Influence of Synoptic‐Scale Waves on the Interdecadal Change in Tropical Cyclone Activity Over the Western North Pacific in the Early 2010s.

In this study, we investigated the interdecadal change in tropical cyclone (TC) activity over the western North Pacific (WNP) in the early 2010s. At the western boundary of the WNP, the interdecadal change in TC activity exhibited a meridional tripole pattern. In contrast to the reduced activity over the northern South China Sea (SCS) and Taiwan, TC activity increased over the southern SCS and to the north of Shanghai after the early 2010s. Herein, we focused on the northern WNP. Over the last decade, frequent TC occurrences have affected East China, Korea and Japan. In this work, we examined the influence of synoptic‐scale waves (SSWs) on the interdecadal change in TC activity. During the 2011–2021 period, SSWs tended to propagate northward, resulting in more TC tracks affecting the northern WNP and surrounding countries. In contrast, the westward‐propagating SSWs before the early 2010s were more likely to favor westward‐moving TCs. Plain Language Summary: Previous studies has revealed that tropical cyclone (TC) activity increased over the southern South China Sea (SCS) and decreased over the northern SCS and Taiwan since the early 2010s. In warming climates, TC activity shows significant poleward extension. Thus, in this study, we broadened the study area to 50°N and focused on the TC activity over the northern western North Pacific (WNP), where most populous region went through increased TC occurrences in the recent decade (2011–2021). The interdecadal change in TC activity exhibited a meridional tripole pattern after the early 2010s over the WNP. Considering tropical synoptic‐scale waves (SSWs) can reflect the general atmospheric inner process, this study investigated the role of SSWs in the interdecadal change in TC activity in the 2010s. During the 2011–2021 period, SSWs tended to propagate northward, resulting in more TC tracks affecting the northern WNP and surrounding countries. In contrast, the westward‐propagating SSWs before the early 2010s were more likely to favor westward‐moving TCs. The synoptic‐scale processes can explain most of the interdecadal changes in the relative vorticity over the northern WNP, showing the critical role of the SSWs on the interdecadal change of TC activity over the WNP in the early 2010s. Key Points: The interdecadal change in tropical cyclone (TC) activity exhibited a meridional tripole pattern after the early 2010s over the western North PacificOver the last decade (2011–2021), frequent TC occurrences have affected East China, Korea and JapanDuring the 2011–2021 period, tropical synoptic‐scale waves tended to propagate northward, which led to more northward‐moving TC tracks [ABSTRACT FROM AUTHOR]