We can’t hear it without special equipment, but the planet almost continually sings with the sound of low-frequency radio signals that derive from lightning strikes. Because the signals are mostly trapped below the ionosphere, a reflective layer 55 miles above the ground, a suitable receiver can pick them up from thousands of miles away. They sound like twigs snapping or bacon frying.
This weird-looking term for them, sferics, is just a respelled version of the last part of atmospherics. Though the strange noises had first been heard by a German physicist, Heinrich Barkhausen, during World War I, the abbreviation appeared from military research around 1945.
An equally important role in making weather an exact science is being played by so-called “sferics” networks, which utilize static from electrical discharges in the atmosphere to investigate weather conditions over oceanic areas, vast land wastes, enemy-held territory and other zones where no surface observation stations can be set up.
The News and Tribune (Jefferson City, Missouri), 7 Oct. 1945.
There’s a complete vocabulary of words to describe various types: tweeks come from lightning that is so far away that the high radio frequencies arrive before the low, resulting in a musical set of clicks and tweets; whistlers are slowly descending tones caused by a similar mechanism, but which acts on bursts of radio waves that travel from pole to pole along magnetic lines of force.
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