[MITgcm-support] SOM problems

[Christopher L. Wolfe]

Jean-Michel,

I think you've put your finger on the problem. Since my density  
function is linear in temperature only, the 'zero' of the temperature  
scale is irrelevant and my forcing temperatures go from -10 to 10. So  
it's probably trying to clip away half of my temperature distribution.  
I'm trying a run without the limiter.

Martin,

Thanks for the tip. I've been running with StaggerTimeStep = .true.  
since my original runs were with 33.

Thanks,
Christopher


On Jan 24, 2008, at 7:44 AM, Jean-Michel Campin wrote:

> Hi Christopher,
>
> Martin is right. An other thing is that 81 try to make
> the advected field positive (I know, we need to add a true
> limiter that would ensure that no local extremum is generated)
> So for cold water (temperature well below 0 celcius), will
> give very strange things. And for salinity (well above 0),
> the limiter will generally have no effect.
> Would recommand to try 80 (no limiter) and see what you get.
>
> Jean-Michel
>
> On Thu, Jan 24, 2008 at 09:18:45AM +0100, Martin Losch wrote:
>> Christopher,
>>
>> some of the multidim-advection schemes require that you set
>> StaggerTimeStep = .true., (in PARM01), to get results that are
>> comparable to non-multidim advection scheme, e.g., when I switched
>> from scheme 2 to scheme 33 I had to do that in order to not destroy
>> my stratification. Maybe that's relevant for SOM as well ...
>>
>> Martin
>>
>> On 24 Jan 2008, at 03:12, Christopher L. Wolfe wrote:
>>
>>>
>>> Hi modelers,
>>>
>>> Does anyone have any experience using Pather's second order moments
>>> (advection scheme 81) with MITgcm?
>>>
>>> I've been trying to use it starting with a well-equilibrated run
>>> using another advection scheme (using the U,V, Eta, and tracer
>>> fields as initial/hydrography fields since SOM requires different
>>> pickup information), but I'm getting really bizarre results. For
>>> one, I'm finding SOM to be *extremely* diffusive: The advection
>>> scheme is destroying tracer variance at twice the rate of diffusion
>>> (which is relatively large at 8e-5 m^2/s). As a result, the
>>> temperature field looks like one you would expect from a system
>>> with much larger explicit diffusion: the temperature fields are
>>> very smooth and the whole basin is becoming vertically unstratified.
>>>
>>> Has anyone used this advection scheme and gotten good results? Is
>>> there anything I need to do with the configuration, other than set
>>> the advection scheme to 81?
>>>
>>> Thanks,
>>> Christopher
>>>
>>> -----------------------------------------------------------
>>> Dr. Christopher L. Wolfe                   858-534-4560
>>> Physical Oceanography Research Division    OAR 357
>>> Scripps Institution of Oceanography, UCSD  clwolfe at ucsd.edu
>>> -----------------------------------------------------------
>>>
>>>
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