What effect does a sudden ionospheric disturbance have on the daytime ionospheric propagation?
It enhances propagation on all HF frequencies
It disrupts signals on lower frequencies more than those on higher frequencies✓Respuesta correcta
It disrupts communications via satellite more than direct communications
None, because only areas on the night side of the Earth are affected
Explicación
A sudden ionospheric disturbance is caused by a burst of solar X-rays that sharply increases ionisation in the ionosphere's lowest layer, where absorption varies roughly as the inverse square of frequency. The lowest HF and MF frequencies are therefore hit hardest while higher frequencies may still get through, and the claim that only Earth's night side is affected is wrong because the disturbance occurs on the sunlit hemisphere.