An Evaluation of Reproducibility of the Pacific Decadal Oscillation in the CMIP3 Simulations

Abstract

Reproducibility of the Pacific Decadal Oscillation (PDO) is evaluated in the sea surface temperature (SST) anomaly field in “the 20th century climate in coupled models” (20C3M) simulations of the 24 CMIP3 models. In this evaluation, we examine how well patterns of the PDO match between the observations and simulations by calculating a metric of the patterns that is a function of their spatial correlation and their standard deviation. Among the CMIP3 models, the models with the high PDO metric reproduce the decadal SST variability with opposing polarities between the central North Pacifc and the tropical Pacific. As observed, temporal correlation between the PDO and decadal-ENSO indices in those simulations are negatively correlated at the statistically-significant level. The sea level pressure and outgoing longwave radiation anomalies onto the decadal-ENSO index in those simulations are realistic both in the tropical Pacific and North Pacific, indicating that this tropicsextratropics linkage in the SST anomaly field is induced by atmospheric teleconnection. This notion is consistent with the previous studies for the natural climate variability. In contrast, the models with the low PDO metric fail to reproduce those characteristics.In the simulations under a middle-range IPCC greenhouse gas emissions scenario (A1B), the PDO indices during the 21st century still represent SST variations on the decadal timescales with superimposition on a linear warming trend. Several models which reproduce the observed PDO pattern in the 20th century record tend to simulate a similar pattern over the 21st century. This indicates that the models with the high PDO metric have their own properties that tend to simulate the natural climate variations with the observed pattern under the global warming condition.