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 electrons striking the upper atmosphere. 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.
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 satellite data 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 upper atmosphere at night, varies according to the season and the 11 year solar cycle.
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Citation:
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).
*Chorus waves: Very low frequency radio waves coming from space and first detected on the ground. So-called because when played back through a loud speaker they sound like the bird’s dawn chorus
*Diffuse aurora: caused when electrons that are trapped in the Earth’s magnetic field are funnelled towards the polar atmosphere. Light is emitted when the electrons collide with neutral atoms in the upper atmosphere. The diffuse aurora is not generally visible to the naked eye but is well captured in satellite images.
*Discrete aurora: known as the Aurora Borealis at the North Pole (above the Arctic circle) and Aurora Australis at the South Pole (above Antarctica). They look like fiery, moving curtains of colourful light and can be seen by the naked eye whereas the diffuse aurora is much fainter but is more extensive and can cover the whole sky.
Issued by the BAS Press Office:
Heather Martin, Tel: +44 (0)1223 221414; mobile: 07740 822229; email: hert@bas.ac.uk
Linda Capper, Tel: +44 (0)1223 221448; mobile: 07714 233744; email: lmca@bas.ac.uk
Scientist contact details:
Prof Richard Horne, British Antarctic Survey (also Honorary Professor at the University of Sheffield)
Tel: +44 (0)1223 221542; Mobile: 0778 6733 667; email: rh@bas.ac.uk
Dr Nigel Meredith, British Antarctic Survey,
Tel: +44 (0)1223 221299; Mobile: 0797 0037 866; email: nmer@bas.ac.uk
Prof Richard Thorne, University of California Los Angeles,
Tel: +001 310 8255974; Mobile: 310 6146630; email: rmt@atmos.ucla.edu
Dr Binbin Ni, University of California Los Angeles,
Tel: +001 310 8251659; Mobile: 310 4029724; email: bbni@atmos.ucla.edu
Dr Xin Tao, University of California Los Angeles,
Tel: +001 310 8251659; Mobile: 832 2096127; email: xtao@atmos.ucla.edu
For stunning broadcast-quality footage and stills of Antarctica, plus a copy of the full Nature paper – Scattering by chorus waves as the dominant cause of diffuse auroral precipitation: ftp://ftp.nerc-bas.ac.uk/pub/photo/Nature-diffuse-aurora/
Images used should be credited to British Antarctic Survey or NASA – please see caption guidelines in the word document found on the above ftp site
Notes for editors:
British Antarctic Survey (BAS), a component of the Natural Environment Research Council, delivers world-leading interdisciplinary research in the Polar Regions. Its skilled science and support staff based in Cambridge, Antarctica and the Arctic, work together to deliver research that underpins a productive economy and contributes to a sustainable world. Its numerous national and international collaborations, leadership role in Antarctic affairs and excellent infrastructure help ensure that the UK maintains a world leading position. BAS has over 450 staff and operates five research stations, two Royal Research Ships and five aircraft in and around Antarctica.
