Factors Controlling Tropical Cyclone Intensification Over the Marginal Seas of China

Xiaomeng Li,Yuqing Wang,Jing Xu,Ruifen Zhan

doi:10.3389/feart.2021.795186

Abstract

Tropical cyclone (TC) intensification over marginal seas, especially rapid intensification (RI), often poses great threat to lives and properties in coastal regions and is subject to large forecast errors. It is thus important to understand the characteristics of TC intensification and the involved key factors affecting TC intensification over marginal seas. In this study, the 6-hourly TC best-track data from Shanghai Typhoon Institute of China Meteorological Administration, ERA-Interim reanalysis data, and TRMM satellite rainfall products are used to analyze and compare the climatological characteristics and key factors of different intensification stratifications over the marginal seas of China (MSC) and the western North Pacific (WNP) during 1980–2018. The statistical results show that TC intensification over the MSC is more likely to occur when TCs experience relatively large intensities, weak vertical wind shear, small translation perpendicular to the coastline, relatively high fullness, strong upper-level divergence, low-level relative vorticity, and high inner-core precipitation rate. The box difference index method is used to quantify the relative contributions of these factors to TC RI. Results show that the initial (relative) intensity contributes the most to TC RI over both the MSC and the WNP. The inner-core precipitation rate and translation perpendicular to the coastline are of second importance to TC RI over the MSC, while both vertical wind shear and TC fullness are crucial to TC RI over the WNP. These findings may help understand TC activity over the MSC and provide a basis for improving intensity prediction of TCs in the MSC.

Highlights

Tropical cyclone (TC) intensification in marginal seas, especially rapid intensification (RI), is a critical and difficult problem in the operational forecast of TCs
Compared with weak TCs with Vmax between 17.2 and 32.6 m s−1, intense TCs with intensity greater than 32.6 m s−1 have relatively lower frequency of intensification cases for intensifying rate smaller than 12 m s−1 (12 h)−1, but a larger weakening rate. This suggests that a TC with weak intensity is more likely to experience a relatively lower intensification rate, while a TC with high intensity increases the potential for weakening, consistent with previous studies (Shu et al, 2012; Xu and Wang, 2018; Fei et al, 2020)
Over the western North Pacific (WNP) (Figures 3A, C), the TC intensification and RI mostly occurred in July-October, with the peak for intensification cases in August and for RI cases in September, respectively (Figure 3A)

Summary

Introduction

Tropical cyclone (TC) intensification in marginal seas, especially rapid intensification (RI), is a critical and difficult problem in the operational forecast of TCs. Supertyphoon Rammasun (1409) experienced two unexpectedly RI periods in the near-coastal regions of the central Philippines and the eastern China, respectively, causing at least 206 deaths and more than $6.5 billion in economic loss. It is, important to understand the characteristics of TC intensification and the key factors affecting TC intensification in marginal seas. Sea surface temperature (SST) is a key in determining the surface enthalpy flux from the underlying ocean to the atmosphere, providing the energy for TC intensification and maintenance (Gao et al, 2016). In addition to SST, the upper ocean heat content (TCHP), the sea temperature averaged in a depth of 0–100 m, the depth of ocean temperature of 26°C isotherm, and the TCinduced ocean cooling may affect TC intensification and maintenance (Lin et al, 2008; Wada, 2015; Miyamoto et al, 2017; Fudeyasu et al, 2018)

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