Averaging daily to monthly values

Stefan Fronzek sfronzek at SONNENKINDER.ORG
Tue Jun 20 04:50:33 EDT 2006


Dear Arindam,

Thanks a lot for your solution -- that is exactly what I was looking for.

See copied below also an alternative solution that Eric DeWeaver has send to
me directly and which I think missed the list (thanks also to Eric).

Regards,
Stefan

On Sat, 17 Jun 2006 15:27:31 -0400, Arindam Chakraborty
<arch at IO.MET.FSU.EDU> wrote:

>hi Stefan,
>        you need to write the monthly means to another file to be able
>to use them as a time series. The following code is an example of
>making monthly means from daily data considering leap years and
>writing to output file.
>
>* Make monthly means from daily data considering leap years.
> reinit
> mday = '31 28 31 30 31 30 31 31 30 31 30 31'
> month = 'jan feb mar apr may jun jul aug sep oct nov dec'
>
> 'open file'
> 'set x 1 ...'
> 'set y 1 ...'
>
> 'set gxout fwrite'
> 'set fwrite outputfile'
>
> yr1 = 1961
> yr2 = 2000
>
> yr = yr1
> while(yr<=yr2)
>  leap = 0
>  if(math_mod(yr,400) = 0 | math_mod(yr,4) = 0 & math_mod(yr,100) != 0)
>   leap = 1
>   say yr' is a leap year.'
>  endif
>  imon = 1
>  while(imon <= 12)
>   md = subwrd(mday,imon)
>   mc = subwrd(month,imon)
>   if(imon = 2); md = md + leap; endif;
>   time1 = '01'mc''yr
>   time2 = md''mc''yr
>*   say time1' 'time2
>   'd ave(yourvariable,time='time1',time='time2')'
>   imon = imon + 1
>  endwhile
>  yr = yr + 1
> endwhile
>
>
>
>----------------------------
> ARINDAM CHAKRABORTY
> Department of Meteorology
> Florida State University
> Tallahassee, FL-32306, USA
> Tel: +001-850-6443524 (Off)
>      +001-850-5758550 (Res)
> Fax: +001-850-6449642
>____________________________
>
>On Sat, 17 Jun 2006, Stefan Fronzek wrote:
>
>> Dear Grads users,
>>
>> I want to calculate monthly averages from daily data covering the period
>> 01jan1961 to 31dec2000. Is there any clever way of using the ave()-function
>> that would account for the varying lengths of the month (including the
>> handling of leap years)?
>>
>> Thanks for any advice,
>> Stefan
>>

Von: Eric DeWeaver <deweaver at ...>
An: Stefan Fronzek <sfronzek at ...>
Betreff: Re: Averaging daily to monthly values
Datum: 17.06.2006 20:32:44
Hi Stefan,

Here's a loop that does something like that:


mostr='Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec'
yr   =1961
yrend=2000
whle(yr <= yrend)
   mo=1
   while (mo <= 12)
     mo1=mo+1;yr1=yr;if(mo1=13);mo1=1;yr1=yr+1;endif
    'set time 00z01'subwrd(mostr,mo)%yr
    'q dims';line=sublin(result,5);d0=subwrd(line,6);t0=subwrd(line,9)
    'set time 00z01'subwrd(mostr,mo1)%yr1
    'q dims';line=sublin(result,5);d1=subwrd(line,6);t1=subwrd(line,9)-1
     say d0'  'd1'  't0'   't1
    'monmean = ave(data,t='t0',t='t1')'
   endwhile
   yr=yr+1
endwhile


The idea is that you start by finding the time index t1 for February
1.  You don't know whether February has 28 or 29 days, so you figure out
the time index t1 for March 1 and then subtract 1.  That gives you the
time index for the last day of February regardless of leap years.

I haven't run this exact code, so there may be errors.

Best Wishes,

Eric



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