ENSO-South China Sea Summer Monsoon Interaction Modulated by the Atlantic Multidecadal Oscillation

The interaction between El Nino-Southern Oscillation (ENSO) and the South China Sea summer monsoon (SCSSM) modulated by the Atlantic multidecadal oscillation (AMO) is investigated in this study. On one hand, the influence of the decaying phase of ENSO on the SCSSM is stronger during negative phases of the AMO than during positive phases. During negative phases of the AMO, El Nino (La Nina) with relatively larger variability leads to a western North Pacific anomalous anticyclone (cyclone) that persists from the ENSO mature winter to the ENSO decaying summer, weakening (strengthening) the SCSSM; on the contrary, during positive phases of the AMO, ENSO with relatively weaker variability cannot influence the SCSSM significantly. On the other hand, the SCSSM has a closer relationship with the subsequent ENSO development during positive phases of the AMO than during negative phases. During positive phases of the AMO, atmospheric teleconnections induced by the warmer North Atlantic result in low pressure and cyclonic anomalies over the South China Sea. Consequently, the stronger than normal SCSSM is accompanied by significant westerly wind anomalies over the western tropical Pacific, which favor the development of El Nino events. However, during negative phases of the AMO, the SCSSM-related westerly wind anomalies are rather weak, having a nonsignificant influence on El Nino development. The results are also demonstrated in model simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5).