快速增強的熱帶氣旋是強度預測誤差的主要來源之一，是值得深入研究的一個重要議題。本研究首先利用季節生成指數(Seasonal Genesis Parameter, SGP)分析近40年熱帶氣旋活躍季節(6月至11月)與非活躍季節(12月至5月)西北太平洋平均的動力與熱力條件。研究結果顯示，西北太平洋在熱帶氣旋活躍季節由相對渦度、垂直風切與科氏力共同組成的動力潛勢基本上都有利於熱帶氣旋的生成，反之在非活躍季節有利於熱帶氣旋形成之動力條件的範圍明顯縮小。在活躍季節北緯30度以南的區域由海洋能量、溼穩定度與溼度參數所組成的熱力潛勢幾乎為正，較大值的區域落在南海東南部以及菲律賓東方與東南方海域，說明這些區域的熱力條件相當有利於熱帶氣旋的形成。非活躍季節熱力潛勢正值區域明顯縮小，並往南移至北緯10度以南。由此可知北緯10度以北區域在非活躍季節較少熱帶氣旋發展主要是因為熱力條件不足所致。為瞭解熱帶氣旋在季節尺度下快速增強的氣候特徵，本研究參考季節生成指數，以信賴域反射最小平方法對近四十年觀測到的熱帶氣旋快速增強季節頻率進行擬合以修改季節生成指數中參數的比重，產生一個新的季節快速增強指數(Seasonal Rapid Intensification Index)。此指數可以估計西北太平洋各區域不同季節會發生快速增強事件的次數。相關性分析的結果顯示此新的指數與觀測到的季節快速增強頻率分布呈高度相關。結果也顯示，垂直風切參數和溼穩定度參數在活躍季節分別於動力與熱力項中扮演重要角色。而科氏力參數與海洋能量參數則在非活躍季節貢獻較大，相對渦度、溼度參數的貢獻則相對較小。

Rapid intensification (RI) of tropical cyclones (TCs) is a main source of intensity forecast errors and merits further study. This study first uses the Seasonal Genesis Parameter (SGP) to analyze the average dynamic and thermodynamic conditions over the western North Pacific during the active TC season (June–November) and the inactive TC season (December–May) over the past four decades. The results show that during the active season, the dynamic potential, which consists of relative vorticity, vertical wind shear, and Coriolis, is generally favorable for TC genesis, whereas the favorable area is greatly reduced during the inactive season. The thermodynamic potential, consisting of ocean energy, moist stability, and humidity, is largely positive south of 30°N in the active season, with maxima over the southeastern South China Sea, east and southeast of the Philippines. During the inactive season, positive thermodynamic potential contracts markedly and shifts south of 10°N, indicating that reduced TC activity north of 10°N is mainly due to insufficient thermodynamic support. To examine the climatological characteristics of RI on the seasonal scale, the SGP is modified by fitting its parameters to the observed RI frequency using the Trust-Region-Reflective Least Squares Algorithm, producing a new Seasonal RI Index. This index estimates the number of RI events occurring in different regions during a season and shows strong spatial correlation with observations. The results also reveal that vertical wind shear and moist stability play important roles within the dynamic and thermodynamic components, respectively, during the active season. In contrast, the Coriolis and ocean energy contribute more during the inactive season, while the contributions from relative vorticity and humidity are relatively small.

Chang, C.-C., and C.-C. Wu, 2017: On the Processes Leading to the Rapid Intensification of Typhoon Megi (2010). J. Atmos. Sci., 74, 1169–1200. https://doi.org/10.1175/jas-d-16-0075.1
Dong, Y., and Q. Li, 2024: Inner-Core Humidification and Prelandfall Rapid Intensification of Typhoon Mekkhala (2020) in Strong Vertical Wind Shear. Mon. Wea. Rev., 152, 2697–2716. https://doi.org/10.1175/mwr-d-23-0225.1
Emanuel, K. A., and D. S. Nolan, 2004: Tropical cyclone activity and the global climate system. 26th Conf. on Hurricanes and Tropical Meteorology, Miami, FL, Amer. Meteor. Soc.,240–241
Frank, W. M., and E. A. Ritchie, 2001: Effects of Vertical Wind Shear on the Intensity and Structure of Numerically Simulated Hurricanes. Mon. Wea. Rev., 129, 2249–2269. https://doi.org/10.1175/1520-0493(2001)129%3C2249:EOVWSO%3E2.0.CO;2
Fudeyasu, H., K. Ito, and Y. Miyamoto, 2018: Characteristics of Tropical Cyclone Rapid Intensification over the Western North Pacific. J. Climate, 31, 8917–8930. https://doi.org/10.1175/jcli-d-17-0653.1
Gray, W. M., 1979: Hurricanes: Their formation, structure and likely role in the tropical circulation. Meteorology over the tropical oceans, Quarterly Journal of the Royal Meteorological Society, 155–218
Hersbach, H.,and Coauthors, 2020: The ERA5 global reanalysis. Q. J. R. Meteorol. Soc., 146, 1999–2049. https://doi.org/10.1002/qj.3803
Holton, J. R., and G. J. Hakim, 2013: An introduction to dynamic meteorology. Academic press,532 pp.
