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標題: | 臺灣地形對於颱風路徑的影響 The Impact of Taiwan Terrain on Tropical Cyclone Track |
作者: | Kuan-Chieh Huang 黃冠捷 |
指導教授: | 吳俊傑 |
關鍵字: | 颱風,地形,路徑偏折,通道效應,非對稱風,無因此參數,位渦趨勢診斷分析, Typhoon,tropical cyclone,Taiwan terrain,track deflection,channeling effect,asymmetric flow,non-dimensional parameter,PV tendency diagnosis, |
出版年 : | 2016 |
學位: | 碩士 |
摘要: | 觀測及數值模擬資料均顯示當颱風接近台灣時,其路徑會受到地形的影響而產生偏折。然而,在過去的研究當中,針對這個問題的原因及機制的探討卻相當有限,因此仍存在許多不確定性。因此本研究使用Advanced Research WRF模式進行高解析的模擬,來探討西行颱風遇到地形時南偏的物理機制。控制組實驗(CTL)的模擬渦旋在接近地形時有逐漸向南偏移的現象,進行內核駛流分析,顯示中低層(650hPa-850hPa)的駛流在接近地形時有向南的分量,並且非常靠近地形時,南偏則主要由中層不對稱風貢獻。透過位渦趨勢分析的結果,渦旋的偏折主要是由水平平流項主導,垂直平流項及加熱項貢獻則相對較小。當渦旋逐漸南偏時,渦旋低層西側的風速隨著時間有增強並向外擴張的現象,東側的風速則沒有明顯的變化;渦旋即將登陸地形時,渦旋中層西側的北風也明顯的增強,也是中層不對稱風出現的主因。進一步使用氣塊逆軌跡分析,則發現在渦旋靠近地形時,在低層的氣塊有逐漸向渦旋西側輻合的現象,此一現象發生在渦旋西側以及地形之間,並伴隨風速的增強,因此推斷為通道效應。透過南北風動量分析,當渦旋逐漸靠近理想地形時,低層的動量向中層傳遞,造成中層不對稱風的發生。本實驗也進行敏感性實驗,探討在不同流域下渦旋運動的特性,並發現在山越陡峭,以及在背景流場速度較慢的情況下,渦旋會有明顯的偏折。但不同於以往的研究,在渦旋不同初始位置的敏感性實驗當中,從地形南側通過的渦旋偏折較為顯著,進一步分析發現,背景流場在地形中心以南有比較明顯的偏折,因此導致了渦旋有比較明顯的南偏。此一結果顯示,地形在不同實驗當中,與背景流場以及渦旋之間的非線性作用,都有可能導致渦旋的路徑產生差異,也是未來實驗探討的重點。 Both observations and numerical studies showed that tropical cyclones (TCs) would experience pronounced track deflection when approaching Taiwan. Observations, particularly those from the in-situ radars, have documented a number of typhoons deflect near the east coast of Taiwan. In order to better understand the roles of the orographic influence on TC movement, this study conducts a series of idealized experiments using the ARW-WRF model with fine horizontal grid spacing. In the control experiment (CTL), the simulated west-moving TC shows distinct southward track deflection when approaching the topography. Mean advection analysis indicates that 650hPa-850hPa asymmetry flow within 100-km results in the southward deflection of the storm. Potential vorticity tendency diagnosis suggests that horizontal advection has the dominant contribution to the deflection of the storm track, while vertical advection and diabatic heating play relatively minor roles. As the vortex experiences the southward deflection, the low-level meridional wind west of the vortex gradually strengthens and expands. Backward trajectory analysis supports the concept of channeling effect, with confluent trajectories of the air parcels when the air column passes through the channel between the terrain and the vortex. By the time when the location of the vortex is about to make landfall, the middle-level northerly asymmetric flow also strengthens. It is the combined effect of the strengthening low-level and mid-level northerly flow that contributes to the southern deflection of the vortex. Meridional wind momentum budget indicates that the vertical momentum advection plays an important role in transporting the momentum upward when the storm approaches the terrain. This study further investigates the key parameter(s) for TC track deflection. The result suggests that when the mountain is steeper, or the background flow is slower, TC track deflection becomes pronounced. The result of TCs approaching Taiwan from different initial places indicates that TCs come from southern part of the terrain has obvious track deflection as compared to TCs approaching from the north. Comparisons among results in this study and some previous studies show high uncertainties of the topographic impact on TC movement under different model settings and flow regimes. The idealized experiments in this study provide new physical insight into the impact of Taiwan terrain on tropical cyclones. Further researches are needed to gain deeper understanding of the dynamics of tropical cyclone track deflection. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/50862 |
DOI: | 10.6342/NTU201600728 |
全文授權: | 有償授權 |
顯示於系所單位: | 大氣科學系 |
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