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北南海內波波動模擬

北南海內波波動模擬. 陳冠宇 、吳瑞中、王玉懷 國立中山大學海下科技暨應用海洋物理研究所. South China Sea (SCS) is famous for large amplitude internal waves. Liu and Hsu, 2004. Field measurement by Prof. Y.H.Wang. A#01 116.55.053E 20.43.974N. 環礁 直徑 25 公里環礁內最深約 16 公尺. 東沙島 長 3 公里寬 1 公里面積 1.74 平方公里.

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北南海內波波動模擬

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  1. 北南海內波波動模擬 陳冠宇、吳瑞中、王玉懷 國立中山大學海下科技暨應用海洋物理研究所

  2. South China Sea (SCS) is famous for large amplitude internal waves Liu and Hsu, 2004

  3. Field measurement by Prof. Y.H.Wang A#01 116.55.053E 20.43.974N • 環礁 直徑25公里環礁內最深約16公尺 • 東沙島長3公里寬1公里面積1.74平方公里

  4. 實測觀測資料顯示，當內波通過東沙環礁時，海水溫度下降約有6~8度，且湧昇上來的冷水時間約有4小時之久。實測觀測資料顯示，當內波通過東沙環礁時，海水溫度下降約有6~8度，且湧昇上來的冷水時間約有4小時之久。 • 但南海的內波時間尺度大約是15分鐘(According to A. K. Liu et al., 2004, internal solitary wave in west SCS has width 1.6 km and wave speed 1.8 m/s; Internal solitary wave in east SCS has width 3 km and wave speed 3 m/s) • 其時間尺度比東沙冷水事件的過程短許多，因此為更進一步了解其物理過程，有必要進行詳細的數值模擬。

  5. 2D Boussinesq type model is not applicable

  6. Model Setup for POM • Domain:116.875°E~117.025°E 20.65°N~20.8°N Grid size:100m 150*150*30 • Simulation Period:2 days • Output: every 30 seconds • The in-situ stratification measured at 300m depth in the east of Dongsha is used as the initial state. • The model is driven by the flow boundary condition in the east • Synolakis found hydrostatic model is suitable for the run-up of tsunami • POM is hydrostatic and is suitable for the run-up problem

  7. 0 12

  8. Bathymetry is provided by the Taiwan Ocean Research Institute

  9. 1.The in-situ stratification is used to get the buoyancy frequency N2. distribution of N is used to obtain the eigenmode for w3. Vertical distribution of u is used as the boundary condition

  10. Variation in time is determined by the KdV soliton solution

  11. Flow Boundary Conditions for ISWs • the KdV theory is based on the inviscid assumption which is not compatible with POM. • Besides, the ISW propagates with a net mass transport, but the eigen mode assumes zero net flux • The vertical flow boundary condition needs to be modified by artificially shifting the altitude of zero-flow. • After a number of experiments on the shifting altitude, ISWs can be generated with some ripples lag behind.

  12. Near Dongsha, a couple of successive internal waves are observed

  13. 在東沙東方製造三個波

  14. Originally there are three ISWs原本三個波

  15. Three waves merge into one結合成一個波

  16. 由於環礁外海淺水處的台階地形使冷水停留在台階上由於環礁外海淺水處的台階地形使冷水停留在台階上

  17. After the runup of the surge, it recede offshore promptly if the shelf does not exist環礁外海淺水處的台階地形使冷水停留在台階上，更進一步延長冷水事件的時間

  18. Discussions on the waveform • 當內波進入大陸斜坡時，波形變成非對稱的前陡後緩波形

  19. 內波若以湧波的形式破碎（即surging breaker），則形成內湧潮（internal bore）或稱內水躍（internal hydraulic jump）波形變成前緩後陡

  20. -30M 1mod 2mod 3mod

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