Hi Saurabh,
You can use 'save' command with 'repeat' loop, every time listing just one subset of the full ensemble variable. For example if your variable is 'var', find the 'I' index range (by 'sh data') and use the following:
Suppose 'I' index ranges from 1 to 144, then your syntax will become as follows (you can further look what 'ilimits' and 'klimits' etc. does) :
save/file=Yourfile.nc/ilimits=1:144/i=1 var[d=1];
repeat/range=2:144/name=aa (save/file=Yourfile.nc/append var[d=1,i=`aa`;])
I hope this is relevant and helps you.