These include short-wave fadeouts in HF propagation, geomagnetic and ionospheric disturbances. Flare Classification Flares are classified in terms of X-ray production and also by apparent optical brightness. M and X class flares are the ones most likely to produce effects on the ionosphere. X class flares are stronger, and produce more significant effects than M class flares. Large bright flares are more energetic, although optical brightness and the effect on the earth are not directly linked.
More intense flares affect all frequencies.
Fadeouts affect only those circuits with a reflection point on the daylight hemisphere of the earth, especially where the sun is close to vertically overhead at the reflection point. The sunspot number is the traditional indicator of activity on the sun usually defined over periods of a day, a month or a year. The daily and monthly sunspot numbers are indicators of transient activity on the sun such as the growth and decay of sunspot regions. The yearly sunspot number is often used to chart the progress of the solar cycle, an approximately 11 year variation of many properties of the sun. Magnetic Activity Magnetic activity is a variation of the magnetic field of the earth as a result of changes in the flow of the solar wind.