STEVE: The Narrow Ribbon of Light That Isn't Quite Aurora — and Why That Makes It Fascinating

It looks like aurora. It appears in the same sky, during similar geomagnetic conditions, and it photographs beautifully. But STEVE — Strong Thermal Emission Velocity Enhancement — is not aurora in the conventional sense. It's produced by a different physical mechanism, appears at different latitudes, and was only brought to scientific attention because citizen aurora photographers noticed something in their images that didn't match any known phenomenon. That backstory alone makes it one of the more interesting subjects in northern lights science.

What STEVE Is

STEVE appears as a narrow, east-west ribbon of mauve or purple-white light — distinctly different in color from the green of conventional aurora borealis. It typically stretches across a large portion of the sky in a relatively straight, smooth arc, often accompanied by a structure called the picket fence — a series of vertical green rays below the main STEVE ribbon.

Conventional aurora is produced by electron precipitation from the magnetosphere along field-aligned currents, exciting oxygen and nitrogen in the ionosphere. STEVE is different. It is caused by a fast-moving ribbon of hot plasma in the subauroral ionosphere — a region equatorward of the normal auroral oval — moving at speeds of several kilometers per second. The heat and friction generated by this fast-moving plasma produce the characteristic mauve emission through a mechanism that is still not fully understood.

What helped me picture it: think of STEVE as the contrail of a very fast-moving stream of plasma cutting through the upper atmosphere — the light produced not by particle collision in the aurora sense, but by the thermal emission of extremely hot, rapidly flowing material.

The Citizen Science Connection

STEVE's story is unusual in space science. Aurora photographers in citizen science networks — particularly a Canadian group called the Alberta Aurora Chasers — began sharing images of a recurring mauve arc that didn't match any known aurora form. Researchers at the University of Calgary investigated, analyzed satellite data alongside the photographic reports, and confirmed in 2018 that STEVE was a previously undescribed phenomenon. The name itself comes from the citizen science community — chosen informally before the physics was understood, as a placeholder name that stuck. For more on how citizen observation contributes to aurora science, see the Citizen Science page in this glossary.

What STEVE Means for Aurora Travelers

STEVE appears at latitudes equatorward of the normal auroral oval — which means it has been documented from locations that rarely see conventional aurora, including parts of the northern United States and central Europe. However, it tends to appear during periods of elevated geomagnetic activity, often in association with substorm events, so being at a high-latitude destination during an active night increases your chances of encountering it.

STEVE events are relatively rare and not yet reliably predictable. The best approach is to be outside during active geomagnetic periods, watch for an unusual mauve or purple-white ribbon distinct from the green aurora, and photograph any unusual forms for later review. Its appearance to the south of the main aurora display — equatorward of the oval — is one of the identifying characteristics in the field.

What STEVE Means for Photographers

STEVE is a genuinely distinctive photographic subject. Its mauve color stands out strongly against conventional green aurora and dark sky, and its smooth, ribbon-like geometry produces clean compositional lines across the frame. Wide-angle lenses that capture both the STEVE ribbon and any associated picket fence structure below it tend to work well.

Exposure settings appropriate for conventional aurora — ISO 1600–3200, f/2.8, 8–15 seconds — generally work for STEVE as well, though its lower surface brightness relative to bright active aurora may benefit from slightly longer exposures or higher ISO during fainter manifestations. Shooting in raw format preserves the most color information for distinguishing the mauve of STEVE from the green of conventional aurora in post-processing.

Return to the full Northern Lights Glossary to continue through the Aurora Visual Forms and Phenomena section.