[ferret_users] seasonal averaging

["nadia.rehman" <nadia.rehman@xxxxxxxxxxxx>]

Hi users,
I have done seasonal averages for ten (1961:1970) years. The procedure i have followed for summer averages is as follows:
use "SRF-ECHAM-1960-70.nc"
let mod1=ta[l=18:21@ave]
let mod2=ta[l=30:33@ave]
let mod3=ta[l=42:45@ave]
let mod4=ta[l=54:57@ave]
let mod5=ta[l=66:69@ave]
let mod6=ta[l=78:81@ave]
let mod7=ta[l=90:93@ave]
let mod8=ta[l=102:105@ave]
let mod9=ta[l=114:117@ave]
let mod10=ta[l=126:129@ave]
let mod11=mod1+mod2+mod3+mod4+mod5+mod6+mod7+mod8+mod9+mod10
let modave=(mod11/10)-273.16

it z short one because i have used it for 10 years but if i want to do it for 30 or 50 years then i think it would be to long and also time taking. Is there any short way to calculate the above summer averages???????????
Thanks  

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Nadia Rehman Yousafzai
Research Fellow (Climate Section)
Global Change Impact Studies Centre
First Floor Saudi Pak tower 
Blue Area Islamabad Pakistan
Ph :   92-51-9219785
Fax : 92-51-9219787 
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