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P. N. Vinayachandran Centre for Atmospheric and Oceanic Sciences (CAOS)

OGCM Configuration. P. N. Vinayachandran Centre for Atmospheric and Oceanic Sciences (CAOS) Indian Institute of Science (IISc) Bangalore 560 012 vinay@caos.iisc.ernet.in. Summer School on Dynamics of North Indian Ocean June-July 2010. OSCAR Currents. Equations of Motion.

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P. N. Vinayachandran Centre for Atmospheric and Oceanic Sciences (CAOS)

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  1. OGCM Configuration P. N. Vinayachandran Centre for Atmospheric and Oceanic Sciences (CAOS) Indian Institute of Science (IISc) Bangalore 560 012 vinay@caos.iisc.ernet.in Summer School on Dynamics of North Indian Ocean June-July 2010

  2. OSCAR Currents

  3. Equations of Motion

  4. Spherical Co-ordinate System r=radius of the earth =latitude =longitude

  5. Equations in Spherical Co-ordinates

  6. Modular Ocean Model Hydrostatic Thin shell Boussinesq Sub-grid scale processes are represented by eddy mixing coefficients

  7. Water column thickness: D = H +  H(x,y) = Ocean depth;  = (x,y,t) is the sea surface deviation from rest (z=0) Kinematic surface and bottome boundary conditions At z= At z=-H Griffies, 2001, MOM4 guide

  8. Equation for free surface Ocean surface is affected by three processes: 1. Convergence of vertically integrated momentum 2. Mass entering through the ocean surface 3. Water column dialations due to changes in vertically inegrated density field (steric effects) Water column thickness: D = H +  For a Boussinesq ocean: Assume volume sources/sinks only at the surface lead to balance of volume per unit area within a ocean column Kinematic surface and bottom boundary conditions At z= At z=-H = volume per unit time per unit horizontal area of freshwater crossing the sea surface = depth integrated horizontal velocity field

  9. Surface dynamic boundary conditions for momentum and freshwater Bottom drag Closed Lateral boundaries : no slip, no normal flow Open lateral boundaries : sponge

  10. Surface heat and fresh water fluxes

  11. Forcing

  12. Smagorinsky viscosity Viscosity depends on flow, nonlinear Viscosity due to unresolved scales are proportional to (deformation rates X △2) Viscosity: Deformation rate: km is the largest resolvable wave number How do you choose ? Grid Reynolds No. should be < 2 Let Then for R < 2 Tracers, Veronis effect, background viscosity Griffies, S. M.: Fundamentals of Ocean Climate Models, Princeton University Press, Princeton, USA, 518+xxxiv pages, 2004.

  13. J. Kurian, Ph. D. Thesis, 2007, IISc

  14. Vertical Mixing Schemes PP KPPMY

  15. Horizontal Grid Size Horizontal grid spacing should resolve the Rossby Radius Rossby radius = cm/f Equatorail Rossby radius =( cm/)1/2 Eqn. 14.83 m m

  16. Model Domain

  17. Vertical Grid

  18. Topography ETOPO5, ETOPO2 & modified Minimum depth of the ocean is 30m. Cells are deepened Isolated ocean points are converted to land Palk strait is closed, Red Sea and Persian Gulf are connected to the Arabian Sea, widened to allow 2 grid points

  19. River Runoff

  20. Spin-up

  21. Sigma – coordinates (Princeton Ocean Model) Mellor, 2002

  22. ROMS Non-linear stretching of the vertical coordinates depending on local water depth Haidvogel et al., 2000

  23. Chassignet et al., 2000

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