Large solar x-ray outbursts can produce sudden and extensive ionization in the lower regions of the earth's ionosphere which can rapidly increase shortwave signal absorption there. Occurring on the sun-facing side of the Earth, these sudden ionospheric disturbances are known as ' shortwave fadeouts ' and can degrade short wave communications for from minutes to hours. Daytime HF communication disruptions due to high solar activity are more common during the years surrounding the peak of the solar cycle. During a solar X-ray outburst, the lower frequencies are the first to suffer. Remember too that that signals crossing daylight paths will be the most affected.
Higher frequencies are also the first to recover after a storm.
Note that this is the opposite to disturbances indirectly caused by geomagnetic storms. As an overall assessment of natural variations in the geomagnetic field, six standard terms are used in reporting geomagnetic activity. Increasing geomagnetic activity corresponds to more and greater perturbations of the geomagnetic field as a result of variations in the solar wind and more energetic solar particle emissions. Using the earlier analogy, imagine the geomagnetic field to be like a weather vane in an increasingly violent windstorm. As the winds increase, the weather vane is continually buffeted by gusts and oscillates about the direction of the prevailing wind.