[ferret_users] error in producing seasonal mask JJAS

[archana shrestha <archanamet@xxxxxxxxx>]

Dear All,

I was trying to make time series of JJAS average (from
merged file). I found an example in the Mail Archive
for JJA. I followed the example and get the list of
JJAS time series. But the value for each year in this
time series is different from that I calculated for
the individual year (individual file). For example,
from the time series data JJAS average for 1961 was
14.17, while from induvidual year it was 12.83. Up to
the COMPRESS output, it matches with individual years
data. I would be grateful if anyone can solve this
problem. The method that I followed and the output are
as follows:

use ATM-ECHAMRF1961-89 !monthly data
let L_indx    = L[GT=rt] 
let yr_months = L_indx- 12*INT((L_indx-1)/12) 
list yr_months 
!masking for the months JJAS
let mask_other_months = IF yr_months GT 5 AND
yr_months LT 10 THEN 1 
!area of interest is x=80:92,y=26:30
let rt_masked = rt[d=1,x=80:92@ave,y=26:30@ave ]*
mask_other_months  
let rt_compr  = COMPRESSL(rt_masked) 
list rt_compr
define axis/t=1:116:1 t116  ! 4 months 29 yrs
=4*29=116
let rt_jjas_all = rt_compr[gt=t116@ASN]
list rt_jjas_all ! it gives correct values as follows
VARIABLE : RT_COMPR[GT=T116@ASN]
             FILENAME : ATM-ECHAMRF1961-89.des
             SUBSET   : 116 points (T)
 1     /   1:  12.24
 2     /   2:  17.95
 3     /   3:  10.47
 4     /   4:  10.72
 5     /   5:   7.39
 6     /   6:  16.71
 7     /   7:   9.40
 8     /   8:   7.22
 9     /   9:  17.95
.................
....
116

define axis/t=1:116:4 t29  
let rt_jjas_av  = rt_jjas_all[gt=t29@AVE] 
define axis/t=1961:1989:1/units=years tyear
let rt_jjas  = rt_jja_av[gt=tyear@ASN] 
list rt_jjas ! these values do not match with
individual year calculation 

VARIABLE : RT_JJAS_AV[GT=TYEAR@ASN]
             FILENAME : ATM-ECHAMRF1961-89.des
             SUBSET   : 29 points (T (YEARS))
 1961   /  1:  14.17
 1962   /  2:  11.19
 1963   /  3:  12.48
 1964   /  4:  13.24
...................
..............
 1989..............

Individual year values are

1961  12.83
1962  10.18
....etc

Thank you in advance

Archana 




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