The phenomenon of ball lightning remains largely a mystery to modern science, although it has at least largely become an accepted, if little understood phenomenon. One of the anomalies of ball lightning that have kept it on the outer margins of scientific respectability has been the seeming ‘impossibility’ of its manifestation and movement – sometimes apparently appearing within buildings and aircraft, or passing through closed windows.
A new theory from Chinese scientist H.-C. Wu, of Zhejiang University, may hold a possible answer to this strange behaviour. Wu has proposed that ball lightning might be ‘microwave bubbles’ formed from radiation emitted by storms, and this could explain their ability to appear or move within enclosed spaces:
Wu theorizes the microwaves arise from a bunch of electrons accelerated to speeds approaching the speed of light when the Earth is struck by lightning. Specifically, the electrons are accelerated by the strong electric field created as a channel of electrons moves stepwise from the base of a cloud toward the ground, just prior to the bright flash we know as a lightning bolt. “At the tip of a lightning stroke reaching the ground,” Wu says, “a relativistic electron bunch can be produced, which in turn excites intense microwave radiation.”
Regardless of their source, the atmospheric microwaves produce plasma by charging up the surrounding air. The radiation exerts sufficient pressure to push the plasma outward into a bubble, which we see as ball lightning. Microwaves trapped inside continue to generate plasma and so maintain the bubble for its brief lifetime. The ball lightning eventually fades as the radiation held within the bubble is dissipated. On the offhand chance the bubble is ruptured, microwaves can leak out and cause the ball to come to an explosive end.
The presence of microwaves and plasma as components of ball lightning can explain several of its properties. For example, microwaves can pass through panes of glass, which is why windows don’t bar the entrance of ball lightning. Microwaves also tend to make an audible noise when they encounter a person’s inner ear, and the plasma they produce will in turn generate acrid-smelling ozone from atmospheric oxygen.
What sets Wu’s microwave origin theory apart is that it explains how ball lightning can appear inside an aircraft. Electrons, being tiny relative to atoms, are able to pass through the metal shell of an aircraft after being accelerated outside of it via a lightning strike. Microwaves are then emitted by the suped-up electrons inside where they form ball lightning. The electron-microwave-plasma pathway also explains the size of ball lightning, since the length of the electron bunch sped up by a lightning strike matches up with the typical 20-50 centimeter diameter of the resulting microwave bubble.