Solar flares produce bursts of ionizing radiation (sudden emission of electrons and protons) which result in geomagnetic storms in the earth's ionosphere. During solar flares the strength of the earth's magnetic field can fluctuate by 10% causing rapid geomagnetic anomalies causing compasses to give false readings. The storms, which may last several days or even weeks, produce widespread changes in the radioreflecting layers of the earth's atmosphere and can upset long-distance radio transmissions. This leads to poor radio reception (and even to complete black out on some frequencies for stations in polar regions), severe interference to telegraph communications, and even overloading of power lines and transformer-blowout. Geomagnetic storms may also affect weather patterns, to an extent which varies with the 11 year sunspot cycle. The storms may begin suddenly and simultaneously all over the earth within about one minute.
Geomagnetic storms have also been linked with mental disorders.