Impact of Spring Sea Surface Temperature Anomalies Over the South Tropical Atlantic on the Western North Pacific Anticyclone in June

ABSTRACT

The western North Pacific anticyclone (WNPAC) is a key circulation system of the East Asian summer monsoon (EASM) and a comprehensive understanding of its variability mechanisms is crucial for improving climate prediction over East Asia. Based on observational and reanalysis data from 1979 to 2020, this study investigates the influences of the preceding winter El Niño‐Southern Oscillation (ENSO) and March–April three‐year high‐pass filtered south tropical Atlantic (STA) sea surface temperature anomalies (SSTA) on the June–July WNPAC. The results indicate a month‐to‐month variation in ENSO impacts that the preceding winter El Niño significantly intensifies the WNPAC in July, whereas its impact on the June WNPAC is relatively weak. In contrast, the March–April three‐year high‐pass filtered STA SSTA exert a significant influence on the June WNPAC, which is largely independent of ENSO. The STA SST warming enhances convection over the tropical Atlantic (TA), triggering a Gill‐type atmospheric response and inducing eastward‐propagating equatorial Kelvin waves toward the western Pacific. The Kelvin waves generate off‐equatorial Ekman divergence, thereby favouring the intensification of the June WNPAC. The enhanced TA convection can also modulate the equatorial Walker circulation, characterised by anomalous ascending motion over the TA, subsidence over the central Pacific and ascending motion over the Maritime Continent. Consequently, anomalous subsidence over the western North Pacific is induced via a local Hadley circulation, which is conducive to the strengthening of the June WNPAC. Therefore, March–April three‐year high‐pass filtered STA SSTA can enhance the June WNPAC through the combined effects of eastward‐propagating Kelvin waves and adjustments in the Walker circulation. Based on the physical processes, a prediction model incorporating the STA SSTA is developed, which demonstrates a significant improvement in prediction skill for the June WNPAC.