[MITgcm-support] noise in high resolution run

[Martin Losch]

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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