臺灣博碩士論文加值系統

快速增強的颱風在預報上一直是個挑戰，由於增強速度快，常使得應變不及而造成重大損害；Charney and Eliassen, 1964; Ogura, 1964和Ooyama, 1969指出，颱風增強的主要因素來自眼牆周圍雲帶的對流系統所造成的正回饋循環。其回饋機制依序為由底層輻合帶動颱風眼牆周遭的氣流上升，而上升氣流致使飽和水氣凝結並於過程中釋放潛熱，而在颱風上層形成暖心，有利維持颱風強度；氣流傳送到颱風頂層後以輻散方式流出，輻散氣流又帶動下層氣流往上升，如此反覆而形成對流的正回饋，使得颱風不斷增強，並且垂直風切須小於一定的門檻值，以免破壞颱風結構，因此在探討快速增強颱風時，在颱風的垂直運動及結構上的幾個重要大氣參數，需要有好的觀測及模擬。
本篇研究選用2010年的快速增強個案梅姬颱風，使用GSI 3D-Var 3.3版本資料同化系統同化高垂直解析度的GPS RO溫、溼度剖線觀測資料，以期獲得更好的模式初始場；接著利用WRF 3.6.1版本進行模擬，結果發現同化GPS RO的實驗組比起只同化GTS觀測資料的實驗組，在強度上有明顯改善且靠近觀測。探討颱風快速增強過程中的幾個重要機制：輻合場、垂直速度、潛熱釋放造成的暖心結構、風切大小、CAPE值和中對流層的相對溼度等，同化RO的實驗組皆有較好的表現。
最後也進行兩個敏感度測試，第一，發現500百帕以下的RO溫、溼度觀測在強度模擬上扮演重要的角色，第二，同化的RO數目減半所模擬的強度大致介於GTS和GTS+RO實驗組之間。

Rapid-Intensification (RI) typhoon forecast remains a critical challenge, it usually causes severe damage all at once. According to the previous research, a critical mechanism for reducing rapid-intensifying typhoons was “the positive feedback” occurred in or near the eyewall region. That is, for low-level convergence enhances upward flow motion, latent heat then releases to surroundings causing a warm-core in mid-upper-level. Warm-core structure helps to maintain typhoon intensity; then divergence in upper level pulls lower flow to transport updraft at the same time, and it finally forms second circulation that intensifies typhoons.
In this study, we conducted a 48-hour data assimilation and a 72-hour forecast experiment by using GSI 3D-Var v3.3 data assimilation system and WRF model 3.6.1 version. An rapid-intensifying typhoon Megi(2010) was chosen to analyze the RI processes from two sets of experiments, i.e., from the assimilation of GTS only and GTS with RO data. These two experiments will used to evaluate two different atmospheric states in the initial fields and followed typhoon forecasts in the RI stages.
Some important RI mechanisms were analyzed, such as convergence, vertical velocity, wind shear, 700 hPa relative humidity and temperature anomaly. GTS+RO experiment gave positive impact to the typhoon simulation.
Sensitivity tests show that RO profiles below 500hPa played an important role in the improvement of intensity; Moreover, assimilating lower number of RO profiles will degrade the forecast performance but not in linear relationship with the used RO data.

摘要 I
Abstract III
誌謝 IV
第一章 緒論 1
1.1前言 1
1.2文獻回顧 3
1.3研究動機與目的 6
第二章 資料介紹 9
2.1 GTS傳統觀測資料 9
2.2 FORMOSAT-3/COSMIC 掩星資料 9
2.3 NCEP FNL 11
2.4 ERA-Interim 再分析資料 11
2.5 JTWC最佳路徑 11
第三章 研究方法 13
3.1掩星觀測產品 13
3.2 GSI資料同化系統 13
3.3 模式介紹 14
3.4 個案介紹 15
3.5 實驗設計 15
第四章 研究結果 17
4.1同化結果分析 17
4.2模擬結果分析 23
第五章 敏感度測試 32
5.1 RO資料同化對於大氣高低層的影響 32
5.2 RO數量的影響 33
第六章 結論 34
參考文獻 38
表 41
圖 43

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