Observed Seasonality of the South Pacific Meridional Mode: The Role of Oceanic Meridional Advective Feedback

The South Pacific Meridional Mode (SPMM) is a dominant air-sea coupling mode in the subtropical southeastern Pacific and a key precursor of equatorial Pacific variability. However, the mechanisms responsible for its distinct seasonality remain inadequately understood. Using reanalysis datasets, we conducted an ocean mixed-layer heat budget analysis to quantify the contributions of dynamic and thermodynamic processes to SPMM seasonality. Results show that while net surface heat flux dominates the sea surface temperature warming associated with SPMM in both boreal summer and winter, this warming is significantly dampened by meridional advective feedback in summer (approximately 47%) but weakly in winter (approximately 14%). Further analysis reveals that the meridional advective feedback is primarily attributed to Ekman heat transport driven by anomalous zonal wind stress. These findings underscore the critical role of meridional advective feedback in modulating SPMM seasonality and provide valuable insights for improving climate predictions related to the SPMM.