“The interaction between these lightning events and the upper atmosphere is not fully understood,” remarked Olivier Chanrion, DTU Space senior researcher. From 400 kilometers altitude above Earth, the International Space Station is gradually transforming that, showing a universe of electrical activity that for decades had only been described in pilots’ anecdotes and occasional photographs.
These brief bursts blue jets, red sprites, ELVES are collectively termed transient luminous events, or TLEs. They explode tens of kilometers high over thunderstorms, in the rarefied atmosphere of the stratosphere and mesosphere, where they can modify atmospheric chemistry, perturb the ionosphere, and even disrupt radio communications. The European Space Agency’s Atmosphere–Space Interactions Monitor (ASIM), attached to the Columbus module’s outside since 2018, is the first instrument set designed explicitly to research them from space. Its two high-speed cameras, three photometers, and X- and gamma-ray detector package captures flashes smaller than the tip of a fingernail and briefer than a millisecond, sensing down to optical wavelengths of ultraviolet and through high-energy photons up to 30 MeV.
The position and sensitivity of ASIM have allowed for accurate measurements that those on the ground fail to capture. One study employed its optical and electromagnetic records in concert to verify that lightning-like lightning at thundercloud tops can induce electromagnetic pulses into the ionosphere to initiate ELVES ultraviolet rings of hundreds of kilometers in diameter that temporarily enhance ionospheric charge. Such perturbations can impair very low frequency (VLF) radio communication links employed in submarine communications. The monitor has also documented ultra-short corona discharges, showing how they pre-condition the higher cloud layers for complete lightning initiation.
Among the most dramatic shots are red sprites jellyfish-shaped filaments of ionized air that hang in the mesosphere for a mere ten milliseconds and blue jets, long spikes of plasma firing from cloud tops into the stratosphere at velocities higher than 100 km/s. In 2015, astronaut Andreas Mogensen captured a pulsating blue jet from the ISS; ASIM has since offered altitude and morphology measurements that directly input into storm electrification models, enhancing aviation advisories for the avoidance of high-field areas.
The ISS cupola has also become an essential platform. With ESA’s Thor-Davis experiment, astronauts install a neuromorphic “event-based” camera behind its windows, one that can capture up to 100,000 frames per second. Unlike traditional sensors, it only detects changes in light, yielding high-temporal-resolution video of lightning branching and filamentation. Such data are confirming laboratory plasma experiments and may make algorithms that notify power grid operators of lightning danger more precise. As Chanrion observed, the system also enables scientists to “check to which extent they are associated with overshooting thundercloud tops that inject greenhouse gases and aerosols in the stratosphere.”
All of lightning’s energy is not visible. Terrestrial gamma-ray flashes (TGFs), which were first discovered in 1991, are the most energetic naturally occurring radiation pulses on Earth, with photon energies of up to 40 MeV and lasting less than 500 microseconds. Produced at altitudes of 9–15 km in thunderstorms, TGFs are associated with negative upward lightning leaders and bremsstrahlung of runaway electrons. ASIM’s Modular X- and Gamma-ray Sensor (MXGS) images the bursts, pinning down their source to tens of kilometers using coded-mask gamma imaging in conjunction with coincident optical lightning information from its Modular Multi-Spectral Imaging Array (MMIA). It has seen more than a thousand TGFs since 2018, some of which occurred in association with the most powerful negative cloud-to-ground strokes in the storm.
Supplementing ASIM, Japan Aerospace Exploration Agency’s Light-1 CubeSat, launched from the ISS, has small scintillation detectors that are tuned to high-energy photons. No larger than a loaf of bread, it charts TGF appearance over equatorial storm belts. By comparing Light-1’s timestamps with ground-based lightning networks, scientists are creating a three-dimensional atlas of gamma-ray hazard areas, data crucial for aviation paths through the tropics where airliners might be exposed to doses of radiation equivalent to a medical X-ray in milliseconds.
The consequences go well beyond safety. TLEs and TGFs transfer nitrogen oxides and ozone between atmospheric layers, affecting radiative balance. Although the overall chemical effect of ELVES and halos is negligible, sprites, blue jets, and impulsive corona discharges may measurably contribute to greenhouse gases such as nitrous oxide, the third most powerful behind carbon dioxide and methane. Including these processes in climate models might refine forecasts of future warming.
With the ISS now known to continue through at least 2030, successors to ASIM stand ready to build this orbital catalog of storm-driven phenomena larger. Engineers have next-generation detectors on the horizon with wider spectral range, faster triggers, and autonomous event typing, and Cubesat fleets could offer near-real-time notifications for mega-sprites or powerful TGFs. With every crossing of the planet, there are additional frames to a previously invisible film of lightning’s high-atmospheric extent, providing not only spectacle, but information connecting weather, climate, and space environment in a unprecedented level of detail.
