Long Periods Of Solar Inactivity

Long Periods Of Solar Inactivity

. Three independent indices demonstrate the existence of long decreases in the level of solar activity, such as the Maunder and Spörer Minimum. The observed annual mean sunspot numbers (scale at right) also follows the 11-year solar activity cycle after 1700. The curve extending from 1000 to 1900 is a proxy sunspot number index derived from measurements of carbon-14 in tree rings. Increased carbon-14 is plotted downward (scale at left-inside), so increased solar activity and larger proxy sunspot numbers correspond to reduced amounts of radiocarbon in the Earth’s atmosphere. Open circles are an index of the occurrence of auroras in the Northern Hemisphere (scale at left-outside). (Courtesy of John A. Eddy.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University