1. Numerical Study of Island Wake in Deep Water Changming (Charles) Dong James McWilliams Alexander Shchepetkin IGPP/UCLA, Los Angels,USA Acknowledgements: J. Molemaker, C. Zhang, M. Blass

2. Introduction Model Configuration Basic Experiment Sensitivity Tests Summary

3. Introduction 2. Wake Classic Fluid Dynamics 3. Wake in geophysical fluid dynamics 1. Observational and numerical evidence

6. a) no separation, laminar boundary layer b) vortex pair with central return flow c) wake formation with wave disturbances along the current/wake interface d) von Karman vortex street (From M. Tomczak, 2000)

7. 1.Shallow water Wolanski (1984) Signell and Geyer (1991) Davies (1995) 2.Deep water Heywood et al (1996) Coutis and Middleton (2002) Two Categories (Tomczak,1988)

8. Basic Experiment Rectangular Domain: 180km x 80km, Water Depth : 500m Island Diameter D= 10km Spatial Resolution : DX = 500 m (160 x 360 x20)

9. Boundary Condition a). Upstream BC (incident flow) b). Downstream BC c). BC neighboring the island

13. Downstream BC: 1.Modified Orlanski radiation (Marchesiello et al, 2001) 2. Specified BC with sponge layer Island BC: Non-slippery with mask

17. Strouhal Number : St=nD/U=0.207

19. Time Series of Lateral Boundary Layer

20. Sensitivity Tests 1.Reynolds number 2.Rotation 3.Island Scale 4.Vertical Shear 5.Stratification

21. Background Horizontal Viscosity μ Grid Reynolds Number Re=dx*U/μ Implicit diffusion associated with upstream- biased advection scheme If Re> 10, scheme diffusion dominates If Re<=10, physical diffusion dominates

23. Re=200 Re=100 Re=25 Re=10 Unknown Re

24. Sensitivity Tests 1. Reynolds Number 2. Rotation 3. Island Scale 4. Vertical Shear 5. Stratification 6. Grid size

26. Sensitivity Tests 1. Reynolds 2. Rotation 3. Island Scale 4. Vertical Shear 5. Stratification

27. St=0.18 St = 0.20St=0.23

28. Sensitivity Tests 1. Reynolds 2. Rotation 3. Island Scale 4. Vertical Shear 5. Stratification

29. Basic CaseWeaker Shear

30. Basic Case

31. Sensitivity Tests 1. Reynolds 2. Rotation 3. Island Scale 4. Vertical Shear 5. Stratification

32. Weaker StratificationBasic Case

33. Weaker StratificationBasic Case

35. Summary 1.ROMS is applied to study the ideal island wake in the dynamically deep water with rotation and stratification. 2. Background eddy viscosity should be chosen appropriately higher spatial resolution show finer structure of eddy activities in the wake. 3. Rotation, island scale, vertical shear and stratification affect the wake structure. The work is still in progress!