Inter‐Basin Interaction Between Variability in the South Atlantic Ocean and the El Niño/Southern Oscillation.

Oceanic variability that interacts with the El Niño/Southern Oscillation (ENSO) has been well identified in most ocean basins; however, the effect of variability over the South Atlantic (SA) on the ENSO is unknown. This study demonstrates that dominant mode of subtropical SA sea surface temperature (SST) variability during the boreal winter, referred to as the South Atlantic Subtropical Dipole (SASD), contributes to occurrence of an El Niño a year later. During a positive SASD, low‐tropospheric anticyclonic circulation anomalies over the mid‐latitude SA reduce convective activities over southeastern South America. The low‐tropospheric divergence anomalies associated with the reduced convection attenuate the occurrence of South American Low‐Level Jet, and moisture supply is directed along the South Atlantic Convergence Zone (SACZ). The increased precipitation over the SACZ leads to an anomalous surface easterly that lowers the SST over the equatorial Atlantic and eventually modulates the zonal Walker circulation, thereby favoring El Niño development. Plain Language Summary: Variability in sea surface temperature occurs over various ocean basins outside the Pacific; these variations, though induced by the El Niño/Southern Oscillation (ENSO), subsequently promote a phase transition of ENSO by feeding back to it during the subsequent seasons. However, the feedback mechanism underlying the effect of climate variability of the South Atlantic (SA) on ENSO has not been fully studied. This study is the first to demonstrate interaction between ENSO and SA climate variability: El Niño induces variability in SA climate, resulting in a phase transition from El Niño to La Niña, and vice versa. For this feedback loop to occur, the climate signal related to the South Atlantic Subtropical Dipole must first be conveyed to the equatorial Atlantic by a modulation in the convective activity over the land area of the South Atlantic Convergence Zone. Key Points: The South Atlantic Subtropical Dipole (SASD) can initiate the El Niño/Southern Oscillation (ENSO) with a 1‐year time lagThe ENSO and South Atlantic climate variability exhibit two‐way interactionsThe sea surface temperature signal related to the SASD modulates precipitation variability along the South Atlantic Convergence Zone [ABSTRACT FROM AUTHOR]