The Asian-Pacific Oscillation pattern in CMIP5 simulations of historical and future climate

Based on the Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations, this article evaluated the performance of 33 coupled models in simulating the summer Asian-Pacific Oscillation (APO) pattern and projected its change under the RCP4.5 and RCP8.5 scenarios. The results show that most of the individual models have good capacity to simulate the climate mean state of the spatial structure of the summer APO pattern, while some have poor skill in modelling its secular trend and interannual variability. The multimodel ensemble mean (MME) generally outperforms the individual models. It not only well reproduces the spatial distribution of the observed APO pattern, but also reasonably captures the observed negative trend and interannual variability of the APO. The MME projects a decrease in the APO intensity towards the end of 21st century under both the RCP4.5 and the RCP8.5 scenarios. Large differences in projected change under the two forcing scenarios start to emerge about in the 2040s, with larger decreasing under the RCP8.5 than that under the RCP4.5. Over the course of the second half of the 21st century, the APO pattern will shift eastward slightly in addition to the weakening in intensity as compared to the 1950-2005 mean climate. For the individual models, the majority of models agree on the sign of projected decreasing change in the APO intensity and also exhibit a stronger change under the RCP8.5 scenario than under the RCP4.5 scenario.