[MITgcm-support] documentation for pkg/smooth

[Matthew Mazloff]

Hi Dimitris

I don't use Gael's standard smoother. I use:

# define ALLOW_SMOOTH2D
# define ALLOW_SMOOTH_CTRL2D
# define ALLOW_SMOOTH3D
# define ALLOW_SMOOTH_CTRL3D
C
# undef ALLOW_SMOOTH_CORREL3D
# undef ALLOW_SMOOTH_CORREL2D

Gael's implementation of Weaver and Courtier 2001 is rigorous. However, in practice, I choose not to use it for a couple reasons and I am happy to discuss if you want. But the primary thing I don't like is the normalization stuff. Also, I find my way more straightforward. The downfall is that when implemented correctly Weaver and Courtier 2001 should be variance preserving and my method is not. (I simply run the diffusion equation on the ctrls.)

Anyway, to help try to address your question: a few years ago I turned Gael's smoother script into matlab to understand what it was doing. The caveat being that this may now be a bit out of date from the way the smoother now works. But it may help you -- so find it attached.

And regarding my opinion on smoothing: It is vital, and Gael's way is great to use. But I highly recommend you make the normalization field manually because it can easily introduce unwanted structure.

Matt

ps> one thing about my way, should you choose to use it, is that it changes the smoother with respect to 
smooth2Dnbt(1)=5000
smooth2D_Lx0(1)=100000.
smooth2D_Ly0(1)=100000.
because there is a missing sqrt of smooth2Dnbt in the main code tree






On Apr 6, 2015, at 4:58 PM, "Menemenlis, Dimitris (329D)" <Dimitris.Menemenlis at jpl.nasa.gov> wrote:

> Dear MITgcmers,
> is any documentation for pkg/smooth available?
> In particular, I am trying to understand how pkg/smooth parameters relate
> the (2 k_1 T)^0.5 length scale discussed in the Weaver and Courtier paper:
> http://mitgcm.org/~gforget/pdfs/weavercourtier01.pdf
> 
> Or more precisely, what is the half-power bandwidth
> of a filter based on following parameters:
> &SMOOTH_NML
> smooth2Dnbt(1)=5000
> smooth2D_Lx0(1)=100000.
> smooth2D_Ly0(1)=100000.
> smooth2Dtype(1)=1
> smooth2Dsize(1)=0
> smooth2Dfilter(1)=0
> 
> Does above define a lowpass filter for scales greater than 100 km,
> 200 km, 628 km, or some other value?
> 
> Thanks, Dimitris
> 
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> MITgcm-support at mitgcm.org
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