Abstract

There has been considerable societal importance placed on the ability to distinguish and predict interannual anomalies of the tropical Pacific’s coupled ocean-atmosphere system. Specific importance has been placed on determining when anomalous conditions follow one of two sets of conditions first described in detail by Bjerknes and commonly referred to as “El Nino” and “La Nina.” Here, we investigate the use of outgoing-longwave-radiation (OLR) as a means of determining “El Nino”-type anomalies operationally and retrospectively.

We find that OLR, averaged over regions which are known to play a role in Bjerknes feedbacks over the tropical Pacific, can be used to unambiguously identify such interannual anomalies and that some OLR-based indices are advantageous in terms of the degree to which anomalous years are clearly distinguished from background variability. Thus, OLR offers a useful perspective on the state of the coupled tropical Pacific system and should be considered when assessing the state of this system, along with other more traditionally discussed variables such as sea surface temperature (SST) and sea level pressure (SLP).