(modified May 12 2017/ page opened  Oct 9 2001 / ukl)


*May 12 2017 *

New evidence for the inversion layer hypothesis
A special type of auroral noise and its source discovered


The analysis of VLF and audio data measured during geomagnetic storms continues. Especially storms during March 17-18, 2013 and 2015 are in the focus. The measurements were done in the vicinity of the village Fiskars in southern Finland (geomagnetic latitude 57.5°N). The latest results obtained in April 2017 supports the hypothesis that the auroral sounds are produced in the temperature inversion layer typically 60-100 meters from the ground. The hypothesis is called: Inversion Layer Hypothesis (ILH).

A new methodology was developed and applied to the data collected during the geomagnetic storm on March 17-18, 2013. A selected set of sound samples with associated VLF signals was fitted to a geometrical model that is based on the ILH. In the case the ILH were false the fitting should not be successful. However, the fitting led to good results that support the hypothesis.

The new method provides a practical tool to estimate the average altitude of the sound sources from the data. This time it even led to a new discovery: a special type of auroral noise was detected and also places of its sources estimated. These new results will be published in the coming 24th International Congress on Sound and Vibration (ICSV24) July 23-27, 2017 in London. The study is supported by the Finnish Cultural Foundation and it continues.

*June 6 2016 *

New measurements confirm the altitude of the auroral sound source - a new hypothesis created


The first report on the main outcomes of the new measurements made during the March 2013 geomagnetic storm will be published in BNAM 2016 in Stockholm, June 20-22, 2016. Also, a new hypothesis on the sound producing mechanism will be presented.

*July 2 2012 *

Sound source - possible associated with aurora borealis - localized!


A recording produced on Sept 9-10 2011 during a geomagnetic storm by using three microphones and a VLF antenna picked up twenty similar clap sounds. Some of them were close enough in order to be detected by all three microphones. The collected data allowed the estimation of the location of the sound source. The sound source was on the open sky. Preliminary results will be published July 10 2012 in Vilnius:

The 19th International Congress on Sound and Vibration, Vilnius, Lithuania, July 08-12 2012.

- This result is an important step in the project since its start in 2000.

- The result shows that the sound source - at this particular case - was real and on the sky, not far away from the ground.

- The result DEOS NOT support speculations like:  the auroral sounds are -

- just illusion

- created by the brain of the observer (purely subjective experience)

- caused by synesthesia (=illness!)

- created in the brain by direct electromagnetic radiation

- created at the tips of the trees

- created by frost and ice  (no frost nor ice on Sept 9 2011)

- created somewhere on the ground – not on the sky

- The result does not explain the physical mechanism behind these clap sounds. It just estimates the location of the sound source of this event!


*August 21 2007 *

Study of Aurora Related Sound and Electric Field Effects [pdf]

This excellent Master's Thesis by Janne Hautsalo describes statistical analysis of sound recordings made at Koli, Finland April 11-12 2001 during a strong geomagnetic storm. 

[read more: Old News]


PROJECT INFO, Old News  etc . . .

Other project related material can be reached via the: MAIN PROJECT PAGE.


Note: The former Helsinki University of Technology, (TKK) Acoustics Laboratory is now part of the Aalto University Department of Signal Processing and Acoustics at School of Electrical Engineering.