The Influences of Atlantic Sea Surface Temperature Anomalies on the ENSO-Independent Interannual Variability of East Asian Summer Monsoon Rainfall

Abstract

Abstract As the most dominant tropical climate mode on the interannual time scale, El Niño–Southern Oscillation (ENSO) is suggested to significantly influence the interannual variation of East Asian summer monsoon rainfall (IEASMR). However, the leading mode of IEASMR remains almost untouched when the impacts of preceding ENSO events are linearly removed, suggesting the existence of alternative impact factors and predictability sources of IEASMR. After removing the impact of ENSO, the sea surface temperature anomalies (SSTAs) over both the tropical Atlantic and extratropical North Atlantic are found to be related to IEASMR through atmospheric teleconnections. Positive SSTA over the tropical Atlantic could induce tropical diabatic heating, which triggers an equivalent barotropic Rossby wave train emanating from the Atlantic, going across the Eurasian continent, and ending with a cyclonic anomaly over northeast Asia. The tropical diabatic heating could also induce western North Pacific anomalous anticyclone via tropical routes. The dipole SSTA pattern with cooling in the west and warming in the east over the extratropical North Atlantic induces local circulation anomalies through heat flux exchange, which could further perturb a Rossby wave train with a cyclonic anomaly over northeast Asia, thus modulating IEASMR. Numerical experiments with prescribed atmospheric heating associated with Atlantic SSTAs could realistically reproduce these teleconnections toward IEASMR. By adding the predictability sources of Atlantic SSTAs, the seasonal hindcast skills of IEASMR could be significantly improved over both the tropical western North Pacific and subtropical land regions such as central China and Japan. Significance Statement The purpose of this article is to identify the alternative impact factors of the interannual variation of East Asian summer monsoon rainfall (IEASMR), after removing the impact of ENSO, considering the limited contribution of ENSO to the variances of IEASMR. Here, we find that the Atlantic sea surface temperature anomalies (SSTAs) play a considerable role in driving IEASMR. The impact of ENSO on IEASMR is mainly confined to the tropical western North Pacific, while the Atlantic SSTAs influence rainfall over subtropical East Asia and the tropical western North Pacific through both tropical and extratropical routes. The results unravel the important roles of Atlantic SSTAs in driving ENSO-independent IEASMR, which will have a large implication for the seasonal prediction of East Asian summer climate.