Hi Chris,
Nice pic!
In response to comments about not seeing them here in OZ, I posted this thread regarding some I took over Quakers Hill NSW in 2005. Not quite the same thing, or as impressive as your shot, but similar I think from the shape and potentially the conditions at the time.
http://www.iceinspace.com.au/forum/s...ad.php?t=33310
Cheers
Chris