Interdecadal changes of the ENSO-induced summertime anomalous western North Pacific anticyclone

Abstract

El Niño–Southern Oscillation (ENSO) events which usually mature during winter can have significant impacts on subsequent summertime western North Pacific anticyclone (WNPAC) and associated East Asian rainfall. Such delayed impacts are known to undergo interdecadal changes, but a systematic investigation on the characteristics of these interdecadal changes and underlying mechanisms remains lacking. Using empirical orthogonal function (EOF) analysis on the 21-yr running regressions of subsequent summertime 850 hPa wind anomalies over the western North Pacific upon wintertime ENSO index for 1950–2024, we find two dominant modes of interdecadal changes in ENSO-induced summertime anomalous WNPAC. The first mode reflects interdecadal changes in intensity of the anomalous WNPAC which are linked to changes in ENSO-induced summertime sea surface temperature (SST) anomalies in the tropical Indian Ocean (TIO) through the TIO capacitor effect. The second mode represents interdecadal zonal displacements of the anomalous WNPAC which are associated with changes in ENSO-induced summertime SST anomalies around the Maritime Continent. After the 1990s, El Niño events tend to cause stronger summertime warm SST anomalies in the region which intensify local convection and Hadley cell, shifting the anomalous WNPAC westward to the South China Sea. Linear baroclinic model experiments support these results and indicate that the identified interdecadal changes can be largely explained by atmospheric responses to changes in ENSO-related tropical diabatic heating anomalies. Our results suggest that interdecadal changes in ENSO-induced summertime anomalous WNPAC arise from two distinct tropical SST teleconnection pathways, providing new insights into ENSO impacts under a changing climate.