# [ncl-talk] calculating and plotting change in standard deviation and change of both skewness and kutosis at 99% percentile

Sri.durgesh Nandini-Weiss sri.durgesh.nandini-weiss at uni-hamburg.de
Wed Oct 30 09:15:32 MDT 2019

```Hello everyone,

I'm attempting to calculating, and plot changes for extreme value from
sea surface height from an ensemble outputs.

For e.g i am trying to analyse the change between 1986-2006 and
2081-2100 at the 99% percentiles from the ensemble from the change in
statistics (mean,  standard deviation and  change of both skewness and
kutosis). I adapted my script from extval_6.ncl

Is the below the correct way?

;************************************************
; extvalv_6.ncl
;
; Concepts illustrated:
;   - Using extval_mlegev  and extval_gev
;   - Calculate basic statistics
;     - Basic statistics of the original sample
;     - Estimate GEV distribution parameters
;   - Creating a 'text' object to attach to a plot
;************************************************

fn  = "zo_hist_1850-2005_ens_1-100.nc" ; define filename [time |
1872] x [ens | 100] x [depth | 1] x [lat | 45] x [lon | 90]

in  = addfile(fn,"r")                                 ; open netcdf file
ts  = in->zo                                          ; read in variable
printVarSummary(ts)

;************************************************
;  calculate deviation from zonal mean
;************************************************
anom = dim_rmvmean_n_Wrap(ts,0)
printVarSummary(anom)

;***************************************************************
;--- "Normal" (conventional) statistical estimates for full sample
;***************************************************************

xStat4 = dim_stat4_n(ts, 0)  ; 1st 4 moments of original sample
printVarSummary(xStat4 )

xAvg   = xStat4(0)              ; original sample mean
xStd   = sqrt(xStat4(1))        ;    "     sample std dev
xSkew  = xStat4(2)              ; skewness; departure from symmetry
xKurt  = xStat4(3)              ; kurtosis; relative to a normal
distribution
xLow   = min(ts)
xMed   = dim_median_n(ts,0)  ; median of original sample
xHi    = max(ts)

;***************************************************************
;--- PLOTS
;***************************************************************

wks  = gsn_open_wks ("pdf","ext6")                ; send graphics to
PNG file

gsn_define_colormap(wks,"default")
plot = new(2, "graphic")

;************************************************
; Panel
;************************************************

resP                     = True                  ; modify the panel plot
resP at gsnMaximize         = True                  ; ps, eps, pdf
resP at gsnPanelMainString  = "River Flow Rate"     ; use this for NCL
V6.4.0 and later
resP at txFontHeightF       = 0.020
gsn_panel(wks,plot,(/1,2/), resP)                ; now draw as one plot

;***************************************************************
;--- create histogram for the original sample
;***************************************************************

resh = True
resh at gsnDraw      = False
resh at gsnFrame     = False
resh2gsnHistogramNumberOfBins = 11

resh at gsFillColor  = "green"
resh at tiMainString = "SSH: N="+ntim
plt_hist          = gsn_histogram(wks, ts ,resh)

;***************************************************************
;--- text object original sample statistics; place on histogram
;***************************************************************

txres                       = True
txres at txFont                = "helvetica-bold"
txres at txFontHeightF         = 0.0150
textSample  = (/"  Mean="+sprintf("%5.1f", xAvg) +"~C~"+  \
"   Std="+sprintf("%5.1f", xStd) +"~C~"+  \
"  Skew="+sprintf("%5.2f", xSkew) +"~C~"+ \
"  Kurt="+sprintf("%5.2f", xKurt) +"~C~"+ \
"  xLow="+sprintf("%5.1f", xLow) +"~C~"+  \
"  xMed="+sprintf("%5.1f", xMed) +"~C~"+  \
"   xHi="+sprintf("%5.1f", xHi ) /)
txBoxSample  = gsn_create_text(wks,textSample, txres)

amres  = True
amres at amParallelPosF   =  0.30             ; move legend to the right
amres at amOrthogonalPosF = -0.10             ; move the legend up
annoSample = gsn_add_annotation(plt_hist, txBoxSample, amres)  ;
Attach string to plot

draw(plt_hist)
frame(wks)

the change in statistics--
Sri Nandini-Weiß
Research Scientist

Universität Hamburg
Center for Earth System Research and Sustainability (CEN)
Cluster of Excellence 'Climate, Climatic Change, and Society' (CLICCS)

Bundesstrasse 53, 20146 Hamburg
Tel: +49 (0) 40 42838 7472

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