El Niño–Southern Oscillation - ENSO

Overview

Floods and mudslides in Ecuador, droughts and wildfires in Australia, and extreme California rainstorms – could all of these events be triggered by the same thing? Yes they can. It’s the El Niño-Southern Oscillation (ENSO), a combination of changes in the ocean and atmosphere that affect weather in many areas of the world.

Normally, trade winds move water at the ocean surface from the eastern tropical Pacific towards the western Pacific. This creates upwelling of cold nutrient-rich water off the coast of Peru and Chile, which supports a diversity of marine life. The western Pacific is in a low pressure system and has wet weather. The eastern Pacific, in a high pressure system, is dry. But every 3 to 7 years the atmosphere and ocean change during El Niño and La Niña events – the two extremes of ENSO.

Learn more on the UCAR Center for science education El Niño-Southern Oscillation page

Historical El Niño and La Niña Episodes

  • NOAA's operational definitions of El Niño and La Niña conditions are based upon the Oceanic Niño Index [ONI]. The ONI is defined as the 3-month running means of SST anomalies in the Niño 3.4 region [5N-5S, 120-170W]. The anomalies are derived from the 1971-2000 SST climatology.
  • The Niño 3.4 anomalies may be thought of as representing the average equatorial SSTs across the Pacific from about the dateline to the South American coast.
  • To be classified as a full-fledged El Niño and La Niña episode the ONI must exceed +0.5 [El Niño] or -0.5 [La Niña] for at least five consecutive months.
  • Based upon these definitions, NOAA lists the following episodes since 1949:

NOAA derived ONI values spanning 1950 - 2008

A combined table is available below or click the links below to view individual results.

ENSO Images

These are some color images associated with:

SOI and precip regression
SOI and precipitation correlation

Seasonal Mean Precipitation

SOI precipitation DJF
SOI precipitation MAM
SOI precipitation JJA
SOI precipitation SON

Correlation of NCEP/NCAR Reanalysis SLP with Tahiti-Darwin SOI

SOI sea level pressure regression

Seasonal Sea Level Pressure

SOI sea level pressure MAM
SOI sea level pressure MAM

NOAA derived ONI values spanning 1950 - 2010

Description: Warm (red) and cold (blue) episodes based on a threshold of +/- 0.5oC for the Oceanic Niño Index (ONI) [3 month running mean of ERSST.v3b SST anomalies in the Niño 3.4 region (5oN-5oS, 120o-170oW)], based on the 1971-2000 base period. For historical purposes cold and warm episodes (blue and red colored numbers) are defined when the threshold is met for a minimum of 5 consecutive over-lapping seasons.

