Comparison of Different El Niño and La Niña Events

While El Niño and La Niña are often associated with consistent climate anomalies throughout the globe, differences in the tropical SST pattern, basic atmospheric state over the globe and "random" climate variability mean that the climate anomalies may not be the same from event to event. These plots give an indication of how similar and how different the atmosphere/ocean can be during events.

Details of Calculations

For each dataset, a plot of anomalies (mean- climatology) is created for ENSO events within the time-period of the dataset. The months start in July before the peak of the event and end in June after the event. Events are selected using the ONI (or Nino 3.4 for years before the ONI is defined). In general, we tried to use matching events for different variables. In addition, the composite, or overall average of the anomalies for all events is created and plotted. Finally, the standard deviation of the anomalies is calculated and plotted so users can see where events tend to differ.

Event Definition

Events are defined by the DJF values of the NOAA Oceanic Nino Index (ONI) for a year. Plots have that value in the title so users can compare stronger to weaker events.


The set of datasets we used are as follows:


One of the main issues with the anomaly plots is there is a strong trend in some variables such as 2m Temperature. This makes anomalies look warmer the later the event and can mask ENSO response to the climate at the time of the event.

Future Additions

As we have the resources, we plan to add the following.
  • Water year to date anomalies for some variables (e.g. Oct-end month)
  • Seasons in addition to months (3-month seasons).
  • Composites of events before 1940, either using the 20CRV3 or some of the longer datasets such as NOAA ERSST.
  • More dataset types such as biological datasets.