The Van Allen Probes EMFISIS Waves instruments detected these signals with three orthogonal magnetic antennas (Bu, Bv, Bw) during UTC hour 03 of September 5, 2012. These were some of the first signals received from our instruments on the newly-launched spacecraft and the Bu component was widely publicized as "Earthsong". There are four separate 6-second snapshots featuring progressively lower-frequency chorus signals. Unlike the original public release, this stereo version includes data from all three magnetic antennas and includes an animation showing the spectral components with a cursor that indicates the time position of the audio track.
Chorus waves in Earth's magnetosphere are generated in the Van Allen radiation belts by electrons spiraling along Earth's magnetic field lines in this region. Once generated, the chorus waves interact with the moving electrons, either accelerating them to higher energies or disturbing the spiral orbit of the electrons and causing them to fall into Earth's upper atmosphere along the magnetic field lines.