forecast modelsthat would give the Southern Hemisphere more warning. "The more events wecollect data on, the better the models will become," Patzert said. "Theobservations will lead the models into the first generation of meaningfulprediction." Print this entire article Subscribe Today Subscribe Today Feeds Contact Us About the Earth Observatory Image Use Policy Privacy Policy & Important Notices The Earth Observatory is part of the EOS Project Science Office located at NASA Goddard Space Flight Center webmaster: Paul Przyborski | NASA official: Lorraine Remer