Response of two atmospheric general circulation models to sea-surface temperature anomalies in the tropical East and West Pacific

Abstract

A substantial anomalous warming of sea-surface temperatures (SSTs) in the tropical Pacific Ocean (an ‘El Nino’) can have profound effects on the atmospheric mid-latitude long waves, leading to severe weather anomalies1–5. However, the magnitude and position of these weather anomalies seem to vary considerably between winters in which El Nino events are in progress2,6,7. In order to forecast with confidence the effects of future El Nino events, it is important to understand the physical reasons for these differences. Motivated by this, we present several atmospheric general circulation experiments which model the atmospheric response to SST anomalies in the tropical East and West Pacific. We have found that the extratropical response to a relatively small West Pacific anomaly can be stronger than and qualitatively different from the response to a much larger East Pacific anomaly. These experiments suggest a possible explanation for the difference in mid-latitude response during the 1976–77 El Nino winter and the El Nino winters of 1972–73 and 1982–83.