NOAA Announces Definitions for El Nino and La Nina

[donsutherland1]

02 October 2003

<b>NOAA Announces Definitions for El Nino and La Nina</b>
Provides first widely accepted characterization of climate phenomena

The National Oceanic and Atmospheric Administration (NOAA) says it has achieved agreement among experts on an operational index and definitions for El Nino and La Nina -- disruptions of the ocean-atmosphere system in the tropical Pacific leading to important consequences for weather around the globe.

According to a September 30 press release, experts in the federal government and academia reached a consensus on the index and definitions after more than a year of study. "Before now, no widely accepted operational definition of El Nino or La Nina existed," said NOAA Administrator Conrad Lautenbacher.

The index is defined as sea surface temperature departures from normal, averaged over three consecutive months, for a critical region of the tropical Pacific that 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. Based on the index, El Nino is characterized by a sea surface temperature increase of 0.5 degrees Celsius or more above normal, and La Nina by a decrease in sea surface temperature of 0.5 degrees Celsius or more.

Departures from average sea surface temperatures in this equatorial Pacific 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.

Following is the text of the press release:

National Oceanic and Atmospheric Administration
September 30, 2003

NOAA GETS U.S. CONSENSUS FOR EL NINO/LA NINA INDEX, DEFINITIONS

El Niño and La Niña may have fizzled, but for scientists at the NOAA, National Oceanic and Atmospheric Administration, their quest to better understand and define these climatic twins is a step closer to resolution. After more than a year of study, NOAA announced today that it has reached a consensus among experts in the federal government and academia for an operational index and definitions for El Niño and La Niña, which are extremes of the El Niño/Southern Oscillation (ENSO) cycle. NOAA is an agency of the U.S. Department of Commerce.

NOAA, in collaboration with experts at the Scripps Institute of Oceanography, the Center for Ocean-Land-Atmosphere Studies (COLA), the Center for Ocean-Atmospheric Prediction Studies (COAPS), the International Research Institute (IRI) for Climate Prediction, the National Center for Atmospheric Research (NCAR), and the University of Washington, has agreed on a primary index for assessing the state of the ENSO cycle. Based on the index, NOAA has developed operational definitions for El Niño and La Niña.

"Before now, no widely accepted operational definition of El Niño or La Niña existed," said retired Navy Vice Admiral Conrad C. Lautenbacher, Jr., Ph.D., under secretary of commerce for oceans and atmosphere and NOAA administrator. "This effort provides for greater consistency of communication between scientists, who monitor and study the ENSO cycle and more uniformity in our message to the public through the media," he added.

The index is defined as three-month averages of sea surface temperature departures from normal for a critical region of the equatorial Pacific (Nino 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 of 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.

NOAA's operational definitions for El Niño and La Niña, based on the index, are:

El Niño: A phenomenon in the equatorial Pacific Ocean characterized by a positive 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 0.5C, averaged over three consecutive months.

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 0.5C, averaged over three consecutive months.

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. Currently, NOAA is engaged in dialogue with the international meteorological community for global acceptance of the index and definitions.

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.

<b>Source: </b>Bureau of International Information Programs, U.S. Department of State