Re: anomalies

[Jaison Kurian <jaison@xxxxxxxxxxxxxxxxxx>]

Hi Wendy Wang,
                Ferret is complaining that it can't see a variable
or time axis in the name "cl". To find the anomalies the script 
should be like

           let h_time = h[t=16-jan-1971:16-dec-1980]
           let h_clim = h_time[gt=month_reg@mod]
           let h_a    = h_time - h_clim[t=16-jan-1971:16-dec-1980]

Have a look at this FAQ :
http://ferret.pmel.noaa.gov/Ferret/FAQ/analysis/daily_climatology.html 

  Here is an example based on the above FAQ but for monthly climatology. 
As you can see there isn't any problems with spatial averaged data.

!---------example.jnl------------------------------

     use monthly_navy_winds

! Define a "monthly climatological axis"

     define axis/T=0:365.2425/EDGES/NPOINTS=12/T0=1-JAN-0001/UNITS=DAYS/MODULO tclim

! Make the "monthly" climatology using @MOD regridding

     let uclim_12mon = uwnd[GT=tclim@MOD]

! Now the climatology & uwnd are in different time grids but we need
!   it on the same grid for calculation of anomalies. Since climatology
!   is on a modulo axis we can directly do it like :
!       uwind's tstart is 16-JAN-1982 20:00
!       uwind's tend   is 17-DEC-1992 03:30

     let uclim       = uclim_12mon[T=16-Jan-1982:17-DEC-1992]

! Find the anomaly

     let uanom       = uwnd - uclim

! plotting 

     set reg/X=180/Y=0 
     plot    uwnd
     plot/ov uclim
     plot/ov uanom
     plot/ov uwnd*0    ! zero line
  
     message
    
     plot uanom[x=60:70@ave,y=0:10@ave]

!---------------------end of example.jnl---------------------


Hope This Helps

With Regards 

Jaison




On Mon, 30 Aug 2004, Wendy Wang wrote:

> Hi ferret_users,
> 
> I try to get anomalies:
> 
> yes? let h_time=h[t=16-jan-1971:16-dec-1980]
> yes? let h_clim=h_time[gt=month_reg@mod]
> yes? let h_a=h-h_clim[gt=cl@asn]
> 
> It works fine with original data. But it seems not work with those
> data averaged or integrated over space:
> 
> yes? list h_a
> **ERROR: unknown defining grid: GT=Cl@ASN
> 
> Does anybody know why? Thanks in advance.
> 
> Wendy Wang
> 
> 

-- 
___________________________________________________

    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
___________________________________________________