Description: Warm (red) and cold (blue) episodes based on a threshold of +/- 0.5oC for the Oceanic Niño Index (ONI) [3 month running mean of ERSST.v3b SST anomalies in the Niño 3.4 region (5oN-5oS, 120o-170oW)], based on the 1971-2000 base period. For historical purposes cold and warm episodes (blue and red colored numbers) are defined when the threshold is met for a minimum of 5 consecutive over-lapping seasons.
Year DJF JFM FMA MAM AMJ MJJ JJA JAS ASO SON OND NDJ
1950
-1.7
-1.5
-1.3
-1.4
-1.3
-1.1
-0.8
-0.8
-0.8
-0.9
-0.9
-1
1951
-1
-0.9
-0.6
 -0.3 -0.2 0.2 0.4
0.7
0.7
0.8
0.7
0.6
1952 0.3 0.1 0.1 0.2 0.1 -0.1 -0.3 -0.3 -0.2 -0.2 -0.1 0
1953 0.2 0.4 0.5 0.5 0.5 0.5 0.4 0.4 0.4 0.4 0.4 0.4
1954 0.5 0.3 -0.1
-0.5
-0.7
-0.7
-0.8
-1
-1.2
-1.1
-1.1
-1.1
1955
-1
-0.9
-0.9
-1
-1
-1
-1
-1
-1.4
-1.8
-2
-1.9
1956
-1.3
-0.9
-0.7
-0.6
-0.6
-0.6
-0.7
-0.8
-0.8
-0.9
-0.9
-0.8
1957
-0.5
 -0.1 0.3
0.6
0.7
0.9
0.9
0.9
0.9
1
1.2
1.5
1958
1.7
1.5
1.2
0.8
0.6
0.5
 0.3 0.1 0 0 0.2 0.4
1959 0.4 0.5 0.4 0.2 0 -0.2 -0.4 -0.5 -0.4 -0.3 -0.2 -0.2
1960 -0.3 -0.3 -0.3 -0.2 -0.2 -0.2 -0.1 0 -0.1 -0.2 -0.2 -0.2
1961 -0.2 -0.2 -0.2 -0.1 0.1 0.2 0 -0.3 -0.6 -0.6 -0.5 -0.4
1962 -0.4 -0.4 -0.4 -0.5 -0.4 -0.4 -0.3 -0.3 -0.5 -0.6 -0.7 -0.7
1963 -0.6 -0.3 0 0.1 0.1 0.3
0.6
0.8
0.9
0.9
1
1
1964
0.8
 0.4 -0.1
-0.5
-0.8
-0.8
-0.9
-1
-1.1
-1.2
-1.2
-1
1965
-0.8
 -0.4 -0.2 0 0.3
0.6
1
1.2
1.4
1.5
1.6
1.5
1966
1.2
1
0.8
0.5
 0.2 0.2 0.2 0 -0.2 -0.2 -0.3 -0.3
1967 -0.4 -0.4 -0.6 -0.5 -0.3 0 0 -0.2 -0.4 -0.5 -0.4
-0.5
1968
-0.7
-0.9
-0.8
-0.7
 -0.3 0 0.3 0.4 0.3 0.4
0.7
0.9
1969
1
1
0.9
0.7
0.6
0.5
 0.4 0.4
0.6
0.7
0.8
0.7
1970
0.5
 0.3 0.2 0.1 0 -0.3
-0.6
-0.8
-0.9
-0.8
-0.9
-1.1
1971
-1.3
-1.3
-1.1
-0.9
-0.8
-0.8
-0.8
-0.8
-0.8
-0.9
-1
-0.9
1972
-0.7
 -0.4 0 0.2
0.5
0.8
1
1.3
1.5
1.8
2
2.1
1973
1.8
1.2
0.5
 -0.1
-0.6
-0.9
-1.1
-1.3
-1.4
-1.7
-2
-2.1
1974
-1.9
-1.7
-1.3
-1.1
-0.9
-0.8
-0.6
-0.5
-0.5
-0.7
-0.9
-0.7
1975
-0.6
-0.6
-0.7
-0.8
-0.9
-1.1
-1.2
-1.3
-1.5
-1.6
-1.7
