Intense magnetic activity disrupts the sun's surface for a period of time that may last anywhere from a few hours to a few weeks.
The area around a sun spot is slightly brighter and radiates increased ultraviolet rays and X-rays, which raises the overall amount of radiation striking Earth.
Scientists have devised a method to calculate the amount of radiation emanating from the sun by correlating radiation levels to the number of sun spots. The increase and decrease of these spots runs in moderately predictable cycles, with an accompanying effect on earthbound radio waves.
As sunspot numbers increase, along with radiation, the ionosphere becomes more ionized and increases the propagation of radio waves from the lower band. UHF and microwave frequency bands are not usually affected.
Low-power stations normally heard over a distance only at night can be listened to from much farther away.