Explosion of an ice chunk in the upper atmosphere? This has happened in the past with enough energy to make people think a nuke had been popped.
That sounds like a plausible explanation or it could be atmospheric sprites.
I wholeheartedly agree.
Small Comets and Our Origins
University of Iowa | circa 1999 | Louis A. Frank
Posted on 10/19/2004 11:13:25 PM PDT by SunkenCiv