Has anyone ever experienced ball lightning? It's very rare, so probably not. My wife's grandmother has. It was in the south of France - in Provence somewhere. Ball lightning came down the chimney and moved slowly across the room - and then crashed into the wall. No damage - apart from her nerves!
My mother did as a child. She said it rolled across a field and killed a horse then set fire to a barn. I looked at some weather records and the date tallied with a freak storm that lasted most of a week.
I was talking to a fellow cyclist about this and he said ball lightning had been seen by his parents outside their home. A friend who lives in France was fishing in the heart of a storm and he told me the strikes were so close that small plasma balls were falling from the surrounding trees. I think these are what are known as 'bead lightning'.
I suspect there are a number of phenomena described as ball lightning. One is falls of fiery solid matter, sometimes described as 'thunderbolts', the main type is the hovering, glowing plasma type object that passes up or down chimneys, through windows and walls and often ends with an explosive crack, sometimes lethal, often not.
Upper atmosphere lightning is strange stuff:
http://en.wikipedia.org/wiki/Upper-atmospheric_lightning