The Controlling of the Subtropical High Leading Modes on the Spatial Pattern of Tropical Cyclone Genesis in the Western North Pacific and Tracks Landing on the East Coast of China

Tingting Fan,Yuxing Yang,Shibin Xu

doi:10.3390/atmos13010079

Abstract

As a prime circulation system, the western Pacific subtropical high (WPSH) significantly impacts tropical cyclone (TC) activities over the western North Pacific (WNP), especially TCs landing on the east coast of China; however, the associated mechanism is not firmly established. This study investigates the underlying dynamic impact of the first two empirical orthogonal function (EOF) modes of the WPSH on the interannual variability in the genesis and number of TCs landing over the WNP. The results show that these two dominant modes control the WNP TC activity over different subregions via different environmental factors. The first mode (EOF1) affects the TC genesis number over region I (105°–128° E, 5°–30° N) (r = −0.49) and region II (130°–175° E, 17°–30° N) (r = −0.5) and controls the TCs landing on the east coast of China, while the second mode (EOF2) affects the TC genesis number over region III (128°–175° E, 5°–17° N) (r = −0.69). The EOF1 mode, a southwest-northeast-oriented enhanced pattern, causes the WPSH to expand (retreat) along the southwest-northeast direction, which makes both mid-low-level relative humidity and low-level vorticity unfavorable (favorable) for TC genesis in region I and region II and steers fewer (more) TC tracks to land on the coast of China. The EOF2 mode features a strengthened WPSH over the southeast quarter of the WNP region. The active (inactive) phases of this mode control the low-level vorticity and vertical wind shear in region III, which lead to less (more) TC genesis over this region. The prediction equations combining the two modes of the WPSH for the total number of TCs and TCs that make landfall show high correlation coefficients. Our findings verify the high prediction skill of the WPSH on WNP TC activities, provide a new way to predict TCs that will make landfall on the east coast of China, and help to improve the future projection of WNP TC activity.

Highlights

The results show that EOF1 of the western Pacific subtropical high (WPSH) contributes 33.6% to the total variance and exhibits a positive anomaly over the entire Indo-Pacific warm pool region with the maximum center north of 20◦ N, while EOF2 contributes 26.1% to the total variance and exhibits a dipole pattern between the Indian Ocean and the Pacific Ocean
The landing rate for EOF2 exhibits a strong negative correlation (r = −0.56) with the mean genesis longitude of tropical cyclone (TC) in region III, implying a more westward shift in the mean genesis location with a higher landing rate of TCs reaching the east coast of China, which is consistent with the composite map (Figure 6b) discussed above
Tokyo-Typhoon Center for the period of 1979–2020, with a particular focus on the TCs landing on the Chinese coast

Summary

Introduction

Xiang et al [38] showed that the two leading modes of the WPSH have a close relationship with the total TC days over the subtropical WNP (r = −0.81). These modes can shift TC formations southeastward/northwestward (EOF1) and control the total TC genesis number (EOF2) in the WNP [14,29]. Wang and Wang [29] introduced a new statistical model to make a seasonal prediction of the genesis number and storm days of the TCs over the WNP using these two modes. A statistical model is used to predict total and landing TC number and TC days

Data and Method

Dominant Modes of the WPSH and Associations with TC Activity

The Steering Flows Associated with the Two Leading Modes of the WPSH Affect

Reproduction and Forecasting of Landing TCs by the Two Leading WPSH Modes

Findings

Summary and Discussion