A natural electromagnetic phenomenon occurring in the very low frequency radio band, characterized by a series of rising acoustic tones that resemble birdsong. It is caused by solar wind particles interacting with the Earth's magnetosphere and is most prominent at local dawn. Radio operators monitor it to gauge space weather conditions that might affect higher-frequency propagation.
Heard on the job
We lost the VLF submarine link for about twenty minutes this morning when the dawn chorus drowned out the signal.