Enhanced seasonal cycle of air‒sea latent heat flux in western boundary current regions due to global warming

Western boundary current (WBC) regions play a critical role in air–sea heat exchange, influencing weather patterns and regulating climate. Despite their importance, how the coupled ocean–atmosphere seasonal variability in these regions responds to global warming remains unclear. Using observations (ERA5 and OAFlux) and Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations, we examine long-term trends in the seasonal amplitudes of sea surface temperature (SST) and latent heat flux (LHF) across major WBC systems. Over the past six decades, SST amplitude has significantly decreased, whereas LHF amplitude has increased. This contrast stems from an enhanced seasonal amplitude of air–sea specific humidity difference, driven by a stronger reduction in near-surface air temperature seasonality relative to SST. Future projections suggest that this thermodynamic mechanism will persist over the next four decades, with strong inter-model agreement confirming the robustness of the trend. Unlike previous studies that mainly focused on the climatological modulation of the SST annual cycle by ocean heat advection in WBC regions, our analysis highlights long-term changes in the coupled SST–LHF seasonal coevolution under global warming. These findings reveal that warming climate to some extent alters the seasonal air–sea coupling in WBC regions, with potential consequences for regional climate variability, extreme weather events, and the global surface energy budget.