Abstract
Previous studies have noted an abrupt decrease in western North Pacific (WNP) tropical cyclone (TC) genesis frequency and a westward shift in genesis location since the late 1990s. The recent application of cluster analysis in TC research shows the effect of detecting the contribution of the Western North Pacific Subtropical High (WNPSH) and the interdecadal Pacific oscillation (IPO) on interdecadal change in WNP TCs. In this work, we also apply a clustering algorithm called pHash + Kmeans to group WNP TCs into three classes based on their genesis environmental conditions. The clustering results show that an abrupt decrease after 1998 is related primarily to a decrease in the dominant class (Class3, located mainly in the southern and eastern WNP), and an increase after 2010 occurs because of a new dominant class (Class1, located mainly in the northwestern WNP), which indicates that the WNP environment suppresses Class3 genesis after 1998 and enhances Class1 genesis after 2010. Three periods (P1: 1979–1997, P2: 1998–2010, and P3: 2011–2020) and three regions (SCS: 100°E-120°E, EQ-30°N; WNP1: 120°E-140°E, EQ-30°N; and WNP2: 140°E-160°W, EQ-30°N) are divided to further confirm the above findings. In P1, high (low) mid-level relative humidity (RH), intense (weak) low-level vorticity, and weak (strong) vertical wind shear (VWS) are distributed in WNP2 (SCS and WNP1), indicating suitable environmental conditions for TC genesis in WNP2 but unsuitable conditions in SCS and WNP1. This situation is the opposite in P2, leading to a decrease in genesis frequency and a westward shift in genesis location. In P3, strong low-pressure vorticity and thermodynamic conditions occur in SCS and WNP1, contributing to an increase in TC genesis frequency.
Highlights
In recent years, interdecadal variation in tropical cyclone (TC) activity over the western North Pacific (WNP) has been an area of active research
Many works have discussed how WNP TC activity has changed in recent decades and the possible reasons
Previous studies have widely reported that an abrupt decrease in TC genesis and a northwestward shift in the TC-active region occurred around the late 1990s (e.g., Chan, 2008; Tu et al., 2011; Liu and Chan, 2013; He et al., 2015; Hong et al., 2016; Huangfu et al., 2017a; Huangfu et al., 2017b)
Summary
Interdecadal variation in tropical cyclone (TC) activity over the western North Pacific (WNP) has been an area of active research. Several studies (Tu et al, 2011; Liu and Chan, 2013; Zhao et al, 2014; Choi et al, 2015; Liu et al, 2019) have indicated that the inactive period of WNP TC activity is closely related to strengthening of vertical wind shear (VWS) over the eastern tropical WNP, which plays a vital role Following these conclusions, Zhang et al (2017) and Zhang et al (2018) noted that the enhancement of warming over the North Atlantic influences interdecadal change in WNP TC frequency by intensifying VWS in the southeastern WNP through the Walker circulation.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
