https://www.ncl.ucar.edu/Document/Functions/Built-in/cdfchi_p.shtml
cdfchi_p
NCL built-in functions (cumulative distribution functions)
p
https://www.ncl.ucar.edu/Document/Functions/Built-in/cdfchi_x.shtml
cdfchi_x
NCL built-in functions (cumulative distribution functions)
x