Solar (‘11 year’) cycle
A quasi-regular modulation of solar activity with varying amplitude and a period of between 9 and 13 years.
Definition courtesy of IPCC AR4.
All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.