[ncl-talk] Query regarding ttest and pdfx function

[Dr. Suman Maity]

Dear all
I am new for ncl and recently started using it. However, I have the
following queries:
1. I have temperature data from the model (time,lat,lon) and observation
(time,lat,lon) with time=122 days (JJAS), lon=692 grid-points and lat=466
grid-points. I want to plot JJAS bias (model-observation) over-layed with
95% significant bias gridpoints as dots.  I took the help of "ttest"
function in ncl. My script is attached herewith. I would like to request
you to check the script and modify if needed. However, general syntax of
ttest is like the following:
prob = ttest(ave1,var1,s1,ave2,var2,s2,iflag,tval_opt)
What is this "s1" and "s2" ? it is mentioned the they gives no. of
statistically independent observation. Am I need to calculate that using
"equiv_sample_size" function? or any constant value will be fine? if yes
what will be the approximate values?

2. I want to generate probability density function of temperature bias over
a region. I have bias data(time,lat,lon). My query is:
1) pdfx function is generally applied on which dimension? I mean time or
space?
2) Is the rand_normal is required in case of my data?
3) In my case bias (model-obs) is a time(122 days) X lon X lat dimension
data. How pdfx function will be applied on that? Will it directly go to the
pdfx function like:
ap = pdfx(bias,0,True)
or
I need to average the bias w.r.t time and then apply  ap =
pdfx(bias,0,True)
Any sort of suggestion will be highly appreciated.
Best
Suman
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Dr. Suman Maity
Research Associate
School of Atmospheric Science
Sun Yat-sen University, Zhuhai campus,Tangjiawan Town
Zhuhai, Guangdong, Postcode-519082,China.
Phone:+86-13543861045 (China), +91-9732636778 (India)
skype: reach2suman
https://www.researchgate.net/profile/Suman_Maity
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