Discover the strongest discharge of energy on Earth

Thunderstorms are one of the most fascinating weather events. They are characterized by their electrical activity in the form of lightning and thunder, caused by the rapid expansion of air surrounding the path of a lightning bolt.

But there’s more going on during a thunderstorm than you can actually see and hear. In 2013, scientists from the University of Bergen, Norway, detected the presence of another type of lightning during a thunderstorm, not visible to the naked eye and producing no sound.

The phenomenon was not really new. In 1991, when it was first detected, it was named ‘black lightning’, but at the time scientists thought it was gamma rays from outer space.

More recent research has confirmed that black lightning is a natural phenomenon that is an integral part of lightning discharge during thunderstorms and is totally terrestrial.

What is Black Lightning?

Black lightning is a burst of gamma rays that is produced by the collision of extremely fast moving electrons and air molecules that occurs during thunderstorms. Researchers also call it a terrestrial gamma flash.

Cumulonimbus is a type of cloud that causes stormy weather. Source: DerTobiSturmjagd/Pixabay

The burst occurs just before ordinary lightning and is thought to be part of the same lightning ‘discharge’ process and to be the most energetic radiation naturally produced on Earth.

In 2013, researchers at the University of Bergen in Norway used data from satellites equipped with gamma ray detectors to identify gamma ray flashes that preceded visible flashes.

This discovery was made fortuitously when two satellites passed directly over the same thunderstorm just as the pulse occurred. The team combined data from satellites and radio waves to reconstruct the ethereal electrical event, which lasts just 300 milliseconds. They concluded that the a dark flash was triggered by the strong electric field that develops just before the visible lightning strikes.

Because more information was needed to verify these hypotheses, lightning researchers are now attempting to collect data from the Atmosphere-Space Interactions Monitor (ASIM), a European Space Agency (ESA) observatory located on the International Space Station (ISS).

ASIM uses X-ray and gamma-ray cameras and detectors that can be used to study lightning in the upper atmosphere and terrestrial gamma-ray (TGF) flashes, also known as dark lightning.

How Was Black Lightning Discovered?

What we now know about black lightning is the result of coincidence.

In 2006, two separate satellites flew within 186 miles (300 km) of an electrical storm in Venezuela. The first satellite was equipped with an optical detector and the second with a gamma ray detector. The first satellite recorded visual information of a flash and the second satellite recorded a flash of gamma radiation preceding the other.

Seven years later, space researcher Nikolai Østgaard and his team at the University of Bergen developed a new search algorithm to reprocess data from the second satellite. This is how they discovered a large number of gamma flashes occurring just before the visible flash – more than had originally been reported.

Additionally, they discovered that at the time of the event, there was a discharge of radio waves recorded by a radio receiver at Duke University in Dunham, North Carolina, approximately 3,000 km from the storm. .

The team believes this is all interconnected as part of the same electrical event and reconstructed it as follows:

Where does lightning come from?

A typical lightning strike occurs when two oppositely electrically charged regions of the atmosphere meet. These regions of the atmosphere are usually the thunderclouds but interactions can also exist between the atmosphere and the ground.

Generally, lightning occurs when Powerful updrafts in cumulonimbus (thunderclouds) force water droplets and ice crystals to rub against each other. This creates an accumulation of positively and negatively charged particles. Updrafts also cause particles to separate— the top of the cloud becomes positively charged while the base of the cloud becomes negatively charged.

Once the negative charge at the bottom of the cloud becomes large enough, it rushes towards Earth. At the same time, the positive charges on the ground are attracted to it and flow upwards. When the two opposite charges meet, a strong electric current, called the return stroke, carries a positive charge through the cloud. This is what we see as the bright flash of a lightning bolt.

Although many believe that lightning travels from the cloud downwards or from the ground, in reality lightning can travel in either direction. The positive charge at ground level attracts the negative charge from above causing current to flow to the ground. At the same time, the positive charge of the ground is drawn upwards in the form of a full strike.

Negatively and positively charged clouds can do the exact same thing in the air, so instead of the lightning appearing to be traveling towards the ground (or upwards from the ground), you would see the lightning pass from cloud to cloud.

The electric field produced in clouds can accelerate electrons to near the speed of light. Electrons can collide with air molecules and generate decelerating radiation, which creates positrons, positively charged subatomic particles with the same mass and charge magnitude as the electron, essentially antimatter particles. When electrons and positrons meet up therethey annihilate each other by emitting gamma rays.

This is how the basic process of lightning discharge can generate dark lightning.

Is black lightning harmful to humans?

Gamma radiation is actually one of the most destructive types of radiation. It is ionizing, which means it can extract electrons from atoms. When it enters cells, it breaks the bonds of DNA molecules, causing genetic damage that can induce cancer.

A typical lightning strikes more or less in one place, but gamma radiation flashes travel very quickly in all directions. As disturbing as it may sound, the reality is that gamma rays from dark lightning tend to dissipate before they become dangerous to living things on Earth.

According to lightning expert John Dwyer of the Florida Institute of Technology, only people traveling by plane during a thunderstorm are likely to receive a large dose of ionizing radiation from black lightning. However, this is mitigated because a) pilots tend to avoid thunderstorms; b) the black flash is not always present – in fact it is thought to occur only once in every thousand visible flashes; and c) even if someone were hit with a significant amount of gamma rays, they would not feel anything.

lightning bolt over the airport near the plane
Source: Pixabay/Stockvault

Thus, the only way to know if passengers are exposed to black lightning and gamma rays is to fly with radiation detectors on board. In order to continue black lightning research, it is best to place gamma ray detectors on satellites, as they have proven useful in the past.

Today, some of the most powerful tools for advancing the search for black lightning are ESA’s Atmosphere-Space Interactions Monitor, located on the International Space Station, and the Fermi Gamma Ray Space Telescope on the Nasa.

The latter was launched in 2008 to study gamma-ray bursts and transients, not specifically for the study of black lightning, but mainly for the study of dark matter, micro-black holes and supernova remnants. .

Gamma Ray Sky by Fermi
View of the gamma sky as reconstructed by Fermi. Source: NASA/Flickr Goddard Space Flight Center

All these phenomena are related to gamma radiation.

In fact, before the discovery of black lightning, scientists thought that gamma radiation came from outer space. What the black lightning phenomenon showed them (and us) is that gamma radiation is not only generated by star death and nuclear explosions, but also by mundane events like thunderstorms that literally unfold above our heads.

Robert M. Larson