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

[Jennifer Adams]

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  
> meanfunction.
>
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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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