[MITgcm-support] Momentum Budget

[Jean-Michel Campin]

Hi Emily,

I am not sure that all the diagnostics needed to close the momentum
budget are there (although I though we put them), and it also depend
on the level of details you are interested in.
There are 2 things that could be useful:
1) write the list of terms (translated in diagnostics output name)
 that you expect to sum to zero in the momentum budget.
2) attached the main parameter files (data, data.pkg, + may be
 few other like data.kpp if you are using kpp).

Thanks,
Jean-Michel

On Thu, Dec 09, 2010 at 01:02:55PM -0500, Emily Shroyer wrote:
> Thanks Matt,
> For some reason things still are not adding up quite right. The balance  
> is almost perfect, until I turn on wind forcing then the sum of terms  
> differs significantly from the total tendency.  I attached a figure of  
> the zonal balance at one grid cell as a function of time. Winds turn on  
> around day 12, the black line and the red dashed line would line up if I  
> was including everything correctly. This is one reason I thought that  
> the vertical viscosity term might be missing, i.e., maybe I am not  
> accounting for the flux of momentum from the surface properly. The other  
> is that if I evaluate this term (nu*d^2u/dz^2) on my own, the difference  
> is roughly correct. I tried manipulating the VISrE_Um and VISrI_Um terms  
> but I am not sure exactly how these are scaled, the units appear to be  
> in m^4/s^2, so surface area alone is not going to work. I will likely  
> just return to estimating a momentum budget from the normal output  
> fields, a little messy and it won't balance perfectly, but at least I  
> know what it does. Thanks again, Emily
>
>
> Matthew Mazloff wrote:
>> Hi Emily,
>>
>> I believe there are a few tricks to this
>>
>> Disclaimer -- this info may be out of date or not apply to your  
>> specific setup....
>>
>>
>> I think the tendency term is in units per day, not per second, so try 
>> rescaling from m/s/d to m/s^2 by dividing by 86400
>>
>> For vector invariant momentum formulation (not sure about flux form) 
>> Um_Advec includes coriolis
>>
>> I believe Um_dPHdx does not include pressure forcing from SSH  
>> gradient, you need to add that in
>>
>> Note that UBotDrag and USidDrag should be in Um_Diss
>>
>> If you want to look at the implicit vertical viscous flux (VISrE_Um)  
>> then I believe this has units m^3/s^2 and so needs to be rescaled by  
>> surface area ( divide by RAW and RAS for zonal, meridionaly momentum  
>> balance respectively) 
>>
>>
>> Hope this helps -- or at least gives you some ideas...
>>
>> -Matt
>>
>>
>>
>> Request to developers...maybe the momentum diagnostics could be  
>> cleaned up?
>>
>>
>>
>>
>> On Dec 7, 2010, at 1:46 PM, Emily Shroyer wrote:
>>
>>> I would like to output terms of the momentum budget using the diagnostic
>>> package. My data.diagnostic file is set as:
>>>
>>> &diagnostics_list
>>>  diag_mnc     = .TRUE.,
>>>  frequency(1) = -43200.,
>>>  filename(1) = 'UmomDiag',
>>>  fields(1,1) = 'TOTUTEND','UBotDrag ','USidDrag
>>> ','Um_Diss','Um_Advec','Um_Cori',
>>>                'Um_dPHdx','Um_Ext','Um_AdvZ3','UDIAG1  ',
>>>
>>>  frequency(2) = -43200.,
>>>  filename(2) = 'VmomDiag',
>>>  fields(1,2) = 'TOTVTEND','VBotDrag ','VSidDrag
>>> ','Vm_Diss','Vm_Advec','Vm_Cori',
>>>                'Vm_dPHdy','Vm_Ext','Vm_AdvZ3','UDIAG2  ',
>>>
>>> &
>>>
>>> The terms Udiag1/2 were added to account for gradients in the sea
>>> surface height. Unfortunately, the total tendency is not quite equal to
>>> the sum of the other terms. I think that difference may be associated
>>> with the implicit diffusivity term? I am using a KPP mixing scheme,
>>> although I have also tried a MY scheme. I spent  a bit of time trying to
>>> decide where best to output this term with a user defined diagnostic
>>> without any result. My questions are 1) Is it likely that this is indeed
>>> the term I am missing in the momentum budget or have a missed something
>>> else? 3) If so, does anyone have a suggestion as to where best to output
>>> this term with the user diagnostic?
>>>
>>> Thanks for any advice, Emily
>>>
>>> -- 
>>> Emily Shroyer, Postdoctoral Scholar
>>>
>>> Woods Hole Oceanographic Institution
>>> Clark 316A, MS #21
>>> Woods Hole, MA 02543
>>>
>>> phone: 508 289 2525
>>>
>>>
>>> _______________________________________________
>>> MITgcm-support mailing list
>>> MITgcm-support at mitgcm.org <mailto:MITgcm-support at mitgcm.org>
>>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>>
>> ------------------------------------------------------------------------
>>
>> _______________________________________________
>> MITgcm-support mailing list
>> MITgcm-support at mitgcm.org
>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>>   
>
>
> -- 
> Emily Shroyer, Postdoctoral Scholar
>
> Woods Hole Oceanographic Institution
> Clark 316A, MS #21
> Woods Hole, MA 02543
>
> phone: 508 289 2525
>


> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-support