-1.7
1976
-1.6
-1.2
-0.8
-0.6
-0.5
 -0.2 0.1 0.3
0.5
0.7
0.8
0.7
1977
0.6
0.5
 0.2 0.2 0.2 0.4 0.4 0.4
0.5
0.6
0.7
0.7
1978
0.7
 0.4 0 -0.3 -0.4 -0.4 -0.4 -0.4 -0.4 -0.3 -0.2 -0.1
1979 -0.1 0 0.1 0.1 0.1 -0.1 0 0.1 0.3 0.4 0.5 0.5
1980 0.5 0.3 0.2 0.2 0.3 0.3 0.2 0 -0.1 -0.1 0 -0.1
1981 -0.3 -0.5 -0.5 -0.4 -0.3 -0.3 -0.4 -0.4 -0.3 -0.2 -0.1 -0.1
1982 0 0.1 0.1 0.3
0.6
0.7
0.7
1
1.5
1.9
2.2
2.3
1983
2.3
2
1.5
1.2
1
0.6
 0.2 -0.2 -0.6 -0.8 -0.9 -0.7
1984 -0.4 -0.2 -0.2 -0.3 -0.5 -0.4 -0.3 -0.2 -0.3
-0.6
-0.9
-1.1
1985
-0.9
-0.8
-0.7
-0.7
-0.7
-0.6
-0.5
-0.5
-0.5
 -0.4 -0.3 -0.4
1986 -0.5 -0.4 -0.2 -0.2 -0.1 0 0.3
0.5
0.7
0.9
1.1
1.2
1987
1.2
1.3
1.2
1.1
1
1.2
1.4
1.6
1.6
1.5
1.3
1.1
1988
0.7
0.5
 0.1 -0.2
-0.7
-1.2
-1.3
-1.2
-1.3
-1.6
-1.9
-1.9
1989
-1.7
-1.5
-1.1
-0.8
-0.6
 -0.4 -0.3 -0.3 -0.3 -0.3 -0.2 -0.1
1990 0.1 0.2 0.2 0.2 0.2 0.2 0.3 0.3 0.3 0.3 0.3 0.4
1991 0.4 0.3 0.3 0.4
0.6
0.8
1
0.9
0.9
1
1.4
1.6
1992
1.8
1.6
1.5
1.4
1.2
0.8
0.5
 0.2 0 -0.1 0 0.2
1993 0.3 0.4 0.6 0.7 0.8 0.7 0.4 0.4 0.4 0.4 0.3 0.2
1994 0.2 0.2 0.3 0.4
0.5
0.5
0.6
0.6
0.7
0.9
1.2
1.3
1995
1.2
0.9
0.7
 0.4 0.3 0.2 0 -0.2
-0.5
-0.6
-0.7
-0.7
1996
-0.7
-0.7
-0.5
 -0.3 -0.1 -0.1 0 -0.1 -0.1 -0.2 -0.3 -0.4
1997 -0.4 -0.3 0 0.4
0.8
1.3
1.7
2
2.2
2.4
2.5
2.5
1998
2.3
1.9
1.5
1
0.5
 0
-0.5
-0.8
-1
-1.1
-1.3
-1.4
1999
-1.4
-1.2
-0.9
-0.8
-0.8
-0.8
-0.9
-0.9
-1
-1.1
-1.3
-1.6
2000
-1.6
-1.4
-1
-0.8
-0.6
-0.5
 -0.4 -0.4 -0.4
-0.5
-0.6
-0.7
2001
-0.6
-0.5
 -0.4 -0.2 -0.1 0.1 0.2 0.2 0.1 0 -0.1 -0.1
2002 -0.1 0.1 0.2 0.4
0.7
0.8
0.9
1
1.1
1.3
1.5
1.4
2003
1.2
0.9
0.5
 0.1 -0.1 0.1 0.4 0.5 0.6 0.5 0.6 0.4
2004 0.4 0.3 0.2 0.2 0.3
0.5
0.7
0.8
0.9
0.8
0.8
0.8
2005
0.7
0.5
 0.4 0.4 0.4 0.4 0.4 0.3 0.2 -0.1 -0.4 -0.7
2006 -0.7 -0.6 -0.4 -0.1 0.1 0.2 0.3
0.5
0.6
0.9
1.1
1.1
2007
0.8
 0.4 0.1 -0.1 -0.1 -0.1 -0.1 -0.4
-0.7
-1
-1.1
-1.3
2008
-1.4
-1.4
-1.1
-0.8
-0.6
 -0.4 -0.1 0 0 0 -0.3 -0.6
2009 -0.8 -0.7 -0.5 -0.1 0.2
0.6
0.7
0.8
0.9
1.2
1.5
1.8
2010
1.7
1.5
1.2
0.8
 0.3

