The chemistry of lightning

The Atmosphere-Space Interactions Monitor arrived yesterday at the International Space Station to peek inside the physics of high-energy phenomena at the edge of space.

With no clouds to obstruct the view, the package will help scientists to understand the anatomy of lightning from 400 km above the planet.

“We will learn more about the impact of severe thunderstorms in the upper layers of the atmosphere, where the electrical discharges happen and what powers them,” explains Torsten Neubert, science team coordinator at the Technical University of Denmark.

The measurements will help us to understand how electric fields within the clouds accelerate electrons to such energies and in such numbers that, in some cases, X-rays and gamma rays can be observed from space.

High up in the atmosphere, the electrical discharges take many forms and exist only briefly – milliseconds at most. These ‘transient luminous events’ include colorful phenomena with fairy tale names: sprites, blue jets and elves.

Sprites are flashes caused by electrical breakdown in the mesosphere, between 50 km and 100 km above the surface. They resemble reddish jellyfish with tentacles streaming down.

The blue jet propagates upwards into the stratosphere from cloud tops. ESA astronaut Andreas Mogensen recorded a pulsating blue jet on camera for the first time during his mission to the International Space Station in 2015.

The highest of all are the elves, concentric rings that often appear as a dim, expanding glow 400 km wide. Electron collisions and excited nitrogen molecules are behind it.

The latest European observatory in space will also detect bursts of gamma rays from thunderstorms accompanied by energetic electrons and their antimatter partners, positrons.