I’m a non-scientist, so this is probably partially understood, somewhat accurate, and certainly dated:

Here is a well-done video from the Sprites Project at the University of Alaska:

During what is normally a cloud to ground lightning strike during a thunderstorm, there is occasionally a discharge of energy above the cloud, high up in the atmosphere.  These phenomenae are called blue jets, red sprites, and elves.  They are faint, require a dark background against which to view them, and also require that you be far enough away to see the storm from a distance (preferably from aircraft or a mountain overlooking a plain).

From Christopher Paul Barrington-Leigh’s abstract here, found at the Conjugate Sprites Project (where I got most of this information) page:

“Sprites are highly structured discharges lasting 5 to 100 ms and extending from 40 to 85 km altitude which result from intense electric fields following a major redistribution of electric charge in the troposphere — usually a positive cloud-to-ground return stroke.”

The Runaway Breakdown thesis here’s a quote from wikipedia by Nikolai Lehtinen:

“In the upper atmosphere, cosmic rays striking air molecules within thunderstorms can supply the relativistic electrons which trigger a breakdown in “runaway” mode. The breakdown region is a conductive plasma many tens of meters long, and it can supply the “seed” which triggers a lightning flash.”

An interesting possibility…

Related On This Site: You can get Walter Lewin’s Lectures at MIT for free:  Repost: From MIT OpenCourseWare: Walter Lewin’s Lecture On Lightning