A link triggered by tropical Pacific sea surface temperature between the East Asian and North American summer monsoon marginal zone precipitation at various time scales

The ocean plays a crucial role in the global and regional climate. Many regional monsoon climates are interlinked by ocean currents and sea surface temperature (SST). The climate link between the East Asian and North American continent has been proposed and verified by many studies. A widely accepted hypothesis is that the precipitation of the monsoon marginal zone is strongly affected by the monsoon intensity. However, our rigorous test does not support a causal relation between precipitation in the monsoon marginal zone and summer monsoon intensity. Here we present systematic analysis with modern observation and simulation datasets, the Holocene paleoclimatic records and simulations from the East Asian summer monsoon (EASM) and North American summer monsoon (NASM) marginal zone to verify the relation between precipitation in the monsoon marginal zone and the ocean. Our results suggest that precipitation of the EASM and NASM marginal zone is affected by the Pacific SST and the El Niño-Southern Oscillation (ENSO) rather than the monsoon intensity. In particular, the impacts of SST lead to synchronous variations in the EASM and NASM marginal zone. With the global warming and increasing ENSO events, precipitation in the monsoon marginal zone, which locates in semi-arid regions, would reduce, resulting in an expansion of the semi-arid region.