The Mystery of Auroral Sounds
Unto K. Laine
During clear dark nights the sky around the northern and southem polar circles are sometimes filled with mystically dancing colorful flames. These works of natural art are called northern lights, or "aurora borealis". For hundreds of years people living in the northern parts of the globe have reported strange sounds heard during the most intense auroral displays. These sounds have posed a mystery for science and so in the 1960ís an attempt was made in Alaska to record them. No clear indication was found and since there is no physical theory able to explain how these sounds could be created, many geophysicists still do not believe that auroral sounds exist.
Ten years ago when I visited Finnish Lapland with some of my friends, we heard strange sounds during an auroral display. This was a motivating experience and caused me to start a project where the primary goal was to find an answer to the question of whether auroral sounds can actually physical exist. Finally, April 2001, after 30 lonely nights outdoors, very interesting sound material was recorded during a strong geomagnetic storm at Koli, in the eastern part of Finland. Even though closer analysis of this material is still going on, we believe that these mystical auroral sounds have now been captured. The recordings will force us to re-evaluate many old myths, e.g., Norwegian sagas about the song of Valkyries.
Imagine that it is a cold, dark winter night. The sky is clear, no wind. You are nestling alone in an old car. Somewhere behind Godís back, as people use to say. The car is parked at the shoulder of a narrow way leading to the fields. The snow covered fields around you form an opening in the surrounding forrest further away. The distance to the closest house and to the closest electrical lines is 3 kilometers. Only sources of light are the thousands stars above your head and the greenish-blue curtains which move softly on the northern sky. Aurora borealis is rising.
On the fields about 10 meters from the car is a satellite antenna. An dish, which works as an acoustic reflector collecting and amplifying sounds from the athmosphere just above it. The sensor of this antenna is changed to a high sensitivity, low noise condenser microphone.
Another antenna used for electric field measurements, picks up VLF signals (very low frequency electro-magnetic waves) just 5 meters from the car. This antenna is made of a telescope rod of class fibre, which rises a thin copper wire straight up from the earth to the hight of 5 meters.
Cabels from the sensors are connected to a small DAT player which is powered by a car battery of its own. You have the headphones on and listen. Sounds made by animals are easily detected. Dogs bark, some nightbirds whistles. But, then something strange happens.
Gradually, in the same time when the Northern Lights come closer and are brighter strange sounds are flowing through the headphones: crackling sounds, bangs like small explosions or shooting, rumble and roar just like close to some factory.
When the sounds grow louder, some birds startle and fly screaming away. Dogs bark more violent.
The light of the aurora makes the snow glow. Just like two full moons on the sky. The sounds heart are louder and more and more strange ones. VLF signal activates like a thunder storm were coming closer. Effects of lightnings in electrical field and in audio signal, but not any clear lightning which could be observed by eye.
In ten minutes everything is over. Lights go away. Darkness increases. Sounds are heart ever further away and ever softer. You may ask yourself, was this a dream or did I see and hear all this...
Read more: http://www.acoustics.hut.fi/projects/aurora/index.html
You may also report about your own auroral sound observations.
(mostly in Finnish - sorry...)
(Text written for the "aurora show" at Eurospeech 2001 closing
ceremony in Aalborg, Denmark)