How to control X axis lines in subplots

[Rishe]

Hi all,

sorry if this question appears as a repeat or novice.

in my subplots i have different y axis but same x axis for all the
plots. however i want to keep the x axis only for the bottom and the
rest of the plots should have no x axis. I understand that i can
remove the xticklabels in other subplots by keep them as an empty
matrix but i want to remove the x axis lines as well. the only way i
can think of is to keep the x axis linecolour as white in other
subplots. but i just wonder whether i could get rid of the x axis
lines totally. (as i can get rid of the top y axis and right x axis
lines by using box command).

any help would be much appreciated

Thanks a lot
Rishe.