[MITgcm-devel] Re: [MITgcm-support] L4rdt

[Jean-Michel Campin]

Hi Martin,

The changes I made in cg2d (between checkpoint61s & checkpoint61t)
could (with some compiler and with optimisation) change the results 
at the truncation level. But unlikely make your set-up blowing up.

Between checkpoint61o and checkpoint61p, could you add back the
KPP bugs ?

Cheers,
Jean-Michel

On Mon, Aug 03, 2009 at 02:37:50PM +0200, Martin Losch wrote:
> Hi there,
>
> I need help (not that this is anything new): I cannot reproduce my  
> experiments after a recent update and I cannot figure out why. The new  
> runs are substatially more energetic (factor 2), especially way below  
> the surface and near the topography; eventually they blow up after  
> 15months of integration with a CFL violation near the bottom/tile-egde- 
> corner/open boundaries. As an illustration I have attached the monitor  
> variable ke_mean for kemean_run06.png (the old run) and  
> kemean_run06_new.png (with new code). I use adv-scheme 33 (no explicit  
> diffusion), viscA4grid, no_slip_bottom and sides, kpp, seaice, obcs.
>
> I still have my old exectuables, but I need some new functionality  
> (pseudo-timestepping for LSOR), so I need the new code. Plus I have made 
> a few changes (new types of OBCS) so that makes tracking down the  
> problem (or simply reverting to old code) even more difficult.
>
> My first candiate was this 4times lower L4rdt, but this does not help  
> much; it reduces the monitored kemean a little: see attached files  
> kemean_run06.png (the old run) and kemean_run06a.png (the new run but  
> with old L4rdt).
> I noticed (very) small differences in my results between checkpoint61o  
> and checkpoint61p (with mom_calc_visc.F still held at 61o) which I  
> cannot explain (but they seem to be small, maybe this KPP fix in 61p?), 
> but all later checkpoints give the same results as 61p. My old runs are 
> close to checkpoint61m.
>
> Now my question: In the list of changes in doc/tag-index I cannot find  
> anything that I would expect to make my integrations more energetic,  
> except for this L4rdt business in mom_calc_visc.F (and I have kept this 
> routine at checkpoint61o). Does anyone have an idea what might have 
> changed that causes so drastic differences.
>
> Martin
>
>




>
> On Aug 3, 2009, at 9:41 AM, Martin Losch wrote:
>
>> 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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