[MITgcm-support] MITgcm-support Digest, Vol 128, Issue 38

[Neil Patel]

thanks for the responses. But out of curiosity, what are the negative consequences of having a viscAhGrid too small? My model ran okay with an even smaller value of viscAhGrid.

Thanks,

Neil


> 
> 
> Neil,
> 
> I think that your viscAhGrid is too small. I?d try something like 0.1
> Also you might want to try biharmonic viscA4Grid.
> 
> The flow dependent viscosity parameterization (especially Leith, see Dimitris suggestion) are usually the most stable choices.
> 
> Martin
> 
> On Feb 28, 2014, at 1:44 AM, Neil Patel <nigellius at gmail.com> wrote:
> 
>> Hi,
>> 
>> I'm having trouble understanding the different viscosity parameters. Read the mitgcm manual many time over but still am confused. From what I can tell:
>> 
>> 1) Vertical eddy viscosity doesn't affect the numerical stability, so choose the value closest to the observations for ViscAr
>> 2) Horizontal eddy viscosity does affect the numerical stability and the number chosen should be similar to various energy scaling / grid parameters.
>> 
>> currently, I'm running a 1/6? resolution simulation. I set 
>> 
>> viscAr=5.6614E-04,
>> 
>> and 
>> 
>> viscAhGrid=0.01,
>> viscAhReMax =0.1,     
>> viscAhGridMax=0.1,  
>> 
>> I'm not sure what the difference between the last two. With the current setup I have, will the viscosity always be within the CFL condition? And so, If my model crashes  ? "SOLUTION IS HEADING OUT OF BOUNDS" is what I've been getting, with the parameters above could the viscosity parameters be the issue or is it soley due to too large a time step. What would be the negative of setting the viscAh parameters to a very low number? Would it be an unphysical ocean or just a poor parametrization of small flows or neither?
>> 
>> I've read the details of the Leith / Smagorinsky parameters. I presume they're a replacement to setting viscAhGrid/viscAhGridMax parameters, but not sure what the advantages or disadvantages of either are.
>> 
>> Thanks for any explanation you can give.
>> 
>> Thanks,
>> 
>> Neil
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> 
>