STEVE is a light display in the night sky that appears as a purple and green ribbon. It was named in late 2016 by people who study the aurora in Alberta, Canada. The name "STEVE" stands for Strong Thermal Emission Velocity Enhancement. Scientists using data from the European Space Agency's Swarm mission discovered that STEVE is caused by a 25 km (about 16 miles) wide ribbon of superheated gas at an altitude of 450 km (about 280 miles). This gas reaches temperatures of 3,000 °C (about 5,430 °F) and moves at a speed of 6 km/s (about 3.7 miles per second), which is much faster than the gas outside the ribbon, which moves at 10 m/s (about 33 feet per second). Although STEVE is not rare, scientists had not studied or described it before 2016.

Discovery and naming

The STEVE phenomenon has been seen by people who take pictures of the aurora for many years. Some records show that people may have noticed STEVE as early as 1705. Notes that look similar to STEVE appear in some observations from 1911 to the 1950s made by Carl Størmer.

The first clear understanding of what STEVE is came later, after members of a Facebook group called Alberta Aurora Chasers gave it the name "proton arc" and said it was caused by a type of aurora. However, physics professor Eric Donovan from the University of Calgary looked at their photos and thought their idea might be wrong because proton auroras are not usually visible. He matched the time and place of STEVE with data from the Swarm satellite and GPS information from a photographer named Song Despins. She provided coordinates from Vimy, Alberta, which helped Donovan connect the data to learn more about the phenomenon.

A photographer named Chris Ratzlaff suggested calling the phenomenon "Steve," inspired by the 2006 movie Over the Hedge. In the movie, characters name a hedge that appears suddenly to make it seem less threatening. Reports about this unusual "aurora" spread quickly online, showing how people can help scientists through projects like Aurorasaurus.

At a meeting in December 2016, Robert Lysak proposed using the name "Steve" as an acronym for "Strong Thermal Emission Velocity Enhancement." This name, "STEVE," is now used by scientists at NASA Goddard Space Flight Center who study the phenomenon.

Occurrence and cause

STEVE phenomena can be seen farther from the poles than the aurora. As of March 2018, they were observed in the United Kingdom, Canada, Alaska, northern U.S. states, Australia, New Zealand, and Denmark. The phenomenon appears as a very narrow arc that stretches for hundreds or thousands of kilometers and runs from east to west. It usually lasts between twenty minutes and one hour. As of March 2018, STEVE phenomena were only seen when an aurora was present. No sightings occurred from October 2016 to February 2017, or from October 2017 to February 2018, leading NASA to believe that STEVE may only appear during certain seasons. However, STEVE was later reported and photographed in South Australia on October 11, 2024, during a geomagnetic storm event.

A study published in March 2018 by Elizabeth A. MacDonald and co-authors in the journal Science Advances suggested that the STEVE phenomenon occurs alongside a subauroral ion drift (SAID), a fast-moving stream of extremely hot particles. STEVE is the first visual effect observed to accompany a SAID.

In August 2018, researchers found that the skyglow of the phenomenon was not caused by particle precipitation (electrons or ions) and could instead form in the ionosphere.

One possible explanation for the glow is that excited nitrogen molecules break apart and interact with oxygen to create glowing nitric oxide.

A study published in Geophysical Research Letters noted that a STEVE phenomenon is often, though not always, seen above a green, "picket-fence" aurora. The picket-fence aurora is created by the precipitation of electrons but forms outside the auroral oval, making its formation different from traditional auroras. The study also found that these phenomena appear in both hemispheres at the same time. Observations of the picket-fence aurora have sometimes occurred without STEVE.

The green light in the picket-fence aurora appears to be linked to swirling patterns in the supersonic flow of charged particles, similar to eddies in a river that move more slowly than the surrounding water. Because of this, the green bars in the picket-fence aurora move more slowly than the purple structures. Some scientists believe this could be caused by turbulence in charged particles from space.

