Evaluation of CMIP5 models in simulating the respective impacts of East Asian winter monsoon and ENSO on the western North Pacific anomalous anticyclone

摘要

This article evaluates the linear isolated impacts of the East Asian winter monsoon (EAWM) and El Nino-Southern Oscillation (ENSO) on the evolution of the western North Pacific anticyclone (WNPAC) using 18 Coupled Model Inter-comparison Project phase 5 (CMIP5) models. The independent effects of ENSO and EAWM (ENSOres and EAWM(res)) are obtained by removing the ENSO-EAWM interaction via linear regression. For the ENSO high-skill (HS) models, which can well simulate an ENSO event, the anomalous WNPAC is confined to low latitudes and sustains from winter to late summer, which bears great resemblance to observational results. In contrast, the ENSO low-skill (LS) models induce an insignificant and weak WNPAC from winter to the following summer. This is related to the simulation biases of ENSOres sea surface temperature anomalies (SSTAs). The ENSO LS models simulate a weak and slowly decaying ENSOres. This bias can induce unreasonable evolution of the WNPAC via producing an unrealistic intensity and location of the anomalous convection activity over the western Pacific, which is the key factor for yielding an ENSOres-related WNPAC. The observed EAWM(res)-related WNPAC appears only in winter and covers a large region. The EAWM HS models, which can well simulate EAWM features, reasonably reproduce the WNPAC in winter. However, the WNPAC is significant and persists to the following summer, which is inconsistent with observations. This bias is related to the EAWM(res)-induced negative SSTA bias in the tropical central Pacific from spring to summer in the EAWM HS models. In contrast, the EAWM LS models, which cannot reasonably simulate EAWM features, are unable to reproduce the WNPAC in winter and the following seasons. Among the 18 state-of-the-art CMIP5 models, the CNRM-CM5 model yields a better performance in simulating the evolution of WNPAC compared with the ENSO HS models and EAWM HS models.