[ncl-talk] eof function
Maria Gehne - NOAA Affiliate
maria.gehne at noaa.gov
Thu Sep 3 16:55:09 MDT 2015
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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