[MITgcm-support] negative salt values

[acondron at sfos.uaf.edu]

Hi Martin

I re-ran my simulation with advection scheme 33, and this has resolved the
issue. Many thanks for the quick response and assistance.

best,
Alan


> Hi Alan,
>
> when you add a lot of fresh water without the proper boundary conditions,
> you are bound to get negative salinities. I believe, that these are the
> important parameters, that turn on the "true" fresh water flux boundary
> conditions together with the non-linear free surface and the z*
> coordinates:
>
>>  implicitFreeSurface=.TRUE.,
>>  exactConserv=.TRUE.,
>>  select_rStar=2,
>>  nonlinFreeSurf=4,
>>  hFacInf=0.2,
>>  hFacSup=2.0,
>>  useRealFreshWaterFlux=.TRUE.,
>
> Are these your parameters?
>
> In the case of large horizontal gradients, there's always the possiblity
> of over/undershoots due to insufficient advection schemes. For your
> experiment you should use something with flux limiter, e.g. 33 or 77 (even
> then, you might get very, very small undershoots, according to my
> experience, in theory this should not happen).
>
> Martin
> On Feb 12, 2010, at 2:22 AM, Alan Condron wrote:
>
>> Hi all
>>
>> I have been doing some experiments simulating large glacial flood
>> events. To simulate such events I'm adding 5 Sv of water as RUNOFF, into
>> 5 model grid boxes in hudson bay .
>> When I attempt to do this in the global_ocean.cs30x15 setup, I find that
>> I can create negative salinity values where I add the flood, and also
>> away from this region as the flood event advects in the model. I also
>> get negative values in a tracer I tag the flood waters with.
>>
>> I was surprised I could get negative salinity values. And I wonder if
>> its simply the case of setting a flag in the set-up to avoid this?
>>
>> Thanks
>> Alan
>>
>> Dr Alan Condron
>> 112 O'Neill
>> P.O. Box 755220
>> University of Alaska Fairbanks
>> Fairbanks, AK 99775-7220
>> Phone: (907) 474-7707
>>
>>
>>
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>
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