NORTH AMERICAN COUNTRIES REACH CONSENSUS ON EL NIÑO DEFINITION
Feb. 23, 2005 — NOAA announced that the NOAA National Weather Service, the Meteorological Service of Canada and the National Meteorological Service of Mexico have reached a consensus on an index and definitions for El Niño and La Niña events (also referred to as the El Niño Southern Oscillation or ENSO). Canada, Mexico and the United States all experience impacts from El Niño and La Niña. (Click the NOAA satellite image for larger view of sea surface temperatures in the Equatorial Pacific Ocean taken Feb. 22, 2005. Please credit “NOAA.”)
"Three nations, on the same continent, agreeing on the index and definitions for such a significant climate feature as El Niño and La Niña goes a long way to aid NOAA in its mission to understand climate variability as well as make climate forecasts in order to protect, restore and manage in light of ENSO related-events and impacts," said retired Navy Vice Admiral Conrad Lautenbacher, Ph.D., undersecretary of commerce for oceans and atmosphere and NOAA administrator.
"The agreement on the index and definitions for North America is a major milestone in climate monitoring," said Brig. Gen. David L. Johnson, U.S. Air Force (Ret.), director of the NOAA National Weather Service. "Having the same operational definitions helps to ensure consistency and further coordination in climate assessments issued by the North American meteorological services."
"We believe it is important that our respective Weather Services adopt a common definition of these phenomena that have significant impacts on the North American climate and are subject to strong media attention," said Marc Denis Everell, assistant deputy minister for the meteorological service of Canada. "Since Canada and the United States share a 5,000 km (3,106 miles) long boundary, it is quite appropriate for both our Services to disseminate similar statements regarding the presence or not of these phenomena. A common definition is a step in the right direction," he added.
"Climatological phenomena, like ENSO, do not recognize political borders. The communities living on either side of the USA-Mexico border are subjected to very similar effects from this kind of phenomena. Furthermore, both communities are very closely related in socioeconomic matters," said Michel Rosengaus, head of unit, national meteorological service of Mexico. "Therefore, this agreement on the definition of El Niño, La Niña or neutral phases, which allows for an objective diagnosis in a uniform way across the whole North American subcontinent, will better serve the public in general."
The index is defined as a three-month average of sea surface temperature departures from normal for a critical region of the equatorial Pacific (Niño 3.4 region; 120W-170W, 5N-5S). This region of the tropical Pacific contains what scientists call the "equatorial cold tongue," a band of cool water that extends along the equator from the coast of South America to the central Pacific Ocean. Departures from average sea surface temperatures in this region are critically important in determining major shifts in the pattern of tropical rainfall, which influence the jet streams and patterns of temperature and precipitation around the world.
operational definitions for El Niño and La Niña, based
on the index, are:
La Niña: A phenomenon in the equatorial Pacific Ocean characterized by a negative sea surface temperature departure from normal (for the 1971-2000 base period) in the Niño 3.4 region greater than or equal in magnitude to 0.5 degrees C (0.9 degrees Fahrenheit), averaged over three consecutive months.
Presently, NOAA is observing and monitoring very weak warm-episode (El Niño) conditions in the tropical Pacific. "This event is much weaker than the very strong 1997-1998 El Niño event," said Vernon Kousky, NOAA's lead El Niño/La Niña expert. "In fact, the recent release of NOAA's ENSO Diagnostic Discussion states it is most likely that weak El Niño conditions will continue to weaken during the next three months. ENSO-neutral conditions will prevail by late Spring and remain through the end of the year," he added.
NOAA began using the index and definitions operationally for monitoring and predicting El Niño and La Niña conditions on September 1, 2003. NOAA issues assessments of ENSO's status in the Monthly Climate Diagnostic Bulletin, the ENSO Diagnostic Discussion and the Weekly ENSO update.
NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nation’s coastal and marine resources. NOAA is part of the U.S. Department of Commerce.
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