Laboratory study of TLEs

Abstract:

Sprites are high-altitude kilometre-scale electrical discharges that happen above thundercloud. Pilot systems are pre-breakdown phenomena that usually attributed to stepped leader development.

In Eindhoven University of Technology we investigate meter-scale laboratory discharges looking for similarities with natural lightning and its related phenomena. Negative lightning possesses step-like propagation behaviour which is associated with space leader formation in front of its main leader. Meter-scale laboratory sparks also develop via formation of a space stem that transforms into a pilot system and finally develops into a space leader in longer gaps. With ns-fast photography we investigated the pilot system formation and found striking similarities with high-altitude sprites. But sprites are different in size, environment and polarity. Laboratory pilot barely reaches 70 cm and develops in STP air, while high-altitude sprites reaches ionosphere stretching for dozens of kilometres. Also sprites are assumed to be of opposite to the pilot polarity. Besides that, the pilots are directly involved in x-ray generation in long laboratory sparks.

The detailed pilot system development process will be shown, in particular focusing on similarities with natural sprites. Basic properties of the x-ray emission will be presented and discussed.