[MITgcm-devel] Re: [MITgcm-support] noise in high resolution run
chris hill
cnh at mit.edu
Fri Mar 31 13:23:50 EST 2006
Hi Martin/Patrick,
Is it possible to transfer everything to a directory on faulks, we can
take a more detailed look while you all drink beer.
Thanks,
Chris
Patrick Heimbach wrote:
>
> Hi all,
>
> I am moving this to the devel list.
>
> Given that we've been seeing also somewhat strange behaviour
> in vertical velocity fields near topography and not so stable
> behaviour of the adjoint as a consequence, I am wondering
> (as is Martin) whether this is indicative of a bug.
> Haven't looked carefully recently (in particular after the adjoint
> bug fix for variable aliasing), will dot it soon, but don't think,
> the 4deg adjoint showed this behaviour in much earlier versions.
>
> The adjoint might actually tell us (if we believe it) where to
> look for potential sources of the problem. I'll try to have
> a look next week.
> But maybe it's all ok...
>
> OK, after making such provocative statement, I'll now
> be offline for a few days (and have beers with Martin instead).
>
> -p.
>
>
>
> Quoting Baylor Fox-Kemper <baylor at MIT.EDU>:
>
>> Hi Martin,
>>
>>> useJamartWetPoints is a good suggestion. I will try that next. Since
>>> the noise seems to be associated with the coasts it sounds like a
>>> good guess. What about the other flags,
>>
>>
>>> useJamartMomAdv
>>
>>
>> I was told that this one doesn't really make sense in terms of
>> conservation near boundaries, I believe. I'm no expert in it, though.
>>
>>> SadournyCoriolis
>>
>>
>> JMC just told me that this is actually NOT the scheme that Sadourny
>> suggests to use, it is really one of the ones that he suggests NOT to
>> use in the same paper! So, I think that for the moment this is
>> probably not a good bet either.
>>
>>> I use
>>> no_slip_sides=.false.,
>>> the sidedrag code is a drag to debug. Each time I have a look at it,
>>> it looks wrong the first time around and then after 3hs of mind warp
>>> it turns out to be right. When I have a look at the plots I find it
>>> hard to believe that there is not a bug in the whatever- part of the
>>> code (doesn't even have to be the viscosity). I guess I have to
>>> start turning off terms and see what happens.
>>
>> sidedrag can't be the problem then...
>>
>> What I fear is what Michael suggests:
>>
>>> we had some problems like this with the NCOM (hydrostatic) at one
>>> time and tried all sorts of things.
>>> it turned out to be an indexing problem in the code.
>>
>> The question is, where?
>> -Baylor
>>
>>> Dimitris,
>>> I don't use KPP so far, although I would like to use in the future
>>> (maybe, I have enough problems as it is (o:). My experience with KPP
>>> is that it tends to amplify noise, but does not generate it (?). In
>>> that case the horizontal filters are useful. In this case, I don't
>>> think that it will help too much, I am afraid, because the noise is
>>> already there without KPP.
>>>
>>> Thanks for your suggestions.
>>> Martin
>>> On Mar 30, 2006, at 8:06 PM, Baylor Fox-Kemper wrote:
>>>
>>>> Hi Martin,
>>>> I've seen similar noise in W in some runs, but not so obviously
>>>> in U and V. Have you tried jamartwetpoints?
>>>> Also, are you using no-slip? We found a few bugs in the sidedrag
>>>> code a while back. It might be worth revisiting...I suppose it is
>>>> possible that there is a problem elsewhere in the viscosity/viscous
>>>> terms code, but I don't know why it would be localized in space.
>>>> -Baylor
>>>>
>>>>
>>>> On Mar 30, 2006, at 8:30 AM, Martin Losch wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> I seem to have a problem with a 1/6 by 1/6*cos(phi) run with open
>>>>> boundaries. The domain is the Drake Passage. A plot of bathymetry
>>>>> and velocities can be found in
>>>>> http://mitgcm.org/~mlosch/noise.png
>>>>>
>>>>> Whatever friction parameters I have tried (viscAh=1e0 to 2e1 and
>>>>> viscA4=1e8 to 4e10, and similar for diffusivities, I also tried
>>>>> the Leith/Smagorinski variants), I seem to get noise in the north
>>>>> western part of the domain. What worries me is, that
>>>>> 1. The noise seems to propagate (compare day 149 to day 214 in the
>>>>> bottom panels of the figure)
>>>>> 2. The noise seems to be mainly in the x-direction
>>>>>
>>>>> I use mom_fluxform. For mom_vecinv the problem is there, too.
>>>>> I use USE_ISOTROPIC_SCALING (for viscosities because my y-grid
>>>>> varies with y) and do not use COSINEMETH_III (although that
>>>>> probably doesn't make much of a difference). When I turn off
>>>>> USE_ISOTROPIC_SCALING, the noise is still there, but the x-
>>>>> alignment is slightly less obvious (although very much present).
>>>>> If the noise were deltaX in both directions, I would be concerned
>>>>> about my friction parameters. Here I suspect a problem in the
>>>>> viscosity implementation, but I cannot see how and were.
>>>>> There is some noise that is produced by the open boundaries, but
>>>>> that usually goes away. I think that the generation of the noise
>>>>> is connected to the topography around the tip of South America
>>>>>
>>>>> I wonder if anyone has seen something like this before. What do
>>>>> you think?
>>>>>
>>>>> Martin
>>>>>
>>>>> _______________________________________________
>>>>> MITgcm-support mailing list
>>>>> MITgcm-support at mitgcm.org
>>>>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>>>>
>>>>
>>>> _______________________________________________
>>>> MITgcm-support mailing list
>>>> MITgcm-support at mitgcm.org
>>>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>>>
>>>
>>> _______________________________________________
>>> MITgcm-support mailing list
>>> MITgcm-support at mitgcm.org
>>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>>
>>
>> _______________________________________________
>> MITgcm-support mailing list
>> MITgcm-support at mitgcm.org
>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>>
>
>
>
> --------------------------------------------------------
> Patrick Heimbach Massachusetts Institute of Technology
> FON: +1/617/253-5259 EAPS, Room 54-1518
> FAX: +1/617/253-4464 77 Massachusetts Avenue
> mailto:heimbach at mit.edu Cambridge MA 02139
> http://www.mit.edu/~heimbach/ USA
>
> _______________________________________________
> MITgcm-devel mailing list
> MITgcm-devel at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-devel
>
More information about the MITgcm-devel
mailing list