[MITgcm-support] noise in high resolution run

[Matthew Mazloff]

Hi Martin,

As you know I've experienced noise near topography as well.   
JamartWetPoints alone and used with useJamartMomAdv caused my model  
to blow up so I didn't experiment to thoroughly with it.
SadournyCoriolis did not reduce the noise, though like  
JamartWetPoints I only tried it with one run.

-good luck,
Matt


On Mar 30, 2006, at 1:23 PM, Martin Losch wrote:

> Hi Baylor, Dimitris,
>
> 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
> SadournyCoriolis
> etc.?
> Any experience with that?
>
> 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.
>
> 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
>>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>>
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