solarcycle

The solar cycle refers to the roughly 11-year cycle of solar activity, as observed in the frequency and size of sunspots and variations in solar emissions. The cycle begins at solar minimum, when few sunspots are present, and progresses to solar maximum, when sunspot number and solar activity are at their peak, before returning to a new minimum. In practice, cycle lengths vary from about 9 to 14 years. The cycle is linked to the Sun's magnetic field; sunspots are intense magnetic regions, and their number tracks changes in global solar magnetic activity. During the course of the cycle the Sun's magnetic polarity reverses near maximum, and a complete magnetic cycle, the Hale cycle, lasts about 22 years.

Measurements of the cycle use indicators such as sunspot number and sunspot area, the 10.7 cm radio flux (F10.7), total solar irradiance, and other proxies. Modern forecasts attempt to predict the strength and timing of solar maximum using dynamo models and statistical methods.

Impact: The cycle modulates space weather. Higher solar activity increases the likelihood of solar flares and coronal mass ejections, enhances solar wind, and raises radiation exposure for spacecraft and astronauts. It can degrade satellite performance and affect high-frequency radio communications and navigation signals on Earth, though ground-based systems are generally resilient. The relationship between solar variability and Earth's climate remains an active area of research; most climatic effects are small and embedded within long-term trends.