The Australian accent is largely non-rhotic, so the ‘r’ isn’t pronounced -
Tiana and Tiarna are pronounced exactly the same.
I suspect that
Tierney pops up as a result of the general popularity of other Tee- names, rather than the other way around. I almost included it in my stats as it tends to show up in the years when lots of
Tiana variations are in the data.
https://nanowrimo.org/participants/christine-seaforth-finch
http://christineseaforthfinch.blogspot.com/