Enhanced influence of tropical Atlantic Sea surface temperature anomalies on east Asian summer monsoon since the late 1970s

Using ERA5 atmospheric reanalysis data and HadISST sea surface temperature (SST) data from 1940 to 2022, the interdecadal fluctuations in the interannual linkage between the tropical Atlantic (TA) SST anomalies (SSTAs) and the East Asian summer monsoon (EASM) are investigated. The interannual relationship between the TA SSTAs and the EASM experienced a notable enhancement after the late 1970s. That is, during the period from 1940 to 1975, no significant interannual relationship was detected between TA SSTAs and EASM. However, from 1978 to 2022, the connections between them became tighter, exhibiting a strong positive correlation. This can be attributed to the warming in the TA during the latter period, which induced a latitudinally elongated low-level cyclonic circulation anomaly extending from the tropical Northeast Pacific to the tropical northern Atlantic due to a Rossby wave response. The anomalous northerly flow to the west of this cyclonic anomaly transported cold air from mid-latitudes into the tropical central Pacific, which may trigger La Nina events in the coming months. Meanwhile, the TA warming generated an anticyclonic circulation anomaly over the Northwest Pacific, resulting in the strengthening of the EASM during 1978-2022. And vice versa. However, such an association was absent during the former period. This interdecadal change in the interannual relationship of TA SSTAs with EASM are associated with the TA warming since the late 1970s. The significant warming trend in TA, along with the increased interannual variations amplitude of its SSTAs,enhanced its remote influence on the EASM.