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The El Niño OLR Index

The El Niño outgoing longwave radiation (OLR) index is an indicator of eastern-central tropical Pacific deep-atmospheric convection conditions. It is calculated with OLR anomalies in the box 160°W - 110°W, 5°S - 5°N.

Over the time for which satellite-based OLR information has been available, the El Niño events distinguished by their OLR behavior (the index's large negative peaks) have predominantly accounted for the familiar El Niño weather associations over North America (Chiodi and Harrison 2013, 2015). NOAA/PMEL hosts an El Niño theme page with further information on the tropical Pacific.

In the Longer Series figure, 30-day running averages are shown. In the Shorter Series figure, weekly averages are shown by the plus signs and the 30-day running average values are shown by the shaded regions.

Data source

The index is calculated using NOAA's OLR-Daily Climate Data Record (CDR) , made available through the University of Maryland (UMD) OLR CDR Portal, and is updated weekly (last update 31-DEC-2023).   get series (netcdf 352kB) » 


The anomaly is calculated relative to a monthly climatological seasonal cycle based on the period 1 Jan 1979-present. The monthly climatology is linearly interpolated to determine weekly/daily anomalies.


The uncertainty of the index is estimated to be 2.0 W m-2 over the period 1979-2013, based on the root-mean-square difference between the NOAA Daily-CDR and NOAA Interpolated OLR data sets.


Chiodi, A. M. and D. E. Harrison, 2013: El Niño Impacts on Seasonal U.S. Atmospheric Circulation, Temperature, and Precipitation Anomalies: The OLR-Event Perspective. J. Climate, 26, 822-837.

Chiodi, A. M. and D. E. Harrison, 2015: Global Seasonal Precipitation Anomalies Robustly Associated with El Niño and La Niña Events - An OLR perspective. J. Climate, 28, 6133-6159. doi:10.1175/JCLI-D-14-00387.1

External Links

The links provided below are external to this Web Site and may have privacy policies different from the privacy policy

The daily averaged values of OLR used to calculate the index shown on this Site are available at the UMD OLR CDR Portal.

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