A quadruplet of Earth satellites has found that the ghostly Northern and Southern Lights are not just a pretty light show, but a complex system of equal and opposite electrical phenomenon.
And they talk. Provided you have the right equipment to listen.
The European Space Agencies Cluster satellites recorded high-frequency radio waves emitted along the Earth's aurora-producing magnetic poles. Researcher Donald Gurnett, at the University of Iowa, described what Cluster heard as:
"Really wild -- like extraterrestrials or something."
Aurorae appear in the Northern and Southern-most skies when packets of electrons released by the Sun are pulled toward Earth's magnetic poles, then slammed against the Earth's ionosphere. The ionosphere is a layer of electrons and ions that surrounds the Earth at an altitude of 43 to 50 miles, and extends to an indefinite height.
The electrons collide with the few gas molecules that exist way up there, and the excited gases glow. The result is a ghostly light as well as inaudible, high-pitched whistles and squeaks, said Gurnett. Results from the research, conducted by Gurnett and other scientists at the University of Iowa's astrophysics department, were presented Dec. 10 at an American Geophysical Union meeting in San Francisco.
Black aurora
Swedish and British astronomers from the European Space Agency announced other findings from Cluster at the meeting. Their research uncovered the cause of "black aurorae," dark bands, squiggles and rings that form within the visible aurorae.
The name black aurora was coined over 40 years ago, when visual observers on Earth first noticed the unusually dark spaces in the Northern Lights.
According to the scientists, black aurorae are caused by holes in the ionosphere, where electrons are sped up and out of it by positively charged magnetic structures. This is exactly opposite of the process that creates visible aurorae.
"Now, with the aid of the four Cluster spacecraft, we have been able to study for the first time the complex physical processes that create these auroral holes," said Goran Marklund, a researcer at the Alfven Laboratory in Sweden.
Observations of the "anti-aurora" took place Jan. 14 in the Northern Hemisphere and Feb. 14 in its southern counterpart. The crafts were at a height of more than 13,422 miles (21,600 km), strung above the Earth like a string of pearls.
The crafts swept from south to north, across the Earth's magnetic fields every 100 seconds. The quadruple set of observations gave the researchers a dynamic picture of the phenomenon's conditions: from different points in the sky, and at slightly different times.
In this way, "Cluster allowed us to discover how the huge vertical structures associated with the black aurora form, how long they last and how they vary with altitude, " Marklund said.
Within the dark aurorae zones, Cluster found a tripling in the upward electrons' energy while it measured the growth of an electric field shaped like a "u". The "u" structure was the site of the electrons' acceleration. By the time the fourth craft took measurements of the same area, the electric field vanished.
"The data show that the structures that create the black aurora extend to altitudes greater than [12,427miles] 20,000 km and that they grow in size and intensify over time scales of a few minutes," Marklund said. He also added that this is about the same time that aurorae take to develop and fade.
"Understanding the development and growth of these dynamic structures associated with the aurora is a major goal of the Cluster mission, and something which cannot be solved by single satellite measurements," he concluded.
Aurora Tonight?
advertisement
