[MITgcm-support] noise in high resolution run

[Baylor Fox-Kemper]

Hi Martin,

> useJamartWetPoints is a good suggestion. I will try that next.  
> Since the noise seems to be associated with the coasts it sounds  
> like a good guess. What about the other flags,

> useJamartMomAdv

I was told that this one doesn't really make sense in terms of  
conservation near boundaries, I believe.  I'm no expert in it, though.

> SadournyCoriolis

JMC just told me that this is actually NOT the scheme that Sadourny  
suggests to use, it is really one of the ones that he suggests NOT to  
use in the same paper!  So, I think that for the moment this is  
probably not a good bet either.

> I use
> no_slip_sides=.false.,
> the sidedrag code is a drag to debug. Each time I have a look at  
> it, it looks wrong the first time around and then after 3hs of mind  
> warp it turns out to be right. When I have a look at the plots I  
> find it hard to believe that there is not a bug in the whatever- 
> part of the code (doesn't even have to be the viscosity). I guess I  
> have to start turning off terms and see what happens.
sidedrag can't be the problem then...

What I fear is what Michael suggests:
> we had some problems like this with the NCOM (hydrostatic) at one  
> time and tried all sorts of things.
> it turned out to be an indexing problem in the code.
The question is, where?
   -Baylor

> Dimitris,
> I don't use KPP so far, although I would like to use in the future  
> (maybe, I have enough problems as it is (o:). My experience with  
> KPP is that it tends to amplify noise, but does not generate it  
> (?). In that case the horizontal filters are useful. In this case,  
> I don't think that it will help too much, I am afraid, because the  
> noise is already there without KPP.
>
> Thanks for your suggestions.
> Martin
> On Mar 30, 2006, at 8:06 PM, Baylor Fox-Kemper wrote:
>
>> Hi Martin,
>>   I've seen similar noise in W in some runs, but not so obviously  
>> in U and V.  Have you tried jamartwetpoints?
>>   Also, are you using no-slip?  We found a few bugs in the  
>> sidedrag code a while back.  It might be worth revisiting...I  
>> suppose it is possible that there is a problem elsewhere in the  
>> viscosity/viscous terms code, but I don't know why it would be  
>> localized in space.
>>   -Baylor
>>
>>
>> On Mar 30, 2006, at 8:30 AM, Martin Losch wrote:
>>
>>> Hi,
>>>
>>> I seem to have a problem with a 1/6 by 1/6*cos(phi) run with open  
>>> boundaries. The domain is the Drake Passage. A plot of bathymetry  
>>> and velocities can be found in
>>> http://mitgcm.org/~mlosch/noise.png
>>>
>>> Whatever friction parameters I have tried (viscAh=1e0 to 2e1 and  
>>> viscA4=1e8 to 4e10, and similar for diffusivities, I also tried  
>>> the Leith/Smagorinski variants), I seem to get noise in the north  
>>> western part of the domain. What worries me is, that
>>> 1. The noise seems to propagate (compare day 149 to day 214 in  
>>> the bottom panels of the figure)
>>> 2. The noise seems to be mainly in the x-direction
>>>
>>> I use mom_fluxform. For mom_vecinv the problem is there, too.
>>> I use USE_ISOTROPIC_SCALING (for viscosities because my y-grid  
>>> varies with y) and do not use COSINEMETH_III (although that  
>>> probably doesn't make much of a difference). When I turn off  
>>> USE_ISOTROPIC_SCALING, the noise is still there, but the x- 
>>> alignment is slightly less obvious (although very much present).  
>>> If the noise were deltaX in both directions, I would be concerned  
>>> about my friction parameters. Here I suspect a problem in the  
>>> viscosity implementation, but I cannot see how and were.
>>> There is some noise that is produced by the open boundaries, but  
>>> that usually goes away. I think that the generation of the noise  
>>> is connected to the topography around the tip of South America
>>>
>>> I wonder if anyone has seen something like this before. What do  
>>> you think?
>>>
>>> Martin
>>>
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>>> MITgcm-support at mitgcm.org
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>>
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