A New Lens on South China Sea Summer Monsoon Onset and Variability

Abstract Monsoon systems are dynamical hubs for teleconnections in regional and global climate. Here, analysis of the vertically‐integrated dry static energy (DSE) budget yields a new metric for tracking the timing and variability of the South China Sea Summer Monsoon (SCSSM). The method unifies previous approaches by linking changes in precipitation and outgoing longwave radiation to initiation of the divergent circulation, thereby establishing an observable proxy for monsoon overturning. The index captures critical transitions, including monsoon onset and organized intraseasonal variability (ISV), and demonstrates robust performance across multiple reanalysis and observational data sets. Composite analysis highlights the key role of ISV, both in SCSSM onset and in the rhythmic pulses that define the ensuing wet season. Our approach further affirms signatures of interdecadal variability in onset timing reported by previous studies. The proposed framework provides a strong foundation for investigating the SCSSM and its role in the regional and global monsoon.