Re: a simple way to calculate monthly mean from 6-hourly data for calandar month?

For averages use

 
http://www.ncl.ucar.edu/Document/Functions/Contributed/dim_avg_n_Wrap.shtml

To do what you want efficiently, you should use
the 'time' variable to partition the data into
year and month segments.

If your 'time' varaiable is (say) "{seconds/hours/days} since ...", use

http://www.ncl.ucar.edu/Document/Functions/Built-in/ut_calendar.shtml

   utc_date = ut_calendar(time, 0)
  ;
  ; Store return information into more meaningful variables.
  ;
    year = floattointeger(utc_date(:,0)) ; Convert to integer for
    month = floattointeger(utc_date(:,1)) ; use sprinti
    day = floattointeger(utc_date(:,2))
    hour = floattointeger(utc_date(:,3))
   ;minute = floattointeger(utc_date(:,4))
   ;second = utc_date(:,5)

    ntim = dimsizes( time )

    yrStrt = year(0)
    yrLast = year(ntim-1)
    nyrs = yrLast-yrStrt+1

    nTIME = 12*nyrs

    xAvg = new ( (/nTime,nlat,mlon/), typeof(p))

    NT = -1
    do yr=yrStrt,yrLast
      do nmo=0,11

         NT = NT+1
         ii = ind(yr.eq.year .and. (nmo+1).eq.month)
         if (.not.ismissing(ii(0))) then
             xAvg(NT,:,:) = dim_avg_n(p(ii,:,:) , 0)
         end if
      end do
    end do

Wei Huang wrote:
> Yang Yang,
>
> You may check:
> http://www.ncl.ucar.edu/Document/Functions/Contributed/dim_sum_n_Wrap.shtml
>
> to see how to do the monthly mean.
>
> Wei Huang
> huangwei@ucar.edu
> VETS/CISL
> National Center for Atmospheric Research
> P.O. Box 3000 (1850 Table Mesa Dr.)
> Boulder, CO 80307-3000 USA
> (303) 497-8924
>
>
>
>
>
> On Oct 14, 2009, at 9:03 PM, Yang Yang wrote:
>
>> Hello:
>>
>> I have 6-hourly data for 30 years. Each file has one year data in a
>> dimension like (time,lat,lon). For some years, the total number of
>> days in Feb. is 29 instead of 28.
>>
>> I would like to calculate monthly mean from the 6-hourly data for
>> Jan., Feb., ..., Dec., respectively, for each year.
>>
>> Is there a simple way in NCL to do the monthly mean?
>>
>> Thank you very much!
>>
>> Ed
>>
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Received on Thu, 15 Oct 2009 01:47:13 -0600