[MITgcm-support] Unexpected noise with RBCS

[Matthew Mazloff]

So when you look at
grep cfl_W STDOUT.0000
the numbers are small (e.g. <= 0.1)
Because this looks like grid scale noise to me. 

It does have some interesting structure. Does it grow with time or stay stable?
If it is growing with time it may just be chaos
If it is not growing in time it is likely numerical noise, and you need to damp it somehow (e.g. increase visc and/or diff, or perhaps change numerics in some way)

Matt


> On Sep 3, 2021, at 2:00 PM, Peng Zhan <peng.zhan at kaust.edu.sa> wrote:
> 
> Hi Matt,
> 
> Thanks for the suggestions.
> The problem still persists even with a very small time step and a long restoring timescale.
> 
> It is so weird that those noises in the rbcs run appear when the relaxMaskFile has non-zero values wherever placed in the wet points.
> I was wondering if anyone has experienced similar problems before?
> 
> Thanks, Peng
> 
> 
> On Fri, Sep 3, 2021 at 12:12 AM Matthew Mazloff <mmazloff at ucsd.edu <mailto:mmazloff at ucsd.edu>> wrote:
> What is your cfl? You may need to reduce your timestep. 
> If you prefer not reducing your timestep you could likely increase your diffusivity or viscosity. 
> 
> (Another possibility is that your restoring timescale is too short, but this seems to be showing up even outside the box.)
>  
> Matt
> 
> 
> 
>> On Sep 2, 2021, at 1:54 PM, Peng Zhan <peng.zhan at kaust.edu.sa <mailto:peng.zhan at kaust.edu.sa>> wrote:
>> 
>> Hi all,
>> 
>> I am running an experiment with rbcs for temperature.
>> 
>> As shown in the following figure a snapshot of the difference between the rbcs run and the free run, while the region to be relaxed can be specified by the relaxMaskFile (roughly the box area), some unexpected noise appears randomly across the domain. 
>> 
>> Any hint to get out of it is highly appreciated!
>> Thanks in advance, Peng
>> <Screen Shot 2021-09-02 at 11.51.13 PM.png>
>> 
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> -- 
> ______________________________
> 
> Dr. Peng Zhan
> Research Scientist
> Physical Science and Engineering Division (PSE)
> King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia
> Mobile: +966 544701621
>  <mailto:peng.zhan at kaust.edu.sa>
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