Interdecadal change in the relationship between the western North Pacific subtropical high and the ENSO

The late-summer western North Pacific subtropical high (WNPSH) has been known to exhibit a strong lagged connection with the El Niño Southern Oscillation (ENSO) of preceding winter. We find that this lagged relationship has been substantially weakened in the recent decades and that, instead, the WNPSH-ENSO connection has become pronounced during early summer. The processes that lead to the changes in the connection are examined by comparing those of the past (1982–1995) and those of the recent (2006–2020) decades. In the earlier period, the sea surface temperature (SST) and the atmospheric responses associated with the WNPSH show a strong resemblance to the decaying ENSO for both early and late summer. Local air-sea interaction mainly regulates the early-summer WNPSH, whereas the Kelvin wave response to Indian Ocean warming largely contributes to the intensification of the late-summer WNPSH. The latter is more related to the delayed ENSO effect, and the strengthening of this remote effect may bring a high correlation between the late-summer WNPSH and ENSO. In contrast, during the recent period, the regional Hadley circulation, associated with the contrasting SST anomalies over the maritime continent (MC) and tropical Central Pacific (TCP), plays a role in maintaining the WNPSH. However, the ENSO-induced SST pattern accompanies the WNPSH only during early summer, while the SST anomalies over the MC and TCP in late summer are too weak to influence the variability of the WNPSH.