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Transcript of P. N. Vinayachandran Centre for Atmospheric and Oceanic Sciences (CAOS) Indian Institute of Science...
P. N. VinayachandranCentre for Atmospheric and Oceanic Sciences (CAOS)
Indian Institute of Science (IISc)Bangalore 560 012
Summer School onDynamics of North Indian Ocean
June-July 2010
OGCM Configuration
Modular Ocean Model
Hydrostatic
Thin shell
Boussinesq
Sub-grid scale processes are represented by eddy mixing coefficients
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=-H
At z=
Griffies, 2001, MOM4 guide
Equation for free surface
For a Boussinesq ocean: Assume volume sources/sinks only at the surface lead tobalance of volume per unit area within a ocean column
Ocean surface is affected by three processes:1. Convergence of vertically integrated momentum2. Mass entering through the ocean surface3. Water column dialations due to changes in vertically inegrated density field (steric effects)
Kinematic surface and bottom boundary conditions
At z=-H
At z=
= volume per unit time per unit horizontal area of freshwater crossing the sea surface
= depth integrated horizontal velocity field
Water column thickness: D = H +
Closed Lateral boundaries : no slip, no normal flow
Open lateral boundaries : sponge
Surface dynamic boundary conditions for momentum and freshwater
Bottom drag
Smagorinsky viscosityViscosity depends on flow, nonlinearViscosity due to unresolved scales are proportional to (deformation rates X △2)
km is the largest resolvable wave number
How do you choose ?
Deformation rate:
Viscosity:
Let
Then for R < 2
Tracers, Veronis effect, background viscosity
Grid Reynolds No. should be < 2
Griffies, S. M.: Fundamentals of Ocean Climate Models, Princeton University Press, Princeton, USA, 518+xxxiv pages, 2004.
Horizontal Grid Size
Rossby radius = cm/f
Equatorail Rossby radius =( cm/)1/2
Eqn. 14.83
m
m
Horizontal grid spacing should resolve the Rossby Radius
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
ROMS
Non-linear stretching of the vertical coordinates depending on local water depth
Haidvogel et al., 2000