[gradsusr] area average method

[Satyaban BishoyiRatna]

Dear Hernán,
Thanks for your reply and sending me the document.
Now, I fully understand about the 'aave' command and it is best to use to calculate area average of a variable.
Also, there is no need to provide any separate weightage like map scale factor., etc either to lat or lon direction.

Thanks.
Regards
Satyaban

On Tue, 17 Aug 2010 19:20:50 +0530  wrote
>Dear Satyaban:
An old printable manual for GrADS (V1.5.1.12) that can be found here:

ftp://grads.iges.org/grads/beta/doc/gadoc151.pdf

says in pages 71-72:


3) The aave function assumes that the world coordinates are longitude in the X dimension and latitude in the Y dimension, and does weighting in the latitude dimension by the delta of the sin of the latitudes. Weighting is also performed appropriately for unequally spaced grids.


I hope this can solve your question.
Regards

Hernán



2010/8/16 Satyaban BishoyiRatna 



Dear Hernán Sala,

I missed 'a' during typing for 'aave' in the second method.

In both the methodology working for 'area average' but which method we should follow. I think the first method will use the map scale factor for calculate area average. Is it really required or 'aave' command will be enough ?


I didn't find any document to use map scale factor for area average calculation.



Thanks.

Satyaban



On Tue, 17 Aug 2010 05:36:19 +0530  wrote

>Dear Satyaban:

I suggest you to see the function aave. You will find more information in:

http://www.iges.org/grads/gadoc/gadocindex

I have used it, for instance, with temperatures from NCEP reanalysis model.





Regards,

Hernán Sala

Instituto Antártico Argentino







2010/8/16 Satyaban BishoyiRatna 







Dear User,



I saw some script, where people follow  two method to calculate the area average value of a specific parameter.







First method is:



'tmp1=ave(tmp*cos(lat*(3.14/180.)),lat=5,lat=50)'



'tmp2=ave(tmp1,lon=40,lon=120)'



'd tmp2'







Second method is:



'tmp1=ave(tmp,lon=60,lon=100,lat=7,lat=40)'



'd tmp1'







Which method one should follow and what the difference one should get.







Thanks.



Regards



Satyaban



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Dr. Satyaban Bishoyi Ratna



CDAC, Pune, India







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Dr. Satyaban Bishoyi Ratna

CDAC, Pune, India



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