Impact of differences in the decaying phase of El Niño on South and East Asia summer monsoon in CMIP5 models

Abstract

The present study examined the ability of Coupled Model Intercomparison Project phase 5 (CMIP5) models in representing the differences in decaying phases of El Niño and their impact on south Asia and east Asia monsoon during June and July (JJ), the early summer monsoon months. El Niño decay is classified into three categories, based on the timing of decay with respect to the summer season after the peak phase of El Niño. Analysis suggests that many CMIP5 models are able to capture the differences in the decaying phase of El Niño. 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 Niña 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 Niño‐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 Niño and associated teleconnections in CMIP5 models.

Weakening Relationship between East Asian Summer Monsoon and Asian-Pacific Oscillation after 1990s

“…For example, the relationship between ENSO and precipitation over northeastern China (western Russia surface temperature) after the mid-1990s (1980s) was strengthened during summer, which means that changes in climate elements in one place are not always affected by the same climate phenomena. Furthermore, some studies have also shown the significant impact of the decaying phase of El Niño on the Asian summer monsoon using CMIP5, indicating that numerical modeling is a valuable way to explore the instability [28]. For these reasons, studying the unstable relationship between two weather systems will provide new ideas for understanding the physical mechanisms existing under the different climate conditions in the future.…”

Influence of El Niño decaying pace on low latitude tropical cyclogenesis over the western North Pacific

“…The difference of atmospheric environment between ST and RT El Niño events not only exists in the tropical region, but also in the subtropical and mid‐latitude. One of the obvious characteristics is the enhanced anticyclone anomalies over the WNP subtropical region during the RT El Niño events (Srinivas et al, 2019; Zhou et al, 2019). The anomalous anticyclone is weak in ST events (Figure 6a), while it is strengthened in RT El Niño events due to the colder SST anomalies in the tropical central‐eastern Pacific (Figure 6b).…”