What Are Red Sprites, the Lightning Above Storms?

Red sprites are brief, crimson electrical discharges that flicker in the mesosphere, roughly 50 to 85 kilometers above powerful thunderstorms. They are triggered by unusually strong positive lightning strikes far below, and they glow red because the discharge excites nitrogen molecules in the thin upper air. To the naked eye they are no more than a blink on the distant horizon — but long-exposure cameras reveal towering structures of red light.

What triggers a sprite above a storm?

Everything starts with how thunderstorms build up enormous electrical charge in the first place. Not all lightning is the same, though. There are two flavors of cloud-to-ground lightning — positive and negative — depending on the kind of charge they send to the ground. Sprites are generated mainly by positive lightning — a far more powerful variant, roughly ten times the strength of the negative kind — even though only about one in ten cloud-to-ground strikes carries a positive charge. And not every positive strike creates a sprite. NASA scientist Dr. Burcu Kosar estimates that only some 2 in 100 of those positive strikes carry enough energy to set one off. They demand powerful, churning storm systems — it is the turbulent mixing that builds the intricate electrical setups lightning needs. The mechanism itself is elegant. When a positive bolt dumps its charge into the ground, the air far above the storm is suddenly gripped by an electric field. That field heats electrically charged particles in the thin upper air, and as those excited particles strike nitrogen molecules, the sky releases brilliant red flashes. Scientists call this electrical breakdown — the moment air, normally an insulator, receives such an extreme voltage that current rushes through it anyway.

Why did it take so long to prove they existed?

Written accounts of strange flashes of light linked to storms date back to the 1700s. The first written account belongs to Johann Georg Estor, a German scholar who in 1730 watched a storm from a mountain peak and described flashes of light firing straight upward.

More than 200 years later, the spectacle was just as bewildering. In the 1980s, NASA pilots described lightning that struck upward, some 2,000 feet above their flight path. The light "shattered in all directions as an egg would do if it were thrown against a ceiling," they reported. But because their observations weren't captured on camera, lightning researchers mostly dismissed the reports. Proof came by accident. In summer 1989, researchers at the University of Minnesota were calibrating a sensitive night-vision camera when it caught an unexplained luminous smudge far above the cloud tops. Shuttle-borne video from 1989 to 1991 captured more of these mysterious flashes. A 1994 research campaign then recorded sprites in color for the first time and pinpointed their height above the storm tops — and the events were dubbed "sprites" for their elusive nature. They are now known as the most commonly observed of a whole family of phenomena called transient luminous events.

What shapes do sprites take?

Sprites are anything but uniform. A single display can span about 10 miles wide and 30 miles from head to tail, starting roughly 45 miles above the ground — while most commercial airplanes fly at only five to seven miles. They take on complex shapes — "like snowflakes; none are identical," Kosar says. There are carrot sprites, so named for their resemblance to a freshly pulled carrot, roots and all. There are column sprites, majestic angels, and the white whale of sprite-chasing: the jellyfish. On camera, sprites may look like they're composed of branches of light, but in reality each branch is created by fast-moving balls of light that barrel down the sky, splitting into ever-smaller pieces. "They looked like fireworks," Kosar said. "Since each is unique, I can look at them all day and never get bored."

Catching one demands patience and darkness. Chasers consider the sweet spot to be 100 to 300 miles from the storm — far enough to see above the clouds — because if the thunderstorm is overhead, any sprite will be obscured by the clouds themselves. Some chasers, like Oklahoma photographer Paul Smith, study weather radar daily and hunt only the most intense cells: stronger storms mean better odds. Beyond a three-day forecast, picking targets is "pretty much reading tarot cards," he told NASA. Dark skies are essential: city glow would drown out the long camera exposures sprites require. It is a safer form of storm-chasing, and it has grown into a community: Kosar runs Spritacular, a citizen-science project that gathers sprite photos and sightings from chasers worldwide into what aims to become the first crowd-sourced sprite database. Note the distinction from ball lightning, the drifting glowing spheres reported during storms — sprites never come near the ground at all.

Are sprites actually lightning — and are they dangerous?

Despite the name, sprites are not lightning in the usual sense. NASA's Earth Observatory describes them as major electrical discharges, but as a cold plasma phenomenon, lacking the searing heat of ordinary lightning bolts — closer to what glows inside a fluorescent tube. Their color tells a story about the air itself: sprites look red because the discharge energizes nitrogen molecules in the thin upper air, and nitrogen answers in red. Different gases would glow differently, but the mesosphere's nitrogen dictates the crimson. To people on the ground, sprites pose no danger — they flicker far too high to touch anything. But they do matter to the sky above. Sprites momentarily reshape the electrically charged layers of the high atmosphere — the same layers that carry radio signals — so strong events can scramble communications. Scientists still don't fully understand why sprites sit offset from their parent lightning flash, how they take on so many shapes and sizes, or what their full impact on the atmosphere and Earth's global electric circuit might be. A single sprite lasts milliseconds, yet it can tower larger than the storm that made it. Proof required a lucky camera in 1989 — and the phenomenon is still surprising scientists, with each storm season adding to a growing database built by volunteers chasing red flashes across dark plains.