St. Elmo's fire is not as rare as some here might think. It can happen day or night though it looks more spectacular at night.
AFAIK it can happen anywhere in the world as it is just basically static.
JRBT I think I have seen what you are talking about. A couple of times at very northerly latitudes I have witnessed what appeared to be the Aurora all around the aircraft including below. Don't know if it was just an illusion or what but stunning all the same.