On the evening of the 7th October the skies of the British North lit up with the spectacular sight of the aurora borealis. A geomagnetic storm (which you can read more about in my previous article on the Carrington Event) resulted in viewings of the Northern Lights as far south as Buckinghamshire. Alongside this, the skies of Scotland and England's Northeast lit up further due a phenomenon known as STEVE.
A photo of the Northern Lights in Scotland courtesy of my Aunt the family group chat (Thank you!)
STEVE - which stands for Strong Thermal Emission Velocity Enhancement - is a relatively new scientific discovery, and refers to the purple streak that can occasionally be seen across the sky during an aurora event. Whilst occurring simultaneously, STEVE and the aurora are distinct phenomenons, with different (albeit only slightly different) causes..
A photo of STEVE in Alberta, Canada (Credit to Wiki)
To explain this, it is important to understand how the aurora themselves form. The aurora borealis (Northern Lights) and aurora australis (Southern Lights) are ribbons of mostly purple and green that can be seen across the sky in the high latitudes, near the Earth's magnetic poles. During a solar flare event the sun releases charged particles that travel across space, reaching the Earth's magnetic field (or magnetosphere). Here, they can either be deflected away and continue on their journey across space, or they can get trapped within the atmosphere, resulting in the aurora. These charged particles interact with gases in the Earth's atmosphere which causes the glowing we see in the sky in a similar process to the way neon lights work. The charged particles are moving around very quickly and essentially bang into gases in the atmosphere, oxygen and nitrogen being the most common. This causes the electrons in the gases' atoms to become 'excited' and they jump around between electron shells within the atom, causing the release of energy in the form of photons (light). Different gases release different wavelengths of energy when excited resulting in different colours of light being emitted. Oxygen releases the characteristic green colour of the aurora, and nitrogen produces the red, purple, and blue hues. The ribbon pattern of these colours in the sky are due to the magnetic field lines of the Earth's magnetosphere, giving the aurora their typical look. These aurora, because they are due to the interaction of solar particles and the magnetosphere, occurs on other planets too. Scientists have captured them on Saturn, Jupiter, Neptune, and Uranus.
An ultraviolet image of Saturn's aurora taken by the Hubble Telescope (Credit to NASA)
The magenta lights in the sky due to STEVE, it turns out, are essentially the same thing, but the heating of the gas particles is not caused by high energy solar particles, instead being caused by very hot, fast moving plasma streams that collide with them gaseous atoms. STEVE, unlike the auroras, occurs at the same time in both the northern and southern hemispheres. This could be due to a high energy source allowing the simultaneous heating of the gases in both hemispheres. The auroras are thought to 'feed' energy down to STEVE, and the phenomenon is often seen during intense geomagnetic storms when the aurora are particularly bright, as it was earlier this month. This being said, STEVE is still somewhat of a scientific mystery and research is ongoing.
Only ever seen during an aurora, STEVE has been described and photographed for decades but was only officially named back in 2016, with the first scientific paper on the concept being published in 2018. It was originally spotted, and brought to the attention of scientists, by a citizen science project in Canada that had been tracking the Northern Lights. A similar project is in pace in the US called Aurorasaurus and has a very interesting website where you can see the chance of seeing aurora in a given location, worth a visit if you want to find out more. The name STEVE was originally just 'Steve', inspired by the animated movie Over the Hedge which I am yet to see. Apparently the animals in the movie discover a hedge and name it Steve in an attempt to make to seem less scary. The amateur astronomers in Canada did the same thing with the new lights in the sky (although not because they were scared, just because they liked the movie). Scientists then came up with the acronym (Strong Thermal Emission Velocity Enhancement) to fit the name STEVE in order to honour the people who first tracked these lights. A cute origin story for a very cool phenomenon. It also goes to show how important citizen science projects are, especially as technology improves in terms of sharing information, it's not just the people in the labs who can do the science anymore!
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