This Supplement is a repeat of that for Week 11.
Prior to 1982, few Americans had ever heard of El Niño. Much media and public attention focused on this large scale anomalous atmospheric and oceanic condition 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 an "ENSO-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. During 2005, the eastern tropical Pacific had below average temperatures, while the central tropical Pacific experienced above average temperatures. By the end of October, equatorial SST anomalies greater than +0.5 Celsius degree were found between Indonesia and 175 degrees W, while negative anomalies less than -0.5 Celsius degrees were observed at most locations between 130 degrees W and the South America coast. As of this writing, forecasters expect ENSO-neutral or weak La Niña conditions over the next 6 to 9 months.
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 SST and other El Niño indicators. You can access these sources to monitor the present conditions across the tropical Pacific, compare recent El Niño events with 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 La Niña theme page is also available.
Another instructive site is the TOPEX/Poseidon and El Niño homepage. The TOPEX/Poseidon satellite, a joint project of U.S. and French scientists, accurately measures global sea level every 10 days. From this altimeter information, the ocean surface topography can be determined and current El Niño or La Niña conditions can be monitored and displayed.
Return to DataStreme WES Website
Prepared by Edward J. Hopkins, Ph.D., email
hopkins@meteor.wisc.edu
ã Copyright, 2005, The American
Meteorological Society.
