About seasonal averaging

Hello,

I am using some SST data to produce seasonal plots (SKT from NCEP/NCAR
Reanalysis from 1948-2008). I would like to use the function
'dim_avg_Wrap' for that. I am producing plots for the seasons DJF, MAM,
JJA and SON.

There is an example from the NCL website that I am using for my plot:
http://www.ncl.ucar.edu/Applications/Scripts/climo_6.ncl

But I have a question there related to the following lines:
*****
season = (/ (/ 5, 6, 7, 8, 9,10/) \ ; May-Oct [summer]
                     (/ 1, 2, 3, 4,11,12/) /) ; Nov-Apr [winter]
i_season = season - 1 ; NCL indices
etc...
do ns=0,1 ; 2 seasons seasonal climatology
sstSeaClm = dim_avg_Wrap( sstClm(lat|:,lon|:,month|i_season(ns,:)) )
etc...
*****
The fact that the dimension 'month' was used in the line corresponding to
'sstSeaClm' assumes that the dataset has a month dimension. The data set I
am working with has a dimensions of (lat, lon, time). The time dimentions
I am splitting into year, month, day, etc... using the ut_calendar
function. Do I need to assign 'month' as a dimension to my dataset to be
able to do seasonal averages using dim_avg_Wrap?

In my script, I have something like this:
***
etc...
   season = (/1,2,12/) ; DJF
   i_season = season-1
   djf_clim = dim_avg_Wrap(sst(lat|:,lon|:,time|i_season(:)))
etc...
***

Since 'month' is not a dimension in my dataset, I used the variable
'time'. How does 'dim_avg_Wrap' average my dataset in this case? Does it
use the indices 1, 2 and 12 from the time variable? Or does it try to look
for the values of 1,2 and 12? Or is it necessary to add the month
dimension to the dataset so that the numbers 1,2 and 12 can be averaged
correctly? If dim_avg_Wrap uses the numbers in the variable 'season' as
indices, and if it averages over those indices for each year, then the
calculation I am doing is correct, since I have monthly data.

I thank you in advance!

Regards,

Michel

-- 
Michel Mesquita
PhD Student
UAF / IARC
michel_at_iarc.uaf.edu
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