Van Allen Probes EMFISIS Waves
Giraffes in space? 2013-10-09

These signals were recorded by the Van Allen Probes B spacecraft EMFISIS Waves instrument on 2013-10-09 during hour 18 UTC. The measurements of three orthogonal magnetic antennas Bu, Bv, and Bw were combined to make this 31-second stereo audio recording.

The video presents a frequency-time spectrogram for the three antennas, with a moving cursor that shows the time position of the audio track. Time advances from left to right along the horizontal axis, frequency ranges from low to high frequencies along the vertical axes, and the amplitude of the signals is color coded with blue indicating weak signals and red indicating strong signals.

The features here look a bit like a herd of giraffes migrating across the African savanna. The low frequency hiss is modulated in the Bu and Bv directions as the spacecraft rotates, becoming alternately louder in the left and right stereo channels. This hiss is probably the source of the "risers" which look like giraffes (or especially long-necked turkeys), with the narrow band frequencies rising with time and then dropping slightly. This is another variation on chorus emissions. The non-linear mechanisms that result in these stimulated emissions are a hot topic of research.