;;snoweurdjfmhighlow.ncl Dr. Sujata Mandke 
;;
begin  
;********************************
; Read monthly Snow   data
;********************************
   diri    = "/home/data/"  			     ; input directory   
   fili    = "swe_mon_jan1979tomay2007smmrssmi.nc"   ; input snow file       
;********************************
   in1  = addfile(diri+fili ,"r")   
   tm    = in1->time   
   ymd     = cd_calendar(tm, -2)  ; yyyymmdd
;;-------
;;;follows selection of time from input file
;period 1982-2006 are selected as SST data 
;;;is available for this period
;;--------
;;;; 
   ymdStrt = 19820101  ; start yyyymmdd
   ymdLast = 20061201   ; end yyyymmdd
   iStrt   = ind(ymd.eq.ymdStrt) ; index start
   iLast   = ind(ymd.eq.ymdLast) ; index last       
   delete(tm)
   delete(ymd)
;**********************************
   snow=  in1->swe(iStrt:iLast,{50:70},{20:140})  ;;;reading snow over Eurasia 50-70N;20-140E
;;------------------------------ 
; 'swe' file contains a _FillValue (-999.0) 
;  when there is no snow cover
;  Therefore _FillValue (-999.0) is set to 0.0
;------------------------------------- 
   snow = where(ismissing(snow), 0.0, snow)
;--------------------------------   
;--Follows averaging snow over DJFM 
;--------------------------------
   y = runave_n_Wrap(snow,4,0,0)
   sdjfm =y(0::12,:,:) 
;;
;;--follows area averaging djfm snow  over Eurasia
  snoweur=wgt_areaave(sdjfm,1.0,1.0,0) ;;;area-averaged snow over Eurasia
   snoweur!0="time"
   snoweur&time=sdjfm&time
;----
  snowstdaneur = dim_standardize_n_Wrap(snoweur, 0, 0)  ;;;standardised djfm snow anomaly over Eurasia 50-70N;20-140E
  snowstdaneur!0= "time" 
;;;---
   snowlow  = where(snowstdaneur.lt.-0.5, snowstdaneur, snowstdaneur@_FillValue)  ; average only negative values values
   snowlow!0="time"
   snowlow&time=sdjfm&time
   snowlowavg=avg(snowlow)
   print(snowlowavg)
;------------
;;  To determine the number of data values used to calculate the average use following: 
    nlow = num(.not.ismissing(snowlow))
    print("no of years snow was low="+nlow)
;;;------
    snowhigh  = where(snowstdaneur.gt.0.5, snowstdaneur, snowstdaneur@_FillValue)  ; average only negative values values
    print(snowhigh)
    snowhighavg=avg(snowhigh)
    print(snowhighavg);
;;-----------
;;  To determine the number of data values used to calculate the average use: 
    nhigh = num(.not.ismissing(snowhigh))
    print("no of years snow was low="+nhigh)
;*********************************
end