颱風蝴蝶(Wutip)於2019年2月在西北太平洋上生成並在7日內快速增強為強烈颱風。然而，與當前颱風研究互相牴觸的是颱風蝴蝶所通過的海洋，其海平面高度比平常低（平均負8.5公分）。顯示當時的海洋環境並不適合其成長。因此，本研究旨在透過一系列的觀測與再分析資料（如 JTWC 最佳颱風路徑、HYCOM、SODA 和ERA5），去瞭解許多不同因素(如大尺度海洋、大氣環境與颱風特徵等)對 Wutip強度的影響。於第一項討論中，透過比較Wutip 與14年內 (2005-2018) 年際及冬季的長期氣候值颱風大小，此研究發現颱風大小對於Wutip的增強並非主因：經由Price 2009模式的敏感性實驗測試發現，Wutip颱風大小約比氣候值要大10%-20%，因此Wutip所引起的海表面溫度冷卻要比氣候值強約15%-30%。接著在第二項討論中，將這14年內所有1 月份的颱風進行比較後發現，較冷的上層垂直海溫結構時常伴隨著較強的海表面溫度冷卻效應，大於2.5℃。因此，較冷的海溫結構可能是限制1月份的歷史紀錄中颱風無法成為強烈颱風的原因。而第三項討論中，在2月份的颱風增強過程中，西北太平洋的東南象限往往是提供能量最顯著的區域。值得注意的是，若Wutip生成或增強於其他象限(西南、西北、東北)則其將無法成為如此強且能破紀錄的颱風。由大氣環境分析發現，較弱的垂直風切 (7-8 m/s) 在1,2月份往往是強烈颱風發展的有利與控制因子;與之相對的是，較乾的中層空氣減慢了強烈颱風與非強烈颱風的增強過程。最後，本研究著重在西北太平洋上的溫暖的海洋結構氣候背景場，以及Wutip颱風生成與快速增強的地點，扮演了至關重要的角色，並探討大氣條件等因素，亦會參與Wutip的快速增強過程。

In February 2019, Wutip was formed and rapidly intensified into a super typhoon in the Western North Pacific, causing the loss of property for the Federated States of Micronesia. The evolution of Wutip case made a huge question for the typhoon forecaster since there were strong negative sea surface height features (roughly -8.5 cm) on their trajectory. Using a series of data such as JTWC’s best-track data, HYCOM, SODA, and ERA5, this study aims to investigate the impact of multiple factors (e.g., the large-scale oceanic environment, the large-scale atmospheric environment, and typhoon characteristics) on Wutip’s intensity. In the first scenario, the Wutip’s size compared to the climatological intensifying typhoons within 14 years (2005 – 2018) in both the annual average and the winter seasons. The result indicated that the typhoon size was not a booster factor for Wutip intensification. The sensitivity experiment from the Price 2009 model showed that a size enlargement of Wutip about 10% – 20% compared to climatology triggered an increase in the TC-induced cooling effect in a range of 15% to 30%. The second scenario was compared with typical tropical storms in January. The result showed that the cooler pre-upper-thermal structure profiles induced a great self-cooling effect over 2.5oC. Thus, this was the reason why historical typhoons of January could not intensify into super typhoons with cooler ocean profiles. Thirdly, the evolution in the southeast quadrant region had a significant contributor to the intensification process of super typhoons in February, especially for Wutip. It is noteworthy that Wutip was unable to break the historical records unless it was formed or intensified in the southeast quadrant region. The moderate vertical wind shear around 7-8 m/s was a favorable and controlling factor for historical super typhoons (STYs) compared to non-super typhoons (non-STYs) in January and February. Contrastingly, the dry air of relative humidity at mid-level just slowed down the intensification process for both STYs and non-STYs. In conclusion, this study emphasizes the crucial role of the thickness of warm climatological background in the Western North Pacific, the geographical location where Wutip formed and rapidly intensified, and the supporting factor from atmospheric conditions during the Wutip intensification process.

摘要 i
Abstract ii
Acknowledgments ii
Table of Contents iv
List of Figures vi
List of Tables xiii
Abbreviation xv
Chapter 1 Introduction 1
1.1 Motivation 1
1.2 Literature Review 2
1.2.2 Typhoon Characteristics on Typhoon Intensification 4
1.2.3 Atmospheric Parameters on Typhoon Intensification 5
1.3 Scientific Issues and Structure of this Dissertation 6
Chapter 2 Data and Methodology 9
2.1 Best-Track Data 9
2.2 Satellite Data 10
2.2.1 Sea Surface Height Anomaly (SSHA) 10
2.2.2 Optimal Interpolation Sea Surface Temperature (OISST) 12
2.3 Reanalysis Data for Upper Ocean Thermal Structure 13
2.3.1 HYCOM Dataset 13
2.3.2 SODA Dataset 14
2.4 Reanalysis Data for Atmospheric Parameters 15
2.4.1 Vertical Wind Shear (VWS) 15
2.4.2 Relative Humidity (RH) 16
2.5 Numerical Model and Sensitivity Experiments 18
2.5.1 Price 2009 Model 18
2.5.2 Sensitivity Experiments 19
2.6 Air-Sea Enthalpy Flux 21
Chapter 3 Results 35
3.1 Pre-existing Oceanic Conditions for Wutip 35
3.2 Spatial and Temporal Distribution of Super Typhoon 38
3.3 Comparing Typhoon Size Between Wutip and Climatology 40
3.4 Comparison between Wutip and Typhoons in January and February 42
3.5 Geographical Location 45
3.6 Atmospheric Environmental Conditions 47
References 95

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