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標題: | 雙颱共伴下之颱風外圍雨帶個案觀測研究 Roles of Interactions of Typhoon Nesat (2017) and Haitang (2017) in the Formation and Structure of Outer Tropical Cyclone Rainbands |
作者: | Yu-Jui Huang 黃宇睿 |
指導教授: | 游政谷(Cheng-Ku Yu) |
關鍵字: | 颱風外圍雨帶,雨帶生成與維持機制,雨帶氣流垂直結構特徵,梯度風平衡,雙颱共伴,地形效應, Typhoon,outer tropical cyclone rainbands,formative mechanism,structural feature,multiple-Doppler-derived wind fields,gradient wind balance, |
出版年 : | 2019 |
學位: | 碩士 |
摘要: | 本研究主要利用氣象都卜勒雷達(七股、墾丁及馬公)觀測資料、National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFS)再分析資料、馬公探空及地面測站資料來檢視發生在台灣西南部並造成顯著降水的颱風外圍雨帶個案(2017年7月29日0800~1200 UTC),此個案期間有尼莎颱風(2017)及海棠颱風(2017)同時影響台灣。藉由多都卜勒雷達反演三維風場探討雨帶之(水平及垂直)降水與氣流結構,並嘗試釐清此雨帶的生成與維持機制及地形可能扮演的角色。
根據回波及氣流垂直結構特徵可將外圍雨帶分為兩區域:靠近沿岸區域具有類似颮線之氣流結構,但不具有冷池特徵;遠離沿岸區域則與颮線之結構特徵不同。詳細分析顯示雨帶在兩區域之結構差異與台灣西南部地形屏障效應有關,氣流會在接近台灣地形附近產生偏折與減速並導致雨帶的輻合增強,進而加強在地形附近的降水強度。針對雨帶南北兩側區域之風場進行徑向動量方程收支計算,結果顯示在雨帶北(南)側的氣流徑向加速度接近於零(較大),表示雨帶北(南)側氣流屬於梯度風平衡(次梯度風),隱含著雨帶可能是透過尼莎颱風自身環流的西北風、西風(梯度風平衡)與雙颱共伴產生的西南風(次梯度風)於底層輻合而生成。時序分析亦指出雨帶南側氣流之徑向加速度與雨帶的發展及維持有密切相關,尼莎颱風環流及雙颱共伴氣流之交互作用可解釋雨帶的生成與維持,而地形效應會改變雨帶局部區域的氣流結構,並加強雨帶與台灣西南部交會處的降水強度。 Outside the eyewall, tropical cyclone rainbands (TCRs) are the most striking and threatening region, causing not only heavy precipitation but intense winds. When Typhoon Nesat (2017) and Haitang (2017) were located near Taiwan, outer TCRs oriented approximately normal to the coast were initiated off the southwestern coast of Taiwan and resulted in the severe flood over the coastal and inland regions. Thus, it is crucial to understand the formative mechanism of the studied TCRs. This study used ground-based dual-Doppler and surface observations and NCEP-CFS reanalysis data to document the structural feature of the outer TCRs. The multiple-Doppler-derived wind fields showed that the formation of the TCRs was related to the low-level convergence between the southwesterly flow and the northwesterly flow. According to the budget analysis of radial momentum equations, the southwesterly flow was more subgradient due to the interaction of Typhoon circulations associated with Nesat and Haitang. In contrast, the northwesterly flow that was dominated by the outer circulation of Typhoon Nesat was close to the gradient wind balance. In addition, the structure of the outer TCRs in the nearshore region is different from that seen in the offshore region, which was caused by more pronounced low-level convergence produced as the coastally blocked flow (south-southwesterly flow) that occurred under low Froude number regime encountered the northwesterly flow. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/74547 |
DOI: | 10.6342/NTU201902680 |
全文授權: | 有償授權 |
顯示於系所單位: | 大氣科學系 |
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