What is “Chorus”?

Chorus or “Dawn Chorus” is a VLF emission that can sound like a flock of birds or the sound of a pond full of frogs or some combination thereof.  The name “dawn” chorus may have originated because it sounds like birds, frogs and insects in the morning or because it is most often heard just after sunrise. Chorus is often heard in the early morning hours during periods of high geomagnetic activity.