[MITgcm-support] Stevens BC

[Martin Losch]

with stevens turned on the normal velocities are vertically averaged, maybe this leads to some very high velocities for your specific data?

Also, I have never run with stevens BCs and nonzero tangential velocities. The code does not reset these to zero, so I would try without specifying tangential velocities (like OBWvFile = ‘’). There’s even a short note (hidden somewhere) in this section of the manual: <https://mitgcm.readthedocs.io/en/latest/phys_pkgs/obcs.html#obcs-calc-stevens>

M.

> On 13. May 2021, at 15:19, Lambert Guo <lanchiyu12 at gmail.com> wrote:
> 
> Hi Martin,
> 
> Sorry for the unclear words. I set the western and northwestern as Stevens BC. I just checked the model's last step output, the model crashed at the western boundary, the third grid point from the western boundary with very large zonal and meridional velocity. These abnormal values didn't occupy all the western boundary but within a very small region.
> 
> Thanks,
> Lambert
> 
> 
> On Thu, May 13, 2021 at 8:53 AM Martin Losch <Martin.Losch at awi.de> wrote:
> Hi Lambert,
> 
> this is way to unspecific to help. You need to find out where the model crashes (near the boundaries?) and then possibly understand if your prescribed files are not correct.
> 
> Martin
> 
> > On 13. May 2021, at 14:37, 赤羽蓝 <lanchiyu12 at gmail.com> wrote:
> > 
> > Hi all,
> > 
> > I am running a regional ocean model with the OBCS package. When I use the Stevens boundary conditions, the model always crashes with "stops due to EXTREME Pot.Temp". The model is OK if I turn off the Stevens BC. I have tried different inflows(outflow) at the Stevens boundary, which encounter the same crashing. The sponge boundary layer didn't help either. I also tried different relaxation time, no help.
> > 
> > Attaching my data.obcs file.
> >   
> > Any ideas will be grateful.
> > 
> > Lambert
> > 
> > # ***************
> > # Open boundaries
> > # ***************
> >  &OBCS_PARM01
> > # This flag turns off checking and fixing problematic topography across
> > # open boundaries.
> >  OB_Jnorth = 360*-1,
> >  OB_Jsouth = 360*1,
> >  OB_Iwest = 528*1,
> >  OB_Ieast = 528*-1,
> >  useOBCSprescribe=.TRUE.,
> >  useStevensWest = .TRUE.,
> >  useStevensNorth = .TRUE.,
> > # useOBCSsponge=.TRUE.,
> >  useOBCSbalance=.FALSE.,
> > # OBCS_balanceFacE = 1.,
> > # OBCS_balanceFacW = 1.,
> > # OBCS_balanceFacN = 1.,
> > # OBCS_balanceFacS = 1.,
> > 
> >  OBNsFile='sn.scs',
> >  OBNtFile='tn.scs',
> >  OBNvFile='vn.scs',
> >  OBNuFile='un.scs',
> > 
> >  OBSsFile='ss.scs',
> >  OBStFile='ts.scs',
> >  OBSvFile='vs.scs',
> >  OBSuFile='us.scs',
> > 
> >  OBEsFile='se.scs',
> >  OBEtFile='te.scs',
> >  OBEvFile='ve.scs',
> >  OBEuFile='ue.scs',
> > 
> >  OBWsFile='sw.scs',
> >  OBWtFile='tw.scs',
> >  OBWvFile='vw.scs',
> >  OBWuFile='uw.scs',
> >  &
> > 
> > # &OBCS_PARM03
> > # Urelaxobcsinner=864000,
> > # Urelaxobcsbound=864000,
> > # Vrelaxobcsinner=864000,
> > # Vrelaxobcsbound=864000,
> > # spongeThickness=5,
> > # &
> > 
> >  &OBCS_PARM04
> >  TrelaxStevens = 86400.,
> >  SrelaxStevens = 86400.,
> >  &
> > _______________________________________________
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> > MITgcm-support at mitgcm.org
> > http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support
> 
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