From False Capture
Whilst you're investigating St. Elmo's Fire why don't you also have a look at 'plasma balls' which are seen following a lightning strike on an aircraft. They are usually about 12" in diameter and travel down the cabin from nose to tail at about waist height. Just like St. Elmo's Fire they are the result of a gas being turned into a plasma (ie. an ionized gas) by a high voltage.
I experienced this phenomena once during the early eighties in a 737-200 while climbing out of Malpensa with a load of Italian schoolchildren in the back. There were thunderstorms in the area when the lightening strike entered the cockpit near the F/O's windscreen wiper. The fireball passed through the flight deck door, travelled down the aisle, frightening the passengers and cabin crew far**less before exiting through the rear galley. We later found a static wick missing from the starboard elevator. Two things remain in my mind. The loudness of the bang, the brightness of the fireball and 130 normally unruly passengers who stayed strapped in their seats for the rest of the flight to Gatwick.