[MITgcm-support] obcs with non linear free surface

[Alexey]

Dear sirs,

I am trying to set MITgcm for the Baltic sea.

For boundary conditions there are temperature, salinity and sea level 
available only.

I guess that with that data for the open boundary (the northern 
boundary) only NONLIN_FRSURF built is possible.

In this case the sea level is overestimated for multi-year runs. From 
the code I figured that the velocities at the boundaries are set to zero,

which, probably, leads to the significant underestimation of the mass 
transport off the basin.

Is that so?

Besides, the simulation presents an steep step-like structure near the 
boundary between the boundary and the inner simulation domain.

Could you please advice me on the code alteration to obtain the 
velocities from the level values?

Which subroutines are to be modified?

data - namelist

rhonil=1027.5,
  rhoConstFresh=999.8,
  eosType='JMD95Z',
  hFacMinDr=50.,
  hFacMin=0.3,
  hFacInf=0.1,
  hFacSup=5.,
  implicitDiffusion=.TRUE.,
  implicitViscosity=.TRUE.,
  viscC4Leith=1.5,
  viscC4Leithd=1.5,
  viscA4GridMax=0.5,
  useAreaViscLength=.TRUE.,
  sideDragFactor=0.,
  highOrderVorticity  = .TRUE.,
  bottomDragQuadratic = 0.0021,
  tempAdvScheme=7,
  saltAdvScheme=7,
  StaggerTimeStep=.TRUE.,
  multiDimAdvection=.TRUE.,
  vectorInvariantMomentum=.TRUE.,
  rigidLid=.FALSE.,
  implicitFreeSurface=.TRUE.,
  exactConserv=.TRUE.,
  debuglevel=-1,
  convertFW2Salt=-1
  useSingleCpuIO=.TRUE.,
  globalFiles=.FALSE.,
  useRealFreshWaterFlux=.TRUE.,
  implicSurfPress = 1.0,
  implicDiv2Dflow = 1.0,
  select_rStar =2,
  nonlinFreeSurf=4,


data.obcs - namelist

  &OBCS_PARM01
  OB_Jnorth(15)=-250,
  OB_Jnorth(16)=-250,
  OB_Jnorth(17)=-250,
  OB_Jnorth(18)=-250,
  OB_Jnorth(19)=-250,
  OB_Jnorth(20)=-250,
  OB_Jnorth(21)=-250,
  OB_Jnorth(22)=-250,
  OB_Jnorth(23)=-250,
  OB_Jnorth(24)=-250,
  OB_Jnorth(25)=-250,
  OB_Jnorth(26)=-250,
  OB_Jnorth(27)=-250,
  OB_Jnorth(28)=-250,
  OB_Jnorth(29)=-250,
  OB_Jnorth(30)=-250,
  OB_Jnorth(31)=-250,
#
  useOBCSprescribe=.TRUE.,
  useOBCSbalance=.TRUE.,
  OBCS_balanceFacN = 2.,
  OBCSfixTopo = .TRUE.,
#
  useOBCSsponge   = .TRUE.,
  useSeaiceSponge = .TRUE.,


  &OBCS_PARM03
  spongeThickness = 5,
  Urelaxobcsinner=108000.0,
  Urelaxobcsbound=10800.0,
  Vrelaxobcsinner=108000.0,
  Vrelaxobcsbound=10800.0,
  &

Sincerely,

Alexey

Russian State Hydrometeorological University

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