Atmospheric rivers (ARs) are a key driver of heavy precipitation in East Asia. The Pacific-Japan (PJ) pattern, as a dominant mode of circulation variability over the East Asia-western North Pacific region, significantly modulates AR activity. Using the JRA-3Q reanalysis and a global AR database, this study reveals a pronounced interdecadal weakening of the relationship between the PJ pattern and ARs in summer over East Asia after 2007/08. This weakening is primarily manifested in three key regions: near Sakhalin Island, the western North Pacific east of Japan, and southeastern China, and is predominantly attributable to reduced linkage between the PJ pattern and high-category ARs. To investigate the physical mechanisms underlying this interdecadal weakening, two diagnostic approaches are proposed to examine the respective contributions of dynamics and thermodynamics. The equivalent qualitative diagnosis reveal that the weakened PJ-AR relationship is mainly driven by changes in the wind field rather than moisture content. Specifically, the altered spatial configuration of the PJ pattern after 2007/08 disrupts the wind field favorable for AR development. The quantitative diagnosis further confirms that the dynamic process (changes of wind), particularly the zonal component, dominates this interdecadal weakening. These findings highlight the importance of considering interdecadal shifts in large-scale circulation when assessing the relationship between climate variability modes and extreme weather systems, and have important implications for seasonal prediction of high-impact AR events and associated hazards in East Asia.

atmospheric river,Pacific-Japan pattern,interdecadal change,water vapor transport