[ncl-talk] correlation between jjas averaged SST and rainfall

[Sujata Mandke]

Dear NCL users,

Greetings! 
I am sorry to disturb you all in your
busy work schedules.

 I want to plot correlation at each grid point between 
June-September (JJAS) averaged SST anomaly and JJAS  
averaged rainfall anomaly, based on 30 years period. 
Input SST and rainfall data are monthly mean. 

I have calculated monthly climatology using “clmMonTLL” 
and then monthly anomaly using “calcMonAnomTLL”. 
Further, averaged monthly anomaly of JJAS months 
using “runave_n_Wrap”, creating JJAS averaged anomalies 
for 30 years period.  Finally plotted correlation map 
using JJAS averaged anomalies of SST and rainfall. 

However, i understand that averaging monthly anomalies 
of June to September months to calculate JJAS averaged 
anomaly is not correct mathematically, because it may 
cancel out positive and negative anomalies resulting 
in wrong JJAS averaged anomaly.  Since NCL has function
for calculating monthly climatology and monthly anomaly, 
so i have calculated JJAS anomaly in this way.

The correct mathematical method is to estimate
JJAS averaged SST for 30 years period and then 
calculate JJAS averaged climatology from these 
30 years JJAS averaged SST and then calculate 
JJAS averaged anomaly.  
I do not know how to perform these steps in NCL. 

I had extensively searched NCL-talk archives but
did not find the answer to my problem.

I am using NCL version 6.4.0 on linux machine. 

Any suggestion would be of great help.
 Many thanks in advance.
With best regards
Dr. Sujata Mandke
scientist, IITM,PUNE, INDIA