Multiple dynamo modes as a mechanism for long-term solar activity variations M. J. Käpylä, P. J. Käpylä, N. Olspert, A. Brandenburg, J. Warnecke, B. B. Karak and J. Pelt A&A, 589 (2016) A56 Published online: 13 April 2016 DOI: 10.1051/0004-6361/201527002