资源环境科技发展态势分析平台

Oceanic variabilities that interact with the El Niño/Southern Oscillation (ENSO) have 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 variability in the dominant subtropical SA SST during the boreal winter, referred to as the South Atlantic Subtropical Dipole (SASD), contributes to the occurrence of an El Niño after a year. 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 the 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 the El Niño development.