(REPHRASE for what transpired over winter and early spring.)
Before 1982, few Americans had ever heard of the term El Niño. Much media and public attention was focused upon this large scale anomalous atmospheric and oceanic condition during the 1997-98 winter when numerous Pacific storms battered the West Coast and Southeast, while the northern tier of states remained exceptionally mild. Briefly, this El Niño event, named after "the Christ child" by Peruvians some 200 years ago, is associated with a noticeable warming of the equatorial Pacific Ocean waters along the South American Coast. This phenomenon that occurs every three to five years produces disastrous effects upon the local economy because the warming causes a reduction in the upwelling of cold water, that reduces the fish population and hence, the income from the fishing industry. During the first several months of 1998, some signs of an opposite condition called La Niña began to appear. The term La Niña was proposed about 1988 to identify a circulation regime associated with anomalously cold ocean waters in the eastern Pacific. At the time of this writing, a major La Niña event has not evolved.
The reason for the attention paid to these events in the equatorial Pacific is that within the last several decades atmospheric and oceanic scientists have suggested a relationship between anomalous weather conditions in many other areas of the world and the El Niño. Research is currently being conducted to understand these "teleconnections" and to explain the causes in an effort to predict future El Niño and La Niña events. Following the significant 1982-83 El Niño event, a major international effort called TOGA (Tropical Oceans, Global Atmosphere) was launched. Between 1985 and 1994, the weather and near-surface ocean conditions in the tropical Pacific were closely monitored by investigators using moored ocean buoys, drifting buoys, ship measurements, and from satellite platforms to include both geosynchronous and polar orbiting satellites. Infrared radiation (IR) sensors onboard the satellites provide a continuous world-wide estimate of the sea surface temperatures (SST). The buoy network and the satellite surveillance, continued under the administration of NOAA, provided the scientific community with the first indications of the major 1997-98 El Niño event. By July of 1997, a major warming of the tropical surface waters in the eastern and central Pacific Ocean was detected, as the SST in some regions reached 4.5 Celsius degrees above the long term climatological mean (called a "positive SST anomaly") extending over an area greater than that of the continental United States. This pattern persisted for the next eight months.
Several Web sites focusing on the El Niño and La Niña provide up-to-date information concerning the SST and other El Niño indicators. You can use these sources to monitor the present conditions across the tropical Pacific, compare the recent El Niño event with other historic predecessors, and learn how these events may affect the weather and climate elsewhere on the planet. A special El Niño theme page produced by the National Oceanic and Atmospheric Administration's Pacific Marine Environmental Laboratory (PMEL) in Seattle, WA contains background information and various types of current information sources. One such source is the set of real time plots of sea surface temperature and wind observations provided by an array of moored ocean buoys in the Pacific Ocean. Other links from this page provide El Niño forecasts and information in a question and answer format.
Another instructive site is the TOPEX/Poseidon and El Niño homepage. The TOPEX/Poseidon satellite, a part of a partnership between U.S. and French scientists, accurately measures global sea level every 10 days. From this altimeter information, current conditions can be monitored and displayed.
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Prepared by Edward J. Hopkins, Ph.D., email hopkins@meteor.wisc.edu
© Copyright, 1999, The American Meteorological
Society.