Northwestwards shift of tropical cyclone genesis position during autumn over the western North Pacific after the late 1990s

Abstract

Previous study has suggested a northwestwards shift of tropical cyclone (TC) genesis position during autumn over the western North Pacific (WNP) after the late 1990s. This study replenishes two mechanisms to explain this inter‐decadal change in the WNP TC genesis position. The first mechanism is related to the mean state change. According to observational analysis and numerical simulations with the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric general circulation model, a La Niña‐type Pacific sea surface temperature (SST) change and the northern Atlantic Ocean warming in the late 1990s cause a dipole pattern of lower‐level circulation change, with cyclone over the northwestern WNP and anticyclone over the southeastern WNP. This pattern is favourable for more TC genesis in the northwestern WNP. The sensitivity experiments show that the contribution from the Pacific Ocean is larger than that from the northern Atlantic Ocean. The second mechanism is related to the change in the intra‐seasonal oscillation intensity, particularly the quasi‐biweekly variation. The activity of intra‐seasonal oscillations over the southeastern WNP shows a decadal decrease around the late 1990s. Meantime, when the intra‐seasonal oscillations with tilted structure move northwestwards, they provide a favourable condition for TC genesis to be located more northwestwards after the late 1990s.

Detecting Interdecadal Change in Western North Pacific Tropical Cyclone Genesis Based on Cluster Analysis Using pHash + Kmeans

“…As revealed by previous studies (Zhang et al, 2017;Zhang et al, 2018;Cao et al, 2020), this intensification of VWS is related to a shift in the Walker circulation induced by enhanced SST warming in the North Atlantic. In the late 1990s, the SST over the Pacific showed a La Niña-like mean state, which could also enhance VWS over the eastern WNP (Hsu et al, 2014;Choi et al, 2015;Hong et al, 2016;Hu et al, 2018;Liu et al, 2019;Cao et al, 2020). Huangfu et al (2018) pointed out that the negative RV anomalies and positive VWS anomalies are possibly associated with downward motion anomalies over the central Pacific.…”

“…Changing dynamic conditions, especially the intensification of VWS over the southern and southeastern WNP, are demonstrated to be the significant modulator for the sudden decrease in eastern WNP TCs (Liu and Chan, 2013;Choi et al, 2015). As revealed by previous studies (Zhang et al, 2017;Zhang et al, 2018;Cao et al, 2020), this intensification of VWS is related to a shift in the Walker circulation induced by enhanced SST warming in the North Atlantic. In the late 1990s, the SST over the Pacific showed a La Niña-like mean state, which could also enhance VWS over the eastern WNP (Hsu et al, 2014;Choi et al, 2015;Hong et al, 2016;Hu et al, 2018;Liu et al, 2019;Cao et al, 2020).…”

“…Hu et al (2018) analysed the change in WNP TC genesis longitude and latitude separately and found that the change in mean longitude is closely linked to ENSO diversity, and the change in mean latitude is dominated by a warming WNP, which is induced by an interdecadal tendency of central Pacific La Niña-like events. Cao et al (2020) indicated that a La Niña event and warming over the North Atlantic occurred in the 1990s and caused a northwestward shift in autumn TCs over the WNP. Additionally, the Western North Pacific Subtropical High (WNPSH) (Kim and Seo, 2016;Wu Q. et al, 2020), the East Asia winter monsoon (Choi et al, 2017), the monsoon trough (MT) (Huangfu et al, 2017a;Huangfu et al, 2017b), and the tropical upper tropospheric trough (Wu et al, 2015) are also essential in modulating interdecadal change in WNP TCs.…”

Distinct Interdecadal Change Contrasts Between Summer and Autumn in Latitude‐Longitude Covariability of Northwest Pacific Typhoon Genesis Locations

“…Studies (e.g., Cao et al., 2020; Hu et al., 2018; Huangfu et al., 2017), however, noted that observed WNP TC activities during autumn were significantly different from those in summer, mainly due to distinct seasonal climate backgrounds (Choi et al., 2019). For example, over 80% of the WNP TCs form within the western Pacific monsoon trough (WPMT) in all calendar months except during the peak summer (July–August; Molinari & Vollaro, 2013).…”

Interdecadal Changes of Characteristics of Tropical Cyclone Rapid Intensification Over Western North Pacific

“…The WNP warm pool associated with the monsoon trough were also key factors to modulate TC tracks and TC genesis [21]- [23]. Meanwhile, some researches reported a trend of poleward TC genesis and poleward migration of TC lifetime maximum intensity, which further increase the hazard exposure of coastal cities outside the tropics [24]- [27]. A warming climate was also considered to have caused the global averaged intensity of TCs to shift towards stronger storms [28]- [30].…”