[ncl-talk] Removing seasonal cycle from monthly data

[Dennis Shea]

Did you even try any of these functions?
Here is one approach using all years.

================================
   fn  = "zo_hist_1850-2005_ens_1-100.nc" ; define filename
   in  = addfile(fn,"r")                  ; open netcdf file
                           ; zo:[time|1872] x [ens|100] x [depth|1] x
[lat|45] x [lon|90]
   x   = in->zo(:,:,0,:,:)
   printVarSummary(x)         ; [time | 1872] x [ens | 100] x [lat | 45] x
[lon | 90]
   printMinMax(x,0)
   print("============")

   xClm  = clmMonTLLL(x)   ; climatologies for each ensemble member
   printVarSummary(xClm)   ; *[month | 12] *x [ens | 100] x [lat | 45] x
[lon | 90]
   printMinMax(xClm,0)
   print("============")

   xAnom = calcMonAnomTLLL(x,xClm)   ; anomalies from each ensemble member
climatology
   printVarSummary(xAnom)  ; [*time | 1872] x [ens | 100] x [lat | 45] x
[lon | 90]*
   printMinMax(xAnom,0)
   print("============")

On Mon, Nov 11, 2019 at 3:48 AM Sri.durgesh Nandini-Weiss via ncl-talk <
ncl-talk at ucar.edu> wrote:

>
> Hello everyone,
>
> I am doing a simple calculation on monthly means data e.g. temp from
> 1850-2000.
>
> I would like to calculate the mean, standard deviation (e.g temp from
> 1986-2006). For this the seasonal cycles of the respective periods should
> be removed otherwise its probably not Gaussian so i want to extract the
> seasonal cycle out of my data.
>
> Are the below steps the correct way to do this? My script is successful in
> retrieving the anomalies.
>
> however i want which function is correct? (rmvmean or calcMonAnomTLLL)
> rmvmean(x): remove mean (and returns deviation from mean)
>
>  calcMonAnomTLLL(x): Anomalies from Annual Cycle: calcMonAnomTLL:
> contributed.ncl
>
> ;=================================================================
> ; Concepts illustrated:
> ;   - Calculates long term monthly means (monthly climatology) from
> monthly data: (time,lev,lat,lon) version
> ;   - Compute monthly anomalies using monthly climatology
> ;   - Calculates climatological anomalies by subtracting the long term
> mean from each point.
> ;   - Assumes monthly data. If the input data contains metadata (e.g.
> coordinate variables and attributes), these will be retained.
> ;==================================================================
>   yrStrt = 1986
>   yrLast = 2006
>
>   f = addfile("zo_hist_1850-2005_ens_1-100.nc","r")
>   TIME   = f->time
>   TIME = TIME-31
>   YYYY   = cd_calendar(TIME,-1)/100                 ; entire file
>   iYYYY  = ind(YYYY.ge.yrStrt .and. YYYY.le.yrLast)  ;this is from 1 Jan
> 1986 to 1 Dec 2006
>
>   zo = f->zo(iYYYY,:,:,:,:)                                       ; [time
> | 240] x [ens:100] x [depth:1] x [lat | 192] x [lon | 288]
>   zo at _FillValue = 9.96921e+36
>   printVarSummary(zo)
>   printMinMax(zo,0)
>
>   zo1 = dim_avg_n_Wrap( zo, 2)                                     ;[time
> | 240] x [ens:100] x [lat | 192] x [lon | 288]
>   printVarSummary(zo1)
>
> ;==================================================================
> ; Compute monthly climatology
> ;==================================================================
>
>   zo2 = clmMonTLLL( zo1 )                                          ;
> [month | 12] x [ens | 100] x [lat | 45] x [lon | 90]
>   printVarSummary(zo2)
>
> ;==================================================================
> ; Compute  monthly anomalies from the above climatology to remove seasonal
> cycle
> ;==================================================================
>
>     zAnom = calcMonAnomTLLL (zo1,zo2)
>     printVarSummary(zAnom)                                        ;[time |
> 240] x [ens | 100] x [lat | 45] x [lon | 90]
>
>     zAnom at long_name = "Anomalies from monthly Climatology"
>     printVarSummary(zAnom)
>     printMinMax(zAnom, 0)
>
>
> Or should i be using rmMonAnnCycLLLT (removes the annual cycle from the
> monthly data) instead?
>
> Would be grateful for some guidance on this!
>
> Sri
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