Enhanced interannual variability of summer synoptic-scale disturbances over the western North Pacific since the late 1980s.

This study reveals a remarkable interdecadal intensification in the interannual variability of summer synoptic-scale disturbances (SSDs) over the western North Pacific (WNP) since the late 1980s. This intensification can be explained by the remarkable difference in circulation anomalies associated with the SSD intensity variability during 1959–1987 (P1) and 1988–2022 (P2). That is, the lower-tropospheric cyclonic circulation anomalies are more significant during P2 than P1. Accordingly, the meridional shear of zonal winds over the WNP is significantly stronger in P2, and thus favors the enhancement of SSD intensity through the kinetic energy conversion from the mean flow to SSDs. Further analysis suggests that the SSD intensity variation is significantly related to the sea surface temperature (SST) anomalies in the equatorial central Pacific and maritime continent in P2, which can induce the cyclonic or anticyclonic circulation anomalies over the WNP, but the SST anomalies are vague in P1. Finally, the more pronounced influence of tropical SST anomalies on circulations and SSDs over the WNP is attributed to the much warmer SSTs over the maritime continent in P2, which intensifies the responses of atmospheric circulations to SST anomalies. [ABSTRACT FROM AUTHOR]