Niño Region 3 and Niño Region 3.4 SST Indices

See also TNI (Trans-Niño Index) and N3.4 (Niño 3.4 Index), which has more up-to-date N3.4 data than below.

Update History:


These data constitute Niño Region 3 and Niño Region 3.4 SST anomalies (indices) in degrees Celsius which are discussed and appear as figures in:

  • Trenberth, K. E. (1997) The Definition of El Niño. Bulletin of the American Meteorological Society, 78, 2771-2777. [pdf]

The Niño 3 Region is bounded by 90°W-150°W and 5°S- 5°N. The Niño 3.4 Region is bounded by 120°W-170°W and 5°S- 5°N.

For a discussion of El Niño events from Niño regions 3 and and 3.5 refer to Trenberth, K. E. (1996) El Niño Definition, Exchanges, Newsletter of the Climate Variability and Predictability Programme (CLIVAR), Volume 1, No.3, 6-8.


The raw data may be obtained from the CPC (Climate Prediction Center, NOAA ) data file "sstoi.indices" :

Please note CPC/NCEP/NOAA has changed their calculations extensively over the years. For example, the base periods have been changed and the Nino 3.4 region values have been corrected. Read more about it: FAQ CPC SST Indices


Monthly means were computed for each time series for the period 1950-1979. These means were then subtracted from their respective time series for the entire data set (1950-1999). Finally, a five-month running mean was applied to each time series.


Time series plots of the Niño 3 (upper) and Niño 3.4 (lower) SST indices as five month running means using data from NOAA and relative to a base period climatology from 1950-1979. Values above thresholds of ±0.5°C for Niño 3 and ±0.4°C for Niño 3.4 are stippled to indicate ENSO events.

For the raw data, click here.

To download ASCII format data file, click here and then use "Save As..." from the "File" dropdown menu to save this file.