资源环境科技发展态势分析平台

The present study examined the ability of Coupled Model Intercomparison Project phase 5 (CMIP5) models in representing the differences in decaying phases of El Nino and their impact on south Asia and east Asia monsoon during June and July (JJ), the early summer monsoon months. El Nino decay is classified into three categories, based on the timing of decay with respect to the summer season after the peak phase of El Nino. Analysis suggests that many CMIP5 models are able to capture the differences in the decaying phase of El Nino. Observed rainfall anomalies are positive over most parts of south and east Asia regions during the early decay (ED) years mainly due to anomalous Tropical Indian Ocean (TIO) Sea Surface Temperature (SST) warming and La Nina like forcing from the eastern Pacific. Most models show significant skill in capturing the positive rainfall anomalies over south Asia and TIO SST warming in ED years. However, many models have failed to represent east Asian rainfall anomalies due to weak Western North Pacific (WNP) anticyclone and its association with El Nino-Southern Oscillation. In case of mid-decay (MD) years, observed rainfall anomalies over south Asia is negative especially in the monsoon trough region and positive over east Asian region. Low-level divergence induced by anomalous WNP anticyclone extending to head Bay of Bengal and Gangetic Plain region in MD years caused low rainfall over south Asia. These features are however not well organized in many CMIP5 models. In no decay (ND) years, the rainfall anomalies over south and east Asia regions are negative in almost all the CMIP5 models, which is consistent with the observations. This study highlights the importance of proper representation of differences in the decaying phase of El Nino and associated teleconnections in CMIP5 models.