風暴潮、潮汐與波浪耦合模式之發展及西北太平洋強烈颱風事件之應用;Development of Storm Surge, Tide, and Wind Wave Coupling Model and Application for Severe Typhoon Events in Northwestern Pacific Ocean

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Title:	風暴潮、潮汐與波浪耦合模式之發展及西北太平洋強烈颱風事件之應用;Development of Storm Surge, Tide, and Wind Wave Coupling Model and Application for Severe Typhoon Events in Northwestern Pacific Ocean
Authors:	蔡育霖;Tsai, Yu-Lin
Contributors:	水文與海洋科學研究所
Keywords:	風暴潮-潮汐-風浪耦合模式;COMCOT-SURGE;SWAN;TPXO8-atlas;2015年蘇迪勒颱風;2015年杜鵑颱風;Surge-Tide-Wave Coupling Model;COMCOT-SURGE;SWAN;TPXO8-atlas;Typhoon Soudelor;Typhoon Dujuan
Date:	2021-10-28
Issue Date:	2021-12-07 11:21:00 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究以風暴潮、潮汐和風浪數值耦合模式，探討西北太平洋強烈颱風造成之風暴潮，在潮汐和風浪影響下，由遠洋至近岸之完整水動力傳遞過程。本研究基於長波海嘯模式COMCOT (COrnell Multi-grid Coupled Tsunami)，發展多重網格風暴潮模式COMCOT-SURGE，可完整模擬風暴潮由生成、傳遞至淹溢等物理過程，並與全球天文潮模式TPXO8-atlas和近岸風浪模式SWAN (Simulating WAve Nearshore) 耦合，於風暴潮模擬內考慮天文潮和波浪能量消散後之輻射應力。本研究利用線性長波於均勻水深之傳播和孤立波圓島溯上等基準案例，驗證COMCOT-SURGE多重耦合巢狀網格之數值穩定性及移動邊界之準確性；此外，COMCOT-SURGE亦與實際觀測水位、全球天文潮模式和調和分析水位等資料比對，驗證其潮汐模擬功能之精準度。待模式驗證後，本研究選訂2015年臺灣東岸登陸之強烈颱風蘇迪勒和杜鵑進行個案分析，且因觀測潮位資料指出颱風期間臺灣東岸有較顯著風暴潮，最大水位抬升高於潮汐約0.8至1.2公尺，因此，本研究針對臺灣東岸、東北岸和東南岸進行重點討論。本研究以歐洲中期天氣預報中心第5代再分析氣象場ECMWF ERA5，驅動風暴潮和風浪模擬，並先以臺灣環海觀測之浮標氣象資料，驗證ERA5風場之準確性，降低後續水動力模擬之可能誤差。耦合模式模擬結果與風暴潮、總水位、示性波高、平均週期、平均波向等觀測資料，均有良好比對結果。本研究亦發現，蘇迪勒颱風和杜鵑颱風登陸期間，臺灣東部沿岸之輻射應力，高於風剪力1至2個量級，且與近岸水位抬升處有高度重合性。本研究進一步透過耦合數值實驗，分析輻射應力對近岸風暴潮之影響，研究結果顯示，臺灣東岸、東北岸和東南岸由風浪能量消散後造成之輻射應力，可使蘇迪勒和杜鵑颱風期間之最大風暴潮高，放大20至50%左右 (約0.1至0.5公尺之水位抬升)，顯示輻射應力對於臺灣東部沿岸之風暴潮模擬是不可缺少的。最後，本研究糞望建立未來風暴潮研究之基準案例，透過蘇迪勒颱風和杜鵑颱風個案，提供未來研究完整之數值模擬結果以及詳盡之潮位及浮標觀測資料，奠定未來風暴潮耦合研究之基石。;This study aims to better understand storm surges due to a severe typhoon from the Western Pacific Ocean propagating from offshore to nearshore with tides and wind waves using a surge-tide-wave coupling model. This study developed the multi-grid COMCOT-SURGE storm surge model based on the well-validated COMCOT (COrnell Multi-grid Coupled Tsunami) tsunami model. COMCOT-SURGE can simulate storm surges from offshore to nearshore, including the full physical processes from generation, propagation, to inundation. Furthermore, COMCOT-SURGE has been coupled with the global tide TPXO8-atlas model and nearshore spectral wave SWAN (Simulating WAve Nearshore) model to consider astronomical tides and wave-enhanced radiation stresses. Linear long wave propagation on a constant water depth and solitary wave runup on a circular island were used to validate the grid nesting function and moving boundary scheme of COMCOT-SURGE. Besides, the accuracy of simulating tides was convinced by validating the modeled tides against observations, TPXO8-atlas, and harmonic analysis. After examining the storm surge model, this study chose the 2015 severe Typhoons Soudelor and Dujuan as case studies. This study focused the discussions on the eastern regions of Taiwan, where the notable storm surges of 0.8–1.2 m were measured from tide gauges in these two typhoon events. ECMWF (European Centre for Medium-Range Weather Forecasts) ERA5 was used to drive surge-tide-wave coupling simulations after being validated by the buoy weather data to minimize the possible error from the inputs. The simulation results agreed with the observed storm surges, water levels, significant wave heights, mean wave periods, and mean wave directions. Besides, the wave-enhanced radiation stress gradient was more considerable than the wind shear stress by one to two orders of magnitude during the passage of Typhoons Soudelor and Dujuan. Thus, this study further carried out numerical experiments to examine the radiation stress effect on coastal storm surges in eastern Taiwan. The results showed that the wave-enhanced radiation stresses contributed to the peak storm surges by about 20–50% along the east coasts of Taiwan during the passage of Typhoons Soudelor and Dujuan. It implies that the radiation stress gradient is vital to predict coastal storm surges on Taiwan’s northeast, east, and southeast coasts. This study hopes to pave the way for future storm surge research by providing the complete surge-tide-wave coupling simulations and a detailed dataset of observed tide gauge data and buoy data.
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