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May 1st 2020

Researchers Discover Different Types of Aurora Borealis

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Scientific discoveries don’t always require new technologies or costly equipment. Sometimes all that is needed is careful observers looking in the right place at the right time. That is how amateur astronomers and professionals recently teamed up to discover glowing “dunes” in the night sky — revealing new and different types of aurora borealis that previously lurked, visible but unnoticed, in the northern night sky.

Northern Lights

The aurora, often called the northern lights, is produced, explains Science Alert, when charged particles from the sun, trapped in Earth’s magnetic field, pass through Earth’s upper atmosphere. The particles knock electrons off of atoms in the atmosphere, ionizing them and thus triggering the eerie but lovely glow of an aurora.

Because Earth’s magnetic field is concentrated toward the magnetic poles, auroras are most often seen from high northern latitudes, in regions like Canada or Scandinavia. (They appear in the far southern sky as well, but few people live in places where southern-sky auroral displays can be seen.)

Even in northern latitudes, the aurora can be elusive. Nights are cold, and because solar particles are correlated to the 11-year sunspot cycle, auroral displays are rare except during the most active phases of the cycle.

When Professionals and Amateurs Team Up

Minna Palmroth, a physicist at the University of Helsinki, was so drawn to the elusive beauty of the aurora that in 2018 she wrote a popular guidebook for Finnish aurora-watchers. In the process of compiling the book, which outlined the different types of aurora borealis, she got in touch with experienced amateur aurora-watchers.

As Business Insider describes, these observers reported that they had seen some auroral displays that were not shown in the book, and did not quite match any of the known different types of aurora borealis. Palmroth’s book project thus launched a new research project as well, with professionals and amateur observers working side by side.

The most common type of auroral display resembles a glowing curtain in the night sky, with light seeming to stream down from a bright upper edge. The auroras that Palmroth’s amateur colleagues were observing looked quite different, like frozen horizontal waves across the sky — hence the name dunes for this new (to us) type of aurora.

This is not the first time in recent years that auroras have delivered surprises. In 2017, according to separate reports in Science Alert, observers in Canada noticed yet another unusual aurora-like display, which researchers dubbed Strong Thermal Emission Velocity Enhancement, or STEVE for short. Scientists now believe that STEVE is not technically a true aurora, but a related phenomenon of the upper atmosphere.

Surprises From the “Ignorosphere”

Compared to purely astronomical phenomena, from planets to supernovae, the aurora borealis and related sky displays are right in our backyard. The various different types of aurora borealis are observed at altitudes between 50 and 100 miles — just short of 65 miles, in the case of dunes.

But as close as this is by astronomical standards, Earth’s upper atmosphere is exceptionally difficult to explore and study. The altitudes at which auroras appear are too high for aircraft or even balloons to reach, but too low for orbiting satellites. This region is so hard to study, says Gizmodo, that scientists have dubbed it the “ignorosphere.”

Dunes and other different types of aurora borealis are not only beautiful, they also provide an opportunity for scientists to study this hard-to-reach region of the upper atmosphere.

A Fascinating Bore

Dune auroras, in particular, are now believed to result from a phenomenon called a mesopheric bore, named by analogy to the tidal bore produced by tides flowing up a river. In the case of a mesopheric bore, oxygen atoms pushed higher in the atmosphere give rise to the distinctive frozen-wave glow of a dune aurora.

But most of all, both dune auroras and STEVE show that Earth’s upper atmosphere still has plenty of surprises still waiting to be discovered. The “ignorosphere” is being ignored no longer. And exploring it doesn’t require a spacecraft or even a telescope — just experienced eyes and a warm jacket for those cold northern nights.

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