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

[Neil Patel]

Thanks. Btw, it looked like my issue was my time step was too big. It was stable for a long time, but eventually crashed with enough model time. I tried using the same time step you described (600 second). Is it possible at 1/6° and Leith Viscosity a larger time step could be stable? Is the time step determined by the CFL criterion or something else?

Thanks,

Neil

> 
> 
> Message: 3
> Date: Thu, 27 Feb 2014 17:25:17 -0800
> From: Dimitris Menemenlis <dmenemenlis at gmail.com>
> To: MITgcm Support <mitgcm-support at mitgcm.org>
> Subject: Re: [MITgcm-support] Viscosity parameters
> Message-ID: <2F879B4C-B263-4645-A0A8-F3E4B2B0C23C at gmail.com>
> Content-Type: text/plain; charset=windows-1252
> 
> If you want to use Leith, you could start by trying:
> 
> viscC4Leith=1.5,
> viscC4Leithd=1.5,
> viscA4GridMax=0.5,
> 
> These are the values we use for the CS510 configuration,
> which is close to 1/6-deg grid spacing around Equator.
> A description of this Leith+ scheme is here:
> http://ecco2.org/manuscripts/2008/FoxKemperMenemenlis08.pdf
> 
> On Feb 27, 2014, at 4:44 PM, Neil Patel <nigellius at gmail.com> wrote:
> 
>> 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.
> 
> 
> 
> 
> ------------------------------
> 
> Message: 4
> Date: Fri, 28 Feb 2014 09:28:40 +0100
> From: Martin Losch <Martin.Losch at awi.de>
> To: MITgcm Support <mitgcm-support at mitgcm.org>
> Subject: Re: [MITgcm-support] Viscosity parameters
> Message-ID: <51D9A937-3899-48A8-8D39-340D3301FAF6 at awi.de>
> Content-Type: text/plain; charset="windows-1252"
> 
> 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
>> _______________________________________________
>> MITgcm-support mailing list
>> MITgcm-support at mitgcm.org
>> http://mitgcm.org/mailman/listinfo/mitgcm-support
> 
> 
> 
> 
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> End of MITgcm-support Digest, Vol 128, Issue 38
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