How well do current climate models simulate two types of El Nino?

Abstract

In this study, we evaluate the fidelity of current climate models in simulating the two types of El Nino events using the pre-industrial output in CMIP3 archives. It is shown that a few climate models simulate the two types of El Nino events to some extent, while most of the models have serious systematic problems in simulating distinctive patterns of sea-surface temperature (SST) and precipitation anomaly associated with the two types of El Nino; that is, they tend to simulate a single type of El Nino. It is shown that the ability of climate models in simulating the two types of El Nino is related to the sensitivity of the atmospheric responses to the SST anomaly patterns. Models whose convective location is shifted to the east (west) as the SST anomaly center moves to the east (west) tends to simulate the two types of El Nino events successfully. On the other hand, models whose location of convective anomaly is confined over the western or central Pacific tends to simulate only the single type of El Nino event. It is also shown that the confinement of the convective anomaly over the western or central Pacific is closely linked to the dry bias and the associated cold bias over the eastern Pacific. That is, because positive El Nino SST anomalies over the eastern Pacific cannot increase local convection effectively when the total SSTs are still too cold due to a cold bias. This implies that the realistic simulation of climatology, especially over the equatorial eastern Pacific, is essential to the successful simulation of the two types of El Nino.