[MITgcm-support] online calculation of energy flux

[Ryan Abernathey]

Wow, great! I didn't know this existed. Thanks Jody.


On Fri, Jan 31, 2014 at 3:06 PM, Jody Klymak <jklymak at uvic.ca> wrote:

> Hi Robert and Sonya,
>
> My online energy diagnostic is at:
>
> https://github.com/jklymak/MITgcmcode
>
> It is after Kang and Fringer, and Kang's thesis, and does a
> barotropic/baroclinic decomposition for the linear terms. The non-linear
> terms are not formally separable, and so I don't separate them! I think I
> have most of the terms correct, but bugs wouldnt surprise me.  Its not well
> documented, but hopefully largely self-explanatory.
>
> It certainly does not attempt to deal w/ model discretization issues or
> calculate explicit dissipation from general dissipative terms.  I would
> suggest that folks who write viscosity submodules should consider
> calculating dissipation for their users!
>
> If anyone uses this, or in particular finds bugs, I'd love to hear about
> it.
>
> Thanks,  Jody
>
>
>
> On Jan 31, 2014, at  10:19 AM, Ryan Abernathey <ryan.abernathey at gmail.com>
> wrote:
>
> Robert and Sonya,
>
> This is an issue that came up at the recent ECCO meeting. Many people
> would probably like to have such kinetic energy diagnostics from MITgcm.
> Although the energy equation is easy to write down, diagnosing all of the
> terms in a way that is consistent with the model discretization can be very
> difficult. Many people have probably tackled it in the past and come up
> with a "good enough" solution, no standard solution has emerged.
>
> Peng's suggestion is correct, but the problem is that mean(up) is not
> currently an available diagnostic. That would be fairly trivial to add,
> especially if you already know how to diagnose it from offline output. The
> current pressure diagnostics are filled in model/src/dynamics.F, which
> could be modified to include the pressure flux term.
>
> More generally, if you want a complete energy budget, you will also want
> the advective transport of kinetic energy, which involves tracking "triple
> correlation" terms such as mean(uv^2). This is similar to the problem
> encountered in the diagnosis of tracer variance budgets. Several people
> (including Jean Michel, myself, and Liam Brannigan) have recently become
> interested in adding such diagnostics to the model. Nonlinear advection
> schemes can make this difficult for tracers, but perhaps the momentum
> advection is actually simpler.
>
> The biggest issue I see in closing the kinetic energy budget is the
> dissipation term (epsilon). If you are doing energy budgets for internal
> waves, presumably this term is a leading order one for you. A robust method
> for diagnosing dissipation (consistent with the numerics and LES options
> such as Smagorinsky) would be a great contribution.
>
> I personally wish the MITgcm community could come together to produce a
> definitive answer to this problem. But of course, it is not a high priority
> for most people, and it is a very difficult numerical problem. Plus it is
> possible that the necessarily diagnostics would significantly slow down the
> code execution. Whatever solution you come up with, you should definitely
> share it with the community, perhaps through the MITgcm_contrib repository,
> for the benefit of the next grad student who is faced with this simple
> sounding but actually very deep task.
>
> Best,
> Ryan
>
>
> On Fri, Jan 31, 2014 at 11:45 AM, Sonya Legg <sonya.legg at noaa.gov> wrote:
>
>>  Hi Robert,
>>
>> You should state that it's the product u'p' that you want, and you want
>> to do it online so that you can calculate time-averages. Otherwise you
>> might get a response that u is already output, as is p, so why do you need
>> to add anything?
>>
>> Sonya
>>
>>
>> On 1/31/2014 11:39 AM, Robert Nazarian wrote:
>>
>> Hi,
>>
>> I'm trying to add an online evaluation of u' and p' to the source code to
>> calculate the energy flux. Is there a particular diagnostic that would be
>> best to do this in? If not, is there a particular subroutine that's ideal
>> to write such a diagnostic? Previously, I did these calculations offline
>> but am hoping to incorporate it into the code itself.
>>
>>  Thanks,
>> Rob
>>
>>  Robert Nazarian
>>
>> Program in Atmospheric and Oceanic Sciences
>>
>> Princeton University
>>
>> rn2 at princeton.edu
>>
>>
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