[gradsusr] weighting in vertical in 'ave' function?

[Raman Aishwarya]

@jma at cola.iges.org
Dear Madam,

I'm eager to speak to you. Apologies for interruption. I had sent u a mail
regarding my internship .I'm raring to speak to you regarding.

Regards,
Aishwarya.

On Fri, Apr 9, 2010 at 12:23 AM, Jennifer Adams <jma at cola.iges.org> wrote:

> Hi, Katrina --
> I did a simple test:
>  ga-> man =
> (u(z=1)+u(z=2)+u(z=3)+u(z=4)+u(z=5)+u(z=6)+u(z=7)+u(z=8)+u(z=9)+u(z=10))/10
>  ga-> avg = ave(u,z=1,z=10)
> ga-> mean = mean(u,z=1,z=10)
> ga-> d avg-man
>  Contouring: -1e-14 to 1e-14 interval 2e-15
> (this is just the noise)
> ga-> d avg-mean
>  Constant field.  Value = 0
>
> So the ave() and mean() functions give the same thing. There is no
> weighting in the vertical. And I am unable to reproduce a significantly
> different average when calculating in manually. How did you calculate "a
> straight average of T over 11 levels" that was different from ave()?
> --Jennifer
>
>  On Apr 7, 2010, at 4:08 PM, Katrina Hales-Garcia wrote:
>
>  Hello,
> I recently joined the grads users' group.  And I do apologize if this topic
> is covered in the old list archives, I haven't been able to access them to
> search.
>
> I am trying to reproduce/understand a value averaged in the vertical over a
> subset of layers.  The variable was defined by something simple like:
>
> define Tave=ave(T,z=1,z=11)
>
> However, I find this is different than a straight average of T over the 11
> levels.  In the documentation, it is noted that ave has some weighting for
> non-linear grid spacing in the y-direction, averaging along latitude.  But I
> haven't found the details of weighting in the vertical.  If I use the
> function 'mean' instead of 'ave' I get the same result (which according to
> the documentation, does not have the non-linear grid space weighting at
> least in the y-direction).  (Excerpt from the documentation below.)
>
> Of course, the data I'm looking at has non-linear spacing in the vertical
> pressure coordinate.  Does anyone have details of how this weighting is
> done?
>
> Thanks much,
> Katrina
>
>  What is in the documentation:
> Usage Note 3
> The average is weighted by grid interval to account for non-linear grid
> spacing. Averages in the latitude dimension are weighted by the difference
> between the sines of the latitude at the northern and southern edges of the
> grid box. The edges of the grid box are always defined as being the midpoint
> between adjacent grid points. To calculate an average without using the
> latitude weighting, use the mean<http://grads.iges.org/grads/gadoc/gradfuncmean.html>
> function.
>
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>
>  --
> Jennifer M. Adams
> IGES/COLA
> 4041 Powder Mill Road, Suite 302
> Calverton, MD 20705
> jma at cola.iges.org
>
>
>
>
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