[ncl-talk] need help to understand how to change the scales in a spectrum plot

[Ruksana Abedin]

Hi,



I have followed the http://www.ncl.ucar.edu/Applications/Scripts/spec_1.ncl
script to plot a spectrum for my data but the specs are very difficult to
visualize clearly in the plot. Data is daily precipitation from model and
two observations for 1988-2007.


1. How to change the x and y axis scales to make it more visible.

2. Can I have the cycles per day instead of months? How to change this
aspect?

3. Can I plot three spectrums for three different files in a panel together?


The variable summary, script and the resultant plot are attached. Your time
and efforts to help me out is highly appreciated.



Variable: PPT_mod
Type: float
Total Size: 25056000 bytes
            6264000 values
Number of Dimensions: 3
Dimensions and sizes:   [time | 7200] x [lat | 30] x [lon | 29]
Coordinates:
            time: [52950.5..60149.5]
            lat: [15.25..29.75]
            lon: [  83..  97]
Number Of Attributes: 10
  z1 :   0
  standard_name :       precipitation_flux
  long_name :   TOTAL PRECIPITATION RATE KG/M2/S
  units :       kg m-2 s-1
  _FillValue :  1e+20
  missing_value :       1e+20
  stash_item :  216
  stash_section :       5
  field_code :  90
  cell_method : time: mean

Variable: PPT_obs1
Type: float
Total Size: 25056000 bytes
            6264000 values
Number of Dimensions: 3
Dimensions and sizes:   [time | 7200] x [lat | 30] x [lon | 29]
Coordinates:
            time: [19880101.5..20071230.5]
            lat: [15.25..29.75]
            lon: [  83..  97]
Number Of Attributes: 5
  long_name :   daily precipitation analysis interpolated onto 0.5deg grids
[mm/day]
  units :       mm/day
  _FillValue :  -99.9
  missing_value :       -99.9
  level_description :   Earth surface

Variable: PPT_obs2
Type: float
Total Size: 25056000 bytes
            6264000 values
Number of Dimensions: 3
Dimensions and sizes:   [time | 7200] x [lat | 30] x [lon | 29]
Coordinates:
            time: [19880101.5..20071230.5]
            lat: [15.25..29.75]
            lon: [  83..  97]
Number Of Attributes: 5
  long_name :   full data daily product version 1 precipitation per grid
  units :       mm/day
  code :        20
  _FillValue :  -99999.99
  missing_value :       -99999.99



;************************************************
begin
;*****************************************************
;read in data
;*****************************************************
f0 = addfile
("/../1WAH_daily_precip_b387clim_Bangladesh_100_1988_2007_land_only.nc",
"r");
f1 = addfile("/../APHRO_1988_2007_correct_daily_precip.nc", "r")
f2 = addfile("/../GPCC_1988_2007_correct_daily_precip.nc","r")

;*****************************************************
; parameters
;*****************************************************

PPT_mod = f0->precip(:,0,:,:)
PPT_mod = PPT_mod*60*60*24
PPT_obs1 = f1->precip
PPT_obs2 = f2->precip

fldmean0 = wgt_areaave_Wrap(PPT_mod,1.0,1.0,1)
fldmean1 = wgt_areaave_Wrap(PPT_obs1,1.0,1.0,1)
fldmean2= wgt_areaave_Wrap(PPT_obs2,1.0,1.0,1)

;printVarSummary(time)

printVarSummary(PPT_mod)
printVarSummary(PPT_obs1)
printVarSummary(PPT_obs2)

;************************************************
; 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(fldmean2,d,sm,pct)
;************************************************
; plotting
;************************************************
   wks  = gsn_open_wks("eps","spec")                ; Opens a eps file

   res = True                       ; no plot mods desired
   res at tiMainString = "Precipitation"                   ; 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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