Rainfall–Mixed Layer–SST Feedback Contributing to Atlantic Meridional Mode Development

Abstract A simple air–sea coupled model for wind–evaporation–sea surface temperature (SST), wind-induced turbulence–mixed layer (ML)–SST, and wind–evaporation–ML–SST feedback is extended to unitedly represent the precipitation anomaly associated with moisture convergence ML depth (MLD) due freshwater-induced buoyancy flux. An eigenanalysis reveals presence of yet another accompanying a cross-equatorial SST gradient. The operates as follows: gradient forces wind anomalies blow toward warmer hemisphere, causing low-level (divergence) hence positive (negative) in (cooler) hemisphere. stratifies (destabilizes) near-surface ocean results shallower (deeper) ML, which enhances (reduces) warming by climatological shortwave radiation, thus provides initial anomaly. strength this similar three known feedbacks terms stability. Sensitivity experiments general circulation MIROC6 reveal that precipitation-induced flux accounts up ∼14% Atlantic meridional mode (AMM) amplitude boreal spring through affecting MLD deep tropics, consistent results, supporting existence feedback. In contrast, evaporation-induced contributes only marginally anomalies. budget from confirms sensitivity changes radiation are important generating AMM, previous observational studies. Significance Statement It year-to-year variations sea north–south tropical can affect climate both surrounding remote regions. study, we used theoretical state-of-the-art models investigate process establish its contribution variability. As result, identified previously unknown contributing atmosphere interact enhance variation, forming loop. particular, state were determined be essential. This 14% during spring.