[gradsusr] Meridional gradient?

[Jeffrey Duda]

Li,
If you want to find a temperature gradient, why not just use cdiff?  Just
realize that you'll have to use the following expression for dy (the
incremental change in meridional distance between grid points, in meters):

dy = Re*cdiff(lat,y)*(3.14159/180)

where Re is the radius of the Earth (about 6.371e6 meters, I believe).
This is to account for the projection Grads uses to display your data.  Hope
this helps.

Jeff Duda

On Mon, May 3, 2010 at 3:20 PM, Li Dong <ldong at unm.edu> wrote:

> Hello list,
>
> I need to calculate the meridional temperature gradient across 20 degree
> latitude belt using global gridded data. Below is what I did:
>
> 'open ta.ctl'
> 'set t 1'
> 'set lev 1000'
> 'set lon 0 360'
> 'set lat -80 80'
> 'define Tgrad=ta(lat+10)-ta(lat-10)'
>
> However, Grads complained "Cannot use an offset value with a varying
> dimension". If I set 'lat' at a fixed value, such as 'set lat 40', the
> above script did work, but the downside is that this only gives
> temperature meridional gradient at the specified latitude instead of
> over the entire latitude range. Any inputs would be highly appreciated!
>
> Best,
>
> Li
>
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-- 
Jeff Duda
Iowa State University
Meteorology Graduate Student
3134 Agronomy Hall
www.meteor.iastate.edu/~jdduda
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