The solar cycle (or solar magnetic activity cycle) is the periodic change in the sun's activity (including changes in the levels of solar radiation and ejection of solar material) and appearance (visible in changes in the number of sunspots, flares, and other visible manifestations). Solar cycles have a duration of about 11 years. They have been observed (by changes in the sun's appearance and by changes seen on Earth, such as auroras) for hundreds of years.
Solar variation causes changes in space weather and to some degree weather and climate on Earth. It causes a periodic change in the amount of irradiation from the Sun that is experienced on Earth.
It is one component of solar variation, the other being aperiodic fluctuations.
Powered by a hydromagnetic dynamo process, driven by the inductive action of internal solar flows, the solar cycle:
- Structures the Sun's atmosphere, its corona and the wind;
- Modulates the solar irradiance;
- Modulates the flux of short-wavelength solar radiation, from ultraviolet to X-ray;
- Modulates the occurrence frequency of solar flares, coronal mass ejections, and other geoeffective solar eruptive phenomena;
- Indirectly modulates the flux of high-energy galactic cosmic rays entering the solar system.
Read more about Solar Cycle: History, Phenomena, Measurement, and Causes, Effects of The Solar Cycle
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