Huan, D., Q. Yan, T. Wei, and N. Jiang, 2023: Understanding the Variation and Mechanisms of Tropical Cyclone Genesis Potential over the Western North Pacific during the Past 20 000 Years. J. Climate, 36, 3343–3356. https://doi.org/10.1175/JCLI-D-22-0638.1
Kaplan, J., and M. DeMaria, 2003: Large-Scale Characteristics of Rapidly Intensifying Tropical Cyclones in the North Atlantic Basin. Weather Forecast., 18, 1093–1108. https://doi.org/10.1175/1520-0434(2003)018%3C1093:LCORIT%3E2.0.CO;2
Kaplan, J., M. DeMaria, and J. A. Knaff, 2010: A Revised Tropical Cyclone Rapid Intensification Index for the Atlantic and Eastern North Pacific Basins. Weather Forecast., 25, 220–241. https://doi.org/10.1175/2009waf2222280.1
Li, Y.-X., and J.-Y. Yu, 2020: Why rare tropical cyclone formation after maturity of super El Niño events in the western North Pacific? Terr. Atmos. Ocean. Sci., 31, 21–32. https://doi.org/10.3319/tao.2019.06.23.01
Lin, I. I.,and Coauthors, 2021: A Tale of Two Rapidly Intensifying Supertyphoons: Hagibis (2019) and Haiyan (2013). Bull. Amer. Meteor. Soc., 102, E1645–E1664. https://doi.org/10.1175/bams-d-20-0223.1
Miyamoto, Y., G. H. Bryan, and R. Rotunno, 2017: An analytical model of maximum potential intensity for tropical cyclones incorporating the effect of ocean mixing. Geophys. Res. Lett., 44, 5826–5835. https://doi.org/10.1002/2017gl073670
Rogers, R., 2010: Convective-Scale Structure and Evolution during a High-Resolution Simulation of Tropical Cyclone Rapid Intensification. J. Atmos. Sci., 67, 44–70. https://doi.org/10.1175/2009jas3122.1
Romps, D. M., 2017: Exact Expression for the Lifting Condensation Level. J. Atmos. Sci., 74, 3891–3900. https://doi.org/10.1175/jas-d-17-0102.1
Shi, D., and G. Chen, 2021: The Implication of Outflow Structure for the Rapid Intensification of Tropical Cyclones under Vertical Wind Shear. Mon. Wea. Rev., 149, 4107–4127. https://doi.org/10.1175/mwr-d-21-0141.1
Shimada, U., 2022: Variability of Environmental Conditions for Tropical Cyclone Rapid Intensification in the Western North Pacific. J. Climate, 35, 4437–4454. https://doi.org/10.1175/jcli-d-21-0751.1
The MathWorks, Inc., 2025: Least-Squares (Model Fitting) Algorithms. Accessed 13 August 2025, https://www.mathworks.com/help/optim/ug/least-squares-model-fitting-algorithms.htm
Wang, B., and X. Zhou, 2007: Climate variation and prediction of rapid intensification in tropical cyclones in the western North Pacific. Meteorol. Atmos. Phys., 99, 1–16. https://doi.org/10.1007/s00703-006-0238-z
Wang, X., C. Wang, L. Zhang, and X. Wang, 2015: Multidecadal Variability of Tropical Cyclone Rapid Intensification in the Western North Pacific. J. Climate, 28, 3806–3820. https://doi.org/10.1175/jcli-d-14-00400.1
Zhao, H., X. Duan, G. B. Raga, and P. J. Klotzbach, 2018: Changes in Characteristics of Rapidly Intensifying Western North Pacific Tropical Cyclones Related to Climate Regime Shifts. J. Climate, 31, 8163–8179. https://doi.org/10.1175/jcli-d-18-0029.1