@APoD
I have a cutting I saved from The Times newspaper dated Aug 12 1994, headlined 'Flashing Jellyfish Fears' : says that lightning storms over America had been generating huge flashes of light, shaped like jellyfish, which baffled NASA scientists, who feared the flashes (nicknamed sprites) could interfere with civil / military aircraft... and the Met Office said the phenomenon had not been witnessed over the British Isles.

And now we have loads of stunning pics, like this one !