The El Niño - Southern Oscillation

Click here for figures from the Trenberth and Caron 2000 SOI paper

NCAR CAS Catalog Climate Indices

Historical El Niño and La Niña Episodes [NOAA]

  • 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:
  • ONI: 1950-1975
  • ONI: 1976-2001
  • ONI: 2002-2008

Relevant Publications

Trenberth, K. E., D. P. Stepaniak and J. M. Caron, 2001: Interannual variations in the atmospheric heat budget. J. Geophys. Res., submitted.

Trenberth, K. E., J. M. Caron, D. P. Stepaniak and S. Worley, 2001: The evolution of ENSO and global atmospheric temperatures. J. Geophys. Res., submitted.

Trenberth, K. E., and D. P. Stepaniak, 2001: Indices of El Niño evolution. J. Climate., 14, 1697-1701. (Download a pdf version of the paper from the author's homepage.)

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. (Download a pdf version of the paper from the author's homepage.)

Trenberth, K. E., 1999: The extreme weather events of 1997 and 1998. Consequences, Vol 5, 1, 2-15.

Lietzke, Christopher E., Thomas H. Vonder Haar, Clara Deser, 1999: Evolutionary Structure of the Eastern Pacific double ITCZ based on Satellite Moisture Profile Retrievals Journal of Climate in press.

Deser, Clara and Catherine 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, Bob and Trenberth, Kevin E., 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 tempe ratures. J. Geophys. Res., 103 (special TOGA issue), 14291--14324.

Trenberth, Kevin E., 1997: The Definition of El Niño. Bulletin of the American Meteorological Society, 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, Clara and Maurice L. Blackmon, 1995: On the Relationship between Tropical and North Pacific Sea Surface Temperature Variations Journal of Climate 8, No. 6, pp.1677-1680.

Deser, Clara, 1994: Daily surface wind variations over the equatorial Pacific Ocean Journal of Geophysical Research 99, No. D11, pp.23071-23078.

Deser, Clara, Susan Wahl, and John 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, Clara, 1992: Diagnosis of the surface momentum balance over the tropical Pacific Ocean Journal of Climate 6, No. 1, pp.64-74.

Deser, Clara, and John M. Wallace 1990: Large-Scale Atmospheric Circulation Features of Warm and Cold Episodes in the Tropical Pacific Journal of Climate Vol. 3, No. 11, pp.1254-1281.

Wallace, John M., Todd P. Mitchell, and Clara Deser 1989: The Influence of Sea-Surface Temperature on Surface Wind in the Eastern Equatorial Pacific: Seasonal and Interannual Variability Journal of 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, Peter B., John M. Wallace, Todd P. Mitchell, and Clara Deser 1988: Correlation Structure of the El Niño/Southern Oscillation Phenomenon Journal of Climate 1, No. 6, pp. 609-625.

Deser, Clara, and John 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.

Related Links

Climate Information Project

NOAA/OGP El Niño - Southern Oscillation Page

Center for Ocean-Atmospheric Prediction Studies (COAPS) ENSO Page

Climate Prediction Center - Analysis + Monitoring Products

The Current State of the Tropical Pacific

The Climate Diagnostics Center

NOAA/PMEL TAO Home Page

NOAA El Niño Page

The International Research Institute (IRI) Page

ECMWF Seasonal Forecasts

Southern Region Headquarters ENSO Page

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