The northern and southern lights are among the most breathtaking celestial displays that sky watchers can hope to witness. Although the two types of auroras seemingly shine in the same electric shades of green, yellow, purple, and — in rare cases — blue, their ethereal glow is actually very different.
As the Inquisitr previously reported, auroras spark into existence when the outflow of charged particles coming from the sun – also known as the solar wind – seeps into our planet’s magnetosphere (the protective bubble around the planet) and meet oxygen and nitrogen molecules.
When solar wind clashes with charged oxygen atoms, it gives birth to green and yellow auroras. Meanwhile, when these highly-charged particles meet nitrogen atoms, they bloom into rare blue auroras.
For years, scientists assumed that the aurora borealis seen around the north pole was the mirror image of the aurora australis lighting up the sky over the south pole. However, in 2009 researchers discovered that this was not the case. In fact, the northern and southern lights actually exhibit striking differences in shape, and also appear to emerge in different locations in the two polar regions.
This phenomenon has since been described as aurora asymmetry. While its causes have largely remained a mystery, a team of scientists from the University of Bergen in Norway believe that they have found the answer to why the northern and southern lights are so different, Phys.org is reporting.
In a new paper published in the Journal of Geophysical Research: Space Physics, the Norwegian team explains that aurora asymmetry is produced by the interaction between the sun’s magnetic field, the solar wind, and the Earth’s magnetotail — a magnetic tail that extends away from our planet, flowing into outer space.
Until now, the differences between the northern and southern lights have largely been put down to the pulling apart and reconnecting of magnetic field lines in the Earth’s magnetic tail — a process called tail reconnection. The new paper, however, shows evidence that the culprit behind aurora asymmetry is actually the solar magnetic field.
When the sun’s magnetic field hits our planet in an east-west direction, its interaction with Earth’s magnetic field is different around each of the two poles.
“This leads to asymmetric loading of pressure onto the Earth’s magnetic field and introduces a tilt in the Earth’s magnetic field on the nightside of the Earth,” explains Phys.org, citing the American Geophysical Union (AGU).
This tilt is what makes north pole auroras take on a different shape from the southern lights and grace the sky in different locations around the two poles.
The video below, uploaded on YouTube by AGU, details the process by way of an animation, which shows how the solar magnetic field merges with that of our planet and twist together, then get pushed into Earth’s magnetic tail by the solar wind. The resulting build-up of magnetic energy and pressure is asymmetric, leading to asymmetric auroras whenever the northern and southern lights form within the tilted field.
In a surprising twist of event, the scientists uncovered that tail reconnection — previously believed to foster aurora asymmetry — may actually serve to blur out these striking differences between the northern and southern lights.
“The reason this is exciting is that earlier we have thought that the asymmetry in the system enters the magnetosphere by a mechanism called tail reconnection,” said study lead author Anders Ohma.
“What this paper shows is that it’s possible that it is actually the opposite: This reconnection in the magnetotail is actually reducing the asymmetry.”
A related paper published by the same team elaborates on the importance of regarding the interactions between the sun and the Earth – also known as the geospace – as an asymmetric system. This second study, published in the journal Annales Geophysicae, details a specific case of aurora asymmetry observed during a geomagnetic storm in August of 2001.
“Without including these asymmetries our understanding of the sun-Earth system will be far from complete and models will not be able to accurately predict the location and timing of geospace phenomena,” said team member Nikolai Østgaard, who is head of the Birkeland Centre for Space Science at the University of Bergen and the lead author of the second study.