Coronal mass ejections from the sun are plasma with magnetic fields. They can collide with Earth’s magnetosphere, causing the auroras that fascinate us. This is a well-known phenomenon in the amateur radio community because of the effect on radio propagation.
This month, astronomers told us a geomagnetic storm was coming a few days in advance. It was the biggest since 2005 but was not a remarkable visual display at my location in central Minnesota, some 46 degrees north of the equator. Thanks to Paul Bruegl in Battle Ground, Wash., for providing a dazzling photo from his neighborhood.
AM Radio
The event had a big effect on AM radio. As most Radio World readers know, AM stations can be heard far away at night because the three-layer ionosphere is 37 to 190 miles above the Earth. These ionized layers reflect medium-frequency radio waves back to Earth at night. The sun changes that so reflections do not occur in the AM band during the day.
KXEL Radio in Waterloo, Iowa sends its 1540 kHz my way with a two-tower 50 kW directional at night. Being about 300 miles away, it is not heard here during the day, but has a strong signal, almost as good as local stations, into my town at night. Its audio was non-existent during the aurora.
WCCO Radio in Minneapolis, Minn., 50 KW on 830 kHz, sounded that night just as they do during the day. They are 125 miles from my location. I normally hear selective fading of their signal at night.
What I am referring to is receiving a ground wave signal from the station, plus a signal that bounces off the ionosphere at night. The signals can combine in phase or can cancel when a time difference of .0006 milliseconds, or multiples of that, between the ground and sky waves are 180 electrical degrees apart. Selective fading creates obnoxious audio distortion for a few seconds and then is repeated again maybe a minute later. Timing of the fading varies because sky reflections vary in altitude. As mentioned, the WCCO night signal sounded like a day signal during the aurora.
Similar interference-free reception happened on semi-local stations, like KKIN(AM) in Aitkin, Minn., which runs 360 watts at night. They are 38 miles from my location. Co-channel beats and adjacent channel chatter were gone. They normally suffer interference at night but were fairly clean because interferers were not reflected down from the sky to compete with their signal.
Higher frequencies are less affected by reflections during the day. On the amateur radio side, I normally participate in a 75-meter (3908 kHz) net where operators from a five-state area check in on Saturday mornings to talk about contacts they made that week to foreign countries via ionospheric reflections. The band was absolutely dead during the solar event. No signals were heard. Even the noise level was low because random noise from elsewhere was not reflected down to my location. Things returned to normal a few days later.
Listening in the 120 through 16-meter (2.3 to 17.9 MHz) shortwave broadcast bands was nearly impossible during the aurora. Also, there were some reported accuracy problems with GPS signals during the event. I haven’t heard a total this time, but some 38 commercial satellites were reported lost in a 2022 storm.
History
A geomagnetic storm can stress the power grid to the point of failure. A 1989 storm induced unwanted currents in power lines causing a nine-hour blackout for 6 million customers in and around Quebec, Canada.
Then of course there is the story from 1859 when telegraph lines became unusable. At least one fire was reported from arcing and sparking at telegraph stations. That one was named the Carrington Event, after British astronomer Richard Carrington for his work in documenting solar flares.
You have likely heard that there is an eleven-year sunspot cycle where the sun goes from being quiet to active, then back again. We are near the active peak in cycle 25 of this documented phenomenon.
Geomagnetic storms have happened before and will happen again. Our increasing dependence on all things electrical for our homes, businesses and communications in our society has made us more vulnerable to Mother Nature’s whims.
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