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Re: 20041027: Time interpolation?

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  • Subject: Re: 20041027: Time interpolation?
  • Date: Wed, 27 Oct 2004 15:34:01 -0400
Thanks, this is exactly what I need!

Regards,


-- 
Christian Pagé
http://meteocentre.com/    http://meteoalerte.com/
Etudiant au Doctorat en Sciences de l'environnement UQAM


On 27 Oct 2004 13:13:10 -0600, Steve Chiswell <address@hidden> wrote:
> On Wed, 2004-10-27 at 12:11, Christian Pagé wrote:
> > Hi everyone,
> >
> > Is there a way to do time interpolation in gempak with a grid file?
> > I have 3-hourly data model data that I would like to interpolate to
> > 1-hourly data. Is it possible?
> >
> > Thanks
> 
> Christian,
> 
> You can use GDDIAG and interpolate a field using the formula:
> Xi = X0 + ( X1 - X0)/(t1 - t0) * (ti - t0)
> where ti is a time in the range t0 to t1.
> 
> As example, here is a script that would interpolate the 3 hourly 500mb
> heights in the eta212 to the f+1 and f+2 times for a a starting forcast
> time, and looped for each 3 hourly forecast interval. The desired
> function could also be looped though the desired parameters as well.
> Note that gddiag is runs twice for each 3 hour forecast interval,
> the first for t+1 hour and the second for t+2 hours.
> 
> Also, you can use the ddt(s) function in place of the sub(s1,s2) and
> use the GDATTIM=time1:time2 time interval.
> 
> Steve Chiswell
> Unidata User Support
> 
> #!/bin/csh -f
> 
> # set starting forecast hour and forecast increment
> @ START = 0
> @ INC = 3
> 
> # set model run time
> set MODTIME="041027/1200"
> 
> # initialize forecast time array
> set FTIM=("" "" "" "")
> 
> while ( $START < 84 )
>    @ STOP = $START + $INC
> 
>    @ TN1 = $START + 1
>    @ TN2 = $START + 2
> 
>    # create forecast fxxx strings
>    set TARR=(${START} $TN1 $TN2 $STOP)
>    @ CNT = 1
>    while ( $CNT <= 4 )
>       if ( $TARR[$CNT] < 10 ) then
>          set FTIM[$CNT] = f00${TARR[$CNT]}
>       else
>          set FTIM[$CNT] = f0${TARR[$CNT]}
>       endif
>       echo look $CNT $TARR[$CNT] ftim $FTIM[$CNT]
>       @ CNT = $CNT + 1
>    end
> 
>    gddiag << EOF
>    GDFILE  = eta212|${MODTIME}
>    GDOUTF  = eta212|${MODTIME}
>    GFUNC   = add(hght,mul(quo(sub(hght^${FTIM[4]},hght),${INC}),1)
>    GDATTIM = $FTIM[1]
>    GLEVEL  = 500
>    GVCORD  = pres
>    GRDNAM  = hght^${MODTIME}${FTIM[2]}
>    GPACK   = grib
>    GRDHDR  =
>    r
> 
>    GFUNC   = add(hght,mul(quo(sub(hght^${FTIM[4]},hght),${INC}),2)
>    GRDNAM  = hght^${MODTIME}${FTIM[3]}
>    r
> 
>    e
> EOF
> 
>    @ START = $START + $INC
> end
> 
>