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Re: R: Re: [ferret_users] Different results between ferret and other softwares

Hi Markus,

| However, I have a doubt about the average to use: is it better to
| use the weighted average or the non-weighted average to compute the
| mean global temperature ?

The weighted average is the average you want, unless you have
specific reasons to use other types of average.

You use numerical models, which are meant to model the reality.
And in reality, the usual mean temperature is

   [integral d(area) T] / (total area).

Ferret computes an approximation to this value using the
gridded T field.  The "weight" we are talking about
is just a natural consequence of this formulation.

Another, practical argument is that a properly-weighted average
depends less on the underlying coordinate system or on the grid
spacing.   Suppose, for example, that you increase the latitudinal
resolution near the equator, so that you have more gridpoints
near the equator.  Your unweighted-average will suddenly rise,
a result which normally you don't want.


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