A History of Solar Activity over Millennia

Abstract

Presented here is a review of present knowledge of the long-term behavior of solar activity on a multi-millennial timescale, as reconstructed using the indirect proxy method.The concept of solar activity is discussed along with an overview of the special indices used to quantify different aspects of variable solar activity, with special emphasis upon sunspot number.Over long timescales, quantitative information about past solar activity can only be obtained using a method based upon indirect proxy, such as the cosmogenic isotopes 14 C and 10 Be in natural stratified archives (e.g., tree rings or ice cores). We give an historical overview of the development of the proxy-based method for past solar-activity reconstruction over millennia, as well as a description of the modern state. Special attention is paid to the verification and cross-calibration of reconstructions. It is argued that this method of cosmogenic isotopes makes a solid basis for studies of solar variability in the past on a long timescale (centuries to millennia) during the Holocene.A separate section is devoted to reconstructions of strong solar-energetic-particle (SEP) events in the past, that suggest that the present-day average SEP flux is broadly consistent with estimates on longer timescales, and that the occurrence of extra-strong events is unlikely.Finally, the main features of the long-term evolution of solar magnetic activity, including the statistics of grand minima and maxima occurrence, are summarized and their possible implications, especially for solar/stellar dynamo theory, are discussed.

The 22-Year Hale Cycle in Cosmic Ray Flux – Evidence for Direct Heliospheric Modulation

“…This is consistent with cosmogenic isotope data, which, in general, do not show strong 22-year Hale cycle variations (Usoskin, 2008).…”

A Remarkable Recent Transition in the Solar Dynamo

“…For a comprehensive review on several aspects of space climate related to cosmic rays, cf. Scherer et al (2006) and for a comprehensive review of solar activity over millennia, Usoskin (2013). Cosmogenic radionuclides also provide records of the paleocosmic radiation that extend to more than 103 centuries into the past and are as such indicators of changes in space climate (e.g.…”

Does theF10.7index correctly describe solar EUV flux during the deep solar minimum of 2007-2009?

“…[2] Solar activity presented by sunspot number varies over different timescales [e.g., Frick et al, 1997;Hathaway and Wilson, 2004;Lundstedt et al, 2005;Usoskin, 2008;Wilson, 1988]. The 11 year solar cycle (SC) is the most prominent variation of solar activity.…”

“…The 11 year solar cycle (SC) is the most prominent variation of solar activity. Though SC variation of solar activity appears repeatedly, it varies from cycle to cycle [e.g., Hathaway and Wilson, 2004;Usoskin, 2008;Wilson, 1988]. The Sun is very quiet during the minimum of SCs 23/24.…”