[MITgcm-support] consatant open boundary flow but interior current changing periodicaly

[Martin Losch]

Hi YuYu,

since we don’t know much about your configuration, there is little to say. Depending your on your stratification etc, you may very well develop instabilities over your sill/sea mount that may look periodic.

If you accidentally started from verification/internal_wave, then your obcs_calc.F has periodic forcing hard coded and your constant forcing in never felt. In that case your should remove obcs_calc.F from your “code” directory and rebuild (make makefile && make CLEAN && make depend && make) to use the default obcs_calc.F (that allows prescribing boundary values.

Sidenote: I think that the Orlanski BC do not allow a net volume/mass flux. Means with your constant inflow you’ll have a dramatic sea-level rise in your domain.

Hope that helps,
Martin

> On 15. Jun 2020, at 16:47, Jody Klymak <jklymak at uvic.ca> wrote:
> 
> Assuming the flow is stratified, I’d expect an inertial response if you start up the flow impulsively.  The inertial rtansiet will die away, but will take a while, so suggest you spin the model up slowly over a few inertial periods if this response is a problem.  
> 
> Cheers,   Jody
> 
>> On 13 Jun 2020, at 23:36, 葉祐瑜 <B05209023 at ntu.edu.tw> wrote:
>> 
>> Hi all,
>> 
>> I am running some implicitfreesurface ocean simulations with grid size 4800*1*150 and with below setting in data.obcs:
>>  
>> &OBCS_PARM01
>> OB_Ieast=1*-1,
>> OB_Iwest=1*1,
>> useOrlanskiEast=.TRUE.,
>> useOBCSprescribe = .TRUE.,
>> OBWuFile = 'uOBW.bin',   (incoming flow is set to be a constant eastward current )
>> &OBCS_PARM02
>> Cmax=0.45,
>> cVelTimeScale=1000.,
>> &
>>  
>> And there is a small sill in the middle of domain. I found that  the output U velocity above the sill seems to chang periodicaly with time, which is different from my expection. I think that U above the sill should not change largely with time because of a consatant current flowing into domain on western boundary. Because I am new to MITgcm, I am not sure whether such changing flow above the sill is ture. Can anyone help me with this issue? Did I make something wrong when setting th model? Thank you for you help!
>>  
>> Best regards,
>>  
>> YuYu Yeh
>> Undergraduated student
>> Department of Atmospheric Sciences, National Taiwan University
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> 
> --
> Jody Klymak    
> http://ocean-physics.seos.uvic.ca/~jklymak/
> 
> 
> 
> 
> 
> 
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