Northern & Southern Aurorae Are Siblings, But Not Twins

by Anne Minard on July 22, 2009

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Asymmetrical aurorae, courtesy of Karl Magnus Laundal and Nature

Asymmetrical aurorae, courtesy of Karl Magnus Laundal and Nature

Seen the Northern Lights and you’ve seen them all, hm? Not so.

It is commonly assumed that the aurora borealis in the Northern Hemisphere and the aurora australis in the Southern Hemisphere are mirror images of each other — but new research has revealed differences between the events.

The aurorae, commonly known as the Northern and Southern Lights, are spectacular natural light displays in the Earth’s upper atmosphere. The phenomenon is caused by charged particles from the solar wind striking atoms and molecules in the atmosphere.

It’s intuitive to think the Northern and Southern Lights are identical, because the charged particles causing the aurora follow the symmetric magnetic field lines connecting the two hemispheres.

But  study co-authors Nikolai Østgaard and Karl Magnus Laundal, both of the University of Bergen in Norway, report in the journal Nature this week that there are differences between the phenomena.

“Here we report observations that clearly contradict the common assumption about symmetric aurora: intense spots are seen at dawn in the Northern summer Hemisphere, and at dusk in the Southern winter Hemisphere,” they write. “The asymmetry is interpreted in terms of inter-hemispheric currents related to seasons, which have been predicted but hitherto had not been seen.”

Østgaard and Laundal based their report on observations from a new set of global imaging cameras at each pole. The authors suggest that the observed asymmetry confirms the existence of inter-hemispheric, field-aligned currents related to the seasons, which had been predicted but never before observed.

Source: Nature

JLGuagliardo July 22, 2009 at 11:28 AM

Might there be a coupling between the auroral asymmetry and the projected solar magnetic, i.e. solar wind, field direction?

Jon Hanford July 23, 2009 at 11:17 AM

What satellite took these images and at what wavelength? I didn’t see mention of either in the abstract from Nature.

Jon Hanford July 24, 2009 at 9:41 AM

I see an article at PhysOrg.com mentions that data from the now defunct IMAGE and Polar satellites were used for their analysis.

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