| 摘要: | 本研究旨在探討東海與黃海的鹽度分層是否導致了2020年8月颱風Bavi在該區域異常增強。鹽度分層是由長江淡水輸入造成的，它可以形成一個阻隔層(Barrier Layer)，減少垂直混合造成的海表冷卻，有利於颱風的發展。本研究使用COAWST耦合模式，結合大氣模式 (WRF)和海洋模式 (ROMS)，對颱風Bavi通過東海與黃海的過程進行了三維模擬，並比較了有無鹽度分層的情況下，颱風強度會如何變化。
本研究分成三個部分，首先對耦合模式中的大氣模式(WRF)及海洋模式(ROMS)的初始場與邊界條件進行測試。大氣模式在模擬的颱風路徑和強度具有良好的效果，路徑平均誤差為39.6km，強度平均誤差為6kts，顯示模式能夠準確模擬颱風與環境風場的互動。在海洋模式中，使用HYCOM、GLORYS和ORAS5三種全球海洋模式進行初始場測試。結果顯示，GLORYS在模擬東海與黃海區域海洋特性方面有較好的表現，因此將其選為後續耦合模式的海洋模式初始場。
第二部份在東海與黃海區域測試了三種垂直混合參數化方案(LMD、MY2.5、GLS)，對於颱風造成的海表溫度冷卻(SSTC)的模擬效果。實驗結果顯示，颱風通過後，海表溫度在颱風路徑下方和右側出現明顯的冷卻，垂直上經歷了強烈的垂直混合，三種方案中，LMD方案呈現最強的冷卻效應，而MY2.5方案最弱。儘管模擬與衛星觀測之間存在一定的差異，但整體來看，LMD方案在模擬SSTC方面與觀測最為接近，因此選擇LMD方案作為耦合模式中的垂直混合參數化方案。
第三部分進行了兩項模擬，一個是模擬具有鹽度分層的真實海洋，另一個則是將海洋鹽度替換成相同數值，不具有鹽度分層的海洋環境。在有和沒有鹽度分層的對比實驗結果顯示，無鹽度分層實驗中，颱風造成最大冷卻比鹽度分層實驗少了約3°C，海洋表面冷卻較弱，颱風獲得的潛熱通量多了9.5％，潛熱通量較高，使得颱風強度較強。存在鹽度分層的情況下，颱風通過時海表冷卻較強，潛熱通量較少，從而使颱風強度相對較弱。
;This study aims to investigate whether the salinity stratification in the East China Sea and the Yellow Sea caused the abnormal intensification of Typhoon Bavi in August 2020. The salinity stratification is caused by the freshwater input from the Changjiang River, which can form a barrier layer (BL) that reduces the sea surface cooling due to vertical mixing, favoring the development of typhoons. This study uses the COAWST coupled model, combining the atmospheric model (WRF) and the ocean model (ROMS), to simulate the three-dimensional process of Typhoon Bavi passing through the East China Sea and the Yellow Sea, and compares how the typhoon intensity changes with and without salinity stratification.
This study is divided into three parts. First, the initial fields and boundary conditions of the atmospheric model (WRF) and the ocean model (ROMS) in the coupled model are tested. The atmospheric model has good performance in simulating the typhoon track and intensity, the average track error is 39.6 km, and the average intensity error is 6 kts, indicating that the model can accurately simulate the interaction between the typhoon and the environmental wind field. In the ocean model, three global ocean models, HYCOM, GLORYS, and ORAS5, are used for initial field testing. The results show that GLORYS has a better performance in simulating the ocean characteristics in the East China Sea and Yellow Sea regions, and therefore is selected as the initial field of the ocean model for the subsequent coupled model.
The second part of the study tests the simulation effects of three vertical mixing parameterization schemes (LMD, MY2.5, GLS) on the sea surface temperature cooling (SSTC) caused by typhoons in the East China Sea and Yellow Sea regions. The experimental results show that after the typhoon passes, the sea surface temperature under and to the right of the typhoon path experiences significant cooling and intense vertical mixing. Among the three schemes, the LMD scheme presents the strongest cooling effect, while the MY2.5 scheme is the weakest. Although there are certain differences between the simulation and satellite observations, overall, the LMD scheme is closest to the observations in simulating SSTC, so the LMD scheme is chosen as the vertical mixing parameterization scheme in the coupled model.
The third part conducted two simulations, one simulating a real ocean with salinity stratification, and the other replacing the ocean salinity with the same value, an ocean environment without salinity stratification. The comparative experimental results of having and not having salinity stratification show that in the experiment without salinity stratification, the maximum SSTC caused by the typhoon is about 3°C less than the salinity stratification experiment, the ocean surface cooling is weaker, the latent heat flux obtained by the typhoon is 9.5% more, the latent heat flux is higher, making the typhoon stronger. In the case of salinity stratification, when the typhoon passes, the sea surface cools more strongly, the latent heat flux is less, thereby making the typhoon relatively weaker. |
