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Relativistic-microwave Theory of Ball Lightning


Relativistic-microwave Theory of Ball Lightning

H-C Wu. Sci Rep.


Ball lightning, a fireball sometimes observed during lightnings, has remained unexplained. Here we present a comprehensive theory for the phenomenon: At the tip of a lightning stroke reaching the ground, a relativistic electron bunch can be produced, which in turn excites intense microwave radiation. The latter ionizes the local air and the radiation pressure evacuates the resulting plasma, forming a spherical plasma bubble that stably traps the radiation. This mechanism is verified by particle simulations. The many known properties of ball lightning, such as the occurrence site, relation to the lightning channels, appearance in aircraft, its shape, size, sound, spark, spectrum, motion, as well as the resulting injuries and damages, are also explained. Our theory suggests that ball lighting can be created in the laboratory or triggered during thunderstorms. Our results should be useful for lightning protection and aviation safety, as well as stimulate research interest in the relativistic regime of microwave physics.


Figure 1
Figure 1. Ball lightning model.
(a) Microwave bubble model. (b) Relativistic electron bunch generation. In the last leader step, a bunch of runaway electrons emerges from the leader tip, accelerates by electric fields between the leader and ground, and undergoes an avalanche. (c) Coherent transition radiation (CTR) of the electron bunch striking the ground or passing through aircraft skins. γ is the relativistic factor of electrons.
Figure 2
Figure 2. PIC results of microwave generation.
Distribution of the initial bunch field and microwave fields at times 0.8 ns, 1.5 ns and 2 ns. The field is normalized to the bunch peak field Eb0. In the leftmost panel, the bunch is left-going to the plasma surface at z = 0. The white circle marks the bunch region with a density of 0.5nb0. The radiation is a reflection of the bunch field and propagates along z. Arrows point to the field propagation direction. Parameters are given in the text and Methods.
Figure 3
Figure 3. PIC results of microwave self-trapping and bubble formation.
Snapshots of the microwave electric field E = |Ex|, magnetic field formula image, electron density ne, and ion density ni from t = 1 ns to 11 ns. Vertical dashed line marks the plasma surface. Parameters are given in the text and Methods.
Figure 4
Figure 4. PIC results of stable microwave bubble.
(a) Snapshots of the microwave electric field E, magnetic field B, electron density ne, and ion density ni at t = 19 ns. White arrows mark the magnetic field direction. (b) Field energy density and plasma density ne,i verses y across the bubble centre. (c) Evolution of the electric field, electric field energy We, and magnetic field energy Wm in the bubble. Parameters are the same as Fig. 3.

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