[ncl-talk] power spectrum analysis

[Dennis Shea]

Not sure of your objective but ...

   spec at frq = spec at frq/30.50                                       ; 30.5
day/month
   res at tiXAxisString = "Frequency (cycles/day)"           ; xaxis
   plot=gsn_csm_xy(wks,spec at frq,spec at spcx,res)     ; create plot

On Fri, Oct 25, 2019 at 9:32 AM Edwin Marco via ncl-talk <ncl-talk at ucar.edu>
wrote:

> Hi,
> I am new to ncl and I have been trying to plot the spectrum of daily
> rainfall data using this kind of script ( attached below) unfortunately I
> am not getting there, please can you help me on how I can modify the
> attached script which was intended for frequency (cycles/month) as to get
> frequency (cycles/day).
> Thanks in advance.
>
> Edwin
>
> spec_1.ncl
> ;
> ; Concepts illustrated:
> ;   - Calculating and plotting spectra
> ;************************************************
> ;
> ; These files are loaded by default in NCL V6.2.0 and newer
> ; load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
> ; load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
> ;************************************************
> begin
> ;************************************************
> ; variable and file handling
> ;************************************************
>    fn  = "SOI_Darwin.nc" ; define filename
>    in  = addfile(fn,"r")                                 ; open netcdf file
>    soi  = in->DSOI                                       ; get data
> ;************************************************
> ; set function arguments
> ;************************************************
> ; detrending opt: 0=>remove mean 1=>remove mean and detrend
>   d = 0
> ; smoothing periodogram: (0 <= sm <= ??.) should be at least 3 and odd
>   sm = 7
> ; percent tapered: (0.0 <= pct <= 1.0) 0.10 common.
>   pct = 0.10
> ;************************************************
> ; calculate spectrum
> ;************************************************
>   spec = specx_anal(soi,d,sm,pct)
> ;************************************************
> ; plotting
> ;************************************************
>    wks  = gsn_open_wks("png","spec")               ; send graphics to PNG file
>
>    res = True					   ; plot mods desired
>    res at tiMainString = "SOI"		           ; title
>    res at tiXAxisString = "Frequency (cycles/month)"  ; xaxis
>    res at tiYAxisString = "Variance"                  ; yaxis
>
>    plot=gsn_csm_xy(wks,spec at frq,spec at spcx,res)     ; create plot
> ;***********************************************
> end
>
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