Re: time_counter as axis

To: Ferret Users <oar.pmel.ferret_users@xxxxxxxx>
Subject: Re: time_counter as axis
From: Jaison Kurian <jaison@xxxxxxxxxxxxxxxxxx>
Date: Thu, 2 Sep 2004 00:23:52 +0530 (IST)
Cc: Ansley Manke <ansley.b.manke@xxxxxxxx>, "Arthur M. Greene" <amg13@xxxxxxxxxxxxx>
In-reply-to: <413604DE.6060106@noaa.gov>
Sender: owner-ferret_users@xxxxxxxxxxxxx
Hi,
     As Ansley pointed out the example script is working fine and 
the climatology is exactly matching with the manually calculated 
mean.

yes? define axis/t=1:60:1 tabs

yes? let v  = 30 - ( sin(t[gt=tabs]) ) + RANDU(t[gt=tabs])

yes? let v_3to5yr = TSEQUENCE(v[L=25:60])

yes? define axis/T=0:`365.2425*3`/NPOINTS=36/EDGES/units=days/\
...? T0="01-JAN-1974:00:00" t3to5yr

yes? let v_3to5yr_t = v_3to5yr[gt=t3to5yr@asn]

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

yes? let v_clim_12mon = v_3to5yr_t[GT=tclim@MOD]

yes? set list/precision=10

yes? cancel mode verify

yes? REPEAT/k=1:12:1 ( ;\ 
...? let mon    = `k`  ;\
...? let v_mean =  ( v_3to5yr_t[l=`mon`] +  v_3to5yr_t[l=`mon+12`] + \
...?                            v_3to5yr_t[l=`mon+24`] )/3 ;\
...? list/nohead mon, v_clim_12mon[l=`mon`], v_mean;\
...?  )
I / *:     1.000000000  31.11149597  31.11149597
I / *:     2.000000000  30.45406342  30.45406342
I / *:     3.000000000  29.73362923  29.73362923
I / *:     4.000000000  29.80100060  29.80100060
I / *:     5.000000000  30.65710258  30.65710258
I / *:     6.000000000  31.01781273  31.01781273
I / *:     7.000000000  31.00856209  31.00856209
I / *:     8.000000000  30.23208427  30.23208427
I / *:     9.000000000  29.78796387  29.78796387
I / *:     10.00000000  29.93144226  29.93144226
I / *:     11.00000000  30.38167381  30.38167381
I / *:     12.00000000  31.16622925  31.16622925
yes?


  If you need any more clarification about the @MOD & @ASN regridding 
functions please let  me know

 With Regards 
 
 Jaison 
 
On Wed, 1 Sep 2004, Ansley Manke wrote:

