Solar flares reached the earth’s atmosphere on May 10 through the 13th which disrupted radio communications. The resulting geomagnetic storm was classified as a G5 category storm and included solar winds traveling at 470 to 500 miles/second. This was the must powerful solar storm since October of 2003 and produced visible aurora as far south as Georgia. Unfortunately for most us in the local area, all we were able to witness as dark clouds and rain.
During the solar storm radio waves that are normally reflected back to earth from the atmosphere were not reflected. On the HF bands one could tune up and down the entire band and not hear a single station. Even the noise floor was low because random electrical noise was not being reflected back down to the earth’s surface. The UHF and VHF bands use line of sight transmissions and were unaffected.
Solar storms have been known to stress the power grid in the past. A 1989 storm produced unusual currents on power lines which caused a nine-hour blackout for 6 million electric customers in Canada. Another example of unusual current on transmission lines was in 1859 when telegraph lines, state of the art communications infrastructure at the time, were reported to arc causing at least one documented fire.
For anyone who tuned around on the AM broadcast band, they likely noticed significant reception changes during the solar storm. AM broadcast stations typically use ground-wave propagation during the daylight hours and sky-wave propagation during the night when the atmosphere is not being charged by solar radiation. One local example is the Philipsburg radio station WLGJ-AM, formerly WPHB-AM, which transmits a 5,000 KW signal during the day and a 37 watt signal at night. The FCC requires these power changes to protect larger stations from sky-wave interference from smaller stations like WLGJ-AM. Normally, at a distance of about 4 miles, the station’s nighttime signal is all but lost in the background noise. During the solar storm WLGJ could clearly be heard, presumably via ground wave signals, without the usual interference or associated noise normally present.
