a question about wgt_areaave_Wrap (wgt_areaave)

From: Song Feng <sfeng2_at_nyahnyahspammersnyahnyah>
Date: Sun, 27 Jul 2008 10:41:55 -0500

Hi All:

I am computing the regional average using wgt_areaave_Wrap with no
weighting. The following are part of the code I used:

begin
;*******************************************
; open file and read in data
;*******************************************
  f = addfile ("out_2.5x2.5.nc", "r") ; the data are in
standard 2.5 lon by 2.5 lat gridpoint.
  t = f->pr(:,:,:) ! read the precipitation

; Compute the regional average over (30-50N, 90-110W). No weighting was
applied.
; tclidiv01 = wgt_areaave_Wrap(t(:,{30:50},{250:270}),1.0,1.0, 0)
  tclidiv01 = wgt_areaave_Wrap(t(:,48:56,100:108),1.0,1.0, 0)
   asciiwrite ("Great.Plains.txt" , sprintf("%9.3f", tclidiv01*86400 ))

However the regional average computed by NCL and the GrADS (using
ave(ave(pr,x=101,x=109),y=49,y=57)) are different. See the following for
an example:

Month, Pr (output by NCL), Pr(output by GrADS).
    1 1.535 1.748
    2 1.718 1.905
    3 1.762 1.740
    4 1.873 1.732
    5 2.307 2.249
    6 2.753 2.773
    7 2.108 2.032
    8 0.961 1.094
    9 1.064 1.279
   10 1.446 1.560
   11 1.738 1.869
   12 1.465 1.685

I used the GrADS many times, so I am pretty sure the regional average
output by GrADS are correct. So, what method the NCL used to compute the
regional average? Is he NCL compute the regional average using certain
kind of weighting (even I specified no weighting)?

Best regards!

Song Feng

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Received on Sun Jul 27 2008 - 09:41:55 MDT

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