p. n. vinayachandran centre for atmospheric and oceanic sciences (caos)
DESCRIPTION
OGCM Configuration. P. N. Vinayachandran Centre for Atmospheric and Oceanic Sciences (CAOS) Indian Institute of Science (IISc) Bangalore 560 012 [email protected]. Summer School on Dynamics of North Indian Ocean June-July 2010. OSCAR Currents. Equations of Motion. - PowerPoint PPT PresentationTRANSCRIPT
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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
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OSCAR Currents
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Equations of Motion
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Spherical Co-ordinate System
r=radius of the earth=latitude=longitude
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Equations in Spherical Co-ordinates
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Modular Ocean Model
Hydrostatic
Thin shell
Boussinesq
Sub-grid scale processes are represented by eddy mixing coefficients
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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
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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 +
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Closed Lateral boundaries : no slip, no normal flow
Open lateral boundaries : sponge
Surface dynamic boundary conditions for momentum and freshwater
Bottom drag
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Surface heat and fresh water fluxes
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Forcing
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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.
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J. Kurian, Ph. D. Thesis, 2007, IISc
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Vertical Mixing Schemes
PP KPPMY
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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
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Model Domain
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Vertical Grid
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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
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River Runoff
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Spin-up
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Sigma – coordinates (Princeton Ocean Model)
Mellor, 2002
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ROMS
Non-linear stretching of the vertical coordinates depending on local water depth
Haidvogel et al., 2000
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Chassignet et al., 2000
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