Assessing El Niño Impact on Climate Anomalies


EOF illustration Click here to see the current state of El Niño


plot  This page allows the user to plot current or historical climate anomalies, and compare those to the linear signal associated with El Niño.

Monthly mean geopotential height at 500 mb is available from January 1948 thru April 2002, while Outgoing Longwave Radiation (OLR) is available from June 1974 to April 2002. By selecting a variable and a time-averaging interval, the observed anomaly for that period is calculated. Anomalies are computed using a 1958-1997 base climatology (1974-1997 for OLR). The OLR anomalies are displayed as rainfall anomalies in mm/day using the Arkin and Meisner (1987) empirical relation.

El Niño's contribution to the observed anomalies is determined by regressing the historical monthly anomalies of each variable onto the equatorial Pacific EOF1 SST time series for 1948-2002 (1974-2002 for OLR). For each variable, there are 12 regression maps, one for each calendar month. For the time-averaging period selected by the user, the corresponding monthly regressions are weighted by the amplitude of the EOF1 principal component and then linearly averaged.

Circulation data are from the NCEP/NCAR reanalysis.

Select the consecutive months for generating the average anomalies, and El Niño's contribution to those anomalies.


  • OLR data are missing from April 1978 to December 1978. These dates are ignored if specified in the time range.
  • This page does not produce a composite for a particular month averaged over many years. If such a composite is desired, see our Composites page.

Choose the Variable:

Time range:
Begin month: Begin year: End month: End year:
Starting latitude at South (-90 to 90): Ending latitude at North:
Eastern most longitude (0 to 360): Western most longitude:

Go here to see the current state of El Niño

 ?? For questions regarding the impact assessments, please e-mail Martin Hoerling at

This is a Research and Development Application