快速增強與緩慢增強熱帶氣旋之比較研究： 觀測分析與數值模擬

Abstract

本研究以2012至2024年間西北太平洋熱帶氣旋為研究對象，根據未來24小時最大持續風速變化，將個案區分為快速增強（Rapid Intensification , RI）與緩慢增強（Slow Intensification, SI）兩組，利用GPM SSMIS降水剖面反演產品之冰水路徑（Ice Water Path, IWP）與雨水路徑（Rain Water Path, RWP），結合全球紅外亮溫 (T_B)資料，探討熱帶氣旋於增強前後內核微物理結構特徵之演變。合成分析結果顯示，RI 與 SI 個案在增強前皆呈現受垂直風切影響之不對稱結構，高 IWP、RWP 及低亮溫區主要集中於下風切象限。然而，自增強開始後，RI 個案之高 IWP 與高 RWP 區域逐漸由下風切象限向上風切象限擴展，使內核熱力結構趨於軸對稱化；相較之下，SI 個案之高值區則始終侷限於下風切半圓。軸對稱率分析進一步指出，RI 個案於各演變階段皆具有較高之軸對稱性，且兩組差異隨時間逐漸擴大。此外，本研究利用 WRF 模式模擬快速增強個案蘇力基（2021）與緩慢增強個案白鹿（2019）。模擬結果指出，蘇力基在快速增強過程中，其潛熱釋放、高 IWP 與高 RWP 結構逐漸向上風切象限發展，形成環繞核心之深厚加熱結構；反之，白鹿之潛熱釋放與降水結構則長期侷限於下風切區域。進一步的降雨類型分析與水氣輸送機制顯示，蘇力基於快速增強後期，其深對流及層狀降水面積在上風切區域皆顯著增加，透過深對流所伴隨之強烈上升運動及水平平流作用，將低層水氣持續輸送至中高層與上風切區域，使上風切半圓逐漸增濕並有利於深對流發展，進而建立更趨軸對稱之潛熱加熱結構，使蘇利基擁有較強的增強速度。相較之下，緩慢增強個案之水平和垂直水氣輸送皆較弱，使上風切區域長期維持乾燥，不利於深對流與潛熱加熱之發展，強度增強相對較平緩。

This study investigates tropical cyclones over the western North Pacific during 2012–2024. Based on the 24-h change in maximum sustained wind speed, the cases were classified into rapid intensification (RI) and slow intensification (SI) groups. Ice water path (IWP), rain water path (RWP), and infrared brightness temperature (Tb) data were used to examine the evolution of inner-core microphysical structures before and after intensification. Composite analyses indicate that both RI and SI cases exhibited asymmetric structures influenced by vertical wind shear before intensification, with high-IWP, high-RWP, and low-Tb regions concentrated in the downshear quadrants. After the onset of intensification, the high-IWP, high-RWP, and low-Tb regions in RI cases expanded into the upshear side, producing a more axisymmetric inner-core structure, whereas those in SI cases remained confined to the downshear semicircle. Axisymmetricity analysis further showed that RI cases were consistently more axisymmetric than SI cases, with the difference increasing over time. In addition, WRF simulations were conducted for the rapidly intensifying Typhoon Surigae (2021) and the slowly intensifying Typhoon Bailu (2019). During rapid intensification, the latent heating, high-IWP, and high-RWP regions of Surigae expanded into the upshear side, forming a deep heating structure around the TC center. In contrast, these features in Bailu remained concentrated in the downshear region. Further analyses indicate that, in Surigae, cyclonic circulation first transported moisture into the initially dry upshear UL quadrant. Subsequently, deep upward motion continuously lifted moisture into the middle and upper troposphere, progressively moistening the upshear region and sustaining convection, thereby supporting continued rapid intensification. Conversely, weaker moisture transport in Bailu confined convection and latent heating to the downshear region, resulting in slower intensification.