Re: Time averaging

oops! I hit the send email inadvertently ..

On Mon, 4 Sep 2006, Dennis Shea wrote:

>> I have a netcdf data in which a variable has dimension like this
>>
>> Number of Dimensions: 4
>> Dimensions and sizes: [time | 425] x [levels | 20] x [latitude | 94] x
>> [longitude | 37]
>> Coordinates:
>> time: [ 0..5088]
>> levels: [1000.. 100]
>> latitude: [-14.87392044067383..33.12910842895508]
>> longitude: [-9.870802819728851..9.55839616060257]
>>
>>
>> Time starts from 00z1March2000 to next 424 time steps with an interval of
>> 12
>> hrs. Suppose for time averaging from 00Z10jun2000 to 12Z14Jun2000, is
>> there
>> any "trick" to use calendar time instead of dimension number for
>> averaging.
>>
>> print(VarName&time) gives 0, 12, 24, 36, .... 5088
>> ____________________________________________________________
>
  Please read about coordinate variables and coordinate subscripting.

  http://www.ncl.ucar.edu/Document/Manuals/Getting_Started/basics.shtml
  http://www.ncl.ucar.edu/Document/Manuals/Ref_Manual/NclVariables.shtml

  Also, if you have not .... please download the pdf mini-language manual
  http://www.ncl.ucar.edu/Document/Manuals/

  -----

  My speculation is that "time" has units of "hours since ..."
  [or some variant "days since .."]

  If that is the case, here is one possible "trick".

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

     time = f->time
     TIME = ut_calendar(time, -3) ; yyyymmddhh

  [2] x = f->X
     printVarSummary(x) ; original variable

     delete(x&time) ; delete original time values associated
                                    ; with the named dimension "time"

     x&time = TIME ; assigne new coordinate values
     printVarSummary(x) ; new variable

[3] http://www.ncl.ucar.edu/Document/Functions/Contributed/dim_avg_Wrap.shtml

      tStrt = 2000061000
      tLast = 2006061412
      xTimeAvg = dim_avg_Wrap( x(levels|:,lat|:,lon|:,{tStrt:tLast}) )
      printVarSummary( xTimeAvg )
_________________________________________

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Received on Mon Sep 04 2006 - 10:05:24 MDT