臺灣博碩士論文加值系統

過去的觀測和數值研究皆顯示，颱風在接近台灣地形時，可能會受地形影響而有偏轉的路徑出現，有時此偏轉運動十分地顯著，甚至偶爾會出現路徑打轉的現象。這些顯著的偏轉或是打轉路徑的發生，很可能會延長及擴大風雨影響台灣的時間和區域，因此這是一個非常重要的颱風預報問題。而過去對此現象的研究仍非常有限，亦缺乏以包含完整物理過程模式所進行之高解析度模擬與深入探討，因此有關地形引起的偏轉運動之動力機制仍有待釐清，而這不僅是颱風預報問題，也是一個相當有趣的基礎學術議題。

本研究將利用MM5中尺度模式進行高解析度 (最高解析度為3公里)的數值模擬，探討柯羅莎颱風 (2007) 打轉運動和台灣地形之關係，及其背後的動力機制；研究結果顯示柯羅莎的偏轉與地形的高度密切相關，當台灣地形高度降低時，柯羅莎的偏轉幅度也減少，反之亦然。若以解析度9公里進行模擬，則無法模擬出柯羅莎顯著的南偏路徑，分析顯示9公里和3公里解析度對地形描述的差異，可能並非造成其模擬路徑有所不同之主因，而此兩種解析度對渦旋結構及其中物理過程之描述對模擬結果的影響則尚待進一步研究。

此外，若以MM5進行包含完整物理過程的高解析度理想氣流和理想渦旋實驗，則發現颱風在接近(離開)地形中、北部(南部)時，有顯著的南(北)偏運動發生；初始位置越北(南)的颱風，其接近(遠離)地形時的南(北)偏的情形就越顯著。

個案模擬與理想實驗均顯示，颱風受地形影響而出現偏轉路徑的同時，颱風和地形之間的低層風速有顯著增強之情形發生，颱風內核區的非對稱流場(asymmetric flow) 也因此產生變化，分析顯示此非對稱流場與偏轉運動有密切關聯。軌跡線分析顯示低層空氣質點經過地形與颱風間的狹小通道時有匯合的情形發生，顯示此風速增強與所謂的通道效應(channeling effect)之概念相當一致。

為了全面性了解此議題，我們計畫進行更多相關的敏感度實驗，探討背景流場速度、渦旋強度與結構、地形和渦旋運動方向之間的角度(impinging angle)所扮演的角色，釐清渦旋遇到地形時發生顯著的偏轉或打轉運動的流制(flow and parameters regimes)。

Both observation and numerical studies showed that typhoons are prone to be deflected when approaching high topography. Sometimes, the track could be sharply deflected, and looping motion might occur. The warning areas, which are lashed by severe rainfall and gust, could shift greatly due to the sharp turn. This is a very important typhoon forecast problem. However, research issues with such unusual typhoon motion have not been well addressed in literatures. Few idealized numerical experiments have been conducted based on a full-physic model with high resolution. The mechanisms leading to the sharp turn, which is an interesting scientific problem, have not been well investigated.

High resolution (3-km) simulations are conducted using MM5 model to investigate the mechanisms leading to the loop motion of the typhoon, and the role of Taiwan topography. The results show that high topography plays an important role in Typhoon Krosa’s looping. The southward track deflection is reduced when the terrain elevations are lowered, and vice versa. An experiment with coarser resolution (9 km) cannot well capture the southward turn. Differences in the topography from two model resolutions appear not critical to the simulated track. Impacts of the model resolution on the vortex structure and physics processes still need to be addressed in the future.

Idealized experiments are also conducted using MM5 model with a 3-km mesh. These simulations show that the more the vortex approaches (leaves) the northern (southern) topography, the more southward (northward) deflection occurs.

Both the real-case and the idealized studies indicate that strong winds at the channel between the storm and topography are enhanced when great deflection occurs. The asymmetric flow within the inner-core appears to contribute to the track deflection. Meanwhile, the backward-trajectory calculation of the low-level air parcels shows the confluent trajectories when the air column passes over the channel between the high terrain and the vortex. The results of the backward trajectory analysis are consistent with the concept of the channeling effect.

To fully investigate this issue, more sensitive experiments will be designed in the future. The impact of the magnitude of the ambient flow, vortex intensity and structure, and the impinging angle will be further studied to identify the flow and parameters regimes leading to the sharp track deflection and the looping motion.

