Science & Technology

Aurora “dune” illuminates the Earth’s atmosphere

The Earth’s atmosphere is relatively thin — imagine an apple skin compared to the fruit itself — but there’s still a lot to learn about it. Now, using the recently discovered aurora as an atmospheric spotlight, a team of amateur astronomy and researchers have discovered evidence of high-altitude atmospheric waves. This discovery sheds light on the structure of the planet’s upper atmosphere, which is famous for being difficult to monitor on spacecraft and balloons.

Mysterious green stripe

Aurora formed when energetic Particles collide with the Earth’s atmosphere, A fascinating sight — their shimmering, waving shape Recorded for thousands of years..

“They are always very mysterious and beautiful,” he said. Matty Herin, An amateur astronomer and photographer living in Lieto, Finland. I discovered the first aurora when I was a teenager.

Herin and other members Ursa Astronomical SocietyThe Finnish Amateur Astronomy Association regularly observes the sky in search of the Northern Lights. On October 7, 2015, they were treated as a sight.

That night, green stripes covered a large area of ​​the sky. An amateur astronomy found it when he trained his camera towards the sky. Green is a common aurora color and is associated with oxygen, but aurora usually resembles an arc, spiral, or curtain. It was surprising to see the stripes, Herin said. “No one knew what they were.” The feature disappeared after a few hours and SkyWatcher submitted a photo.

Three years later, Helin and other Ursa members gathered online to celebrate the release of. A new book about the aurora..Co-authored book Minna PalmrosA space physicist at the University of Helsinki, Finland, features photos of club members.

Dash outside

By convention, Herin took some empty photos during the celebration. He was surprised to recapture the green stripes he hadn’t seen since 2015. “I immediately informed Minna and others,” he said. Aurora enthusiasts from Finland and Sweden rushed outside to photograph the elusive features.

Ursa member Emma Bruus took a photo from central Finland. She said it was fun to participate in such a collaborative effort. And it was particularly exciting, as the observations led to the start of research collaboration, Bruce said. “When we were doing scientific research, we didn’t know that.”

Bruce and Herin, along with other Ursa members, worked with Palmros and some of her colleagues to analyze the observations collected on October 7, 2018. By then, the green stripes had the nickname “Dune”. (“Imagine you’re actually looking at the dunes,” says Palmroth.)

The dunes are a true aurora, and unlike the atmospheric phenomenon known as STEVE (a powerful increase in heat release rate), we believe in collaboration. It became a hot topic a few years ago.. STEVE is believed to be caused by moving the plasma rather than the particles colliding with the Earth’s atmosphere.

The team began by analyzing two images of dunes taken at 19:41 local time from two different locations in Finland. Using planetarium software, team members identified the stars behind the six stripes in the dunes. We then applied trigonometry to calculate that all stripes were at an altitude of about 100 km. Advanced of other known aurora features..

Areas that have long been ignored

That part of the Earth’s atmosphere, Upper mesosphere, Especially difficult to study. It is difficult to send a spacecraft there because there is a considerable amount of frictional heating near the earth. At the same time, most balloons are too expensive to reach. “It’s a very difficult area to measure,” Palmroth said. So scientists jokingly called this atmosphere “ignorosphere.. Perhaps the dunes could literally shed light on the upper mesosphere, the team hoped.

Researchers began by asking basic questions: what determines the structure of the dunes? The stripes are hundreds of kilometers long and are usually about 50 kilometers apart. The team concluded that something must have changed to explain the alternating areas of relative lightness and darkness of the aurora.

They proposed two hypotheses: the flux of particles colliding with the atmosphere (source) is changing, or the number of oxygen atoms in the atmosphere (target) is changing.

To test the first theory, researchers used measurements from orbiting GPS satellites. Total number of vertical electrons On the sand dunes. (Electrons make up most of the particles that collide with the Earth’s atmosphere to produce aurora of visible light.) They find that dunes tend to coincide with regions of higher electron content than normal. discovered. However, due to the limited spatial resolution of the data, the team was unable to investigate changes in electron density on the scale of dune stripes.

They then used a ground base Magnetometer It tracks the movement of electrons in the Earth’s atmosphere, or electric current, at altitudes below the dunes. The team found a noticeable eastward stream at the location of the dunes.

The team concluded that these measurements reveal a wide range of altitude enhancements. However, the dunes themselves only occur in the relatively thin atmosphere near 100 km altitude. Therefore, the team suggested that the difference in the flux of electrons colliding with the atmosphere is unlikely to be the cause of the dune structure.

Sky waves

It leaves a second hypothesis, collaborative research has concluded: dunes appear to be due to changes in the number of oxygen atoms in the atmosphere. And the team suggested that a rare atmospheric wave known as the “mesospheric bore” was likely the cause of these fluctuations.

Atmospheric temperature reversals and wind shears can cause mesospheric bores. This manifests itself as changes in air density that can propagate over long distances. (They are similar to Tidal bore observed in some rivers.. )

The team suggested that changes in the density of oxygen atoms in the mesospheric bores were responsible for the characteristic streaks in the dunes. “The aurora illuminates this wave that is already in the atmosphere,” Palmroth said. She said it was the first time a mesospheric boa had been tracked in the aurora. “This is a new phenomenon.”

These results are Published last year AGU progress It is on page 1 of the first issue. “We are really proud to be the first article published in. AGU progress“Palm Ross said.

This discovery literally spotlights the bores of the mesosphere, and it’s amazing to find them very close to the Earth’s poles, he said. Viga Jardora CourtHe is a space physicist at NASA Goddard Space Flight Center in Greenbelt, Maryland, and is not involved in the research. “This is a whole new result.”

The work also highlights the important contributions of science enthusiasts and community groups, Gajardra Court said. An amateur with a camera has made an important step into a stationary research facility, she said. “They have the advantage of going where the phenomenon is happening.”

— Catherine Korney (@KatherineKornei), Science writer

Aurora “dune” illuminates the Earth’s atmosphere Aurora “dune” illuminates the Earth’s atmosphere

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