ARCHIVE - Auroral Sound

Humans have described experiences of hearing the aurora for maybe as long as they have seen it. They say that it sounds like crackling, hissing, popping and swooshing that usually corresponds with the motion of the light. There are many explanations for how this sound might be created, but there is one thing that makes audible sounds questionable: the speed of sound and the distance from the aurora to the ground. Sound waves take about 6 minutes to travel from the aurora to a person standing directly under it. This means if sound were able to reach the ground and still be in the audible range, the sounds being heard would correspond to what one saw at least 6 minutes ago.

It is common that in a group of people watching the aurora not all of them with hear it. In addition, there has never been a recording of audible sounds related to the aurora, even with today’s sensitive equipment.

Some theories about the audibility of aurorae are:

Psychological –We expect a sound with lightning or explosions and know the soft crackling in a fireplace or the roar of a bonfire. We see these fiery, dancing colors in the sky and expect to hear a sound, so our brains create the sound for us.

Electrostatic – there are variations in the atmosphere during geomagnetic storms which may induce static electricity in surrounding objects (i.e. clothing, trees, etc).

Freezing breath - at very cold temperatures, we can hear the moisture in our breath turn to ice crystals as it makes contact with the cold air.

Although we have no evidence of audible sound, there is evidence of infrasound associated with aurorae (Wilson and Olson, 2003). Humans can hear a large range of frequencies – from about 20 Hertz (Hz = cycles per second) to about 20,000 Hz. Infrasound is simply sound waves that are inaudible to the human ear – below 20 Hz. The infrasound observed with aurorae is usually about 0.1 – 1.0 Hz. An interesting side note is that it has been found that migratory animals, from elephants to Atlantic cod, may use infrasound to communicate over long distances (Ramsayer, 2004).

Is it possible that these infrasonic acoustic waves originate from the magnetic waves created by geomagnetic storms?

Does a similar wave transformation occur elsewhere?

Sources:

Ramsayer, K. “Infrasonic Symphony.” Science News, 165(2), 26-28, 2004

Wilson, C.R. and J.V. Olson. “Auroral Infrasound Observed at I53US at Fairbanks, Alaska.” American Geophysical Union, Fall Meeting, 2003