Synopsis: A Crackling in the Air

Cosmic-ray-induced discharges from tiny bits of water or ice in thunderclouds may explain how a lightning strike is initiated.

After centuries of observation, lightning is still a puzzle: it is not yet fully known how thunderclouds acquire electrical charge and what initiates the discharge. Two factors are thought to be important: small water or ice particles inside clouds (so-called hydrometeors) and showers of electrons created by cosmic rays. In Physical Review Letters, Alex Gurevich at the Russian Academy of Science, and Anatoly Karashtin at the Radiophysical Research Institute, Nizhny Novgorod, Russia, report a new analysis of radio pulses emitted at the onset of lightning strikes, suggesting how lightning initiation can arise from a combination of the two factors. Specifically, they show microdischarges at hydrometeors can amplify cosmic-ray-initiated breakdown.

The authors analyzed the temporal structure of radio emissions from 3800 lightning strikes in Russia and Kazakhstan. Hundreds or thousands of short and rather strong radio pulses occur as the lightning is preparing to strike and their shape matches models of electrical breakdown triggered by electron showers generated by energetic cosmic rays. The amplitude of the radio emissions is consistent with cosmic-ray particles having an energy around 1017 electron volts (eV), but cosmic rays of this energy are too rare to justify the measured data.

Gurevich and Karashtin suggest that hydrometeors are becoming electrically polarized as the strong electric field inside the cloud builds up. As the field reaches a threshold, microdischarges occur near the droplets. These microdischarges are initiated and synchronized by a large shower of electrons generated by a runaway breakdown avalanche triggered by cosmic rays. In this case, cosmic-ray particles of energy 1012 eV, which are much more common, are sufficient to explain the observed radio pulse amplitudes prior to the lightning discharge. – David Voss


Features

More Features »

Announcements

More Announcements »

Subject Areas

Interdisciplinary PhysicsGeophysics

Previous Synopsis

Next Synopsis

Related Articles

Focus: Astronomy Students Not Learning the Basics
Interdisciplinary Physics

Focus: Astronomy Students Not Learning the Basics

Nearly half of middle school students in a Norwegian study thought that planets are bigger than stars, even after astronomy instruction. Read More »

Synopsis: Climate Noise Has Shades of Pink
Geophysics

Synopsis: Climate Noise Has Shades of Pink

Temperatures on Earth’s surface exhibit “pink noise”—a finding that could explain the global warming hiatus in the first decade of this century. Read More »

Synopsis: Social Determinants of Epidemic Growth
Complex Systems

Synopsis: Social Determinants of Epidemic Growth

A new network model reveals that social mixing and mobility can determine the areas of a city that are critical in provoking an epidemic outbreak. Read More »

More Articles