Single hemisphere air-sea interaction shapes the South Pacific surface warming and wind change

The projected increase in the sea surface temperature (SST) into the 21st century exhibits a robust southeastern minimum (SEM) pattern in the subtropical Pacific. Despite the agreement between observations and climate models, this pattern remains poorly addressed, with gaps in the proposed mechanisms. Here, we discover a novel air-sea interaction responsible for SEM formation, associated with the changes in the South Pacific subtropical anticyclone (SPSA) and seeded by both the direct CO2 effect and poleward expansion of the tropics. A spatially uniform SST increase leads to anomalous southeasterly winds that can cause cooling in the southern SEM region because of a southwestward shift in the SPSA. With direct CO2 forcing and SST pattern change, an SPSA intensification extends these wind patterns further north to cover the entire SEM. During extension, an anomalous anticyclone is generated by the negative SST anomaly and is vertically inclined southwards by tropospheric warming in the subtropics, due to distinct atmospheric dynamics associated with increasing dry stability. This drives evaporative heat loss over the previously cooled ocean and sustains the SEM SST-wind complex, which is enhanced by cloud feedback. Such an interactive loop is manifested as a single hemisphere wind-evaporation-SST feedback, rather than a cross-equatorial process.