[MITgcm-support] SSH drift and obcs again

[Martin Losch]

Hi Tom,
I don't know if we are talking about the same thing. This is what I 
tried:
I used your gendata.m, that was attached to your previous email. 
data.obcs looks like this:
# Open-boundaries
  &OBCS_PARM01
  OB_Jnorth=80*-1,
  OB_Jsouth=80*1,
  OB_Ieast=42*-1,
  OB_Iwest=42*1,
#useOrlanskiNorth=.TRUE.,
#useOrlanskiSouth=.TRUE.,
#useOrlanskiEast=.TRUE.,
#useOrlanskiWest=.FALSE.,
  useOBCSprescribe = .TRUE.,
  OBNuFile = 'OBmeridU.bin',
  OBSuFile = 'OBmeridU.bin',
  OBWuFile = 'OBzonalU.bin',
  OBEuFile = 'OBzonalU.bin',
  OBNvFile = 'OBmeridV.bin',
  OBSvFile = 'OBmeridV.bin',
  OBWvFile = 'OBzonalV.bin',
  OBEvFile = 'OBzonalV.bin',
  OBWsFile = 'OBzonalS.bin',
  OBWptrFile(1) = 'OBzonalS.bin',
  &

# Orlanski parameters
  &OBCS_PARM02
#Cmax=0.45,
#cVelTimeScale=1000.,
  &

I have no drift at all, everything look OK. The solution looks 
different from having no v-compontent at the boundaries, as it should.
Next, I changed one input file to:
OBNvFile = 'OBmeridU.bin',
So that now my meridional velocities are not longer balanced (boundary 
values are u=25cm/s and v=35cm/s in your gendata.m) and there should be 
a divergence of flow. In 10 time steps I get a drift of nearly 13m in 
Eta.

Just to make sure I reverted back to the above data.obcs and I 
commented the following lines:
  OBEuFile = 'OBzonalU.bin',
  OBNvFile = 'OBmeridV.bin',
so that there is no normal outflow at the north and the east, and in 10 
time steps Eta drifts by 60m.

To me, everything looks OK.
Martin

PS. I couldn't find a bessel function bump in gendata.m, just the 
default gaussian bump. Maybe you didn't attach the correct file?


On Nov 8, 2005, at 11:07 PM, Thomas Haine wrote:

> Adding topography (bessel function bump in attached gendata.m) still
> works.
>
> Even when I break the symmetry in the obc currents by adding random
> perturbations with zero convergence and topography (see attached
> gendata.m again) it still works.
>
> I'm still confused!
>
> Tom.
>
> On Tue, 2005-11-08 at 08:57 -0500, Alistair Adcroft wrote:
>> Thomas Haine wrote:
>>> Hi Martin,
>>>
>>> I'm confused. exp4 has zero eta drift in the standard configuration 
>>> in
>>> the latest code. The cg2d rhs is also very near zero. Yet there is
>>> normal flow through the domain. If I add a meridional component to 
>>> the
>>> normal flow the results are, essentially, the same.
>>>
>>> Also, (max, min) eta is +/-10m after 1 step. Is this correct?
>>>
>>> So, I can't reproduce the problem I've seen in exp4 and I don't know
>>> why.
>>
>> Add some topography to see if that changes things...
>>
>> A.
>
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