Scientists Don’t Know What Causes Mysterious Purple Skyglow

Scientists Don’t Know What Causes Mysterious Purple Skyglow

The ethereal green glow of the northern lights is a well-understood phenomenon, but that doesn’t make it any less lovely. A different atmospheric light show is still puzzling scientists. It is currently known as the Strong Thermal Emission Velocity Enhancement or STEVE for short. Amateur photographers have caught hints of STEVE for years, but scientists only recently started examining the effect. The only thing we can be sure of at this point is that STEVE is much more majestic than its name.

The northern lights (also known as the aurora borealis) is the result of the solar wind striking the magnetosphere and producing showers of light. Auroras aren’t confined to the northern latitudes — you’ll find them near the south pole as well. They can cover large swaths of the globe when solar activity is at its maximum, but STEVE is different. It’s smaller and very much not an aurora. Yes, the NASA video below calls it an aurora, but it’s a few months old. Sometimes science moves fast.

STEVE is a narrow, purplish band of color that tends to occur alongside the northern lights. It can stretch more than 600 miles (1,000 kilometers) across the sky. Unlike the northern lights, STEVE only appears several times each year, which has made it difficult to study. That led many scientists to assume that STEVE was just part of the aurora process we already knew about until just recently.

A new analysis from the University of Calgary and the University of California calls the traditional wisdom into question. NOAA’s Polar Orbiting Environmental Satellite 17 (POES-17) circles the globe 14 times per day, and it happened that its path took it directly over top of a STEVE event recently. POES-17 has an instrument that can measure charged particles in the atmosphere, but it found none of them associated with STEVE. Additional observations from ground-based cameras confirm the data.

The study doesn’t go into detail on what STEVE is, but it seems it’s not an aurora of any sort. The researchers are currently calling this phenomenon a “sky glow.” Just because we don’t know what STEVE is doesn’t mean there aren’t credible hypotheses. Scientists using data from POES-17 believe STEVE originates in the ionosphere. This instrument detects no charged particles, but streams of fast ions or hot electrons could be responsible for STEVE’s light emissions.

Researchers will probably work out the mechanism that produces STEVE now that it’s hit the scientific mainstream. So, just sit back, relax, and enjoy the mystery while you can.

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