[MITgcm-support] dic pkg and PTRACERS_addSrelax2EmP

[David Munday]

Dear MITgcmers,

Does anyone have any experience with combining the dic package with the PTRACERS_addSrelax2EmP flag?

I recently turned on the flag in my own biogeochemical experiments to check how much of a difference the implied freshwater forcing really makes. To my surprise, my simulation went from extremely precise conservation of the total amount of biogeochemical tracers to losing phosphate and DIC, whilst gaining alkalinity, throughout the length of the run (normally long enough for the whole system to come to a steady state). The change is monotonic, after an initial adjustment, and is large enough that it significantly disrupts calculations based on assuming fixed mean concentrations. I ran a quick test over night with a just a single (non-biogeochemical) tracer and the total tracer seems to be conserved much more precisely, although the mean value does increase minutely (wrt the amount the dic tracers change by).

I'm using a linear implicit free surface and I spent yesterday looking over the documentation and checking old support list messages. This has led me to wonder if this could be related to the slight loss of heat/salt with such a free surface that the linFSConserveTr flag corrects for, and have just hacked together an attempt to add the same correction to the ptracers. I'm not particularly confident that this is the culprit, however, and was hoping someone might have some more insight.

Best wishes,

Dave

On 10 Sep 2010, at 10:39, Christoph Voelker wrote:

> Hi Jean-Michel,
> 
> thanks a lot! I have updated my code and started a new experient and it seems to work perfectly
> 
> Cheers, and thanks again!
> Christoph
> 
> Jean-Michel Campin wrote:
>> Hi Christoph,
>> I have added the few pieces of code that should do the job.
>>> option for ptracer to convert Salt Relax into additional EmP.
>>>  tested in exp. global_ocean.90x40x15.dwnslp (update output)
>> You can try it by updating your code and setting  PTRACERS_addSrelax2EmP=.TRUE.,
>> in data.ptracers (there is an example in
>> verification/global_ocean.90x40x15/input.dwnslp/data.ptracers)
>> Let me know if something does not work as expected.
>> Cheers,
>> Jean-Michel
>> On Wed, Sep 01, 2010 at 02:07:01PM -0400, Jean-Michel Campin wrote:
>>> Hi Christoph,
>>> 
>>> Yes, this is an issue that has been floating around for some time
>>> (see, e.g., the "ALLOW_OLD_VIRTUALFLUX" in pkg/dic/alk_surfforcing.F).
>>> We could add a flag in data.ptracers (off by default) that would
>>> do it. I can have something ready to test/check-in by the end of the week.
>>> 
>>> Cheers,
>>> Jean-Michel
>>> 
>>> On Tue, Aug 31, 2010 at 10:43:27AM +0200, Christoph Voelker wrote:
>>>> Dear colleagues,
>>>> 
>>>> when working with passive tracers in an ocean configuration of MITgcm  one can define the concentration of the tracers in atmospheric water via  the variable PTRACERS_EmPmR, such that evaporation, precipitation and  runoff change the surface concentration of the tracers.
>>>> But if one does (additional) restoring of salinity, the implied  freshwater flux does not enter the tracer balance in the surface model  layers: the tracer balance (ptracers_forcing_surf.F) uses PmEpR, which  does not contain the restoring term.
>>>> I think that there are good reasons to do so (i.e. it is a feature, not  a bug); and if one uses only a weak salinity restoring to prevent model  drift on top of freshwater fluxes from bulk formulae as I am doing  normally this is not a big deal anyway.
>>>> 
>>>> But I am now running a pretty extreme case with strong salinity  restoring (to estimates of glacial SSS) and would like to include the  implied freshwater fluxes into the tracer balances. Has anyone esle had  this problem before and possibly solved/coded the terms in  ptracers_forcing_surf.F? Are there further things one would have to  consider?
>>>> 
>>>> Cheers, Christoph
>>>> -- 
>>>> Dr. Christoph Voelker / Alfred-Wegener Institute for Polar and Marine  Research
>>>> email: cvoelker at awi-bremerhaven.de / tel.#: ++49 471 4831 1848 /
>>>> mail: PO Box 120161, 27515 Bremerhaven, Germany
>>>> 
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> 
> -- 
> Dr. Christoph Voelker / Alfred-Wegener Institute for Polar and Marine
> Research
> email: cvoelker at awi-bremerhaven.de / tel.#: ++49 471 4831 1848 /
> mail: PO Box 120161, 27515 Bremerhaven, Germany
> 
> 
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Dr. David R. Munday
University of Oxford
Atmospheric, Oceanic, and Planetary Physics
Clarendon Laboratory
Parks Road
Oxford
OX1 3PU
U.K.                 01865 284 329

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"But I, being poor, have only my dreams;
I have spread my dreams under your feet;
Tread softly because you tread on my dreams."
     - W.B. Yeats, He Wishes for the Cloths of Heaven -

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