[MITgcm-support] How to use OBCS and add the Sponges layer?

[Chun-Yan Zhou]

Dear all,
 
I am trying to do quite a simple configuration: The model domain covers
a continental slope and neighbouring parts of the deep ocean and shelf.
A barotropic tidal flow into the model domain from the east open
boundary (2D problem, no y-dependency, no Coriolis). My basin is 300km
across and I use dx=500m and dz=100*25m (i.e. grid dimensions is
600x1x100).
Furthermore, I want to add a sponge-layer (50 Km width) at the lateral
boundary of the deep ocean (the west boundary) to absorb the baroclinic
fields.
  I have read the OBCS package in the manual and the examples but still
can not understand well.
OBCS_OPTIONS.h
#include "CPP_OPTIONS.h"
 
#ifdef ALLOW_OBCS
 
C Enable individual open boundaries
#undef ALLOW_OBCS_NORTH
#undef ALLOW_OBCS_SOUTH
#define ALLOW_OBCS_EAST
#define ALLOW_OBCS_WEST
 
C This include hooks to the Orlanski Open Boundary Radiation code
#define ALLOW_ORLANSKI
 
C Enable OB values to be prescribed via external fields that are read
C from a file
#define ALLOW_OBCS_PRESCRIBE
 
C This includes hooks to sponge layer treatment of uvel, vvel
#define ALLOW_OBCS_SPONGE
 
C balance barotropic velocity
#define ALLOW_OBCS_BALANCE
 
C     The following five CPP options are experimental and aim to deal
C     with artifacts due to the low-frequency specification of sea-ice
C     boundary conditions compared to the model forcing frequency.
C     Ice convergence at edges can cause model to blow up.  The
C     following CPP option fixes this problem at the expense of less
C     accurate boundary conditions.
#undef OBCS_SEAICE_AVOID_CONVERGENCE
 
C     Smooth the component of sea-ice velocity perpendicular to the
edge.
#undef OBCS_SEAICE_SMOOTH_UVICE_PERP
 
C     Smooth the component of sea ice velocity parallel to the edge.
#undef OBCS_SEAICE_SMOOTH_UVICE_PAR
 
C     Smooth the tracer sea-ice variables near the edges.
#undef OBCS_SEAICE_SMOOTH_EDGE
 
C     Compute rather than specify seaice velocities at the edges.
#undef OBCS_SEAICE_COMPUTE_UVICE
 
#endif /* ALLOW_OBCS */
#endif /* OBCS_OPTIONS_H */
 
 
Data.obcs
# Open-boundaries
 &OBCS_PARM01
 OB_Ieast=600*1, ( is this right?)
 OB_Iwest=1*1,  ( is this right?)
 useOrlanskiEast=.TRUE.,
 useOBCSbalance=.TRUE.,
 useOBCSsponge=.TRUE.,
 #
 useOBCSprescribe=1,
 #
 OBEuFile = 'OBzonalU.bin',
 &
 
# Orlanski parameters
 &OBCS_PARM02
 Cmax=0.45,
 cVelTimeScale=1000.,
 &
 
 # Sponge-layer parameters
 &OBCS_PARM03
 spongeThickness=100,
  Urelaxobcsinner = long relaxation time scale of your choice,
  Urelaxobcsbound= short relaxation time scale,(is there any method to
give these two parameters?)
  spongeThickness = # grid points,( how to describe the sponges
position between (1,1 and 100,1)? )
 
 &
 
I am appreciate any help/advices; if you need more info let me know.
Thanks in advance.
Chunyan


 
Chunyan Zhou
Division of Civil Engineering
School of Engineering, Physics and Mathematics
College of Art, Science and Engineering
Fulton Building
University of Dundee
Dundee DD1 4HN
 
 

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