[MITgcm-support] noise in high resolution run

[Matthew Mazloff]

Hi Martin,

I don't think my noise had a specific orientation.  I can look to see  
if I still have an old field laying around and get back to you.  My  
noise showed up near antarctica and was patchy.  It definitely was  
not related to the open boundary; I feel it was related to flow near  
the Antarctic topography.  As you know, the noise was eliminated by  
turning up the viscosity in the bottom 2 cells.  Yet my noise in U  
did look similar to what you have.  I will try to find an old field.

-Matt


On Mar 30, 2006, at 2:51 PM, Martin Losch wrote:

> Hi Matt, thanks for your comments. I did try your bottom enhanced  
> viscosity, but that did not change a thing. Can you remember, if  
> "your" noise was similarily oriented as "mine" in
> http://mitgcm.org/~mlosch/noise.png
> ?
> M
> On Mar 30, 2006, at 8:39 PM, Matthew Mazloff wrote:
>
>> 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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