Increasing activity of tropical cyclones in East Asia during the mature boreal autumn linked to long-term climate variability

Il-Ju Moon,Joseph Basconcillo

doi:10.1038/s41612-021-00222-6

Il-Ju Moon, Joseph Basconcillo

Open Access

https://doi.org/10.1038/s41612-021-00222-6

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Abstract

In recent years, the East Asian (EA) region experienced escalated cost of damages associated with tropical cyclones (TC) during the mature boreal autumn (i.e., September−October). Questions arise whether such increased TC-associated cost of damages are indicative of increasing activity of TCs in EA, particularly during the mature boreal autumn. Here we show evidence of significantly increasing activity of TCs in EA from 1981 to 2019 that is mainly accompanied by an abrupt regime shift in TC passage frequency since 1998. Such trend and shift are robustly linked to the shift of the Pacific Decadal Oscillation (PDO) to its negative phase in the mid-1990s. Characterized by warm sea surface temperature anomalies in the subtropical North Pacific, a negative PDO phase is related to the weakening of the East Asian subtropical jetstream and the westward displacement of the WNP subtropical high, which initiates a favorable steering environment for increased TC passages into the EA region. Contrasting environmental patterns are associated in a positive PDO phase. Considering the prominence of EA in the global economy, our paper contributes additional insights on long-term tropical cyclone risk reduction and management in the region.

Highlights

In a year, there are about 25 tropical cyclones (TCs) that develop in the Western North Pacific (WNP) where 12 of the said number normally pass through East Asia (EA) (Fig. 1a, b)
These imply that the recent increase in TC activity in EA and the associated cost of damages is mainly due to the increased TC activity in SO, which is yet another reason why seasonal scaling is a considerable concern in TC variability studies
We extended our analysis of TC passage frequency to cover the period 1951−2019 and results show that the significant correlation of Pacific Decadal Oscillation (PDO) and extended TC passage frequency persists (r = −0.40, p = 0.001), which suggests that our findings remain applicable even in an extended temporal coverage

Summary

Introduction

There are about 25 tropical cyclones (TCs) that develop in the Western North Pacific (WNP) where 12 of the said number normally pass through East Asia (EA) (Fig. 1a, b) (see “Methods” on the definition of regional domains). The entire TC season in EA runs from June to October (JJASO), peaks in the boreal summer (i.e., June−August, JJA), and dips in the boreal autumn (i.e., September−November, SON). About 62% of the TCs that pass through EA happen in JJA while the remaining 38% occur in SON. 93% of the total TC passages in EA during SON occur during the mature boreal autumn (September−October, SO) while only 7% or less than one TC passage is normally observed during the late boreal autumn (i.e., November). We question whether such detected trend in TC-associated cost of damages is indicative of increasing activity of TCs in the EA region, during the mature boreal autumn, and where such increasing signal can be attributed

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Conclusion