[MITgcm-support] Momentum Budget
Emily Shroyer
eshroyer at whoi.edu
Fri Dec 10 08:30:20 EST 2010
Thanks for the help. I assume that the following should add up to the
total momentum tendency:
TOTUTEND/86400=Um_Diss+Um_Advec+Um_Cori+Um_dPHdx+Um_Ext+UDIAG1
with a similar balance for the v-momentum equation. Note that UDIAG1
accounts for the sea-surface gradient. I have also appended data,
data.pkg, data.kpp. The only thing that should look unfamiliar is a
package named rlx. This is based off the rbcs package but it relaxes the
momentum to a certain state in a masked region. I have been careful to
only look at the budget well upstream, outside of this region.
I am fairly certain that I am missing a term related to the vertical
viscosity. This may have something to do with my set-up of KPP, but I
did try turning it off and I was still having problems. The imbalance is
only significant in the equation when I turn on the winds. In the
surface cell the correction is in the opposite direction of those below.
I think this is because I am adding in the term for momentum input from
the wind (Um_Ext), but not the total loss to viscosity. Beneath the
surface the correction is of the opposite sign, i.e., I am only not
accounting for viscosity correctly. The imbalance decreases with depth,
and is negligible at a certain point. The correction seems to be of the
same shape and magnitude as the approximate term for the vertical
viscosity nu_{kpp}*d2u/dz2. Its also of (roughly) the same shape as
VISrE_Um. Any advice would be appreciated. Emily
Jean-Michel Campin wrote:
> 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
>>
>
>
> _______________________________________________
> 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
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: data
URL: <http://mitgcm.org/pipermail/mitgcm-support/attachments/20101210/bc4557fd/attachment.el>
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: data.kpp
URL: <http://mitgcm.org/pipermail/mitgcm-support/attachments/20101210/bc4557fd/attachment-0001.el>
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: data.pkg
URL: <http://mitgcm.org/pipermail/mitgcm-support/attachments/20101210/bc4557fd/attachment-0002.el>
More information about the MITgcm-support
mailing list