致謝 .....................................................I
摘要 ....................................................II
Abstract ...............................................III
目錄 ....................................................IV
圖表目錄 ................................................VI

第一章 前言 ..............................................1
1.1 相關研究成果回顧 .....................................2
1.1.1 觀測分析研究 .......................................2
1.1.2 數值模擬研究 .......................................3
1.1.2.1 個案研究 .........................................3
1.1.2.2 理想實驗研究 .....................................4
1.2 歷史上侵台颱風之打轉運動 .............................5
1.3 研究目的 .............................................6
1.4 個案簡介 .............................................6
第二章 研究工具與方法 ...................................8
2.1 模式介紹 .............................................8
2.2 模式設定與初始場 ....................................11
2.2.1 模式設定 ..........................................11
2.2.2 柯羅莎颱風之模式初始場 ............................12
2.2.3 理想數值實驗之模式初始場 ..........................13
2.2.3.1 理論及設定 ......................................13
2.2.3.2 理想地形 ........................................14
2.2.3.3 背景流場預跑時間之選取 ..........................15
2.2.3.4 理想渦旋預跑時間的選擇 ..........................17
2.2.3.5 建立完成的理想模式初始場 ........................17
2.4 實驗設計 ............................................18
2.4.1 柯羅莎颱風的實驗設計 ..............................18
2.4.2 理想數值實驗的實驗設計 ............................19
2.5 颱風中心之定位 ......................................19
第三章 模擬結果與分析 ...................................20
3.1 柯羅莎颱風 ..........................................20
3.1.1 CTRL及OC實驗 .....................................20
3.1.1.1 CTRL和OC之模擬路徑 ..............................20
3.1.1.2 CTRL和OC之風場演變 ..............................21
3.1.1.3 颱風內核區之非對稱流場 ..........................22
3.1.1.4 氣流軌跡線分析(Backward trajectories analysis) ..23
3.1.2 台灣地形高度所扮演的角色 ..........................25
3.1.3 模式解析度之敏感度測試 ............................25
3.1.4 台灣地形三度空間下的複雜度之敏感度測試 ............25
3.2 理想數值實驗 ........................................26
3.2.1 路徑 ..............................................26
3.2.2 風場 ..............................................27
3.2.3 氣流軌跡線分析(Backward trajectories analysis).....28
第四章 討論 .............................................29
第五章 後續工作 .........................................32
5.1 通道效應的量化 ......................................32
5.2 各種物理過程及解析度所扮演的角色 ....................32
5.3 背景流場和渦旋結構的敏感度實驗 ......................33
5.4 其他地形相關議題與敏感度測試 ........................34
參考文獻 ................................................35

