The Solar Cycle

Sunspots provided the first evidence for the 11-year cycle of solar activity and continue to provide key indicators of the level and nature of solar activity. Solar flares, prominence eruptions, and coronal mass ejections increase in frequency as the number of sunspots increases during the rising phase of the solar cycle. The total irradiance of the Sun and its irradiance in ultraviolet light and x-rays also increase as the sunspot number increases. On the other hand, the flux of galactic cosmic rays reaching Earth decreases as the sunspot number increases. These changes in the heliospheric environment produce significant effects on our environment. Our technological assets, in space, in the air, and on the ground, can be adversely affected by solar activity. Satellite drag, single-event upsets in electronic components, radio communication outages, power outages, and terrestrial climate can all be influenced by solar activity. In this lecture I will describe many of the significant characteristics of the solar cycle, their roots in solar magnetism, the mechanisms of the Sun's magnetic dynamo, and predictions for the amplitude and timing of next solar cycle.