Re: about spatial Fourier decomposition

From: Dennis Shea (shea AT XXXXXX)
Date: Wed Apr 21 2004 - 11:58:45 MDT

>I have a easy question , I want to get long wave(1-3)
>and short wave(4-) by spatial Fourier decomposition ,
>do NCL have a function can do this?
>x(lat ,lon)---> xwave
>
>Thanks for any suggestion! 

--
Yes, of course. One approach is to use the FFT routines: ezfftf, ezfftb
(Missing data are not allowed.)

See Example 3

--
      nLong  = 3
      xLong  = x
      xShort = x

      ab     = ezfftf(x)
      
      xLong  = ezfftb(ab(:,0:nLong-1), 0.0)  ; total amplitude (1-3)
      xLong@long_name  = "Long Waves"
      
      xShort = ezfftb(ab(:,nLong: ), 0.0)    ; total amplitude (4-nlon/2)
      xShort@long_name = "Short Waves"

--

Youc could also try the spherical harmonic analysis/synthesis
family of functions "sha*" and "shs*"

good luck
D

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