[MITgcm-support] negative salt values

[Dimitris Menemenlis]

Alan, for the CS510 configuration, we found that advection scheme 33 was too diffusive
and that it quickly erodes thermocline and halocline, especially in Arctic Ocean.
We typically use advection scheme 7.

What advection scheme was causing you to get negative salinity?

Dimitris

Dimitris Menemenlis <menemenlis at jpl.nasa.gov>
Jet Propulsion Lab, California Institute of Technology
MS 300-323, 4800 Oak Grove Dr, Pasadena CA 91109-8099, USA
tel: 818-354-1656;  cell: 818-625-6498;  fax: 818-393-6720

On Feb 13, 2010, at 12:45 PM, acondron at sfos.uaf.edu wrote:

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