[ncl-talk] plot the dot on the grids with significant trends

[WUJIE]

Hi NCL users,

I am trying to plot the spatial distribution of the trends in annual evaporation. My plan is to show trends for all grids but cover those grids with dots if its trends are significant (i.e. p<0.05).


I calculate rc using the NCL guide and use rc_sig to show only the sigificant trend. I have tested the way to derive rc is correct. I then tried the procedure gsn_coordinates but I got a very big PDF which shows all black. Does any one can help me on this?


If what I did is not correct, could you please give me some clues for drawing such plots?


Thanks so much


Jie.






;----ATTACH CODES HERE-----
;-----------read data and calculate rc------
  Ea                 = ncfile->Ea  ; mm/month
  Ea_annual      = month_to_annual (Ea, 0)  ; monthly to annaul
  
  Ea_annual!0    = "time"
  Ea_annual&time =(/ispan(1980,2015,1)/)  


  Ea_annual_0  = Ea_annual (lat|:,lon|:,time|:)  ;re-order to make time as rightmost
  
  time         = Ea_annual_0&time 
  rc            = regCoef(time,Ea_annual_0)    ;tends with /plat,plon/


  rc at long_name = "Trend of annual Ea"     ; trend
  rc at units         = "(mm yr~S~-1~N~)"  
  
  printVarSummary(rc)
  printMinMax (rc, True)
  
 ;-----make all data become (plat,plon)------
  tval = onedtond(rc at tval , dimsizes(rc))
  df   = onedtond(rc at nptxy, dimsizes(rc)) - 2   ;The FillValue grid will be =0 for nptxy. So df may<0
  df at _FillValue=-9999
  df   = where(df.le.0,df at _FillValue,df)
  
  b    = tval      ; b must be same size as tval (and df)
  b    = 0.5
  
;----betainc (x,a,b): 0<x<1, a>0,b>0)-----
;----ony if this value<0.05, means p<0.05----
  prob = betainc(df/(df+tval^2), df/2.0, b)    
  copy_VarCoords(Ea_annual_0(:,:,0), prob)


 ;-----only significant rc with p<0.05-------
  rc_sig = new ((/plat,plon/),float)
  rc_sig at _FillValue=-9999
  copy_VarCoords(Ea_annual_0(:,:,0), rc_sig)
  rc_sig= where(prob.lt.0.05,rc,rc_sig at _FillValue)


HERE SKIP SOME LINES




;---plot------------------
   plot=new(1,graphic)
   plot = gsn_csm_contour_map_overlay(wks,rc,Basin,res,res2)
  
   pres                   = True
   pres at gsMarkerSizeF     = 0.007  ; default is 0.007
   gsn_coordinates(wks,plot,rc_sig,pres)



end
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