Keywords:trans-basin interaction, seasonal prediction, monsoon, ENSO
The Asian summer monsoon interacts with the tropical oceans through various processes. Relations between the El Niño–Southern Oscillation (ENSO) in the equatorial Pacific and the Asian summer monsoon has been a major topic for the Asian monsoon study. Prior studies found that the association between the seasonal prediction skill and reproducibility of ENSO–monsoon relationship in climate models. However, its complete mechanisms including its pathways, decadal modulations and statistical robustness, are still unclear. Recently, a broader concept of the trans-basin interactions across global tropical oceans including the Atlantic has been put forward by Cai et al (2019). Based on the recent understanding, we recognize that the ENSO–monsoon relationship requires reconsideration in light of the trans-basin interactions among the tropical Pacific, Indian Ocean and Atlantic. The present study analyzes ensemble hindcast experiments with the latest seasonal prediction system at the Japan Meteorological Agency, JMA/MRI-CPS2, to investigate the ENSO–monsoon relationship and seasonal predictability through the trans-basin interactions. The ensemble simulations initialized with observed conditions provide us with another tool, in addition to historical observations and pacemaker experiments, to examine the trans-basin interaction processes and resultant predictability. The model reproduces the trans-basin interactions generally well. Results present marked variability of the Indo-western Pacific Ocean Capacitor (IPOC) mode and its pervasive influence over the Asian monsoon, giving much longer predictability than previously thought. The model captures the multiple interactions between the interannual variability in the tropical Indian Ocean, Pacific and Atlantic. A better representation of the interannual trans-basin interaction is the key to success of the extended long-range climate prediction of the Asian summer monsoon.