中央氣象局，歷史颱風資料庫。
謝信良、王時鼎、鄭明典、葉天降、丘台光，1998：百年侵台颱風路徑圖集及其應用。中央氣象局氣象科技研究中心。共497頁。
謝信良、王時鼎、鄭明典、葉天降、丘台光，1996-2000：台灣地區颱風預報輔助系統建立之研究。中央氣象局氣象科技研究中心。共370頁。
簡國基，2000：台灣地形對侵台颱風之影響－ TCM-90個案之模擬與分析。國立台灣大學大氣科學研究所博士論文。共310頁。
Anthes, R. A., T. T., Warner, 1978: Development of hydrodynamical models suitable for air pollution and other meteorological studies. Mon. Wea. Rev., 106, 1045-1078.
____, E. –Y. Hsie, and Y. H. Kuo, 1987: Description of Penn State/NCAR Mesoscale Model Version 4 (MM4). NACR/TN-282+STR, National Center for Atmospheric Research, Boulder, CO, 66 pp.
Bender, M. A., R. E. Tuleya, and Y. Kurihara, 1987: A numerical study of the effect of island terrain on tropical cyclones. Mon. Wea. Rev., 115, 130-155.
Blackdar, A., K., 1976: Modeling the nocturnal boundary layer. Preprints of Third Symposium on Atmospheric Turbulence and Air Quality, Raleigh, NC, 19-22 October 1976, Amer. Meteor. Soc., Boston, 46-49.
Brand, S., and J. W. Blelloch, 1974: Changes in the characteristics of typhoons crossing the island of Taiwan. Mon. Wea. Rev., 102, 708-713.
Chan, C. L., and W. M. Gray, 1982: Tropical cyclone movement and surrounding flow relationship. Mon. Wea. Rev., 110, 1354-1376.
____, C. L., and R. T. Williams, 1987: Analytical and numerical studies of the beta-effect in tropical cyclone motion. Part I: Zero mean flow. J. Atmos. Sci., 44, 1257-1265.
Chang, S.-W., and R. V. Madala, 1980: Numerical simulation of the influence of sea surface temperature on translating tropical cyclones. J. Atmos. Sci., 36, 2617-2630.
____, 1982: The orographic effects induced by an island mountain range on propagating tropical cyclones. Mon. Wea. Rev., 110, 1255-1270.
Charney, 1955: The use of primitive equations of motion in numerical prediction. Tellus, 7, 22-26.
Chou, K.-H., and C.-C., Wu, 2008: Typhoon Initialization in a Mesoscale model- Combination of the Bogused Vortex and the Dropwindsonde Data in DOTSTAR. Mon. Wea. Rev., 136, 865-879.
DeMaria M., C. –L., Chan, 1984: Comments on “A numerical study of the interaction between two tropical cyclones”. Mon. Wea. Rev., 112, 1643-1645.
Dudhia, J., 1989: Numerical study of convection observed during the winter monsoon experiment using a mesoscale two-dimensional model. J. Amots. Sci., 46, 3077-3107.
Fiorino, M. J., and R. L., Elsberry, 1989: Some aspects of vortex structure related to tropical cyclone motion. J. Atmos. Sci., 46, 975-990.
Grell, G. A., J. Dudhia and D. R. Stauffer, 1993: A description of the fifth-generation Penn State/NCAR mesoscale model (MM5). NCAR Technical Note, NCAR/TN-198+STR. 117 pp.
Holt, T., S. W. Chang, and R, Raman, 1990: A numerical study of coastal cyclogenesis in GALE IOP 2: Sensitivity to PBL parameterizations. Mon. Wea. Rev., 118, 234-257.
Huang, T.-S., M. Montgomery, and C.-C. Wu, 2008: Sensitivities of hurricane intensity to planetary boundary layer schemes in a full physics three dimensional nonhydrostatic mesoscale model. Proc., 28th Conference on Hurricanes and Tropical Meteorology. Amer. Meteor. Soc., Boston MA. 3A.5.
Jian, G.-J., and C.-C., Wu, 2008: A numerical study of the track deflection of super-typhoon Haitang (2005) prior to its landfall in Taiwan. Mon. Wea. Rev., 136, 598-615.
Jordan, C. L., 1958: Mean soundings for the West Indies area. J. Meteor., 15, 91–97.
Kuo, H. –C., R. T. Williams, J. –H., Chen, and Y. –L., Chen, 2001: Topographic Effects on Barotropic Vortex Motion: No Mean Flow. J. Atmos. Sci. 58, 1310-1327
Kurihara, Y., M. A. Bender, R. E., Tuleya, and R. J. Ross, 1995: Improvements in the GFDL hurricane prediction system. Mon. Wea. Rev., 123, 2971-2801.
Lin, Y.-L., J. Han, D. W. Hamilton, C. –Y., Huang, 1999: Orographic influence on a drifting Cyclone. J. Atmos. Sci., 56, 534-562.
____, S.-Y., Chen, C. M. Hill, and C.-Y., Huang, 2005: Control parameters for the influence of a mesoscale mountain range on cyclone track continuity and deflection. Amer. Meteor. Soc., 62, 1849-1866.
Madala, R. V., S. W. Chang, U. C. Mohanty, S. C. Madan, R. K. Paliwal, V. B. Sarin, T. Holt and S. Raman, 1987: Description of Naval Research Laboratory limited area dynamical weather prediction model. NRL Tech. Rep. No. 5992, Washington D. C., 131 pp.
Neumann, C. J., 1979: On the use of deep-layer mean geopotential height fields in statistical prediction of tropical cyclone motion. Preprints, Sixth of Conf. on Probability and Statistics in Atmosphere Sciences, Banff, AB, Canada, Amer. Meteor. Soc., 32-38.
Smith, 1989a: Mountain-induced stagnation points in hydrostatic flow. Tellus, 41A, 270-230.
____, 1989b: Comment on “Low-Froude-number flow pass three-dimensional obstacles. Part I: Baroclinically generated lee vortices.” J. Atmos. Sci., 52, 436-454.
Smolarkiewicz, P., and R. Rotunno, 1989: Low-Froude-number flow pass three-dimensional obstacles. Part I: Baroclinically generated lee vortices. J. Atmos. Sci., 46, 1154-1164.
Wang, S.-T., 1980: Prediction of the behavior and strength of typhoons in Taiwan and its vicinity (in Chinese). National Science Council Research Rep., 108, Taipei, Taiwan, 100 pp.
Wu, C.-C., and Y.-H. Kuo, 1999: Typhoons affecting Taiwan: current understanding and future challenges. Bull. Amer. Meteor. Soc., 80, 67-80
____, 2001: Numerical simulation of Typhoon Gladys (1994) and its interaction with Taiwan terrain using the GFDL hurricane model. Mon. Wea. Rev., 129, 1533-1549.
____, T.-H. Yeh, Y.-H. Kuo, and W. Wang, 2002: Rainfall simulation associated with Typhoon Herb (1996) near Taiwan. Part I: The topographic effect. Wea. Forecasting, 17, 1001-1015
____, T.-S., Huang, W.-P., Huang, and K.-H., Chou, 2003: A new look at the binary interaction: Potential vorticity diagnosis of the unusual southward movement of Typhoon Bopha (2000) and its interaction with Typhoon Saomai (2000). Mon. Wea. Rev., 131, 1289-1300.
Yeh, T.-C., and R. L. Elsberry, 1993a: Interaction of typhoons with the Taiwan orography. Part I: Upstream Track deflection. Mon. Wea. Rev., 121, 3193-3212.
____, and ____, 1993b: Interaction of typhoons with the Taiwan orography. Part II: Continuous and discontinuous tracks across the island. Mon. Wea. Rev., 121, 3213-3233.