Prior to 1982, few Americans had ever heard of El Niño. Much media and public attention focused on these large scale anomalous atmospheric and oceanic conditions during the winter of 1997-98 when numerous Pacific storms battered the West Coast and Southeast, while the northern tier of states remained exceptionally mild. Briefly, El Niño, named for "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. Occurring every three to five years, this phenomenon has disastrous effects upon the local economy because the warming is associated with a reduction in the upwelling of nutrient-rich cold water—decreasing the fish population and hence income from the fishing industry. Some scientists use the term ENSO, a contraction for El Niño and Southern Oscillation.
Right after the El Niño peaked in early 1998, the opposite condition, called La Niña, appeared. The term La Niña was proposed about 1988 to identify a circulation regime associated with anomalously cold ocean waters in the eastern tropical Pacific. Moderate La Niña conditions reappeared over portions of the eastern and central Pacific at the end of 2000 and into February 2001, then disappeared by late March, with a return to slightly negative sea-surface temperature (SST) anomalies across the eastern Pacific during late 2001. For some scientists, the situation that continued into early 2002 was what they termed a "neutral" period. By late spring, scientists were forecasting the onset of another El Niño event, which was anticipated to be weaker than the recent major El Niño of 1997-98. During late 2002, warmer waters developed across the equatorial Pacific, with the largest temperature anomalies found just east of the International Dateline, with temperatures on the order of 2 to 3 Celsius degrees above normal sea-surface temperatures for the region, indicative of a "warm-phase ENSO" or El Niño episode. Slightly below average temperatures were detected across the eastern Pacific during 2003, but in 2004, scientists were warning of another weak El Niño. With some slight interruptions, these weak El Niño conditions continued through mid 2005, when another La Niña event unfolded as the eastern Pacific had below average temperatures, while the central Pacific experienced above average temperatures. This La Niña event was short-lived, as warming of the eastern Pacific during 2006, provided early signs that an El Niño was forming. However, in early 2007 the temperature pattern changed, leading to a change from El Niño to La Niña conditions. The La Niña event that developed during 2007 continued into early 2008 with sea-surface temperatures more than one Celsius degree below the long-term average across the equatorial Pacific from off the coast of South America to west of the Dateline.
As of this writing, an ENSO-neutral condition was continuing with the sea surface temperatures across much of the equatorial Pacific remaining close to the long-term average. An area with "negative SST anomalies" (observed surface temperatures lower than long-term averages) had expanded eastward to near the coast of South America in the east-central Pacific, with SST anomalies remaining on the order of -0.5 Celsius degrees near the South American coast. Positive SST anomalies were found across the western equatorial Pacific. Scientists believe that this current condition should continue into early 2009.
The reason so much attention is paid to these events in the equatorial Pacific is that within the last several decades atmospheric and oceanic scientists have suggested a relationship between unusual or extreme weather conditions in many other areas of the world and the El Niño events in the eastern tropical Pacific. Research is currently underway to better understand these so-called "teleconnections" and to explain the causes in an effort to predict future El Niño and La Niña events and their impacts. In fact, the terms El Niño and La Niña now refer to the larger scale anomalous atmospheric and oceanic patterns seen across the globe. 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 satellites in both geosynchronous and polar orbits. Infrared radiation (IR) sensors onboard the satellites provide continuous worldwide estimates of sea surface temperatures (SST). The "Pacific ENSO Conditions" link from the DataStreme WES Website contains the most recent analyzed charts of Observed Sea Surface Temperatures (in degrees Celsius) and the Sea Surface Temperature Anomaly (defined as the difference between the observed and the 1971-2000 average temperature values in Celsius degrees). These observed SST data, obtained from a seven-day average of in-situ (buoy and ship) and satellite data, are plotted on a one-degree latitude/longitude grid.
The buoy network and satellite surveillance, continued under the direction of the National Oceanic and Atmospheric Administration (NOAA), provided the scientific community with the first indications of the developing major 1997-98 El Niño event. By July 1997, a major warming of the tropical surface waters in the eastern and central Pacific Ocean was detected, as the SST reached 4.5 Celsius degrees above the long-term climatological mean (called a "positive SST anomaly") over an area greater than that of the continental United States. This pattern persisted over the next eight months. By late 1998, negative SST anomalies developed in the eastern Pacific, and as noted above, La Niña, (the cold phase) was underway.
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 NOAA's Pacific Marine Environmental Laboratory (PMEL) in Seattle, WA contains background information and various 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. A NOAA La Niña theme page is also available.
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 measured global sea level every 10 days. From this altimeter information, current El Niño and La Niña conditions were monitored and displayed. However, in January 2006, this mission finally ended after 13 years and 5 months of service when the spacecraft lost its ability to maneuver. The Jason satellite, which had been launched in December 2001, now makes measurements of global sea level.
Return to DataStreme WES Website
Prepared by Edward J. Hopkins, Ph.D., email
hopkins@meteor.wisc.edu
ã Copyright, 2008, The American
Meteorological Society.