Lightning strikes link weather on earth and weather in space  Premium

Trillions of charged particles in Earth's radiation belts interact with lightning, impacting space weather and spacecraft design.

There are trillions of charged particles – protons and electrons, the basic building blocks of matter – whizzing around above your head at any given time. These high-energy particles, which can travel at close to the speed of light, typically remain thousands of kilometres away from the earth, trapped there by the shape of the earth’s magnetic field.

Occasionally, though, an event happens that can jostle them out of place, sending electrons raining down into the earth’s atmosphere. These high-energy particles in space make up what are known as the Van Allen radiation belts, and their discovery was one of the first of the space age. A new study from my research team has found that electromagnetic waves generated by lightning can trigger these electron showers.

At the start of the space race in the 1950s, professor James Van Allen and his research team at the University of Iowa were tasked with building an experiment to fly on the United States’ very first satellite, Explorer 1. They designed sensors to study cosmic radiation, which is caused by high-energy particles originating from the Sun, the Milky Way galaxy, or beyond.

After Explorer 1 launched, though, they noticed that their instrument was detecting significantly higher levels of radiation than expected. Rather than measuring a distant source of radiation beyond our solar system, they appeared to be measuring a local and extremely intense source.

This measurement led to the discovery of the Van Allen radiation belts, two doughnut-shaped regions of high-energy electrons and ions encircling the planet.

Scientists believe that the inner radiation belt, peaking about 1,000 km from the earth, is composed of electrons and high-energy protons and is relatively stable over time.

The outer radiation belt, about three times farther away, is made up of high-energy electrons. This belt can be highly dynamic. Its location, density and energy content may vary significantly by the hour in response to solar activity.