Australasian Science Magazine

By Stephen Luntz

The existence of ball lightning was once disputed. There have now been so many reliable reports of glowing balls, particularly during and after thunderstorms, that it has been accepted as a genuine phenomenon, but the cause has remained mysterious. Books on the topic admit to puzzlement, particularly at reports of ball lightning occurring inside houses and aeroplanes.

Now, in a paper published in the Journal of Geophysical Research – Atmospheres, Dr John Lowke of CSIRO Materials Science and Manufacturing has concluded that many cases of ball lightning are caused by ions left over after lightning strikes. “During electrical storms there is a very high density of ions. After a strike there is a much lower intensity, but there might still be ions left behind. These get swept to the ground and form into glowing balls.”

Lowke says indoor observations of ball lightning could be a result of ions building up outside a window and creating an electric field of around 2.7 kV/cm, which is strong enough to ionise the air on the other side, generating an indoor ball.

“When the ions hit glass they tend to stick to it as an insulator, and the field is created on the other side,” Lowke says. “If the field is high enough it can accelerate electrons so that when they hit oxygen atoms they eject electrons and we have positive ions that are attracted to the ions on the other side of the window. Negative ions are repelled and form the ball.”

Reports of sightings by pilots outside thunderstorms are attributed to ions generated by the aircraft’s radar operating at maximum power in the face of dense fog.

Although there have been reports of injuries and even deaths from ball lightning, Lowke believes these must be from different phenomena. “I don’t think it is dangerous at all. About a third end in a bang, which I call a brown paper bag bang because it is similar to popping a bag.

“A crucial proof of any theory of ball lightning would be if the theory could be used to make ball lightning,” Lowke continues. Tests of a theory that the phenomenon is caused by the burning of silicon have produced small glowing balls, but nothing like the grapefruit-sized objects described by many witnesses.