Relevant Publications:

  • Trenberth, K. E., D. P. Stepaniak and J. M. Caron, 2002: Interannual variations in the atmospheric heat budget. J. Geophys. Res., 107, D8, 10.1029/2000JD000297.
  • Trenberth, K. E., J. M. Caron, D. P. Stepaniak and S. Worley, 2002: The evolution of ENSO and global atmospheric temperatures. J. Geophys. Res., 107, D8, 10.1029/2000JD000298.
  • Trenberth, K. E., and D. P. Stepaniak, 2001: Indices of El Niño evolution. J. Climate., 14, 1697-1701.
  • Trenberth, K. E., and J. M. Caron 2000: The Southern Oscillation Revisited: Sea level pressures, surface temperatures and precipitation. Journal of Climate, 13, pp. 4358-4365.
  • Trenberth, K. E., 1999: The extreme weather events of 1997 and 1998. Consequences, Vol 5, 1, 2-15.
  • Lietzke, C. E., T. H. Vonder Haar, C. Deser, 1999: Evolutionary Structure of the Eastern Pacific double ITCZ based on Satellite Moisture Profile Retrievals, J. Climate, 14, 743-751.
  • Deser, C. and C. Smith 1998: Diurnal and semidiurnal variations of the surface wind field over the tropical Pacific Ocean.Journal of Climate 11, No. 7, pp.1730-1748.
  • Henson, B. and K.E. Trenberth, 1998: Children of the Tropics: El Niño and La Niña. From the Learning about Science Easily and Readily Series (LASERS).
  • Trenberth, K. E., G. W. Branstator, D. Karoly, A. Kumar, N-C. Lau, and C. Ropelewski, 1998: Progress during TOGA in understanding and modeling global teleconnections associated with tropical sea surface temperatures. J. Geophys. Res., 103 (special TOGA issue), 14291--14324.
  • Trenberth, K. E., 1997: The Definition of El Niño. BAMS, 78, 2771-2777. (All figures and tables are current through December 1999.) Table of El Niño and La Niña Events
  • Trenberth, K. E. and T. J. Hoar, 1997: El Niño and climate change. Geophys. Res. Lett., 24, 3057-3060.
  • Trenberth, K. E. and Guillemot, C. J., 1996: Physical processes involved in the 1988 drought and 1993 floods in North America., J. Climate, 9, 1288-1298.
  • Trenberth, K., and T. J. Hoar, 1995: The 1990-1995 El Niño-Southern Oscillation Event: Longest on Record. Geophysical Research Letters, 23, 57-60.
  • Deser, C. and M. L. Blackmon, 1995: On the Relationship between Tropical and North Pacific Sea Surface Temperature Variations, J. Climate 8, No. 6, pp.1677-1680.
  • Deser, C., 1994: Daily surface wind variations over the equatorial Pacific Ocean Journal of Geophysical Research 99, No. D11, pp.23071-23078.
  • Deser, C., S. Wahl, and J. J. Bates, 1993: The Influence of Sea Surface Temperature Gradients on Stratiform Cloudiness along the Equatorial Front in the Pacific Ocean Journal of Climate 6, No. 6, pp.1172-1180.
  • Deser, C., 1992: Diagnosis of the surface momentum balance over the tropical Pacific Ocean J. Climate 6, No. 1, pp.64-74.
  • Deser, C. and J. M. Wallace 1990: Large-Scale Atmospheric Circulation Features of Warm and Cold Episodes in the Tropical Pacific J. Climate Vol. 3, No. 11, pp.1254-1281.
  • Wallace, J. M., T. P. Mitchell, and C. Deser 1989: The Influence of Sea-Surface Temperature on Surface Wind in the Eastern Equatorial Pacific: Seasonal and Interannual Variability J. Climate 2, No. 12, pp.1492-1499.
  • Richey, J.E., C. Nobre, and C. Deser, 1989:Amazon River discharge and climate variability: 1903-1985 Science 246, pp. 101-103.
  • Wright, P. B., J. M. Wallace, T. P. Mitchell, and C. Deser 1988: Correlation Structure of the El Niño/Southern Oscillation Phenomenon J. Climate 1, No. 6, pp. 609-625.
  • Deser, C., and J. M. Wallace 1987: El Niño events and their relationship to the Southern Oscillation: 1925-1986 Journal of Geophysical Research 92, No. C13, pp.14189-14196.

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