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

Martin Losch Martin.Losch at awi.de
Mon Jun 15 11:08:04 EDT 2020


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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>> MITgcm-support at mitgcm.org
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> 
> --
> Jody Klymak    
> http://ocean-physics.seos.uvic.ca/~jklymak/
> 
> 
> 
> 
> 
> 
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