Radio atmospheric signal

A radio atmospheric signal, or sferic, is a broadband electromagnetic pulse produced by a natural lightning discharge in the atmosphere. Because it can travel long distances through the waveguide formed between Earth's surface and the ionosphere with little loss of strength, a sferic can be detected by a receiver thousands of kilometers from the lightning that produced it, appearing as a sharp spike on a time-domain plot and as a vertical stripe spanning a few to several tens of kilohertz on a spectrogram. A sferic that has traveled more than about 2,000 kilometers arrives with its component frequencies slightly separated in time, producing a related signal called a tweek, and a sferic whose energy instead escapes upward into the magnetosphere disperses further and becomes the related phenomenon known as a whistler. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/