Interannual Impact of the South Indian Ocean Subantarctic Front on Storm Track and the Mean‐Flow

Abstract This study examines how the Subantarctic Front (SAF) in the South Indian Ocean (SIO) modulates storm track activity and the mean atmospheric circulation on interannual timescales, and elucidates the associated energy‐conversion pathways underlying midlatitude air–sea interactions. Based on 45 years (1979–2023) of ERA5 reanalysis, the SAF is identified from the meridional gradient of sea surface temperature (SST), and indices representing its intensity and latitudinal position are constructed. Lag‐regression analysis based on these new indices shows that anomalies in SAF intensity and position modulate lower‐tropospheric baroclinicity, thereby reorganizing the storm track activity. Diagnoses from the EAPE budget reveal that the dominant energy pathway follows the mean available potential energy (MAPE) to eddy available potential energy (EAPE) to eddy kinetic energy (EKE) sequence, highlighting the importance of baroclinic processes. In the EKE budget, barotropic conversion (from mean kinetic energy (MKE) to EKE) is weaker than baroclinic conversions in the mid‐to‐lower troposphere, but shows its clearest signature in the upper troposphere, consistent with the prominent upper‐level dynamical contribution diagnosed from the geopotential‐tendency framework. The accompanying equivalent‐barotropic mean‐flow adjustment is diagnosed to receive a leading contribution from the eddy vorticity flux forcing. These findings highlight the critical role of frontal variability in shaping the Southern Hemisphere storm track and large‐scale atmospheric circulation, providing new insight into midlatitude atmosphere–ocean coupling.