CDO

Hi there,

I'm calculating the ensemble median of an ensemble with four members using

cdo enspctl,50 ifile1 ifile2 ifile3 ifile4 ofile

When I checked the output I came across something unexpected. The ensemble median is exactly equal to one of the members. It is the member n/2 of the sorted list i=1,...,n; n=4. For four members I did expect the median to be the arithmetic mean of the two middle members. When I use five ensemble members I get what I expected. The ensemble median is equal to the middle member of the distribution (n+1)/2.

I thought four members is maybe too few to get cdo enspctl,50 working properly. I tried to fool the algorithm and used the four members twice to get n=8. Still the median is equal to the root of the min-heap, not the arithmetic mean of the two roots. With six different ensemble members I also get an ensemble median which is equal to the member n/2 of the sorted list i=1,...,n; n=6.

I couldn't find any detailed description of the cdo enspctl operator. Maybe I am expecting something, that cdo is not supposed to do. Is there anyone who could comment on this?

Thanks,

Christian