[MITgcm-support] L4rdt

[Martin Losch]

Sorry for the confusion,

1. I was talking about L4rdt (I was just omitting the 1/deltatmom  
part, because it's always the same), which applies only when you use  
viscA4grid and/or viscA4max, as far as I can see.
2. Reverting to old code does not fix my problem, so it's something  
else.
3. I do not think that anybody other than us reads the doc/tag-index  
(also the  comment in there just says "fix L4rdt", but not with what  
effect)

I'll keep searching ...

Martin

On Aug 3, 2009, at 2:04 AM, David Ferreira wrote:

> Dimitris Menemenlis wrote:
>> David, does necessity to pump up viscA4grid also carry over to  
>> viscA4GridMax?
>>
>> Specifically, for the CS510 configuration we use
>> viscC4Leith=1.5,
>> viscC4Leithd=1.5,
>> viscA4GridMax=0.5,
>>
>> Recently I have noticed a little more grid scale noise than before  
>> but it is hard
>> to separate this from other modifications to code and model  
>> configuration
>>
>> Do I need to increase  viscA4GridMax by about 30%, as per Martin's  
>> email,
>> to recover previous set up?
> Dimitri,
> looks like the changes in L4rdt also apply to viscA4GridMax.
> But I'm not sure about those 30% of Martin: he was talking about L4,  
> not L4rdt.
> In fact, I'm not even sure that L4 is used in mom_cal_visc.F.
> david
>
>
>
>
>>
>> Thanks, Dimitris
>>
>> On Jul 31, 2009, at 1:02 PM, David Ferreira wrote:
>>
>>> Martin,
>>> I put a note in the tag-index about the L4rdt fix !
>>> Surely, everybody reads it regularly...
>>> Anyway, the viscosity at the corner points were 4 times those at the
>>> center points, so
>>> the "effective" viscosity was larger than intended. And indeed,  
>>> with the
>>> new code, it will
>>> probably be necessary to pump up a bit viscA4grid.
>>> That said, I don't think that L4 was changed by the code  
>>> modification,
>>> only L4rdt.
>>> Are you sure there is not something else going on ?
>>> Cheers,
>>> david
>>
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