Van Allen Probes EMFISIS/Waves
Whistlers from 2012-09-11

The Van Allen Probes EMFISIS Waves instruments detected these signals with two orthogonal magnetic antennas (Bv and Bu) during UTC hour 18 of September 11, 2012. The predominant feature is a barrage of whistlers which originate with lightning discharges on Earth. These signals propogate along magnetic field lines through the thin ionized gasses of space which allow the higher frequencies to travel faster than the lower frequencies. This results in a frequency dispersion and the characteristic whistling tone, which also sounds a little like science-fiction movie sound effects. The animation shows the individual 6-second or 12-second snapshots with a moving cursor that indicates the time position of the audio track.