Runaway breakdown is a theory of

lightning Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an average ...

initiation proposed by Alex Gurevich in 1992.

Electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...

s in air have a

mean free path In physics, mean free path is the average distance over which a moving particle (such as an atom, a molecule, or a photon) travels before substantially changing its direction or energy (or, in a specific context, other properties), typically as ...

of ~1 cm. Fast electrons which move at a large fraction of the

speed of light The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit fo ...

have a mean free path up to 100 times longer. Given the long free paths, an

electric field An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field ...

can accelerate these electrons to energies far higher than that of initially static electrons. If they strike air molecules, more relativistic electrons will be released, creating an avalanche multiplication of "runaway" electrons. This process, relativistic runaway electron avalanche, has been hypothesized to lead to

electrical breakdown Electrical breakdown or dielectric breakdown is a process that occurs when an electrical insulating material, subjected to a high enough voltage, suddenly becomes an electrical conductor and electric current flows through it. All insulating mate ...

in thunderstorms, but only when a source of high-energy electrons from a

cosmic ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...

is present to start the "runaway" process. The resulting conductive plasma trail, many tens of meters long, is suggested to supply the "seed" which triggers a lightning flash.

References

External links

How cosmic rays trigger lightning strikesRunaway Breakdown and the Mysteries of Lightning - Physics Today May 2005
Also available on-line at: http://www.phy.olemiss.edu/~jgladden/phys510/spring06/Gurevich.pdf .

Lightning {{astrophysics-stub

See also

References

External links