Seasonality of the South Pacific Meridional Mode: Role of Oceanic Meridional Advection Feedback Beyond Thermodynamics Dominance

Abstract The South Pacific Meridional Mode (SPMM), a dominant air‐sea coupling mode in the subtropical southeastern Pacific, serves as a precursor to equatorial Pacific variability. Its seasonality, however, shows an out‐of‐phase relation between sea surface temperature (SST) (peaking in December–February, DJF) and wind (peaking in June–August, JJA) indices that remain unclear. Through a mixed‐layer heat budget analysis, we reveal that thermodynamical wind‐evaporation‐SST feedback dominates SPMM‐SST growth, with its efficiency controlled by the seasonal cycle of mixed‐layer depth, dominating SPMM seasonality. Dynamical processes suppress SPMM‐SST anomalies, with meridional advection acting as the dominant damping mechanism in both JJA and DJF, and being particularly strong in JJA. Stronger meridional advection damping in JJA enlarges the DJF peak of SPMM‐SST, indicating a role beyond thermodynamics. Further investigation reveals that the meridional advection arises largely from wind stress‐driven Ekman transport. These findings highlight the importance of meridional advection process in shaping SPMM seasonality, offering insights for improving SPMM‐related climate predictability.