Dawn in Space
http://www.esa.int/esaSC/SEMLAJWO4HD_index_0.html
'Dawn chorus' signals detected by ESA Cluster's WBD (Wide Band Data) instrument.
High-energy electrons get trapped in the Earth's radiation belts. When they are accelerated by the electromagnetic field, they produce this familiar sound. With the help of missions studying particles in space like the four Cluster spacecraft, ESA scientists are investigating how the electrons are accelerated and how the sound like the 'dawn chorus' of birds is created.