Wednesday, October 13, 2004

atmospheric sound

The VLF (Very Long Frequency) radio receivers at NASA's Marshall Space Flight Center in Huntsville Alabama are listening to the sounds the earth's atmosphere makes. And they're broadcasting it live over the internet. The best times to listen are at dawn and dusk, 1200 UT and 2200 UT respectively, when the atmosphere is most active near the receivers.

The dynamic spectra of these events is interesting... the one shown above is called a 'whistler', because as a signal travels through the atmosphere it gets spread out, higher-frequency components of the signal travelling faster than lower-frequency ones. The result is that a single blip can appear to be a multi-second swoop when viewed from here at the bottom of the atmospheric well.