Dellinger effect
Solar flares are large bursts of energy coming from the sun. On Earth, these flares disrupt radio communication. In years when there are many such flares, the energy they release can charge what is known as the D-layer of the Ionosphere, up to about  above the earth. This changes the way this layer reflects or absorbs short wave radio waves. This effect only occurs on the day-side of the earth (on the night-side, there's little radiation from the sun. The effect will atenuate signals with a frequency of up to 300 MHz. The phenomenon can last from several minutes, to several hours. In English, the effect is also called short wave fadeout.