"SID" stands for Sudden Ionospheric Disturbance, and a "SID monitor" is a radio receiver that monitors ~20 kHz signals from distant transmitters. "My system easily detected the effects of the solar flare," says Karlovsky. "I monitor two stations: DHO38 in Germany (23.4 kHz) and GQD in Great Britian (22.1 kHz). The German signal was most strongly boosted."
With solar activity on the rise, sudden ionospheric disturbances will become more common. Interested? Stanford University tells you how to build your own SID monitor.