[ncl-talk] eof function

[Vanúcia Schumacher]

The difference between results generated by NCL and Fortran or ferret is in the amplitude! Using the same data set!I wonder if this difference in amplitude (very low values for NCL) is due to normalization inserted in eofunc_wrap function, would it?



From: maria.gehne at noaa.gov
Date: Thu, 3 Sep 2015 16:55:09 -0600
Subject: Re: [ncl-talk] eof function
To: vanucia-schumacher at hotmail.com
CC: ncl-talk at ucar.edu

I don't think you attached the figure you meant to attach. 
EOFs have no fixed normalization. The value of the patterns (EOFs) and principal components (the time series associated with the patterns) depends on how you normalize. The conventions on how to normalize differ between applications.The only value that is fixed coming out of an EOF analysis are the singular values (the percentage of variance of the EOFs).
Are the spatial patterns the same between Fortran, Ferret and NCL, even if they don't have the same amplitude? What about the time series? If both patterns and time series have a different amplitude maybe that's where the normalization is different.
For NCL the website for the EOF function states:The returned values are normalized such that the sum of squares for each EOF pattern equals one. To denormalize the returned EOFs multiply by the square root of the associated eigenvalue (aka, the singular value).
  
Check if the Fortran and Ferret EOF patterns are normalized in the same way, or not.

Hope this helps,Maria
On Thu, Sep 3, 2015 at 2:59 PM, Vanúcia Schumacher <vanucia-schumacher at hotmail.com> wrote:




The values of EOF (output) are different, as attached (figure)

From: vanucia-schumacher at hotmail.com
To: shea at ucar.edu
Subject: RE: [ncl-talk] eof function
Date: Thu, 3 Sep 2015 17:57:45 -0300




The values of EOF output are different, as attached (figure)


> Date: Thu, 3 Sep 2015 14:51:19 -0600
> Subject: Re: [ncl-talk] eof function
> From: shea at ucar.edu
> To: vanucia-schumacher at hotmail.com
> CC: ncl-talk at ucar.edu
> 
> Different normalizations by the EOFs?
> 
> On Thu, Sep 3, 2015 at 1:44 PM, Vanúcia Schumacher
> <vanucia-schumacher at hotmail.com> wrote:
> > Dear NCL users,
> >
> > I calculated the EOF for the Pacific region ({-20:20},{140:290}) using the
> > function of NCL (eofunc_Wrap) and tested with other programs (ferret and
> > fortran ) and the values of EOF using the NCL are very small compared with
> > the other tested outputs.
> >
> > Using Fortran and Ferret - values between 0.6 to -0.2
> > Using NCL function - values between  0.14 to -0.10
> >
> >
> > Could someone explain to me why this happens?
> >
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