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STEVE phenomenon: Why the solar storm is an astronomical wonder

Earlier this week, a beautiful purple streak appeared across the night sky in Canada; here's everything you need to know

STEVE: a purple streak across the night sky.
STEVE: a purple streak across the night sky. (Source: NASA, Neil Zeller)

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A sudden solar storm struck the Earth's magnetic field late on August 7 night. Strong Thermal Emission Velocity Enhancement, or STEVE for short, is a puzzling aurora-like phenomenon that appeared as a result of the storm's collision with our planet's outer shield. STEVE first appeared in the sky in 2017 and has been appearing often since.

With green picket fences surrounding it occasionally, this purple streak of light stretched across the night sky, baffling onlookers. It stands out sharply from the typical auroras we are accustomed to, and it also appears significantly lower in the atmosphere. Twitter user Alan Dyer took to the platform to share some images of this stunning phenomenon.

When STEVE first appeared in the sky, it baffled scientists and astronomy enthusiasts alike. However, ever since, a general understanding of the factors that lead to the appearance of STEVE has begun to emerge among scientists. So, what is STEVE and how is it different from the usual Aurora Borealis on Earth?

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What is STEVE and how did it get its name?

While there is evidence to support the claim that the phenomenon has been visible in the sky since 1705, it wasn't until members of the Facebook group Alberta Aurora Chasers gave it a name - claiming it was a proton aurora, and started referring to it as a "proton arc" - that the phenomenon's nature was correctly identified. Photographer Chris Ratzlaff, one of the observers, proposed calling the phenomenon "Steve" after an event shown in the animated comedy film "Over the Hedge" in 2006.


How does it occur?

The phenomenon is believed to be caused by a 25 km wide ribbon of hot plasma moving at a speed of 6 km/s (compared to 10 m/s outside the ribbon) at an altitude of 450 km, according to the analysis of satellite data from the European Space Agency's Swarm mission. 

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STEVE has been observed in New Zealand, Canada, Alaska and the United Kingdom during a specific time of the year - between October to February which lead NASA scientists to believe that its occurrence is related to seasons. However, in August 2018, scientists discovered that the phenomenon's skyglow might be produced in the ionosphere because it was not connected to particle precipitation (either electrons or ions). 


How is it different from Aurora Borealis?

Disturbances in the Earth's magnetosphere due to solar wind cause Auroras. These disturbances occur because of enhancements in the speed of the solar wind from coronal holes and coronal mass ejections. "When we see the glowing aurora, we are watching a billion individual collisions, lighting up the magnetic field lines of Earth," reads the NASA website. 

While the skylights, STEVE and the Auroras might seem similar, they are nothing alike. To begin with, the STEVE phenomenon is closer to the equator than the Auroras. 

"STEVE is different from the usual aurora, but it is made of light and it is driven by the auroral system. In finding these tiny little streaks, we may be learning something fundamentally new in how green auroral light can be produced," says Elizabeth MacDonald, a space scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland on the NASA website.

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