Stephen P. McGreevy: Alberta Wavering Tones (1996)
Whistlers are magnificent sounding bursts of ELF/VLF radio energy initiated by lightning strikes which “fall” in pitch. Lightning stroke energy happens at all electromagnetic frequencies simultaneously—that is, from “DC to Light.” Indeed, the Earth is literally bathed in lightning-stroke radio energy from an estimated 1,500 to 2,000 lightning storms in progress at any given time, triggering over a million lightning strikes daily. The total energy output of lightning storms far exceeds the combined power output of all man-made radio signals and electric power generated from power plants.
Whistlers also owe their existence to Earth’s magnetic field (magnetosphere), which surrounds the planet like an enormous glove, and also to the Sun. Streaming from the Sun is the Solar Wind, which consists of energy and charged particles, called ions. And so, the combination of the Sun’s Solar Wind, the Earth’s magnnetosphere surrounding the entire Planet, and lightning storms all interact to create the intriguing sounds and great varieties of whistlers.
How whistlers happen from this combination of natural solar-terrestrial forces is (briefly) as follows: Some of the radio energy bursts from lightning strokes travel into space beyond Earth’s ionosphere layers and into the magnetosphere, where they follow approximately the lines-of-force of the Earth’s magnetic field to the opposite polar hemisphere along “ducts” formed by ions streaming toward Earth from the Sun’s Solar Wind. Solar-Wind ions get trapped in and aligned with Earth’s magnetic field. As the lightning energy travels along a field-aligned duct, its radio frequencies become spread out (dispersed) in a similar fashion to light shining into a glass prism. The higher radio frequencies arrive before the lower frequencies, resulting in a downward falling tone of varying purity.
In this manner, a whistler will be heard many thousands of miles from its initiating lightning stroke—and in the opposite polar hemisphere! Lightning storms in British Columbia and Alaska may produce whistlers that are heard in New Zealand. Likewise, lightning storms in eastern North America may produce whistlers that are heard in southern Argentina or even Antarctica.
(Source: archive.org)
