The Influence of ENSO on Decadal Variations in the Relationship between the East Asian and Western North Pacific Summer Monsoons

Abstract

A recent study suggested that the relationship between the East Asian summer monsoon (EASM) and the western North Pacific summer monsoon (WNPSM) experienced a decadal change around 1993?94. Based on a longer-term integration of a hybrid coupled model, the present study investigates decadal variations in the relationship between the EASM and the WNPSM. Apparent decadal variations in the above relationship have been identified in the model simulation. The authors have analyzed the spatial pattern and variability during strong and weak EASM?WNPSM correlation periods. The purpose of this study is to understand potential reasons for decadal variations in the relationship between the two submonsoons. It is found that the precipitation variability associated with the WNPSM (ENSO) is enhanced over the East Asia and western North Pacific regions during periods when the EASM?WNPSM relationship is strong (weak). The large variability in precipitation associated with the WNPSM during strong periods strengthens the Pacific?Japan-like atmospheric teleconnection from the tropical western Pacific. In contrast, the Pacific?Japan-like pattern is not significant during weak periods. On the other hand, the large ENSO amplitude during weak periods results in an enhanced precipitation variability associated with ENSO. The results suggest that ENSO can destructively interfere with the relationship between the EASM and the WNPSM.