Scientists found out why lightning strikes twice in one place

(ORDO NEWS) — A scientist from the Institute of Applied Physics of the Russian Academy of Sciences described the mechanism underlying the structural asymmetry of lightning with respect to the change in the polarity of its electric current.

The asymmetry of electrical polarity is the most important aspect of the physics of lightning, the understanding of which is necessary for the development of means of protecting objects and the population from this natural phenomenon. The article was published in the journal Atmospheric Research.

The structure of a lightning discharge is a network of plasma channels, positive and negative leaders, propagating in opposite directions from the point of origin. Previously, it was believed that the discharge develops symmetrically, while the difference between the opposite ends of the lightning was not taken into account.

It was believed that the growth rate is the same at both poles, and the current distribution is uniform. In such a system, the point of zero charge of the cover of the leader channel – the reversal point – coincides with the point of initiation of the lightning system.

However, the electron mobility is more than two orders of magnitude higher than the ion mobility. Electrons are the only charge carrier in lightning, and their behavior differs at opposite ends of the system. Researchers from the Institute of Applied Physics of the Russian Academy of Sciences proved that

“Lightning can be called a self-developing transport system. Its growth is associated with the high value of the electric field at its ends. At the same time, the critical value of the growth field for positive leaders is less than on the negative periphery.

Thus, it is easier for lightning to develop in the positive direction, which leads to an excess of the total current at the positive periphery of the discharge tree. It is the difference in peripheral currents that ensures the movement of the reverse point, ”says Dmitry Iudin, project manager for a grant from the Russian Science Foundation.

Thousands of people are killed and injured every year from thunderstorms. Lightning also poses a threat to the normal operation of technical devices; modern low-current electronics are especially vulnerable. This makes lightning the second most dangerous natural phenomenon after flooding.

Understanding the asymmetric dynamics of the reversal point helps explain when lightning strikes twice in the same place. When the positive leader is heading towards the ground, the reversal point also moves downward and is at a low altitude when the leader touches the surface. In the case of the moment of contact with the ground, the reversal point is high in the cloud.

After the leader reaches the ground, the ionization shock wave propagates upward and moves to the reversal point. In the first case, the reverse shock wave carries a negative charge, “captures” the reversal point and accelerates its movement to the ground. Thus, a positive discharge leads to the termination of the existence of the system. In the case of a negative wave of a reverse impact, it carries a positive charge to the ground, loses its strength, and later “captures” the reverse point.

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