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New mysteries of the aurora
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"The mystery is left more mysterious than ever."
~ Sir Arthur Schuster


While many people are drawn to the aurora's mysterious beauty, it is the gateway to the great puzzles of Earth's own upper atmosphere.


Aurora morphology - while the fundamental aspects of auroral light production are understood, very little is known about how the delicate shape of the curtains is produced. Computers modeling the curtains tend to produce thicker bands.

Black aurora - sometimes what appears to be a black auroral curtain is observed within a diffuse arc. Black aurora are apparently gaps in the curtain caused when electrons are accelerated upward away from the earth rather than downward in normal auroral fashion.

Theta aurora - sometimes arcs cut across the auroral oval. These unusual shapes are called "theta aurora." There is no clear consensus among researchers as to the cause.

Enhanced lower border - a narrow, bright, horizontal band will sometimes appear across the lower edge of the aurora. The cause is unknown.

Aurora as a remote sensing tool - in theory, because the aurora is a product of upper atmosphere physics, it could be used as indicators of changes in the upper atmosphere. Changes in temperature, movement, etc. of the upper atmosphere would be reflected in auroral behavior.

A black aurora divides a
diffuse arc
click to see larger image

Helpful links

Poker Flat Research Range

Black Aurora pictures & movies

Cluster quartet probes the
secrets of the black aurora

Barring the Earth's Halo

A black aurora
click to see animation

Theta aurora
click to see animation

Auroral sound - Technically it should be impossible to hear the aurora from the ground because the lowest edge is 60 miles (100km) away and the atmosphere at that height is too thin to transmit sound waves. However, reports of whooshing and crackling noises associated with active aurora persist. Some early explorers found that covering their colleagues eyes made the sound disappear. The perception of sound could be caused by "signal leakage" from overstimulated visual centers in the brain or by energetic phenomena associated with the aurora. Recently, research groups in Denmark and Finland claim to have recorded sounds. A number of theories regarding the perception of auroral noises abound. However, there is no consensus as to whether one can actually hear the aurora.




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site last modified: August 2003 maintained by Asahi Aurora Web Author