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The Solar Eclipse Shifted Time Signals In The USA

The US National Institute of Standards and Technology (NIST) has a radio station in Fort Collins, Colorado. Call letters: WWV. Operating at multiple shortwave frequencies, WWV broadcasts precise time and frequency information 24/7 to listeners worldwide. On April 8, 2024, the frequency of WWV shifted:

This plot also contains data from WWV's sister station in Hawaii, WWVH

"It was the solar eclipse," says ham radio operator Kristina Collins (W8EDU) of Cleveland, Ohio, who assembled records from 13 monitoring stations in and around the path of totality. "The HamSCI Personal Space Weather Station Network's Grape stations measure Doppler shift in the carrier signal of time standard radio stations such as WWV. On April 8th, the network saw a distinct S-curve signature associated with the eclipse."

The Doppler shift occured when the shadow of the Moon pierced the ionosphere, creating a temporary hole where ionization was reduced. This, in turn, altered the "skip distance" from transmitters to receivers, as shown in the diagram below:

Because the skip point was moving, reflected radio signals were naturally Doppler-shifted. reader and senior physicist Larry Carr of Brookhaven National Labs made this calculation: "Using the 10 MHz WWV frequency, an average shift of about 1/2 Hz implies the layer bottom (the 'skip point') was moving at speeds up to 15 m/s. During the entire eclipse, the reflecting layer moved on the order of 50 km."

The total Doppler shift was only a few cycles per second, similar to normal night-day variations, so no one actually lost track of time during the eclipse. Nevertheless, it is a fascinating demonstration of an eclipse's power to touch the Earth.


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