Re: working with JJAS time period of different years

[Jaison Kurian <jaison@xxxxxxxxxxxxxxxxxx>]

Hi Roxy,
         The FAQ suggested by Ansley explains the basic method to get
seasonal data. I just want to add an easy way to pick the "L" or "T" for 
the desired(here JJAS)  season of each year and create new variables : one 
with only JJAS data (no information about other months) and other one with 
missing values for rest of the months.

 From your mail....
>       var=precip[t=01-jun-1998:30-sep-1998]
>       save/file=precip_jjas.cdf var

     To precip_jjas.cdf you can't add data(var) for jun-sep1999. For 
doing this you must have opened precip_jjas.cdf with proper "LLIMITS"
so that you can add "var" for other time periods to this file. If you 
want more information please refer user manual Ch10 Sec2 & this mail
in the archive
http://ferret.pmel.noaa.gov/Ferret/Mail_Archives/fu_2001/msg00282.html  
          
!----------extract_jjas.jnl-------------

! let us make some dummy data (pentad)

    define axis/t="01-JAN-1998":"31-DEC-2002":5/unit=days tpent
    let myvar = sin(t[gt=tpent]/250)
    set var/title="Pentad Rainfall data 1998-2002"/units="mm/day" myvar

! get T0 & time units of the variable for later use
 
    define symbol tzero  = `myvar,return=T0`
    define symbol tunits = `myvar,return=TUNIT`

! get the "time values" of JJAS from 1998 to 2002 in a text file

    sp rm -f dummy.dat
    REPEAT/L=1998:2002 ( ;\
         set reg/t="01-JUN-`L`":"30-SEP-`L`" ;\
         let tim = t[gt=myvar] ;\
         list/nohead/quiet/file=dummy.dat/format=(2x,f8.2)/append tim ;\
       )
! read the time values from dummy.dat and do the "exact" regridding

    cancel reg/all ; cancel var tim
    file/var=tim dummy.dat   
    define axis/t/T0=($tzero)/units=($tunits)/from_data tax=tim
   
    let var_jjas = myvar[gt=tax@xact]   

       ! above variable doesn't have any information about months other 
       ! than JJAS...hence while plotting Ferret will linearly interpolate
       ! the values for those missing months

    let rain = var_jjas[gt=myvar@xact]  

       ! above variable will have the information "missing_value" for 
       ! months other than JJAS..hence Ferret will not perform any 
       ! interpolation  

    set var/title="Seasonal(JJAS) Rainfall"/units="mm/day" rain

! cross-checking

    plot/line=4/dash myvar
    plot/ov rain        
    
! save to a netCDF file

    ! save/file=rain_JJAS.nc/append rain

! remove the dummy file

    sp rm -f dummy.dat

!-------end of extract_jjas.jnl----------------------

Hope This Helps

With Regards

Jaison 



On 23 Aug 2004, Roxy Mathew wrote:

> Hi Ferreters, I have a netcdf file with precipitation
> from Jan 1998 to Dec 2002 (pentad values).
> I want but to work with the JJAS time period only.
> Is there any way I can extract the JJAS time period
> of all the years to a new netcdf file?
> Or is there another way I can process the JJAS months
> together?
> I tried with the following method but it is not working:
> 
> 	var=precip[t=01-jun-1998:30-sep-1998]
> 	save/file=precip_jjas.cdf var
> 	var=precip[t=01-jun-1999:30-sep-1999]
> 	save/append/file=precip_jjas.cdf var
> 
> Thanks for any help :) Cheers, Roxy
> 
> EES, Hokkaido University
> Sapporo, Japan
> 

-- 
___________________________________________________

    Jaison Kurian                           
    Centre for Atmospheric and Oceanic Sciences
    Indian Institute of Science
    B A N G A L O R E   560 012
    Ph: +91-80-3942505
        +91-80-3600450
    Fax:+91-80-3600865
___________________________________________________