> Hi Arthur,
> It sounds like you've about got it. I don't see anything wrong
> with your commands. Ferret does not interpolate your data to
> days as it's computing the monthly climatology; days are the
> coordinate units but the monthly data is kept as monthly data.
> 
> This example works correctly, just using all of your commands
> but just integers as the data.  See if any of the list commands I
> have here help you figure out what's happening with your data:
> 
>   yes? let v_3to5yr = tsequence(t[t=25:60])
>   yes? list/L=1:5  v_3to5yr
>              VARIABLE : TSEQUENCE(T[T=25:60])
>              SUBSET   : 5 points (T)
>    1   / 1:  25.00
>    2   / 2:  26.00
>    3   / 3:  27.00
>    4   / 4:  28.00
>    5   / 5:  29.00
> 
>   yes? def axis/t=0:1095.7275/npoints=36/edges/units=days/\
>      t0="01-jan-1974:00:00" t3to5yr
>   yes? let v_3to5yr_t = v_3to5yr[gt=t3to5yr@asn]
> 
>   yes? def axis/t=0:365.2425/edges/npoints=12/
>      \t0=1-jan-0001/units=days/modulo tclim
>   yes? let v_clim_12mon = v_3to5yr_t[gt=tclim@mod]
> 
>   yes? list v_clim_12mon
>              VARIABLE : V_3TO5YR_T[GT=TCLIM@MOD]
>              SUBSET   : 12 points (TIME)
>    16-JAN      /  1:  37.00
>    15-FEB      /  2:  38.00
>    18-MAR      /  3:  39.00
>    17-APR      /  4:  40.00
>    17-MAY      /  5:  41.00
>    17-JUN      /  6:  42.00
>    17-JUL      /  7:  43.00
>    17-AUG      /  8:  44.00
>    16-SEP      /  9:  45.00
>    17-OCT      / 10:  46.00
>    16-NOV      / 11:  47.00
>    17-DEC      / 12:  48.00
> 
>      ! Check some averages
>   yes? list v_3to5yr_t[l=1:36:12]  ! January values averaged
>              VARIABLE : V_3TO5YR[GT=T3TO5YR@ASN]
>                         regrid: 365 day on T
>              SUBSET   : 3 points (TIME)
>    JAN-1974 / 1:  25.00
>    JAN-1975 / 2:  37.00
>    JAN-1976 / 3:  49.00
> 
>   yes? list (28+40+52)/3    ! mean agrees with Jan of v_clim_12mon
>              VARIABLE : (28+40+52)/3
>           40.00
> 
> 
>   yes? list v_3to5yr_t[l=4:36:12]  ! April values averaged
>              VARIABLE : V_3TO5YR[GT=T3TO5YR@ASN]
>                         regrid: 365 day on T
>              SUBSET   : 3 points (TIME)
>    APR-1974 / 1:  28.00
>    APR-1975 / 2:  40.00
>    APR-1976 / 3:  52.00
>   yes? list (25+37+49)/3    ! mean agrees with Apr of v_clim_12mon
>              VARIABLE : (25+37+49)/3
>           37.00
> 
> 
> 
> Arthur M. Greene wrote:
> 
> >Hi Jason,
> >
> >Thanks for the reply! Here's what I've been able to do (There are 5
> >years of monthly variable v; we wish to construct a climatology for the
> >last three years):
> >
> >let v_3to5yr = tsequence(v[L=25:60])   ! Extract desired time slice
> >
> >define axis/T=0:1095.7275/npoints=36/edges/units=days/\
> >T0="01-jan-1974:00:00" t3to5yr
> >
> >let v_3to5yr_t = v_3to5yr[GT=t3to5yr@asn]
> >
> >So far, so good. I now have three years of data on a real-time axis,
> >beginning with jan-1974. The plot looks OK. Now for the climatology:
> >
> >define axis/T=0:365.2425/EDGES/NPOINTS=12/\
> >T0=1-JAN-0001/UNITS=DAYS/MODULO tclim
> >
> >let v_clim_12mon = v_3to5yr_t[GT=tclim@MOD]
> >
> >This does produce a 12-month plot that _looks_ like a climatology (i.e.,
> >x-axis reads Jan, Feb, Mar...), but the values are not equal to the
> >averages of the corresponding month's values in v_3to5yr_t, i.e.,
> >v(Jan,v_clim_12mon) <> (Sum of Jan vals in v_3to5mon)/3. So perhaps I
> >don't understand how the MOD (or ASN, for that matter) climatologies are
> >actually computed. Even if the 36 months of data were interpolated into
> >daily values, and the appropriate daily values averaged to produce the
> >monthly climatology, the resultant would not appear to be correct. The
> >docs do not seem to clarify exactly how these climatologies are computed
> >(or maybe I need a refresher!)
> >
> >Your comments greatly appreciated!
> >
> >Thanks,
> >
> >Arthur
> >
> >On Wed, 2004-09-01 at 08:33, Jaison Kurian wrote:
> >
> >  
> >
> >>! --------------example.jnl--------------------------------
> >>   ! extract last three years data ie. abstract index L=25:60
> >>
> >>   let v_3to5yr = TSEQUENCE(v[L=25:60])
> >>
> >>   ! define monthly time axis from JAN-1997 to DEC-1999 & assign it
> >>   !     T=0:`365.2425*3`/NPOINTS=36/UNITS=DAYS together will make it for 
> >>   !      3 years and  T0 will take care of actual year stamp.
> >>
> >>      define axis/T=0:`365.2425*3`/NPOINTS=36/EDGES/units=days/\
> >>                  T0="01-JAN-1997:00:00" t3to5yr
> >>
> >>      let v_3to5yr_t = v_3to5yr[gt=t3to5yr@asn] 
> >>
> >>   ! Define a monthly climatological axis 
> >>   
> >>      define axis/T=0:365.2425/EDGES/NPOINTS=12/T0=1-JAN-0001/\
> >>                     UNITS=DAYS/MODULO tclim
> >>
> >>   ! Find monthly climatology by "MODULO" regridding
> >>
> >>      let v_clim_12mon = v_3to5yr_t[GT=tclim@MOD]
> >>      plot v_clim_12mon     
> >>
> >>! If you want to find anomaly or want to plot the climatology
> >>!   over the data then please refer :
> >>!   http://ferret.pmel.noaa.gov/Ferret/Mail_Archives/fu_2003/msg01470.html
> >>
> >>!---------------------- end of example.jnl-------------
> >>    
> >>
> >
> >
> >  
> >
> 

-- 
___________________________________________________

    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
___________________________________________________
References:
- Re: time_counter as axis
  - From: Ansley Manke
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