New space research settles years of scientific debate

Oct 20, 2010
The 'aurora australis' (known as the southern lights) seen in Antarctica. The 'aurora australis' look like fiery, moving curtains of colourful light and can be seen by the naked eye whereas the diffuse aurora is much fainter (viewed via satellite), but is more extensive.

(PhysOrg.com) -- New space research published this week (Thursday 21 October) in the journal Nature, has settled decades of scientific debate. Researchers from the University of California (UCLA) and British Antarctic Survey (BAS) have found the final link between electrons trapped in space and the glow of light from the upper atmosphere known as the diffuse aurora. The research will help us understand 'space weather', with benefits for the satellite, power grid and aviation industries, and how space storms affect the Earth's atmosphere from the top down.

Scientists have long understood that the 'diffuse aurora' is caused by striking the upper . However, the electrons are normally trapped much higher up in the Earth's magnetic field through a long chain of events starting with the Sun. The problem is to understand how these electrons reach the atmosphere.

Since the 1970s scientists have debated whether very low frequency (VLF) radio waves could scatter the trapped electrons into the atmosphere. Two types of VLF waves were identified in space as the possible cause of the 'diffuse aurora', but despite years of argument and research no conclusive result had been possible. The new research shows, without doubt, that VLF waves known as 'chorus' are responsible; so-called since the signals detected by ground-based recording equipment sound like the bird's dawn chorus when played back through a loud speaker.

Through detailed analysis of satellite data the authors were able to calculate the effects on the trapped electrons and identify which radio waves were causing the scattering.

Satellite image of 'diffuse aurora' seen over Antarctica in the southern hemisphere. Image Credit: NASA

Lead author Professor Richard Thorne from UCLA says,

"The breakthrough came when we realised that the electrons being lost from space to the Earth's atmosphere were leaving a signature, effectively telling a story about how they were being scattered. We could then analyse our on the two types of VLF waves and by running calculations on them – including the rate at which the electrons were being lost to the Earth's atmosphere – we could clearly see that chorus waves were the cause of the scattering."

Professor Richard Horne from British Antarctic Survey says,

"Our finding is an important one because it will help scientists to understand how the diffuse aurora leads to changes in the chemistry of the Earth's upper atmosphere, including effects on ozone at high altitude, which may affect temperature right through the atmosphere.

"We are also including the VLF waves into computer models to help predict 'space weather' which not only affects satellites and power grids, but also the accuracy of GPS navigation and high frequency radio communications with aircraft on polar routes."

The 'diffuse aurora', is not the same as the 'discrete aurora' known as the northern and southern lights. 'Discrete aurora' look like fiery moving curtains of colourful light and can be seen by the naked eye, whereas the diffuse aurora is much fainter but more extensive. The 'diffuse aurora', which typically accounts for three-quarters of the energy input into the at night, varies according to the season and the 11 year solar cycle.

Explore further: SDO captures images of two mid-level flares

More information: Thorne, R. M., Ni, B., Tao, X., Horne, R. B., & Meredith N. P., Scattering by chorus waves as the dominant cause of diffuse auroral precipitation, Nature, doi:10.1038/nature09467 (2010).

Related Stories

Canadian space agency beams northern lights over Web

Sep 20, 2010

Skywatchers can turn their gaze to a computer for a glimpse of the northern lights: the Canadian Space Agency on Monday launched an online observatory streaming the aurora borealis live over the Internet.

Recommended for you

SDO captures images of two mid-level flares

Dec 19, 2014

The sun emitted a mid-level flare on Dec. 18, 2014, at 4:58 p.m. EST. NASA's Solar Dynamics Observatory, which watches the sun constantly, captured an image of the event. Solar flares are powerful bursts ...

Why is Venus so horrible?

Dec 19, 2014

Venus sucks. Seriously, it's the worst. The global temperature is as hot as an oven, the atmospheric pressure is 90 times Earth, and it rains sulfuric acid. Every part of the surface of Venus would kill you ...

Image: Christmas wrapping the Sentinel-3A antenna

Dec 19, 2014

The moment a team of technicians, gowned like hospital surgeons, wraps the Sentinel-3A radar altimeter in multilayer insulation to protect it from the temperature extremes found in Earth orbit.

Video: Flying over Becquerel

Dec 19, 2014

This latest release from the camera on ESA's Mars Express is a simulated flight over the Becquerel crater, showing large-scale deposits of sedimentary material.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.