Research

• "How I Met Steve" – Eric Donovan's Presentation to the 2017 ESA Earth Explorer Missions Science Meeting, March 20, 2017 (1:08:30 – 1:26:00)
• "On the Location of Steve, the Mysterious Subauroral Feature"

• "New Science in Plain Sight: Citizen Scientists Help Discover Light Patterns in the Upper Atmosphere"
• "On the Origin of STEVE: Particle Rain or Ionospheric Light?"
• "Historical Observations of STEVE"
• "What Else Can Citizen Science and Amateur Observations Reveal About STEVE?"
• "From the Spark to the Fire: Reflections on Five Years of Public Participation in Aurora Research"
• "On the Origin and Geomagnetic Conditions of STEVE's Formation"
• "A Statistical Analysis of STEVE"

• "How Did We Miss This? An Upper Atmospheric Discovery Named STEVE"
• "First Observations From the TREx Spectrograph: The Light Spectrum of STEVE and the Picket Fence Phenomena"
• "Color Ratios of Subauroral (STEVE) Arcs"
• "A New Dataset of STEVE-Related Observations Across Multiple Solar Cycles"
• "Subauroral Green STEVE Arcs: Evidence for Low-Energy Excitation"
• "Magnetospheric Signatures of STEVE: Implications for Magnetospheric Energy and Interhemispheric Conjugacy"
• "High-Latitude Ionospheric Electrodynamics During STEVE Events Reported by Citizen Scientists"
• "Steve: The Light Signature of Intense Subauroral Ion Drifts"
• "Light Spectra and Emission Heights of Double-Layer STEVE: A Case Study"
• "The Vertical Distribution of Light Emissions in a STEVE and Picket Fence Event"
• "Identifying STEVE's Magnetospheric Driver Using Ground and Space Observations"
• "STEVE and the Picket Fence: Evidence of Feedback-Unstable Magnetosphere-Ionosphere Interaction"
• "Possible Evidence of STEVE in Dynamics Explorer-2 Data"

• "Early Ground-Based Work by Auroral Pioneer Carl Størmer on High-Altitude Detached Subauroral Arcs Now Known as 'STEVE'"
• "Early Evidence of Isolated Auroral Structures in the 100 km Height Range Observed at Subauroral Latitudes by Auroral Pioneer Carl Størmer"
• "Magnetospheric Conditions for STEVE and SAID: Particle Injection, Substorm Surge, and Field-Aligned Currents"
• "Neutral Wind Dynamics Before STEVE and Their Possible Role in STEVE Formation"
• "A Mechanism for the STEVE Continuum Emission"
• "High-Latitude Ionospheric Electrodynamics During STEVE Events"
• "Dynamics of Auroral Precipitation Boundaries Linked to STEVE and SAID"
• "The Apparent Motion of STEVE and the Picket Fence Phenomena"
• "Characteristics of Fragmented Aurora-Like Emissions (FAEs) Observed on Svalbard"
• "Fragmented Aurora-Like Emissions (FAEs): A New Type of Aurora-Like Phenomenon"

• "Multi-Wavelength Imaging Observations of STEVE at Athabasca, Canada"
• "Recording Synchronous Geomagnetic Pulsations and Proton Aurora During a Substorm on March 1, 2017"
• "First Simultaneous Observation of STEVE and SAR Arc Combining Citizen Science, All-Sky Images, and Satellite Data"
• "Proton Aurora and Light Emissions in the Subauroral Region"
• "Robust Techniques to Improve Triangulation of Citizen Science STEVE Observations"
• "Comparison of SAR Arc, STEVE, and Picket Fence Dynamics at the Maimaga Subauroral Station on March 1, 2017"
• "Improved Analysis of STEVE Photographs"

• "Rainbow of the Night: First Direct Observation of a SAR Arc Evolving into STEVE"
• "Auroral Structures: Highlighting the Importance of Meso-Scale Magnetosphere-Ionosphere Coupling"

• "It's Not Easy Being Green: Kinetic Modeling of the Light Spectrum in STEVE's Picket Fence"

• "Unsolved Problems in Strong Thermal Emission Velocity Enhancement (STEVE) and the Picket Fence"

• "Unexpected STEVE Observations at High Latitude During Quiet Geomagnetic Conditions"