The Maunder Minimum Is Not as Grand as It Seemed to Be

et al. 2015

A&A

Aims. The Maunder minimum (MM) of greatly reduced solar activity took place in 1645-1715, but the exact level of sunspot activity is uncertain because it is based, to a large extent, on historical generic statements of the absence of spots on the Sun. Using a conservative approach, we aim to assess the level and length of solar cycle during the MM on the basis of direct historical records by astronomers of that time. Methods. A database of the active and inactive days (days with and without recorded sunspots on the solar disc) is constructed for three models of different levels of conservatism (loose, optimum, and strict models) regarding generic no-spot records. We used the active day fraction to estimate the group sunspot number during the MM.

Section: Sunspot Numberscontrasting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

Level and length of cyclic solar activity during the Maunder minimum as deduced from the active-day statistics

Vaquero

Kovaltsov

et al. 2015

A&A

“…On the other hand, sunspots appeared rarely (during ∼2% of the days) and seemingly sporadically, without an indication of the 11-year cycle. Some recent studies suggested that the sunspot activity level might have been underestimated during MM: Zolotova and Ponyavin (2015) proposed that the annual number of sunspot groups was as high as 3-8 (the sunspot number 50-100) during MM, Svalgaard and Schatten (2016) proposed much more modest peak annual number of sunspot groups as 2-3 (25 -40 in sunspot number) but still too high. These claims were based on the fact that original data include many generic statements of the absence of sunspots for long periods of time, and should be dismissed.…”

Section: The Maunder Minimummentioning

confidence: 99%

A history of solar activity over millennia

2017

Living Rev Sol Phys

383

241

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 proxies, 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

“…Some of these suggestions were based on a mathematical synthesis using empirical rules in a way similar to Schove (1955) and Nagovitsyn (1997) and therefore are not true reconstructions. Some others used a re-analysis of the direct A&A 581, A95 (2015) data series (Rek 2013;Zolotova & Ponyavin 2015) and provide claimed assessments of the solar variability. While earlier suggestions have been convincingly rebutted by Eddy (1983), the most recent ones are still circulating.…”

Section: Introductionmentioning

confidence: 99%

The Maunder minimum (1645–1715) was indeed a grand minimum: A reassessment of multiple datasets

Arlt

Asvestari

et al. 2015

A&A

188

172

Aims. Although the time of the Maunder minimum (1645-1715) is widely known as a period of extremely low solar activity, it is still being debated whether solar activity during that period might have been moderate or even higher than the current solar cycle #24. We have revisited all existing evidence and datasets, both direct and indirect, to assess the level of solar activity during the Maunder minimum. Methods. We discuss the East Asian naked-eye sunspot observations, the telescopic solar observations, the fraction of sunspot active days, the latitudinal extent of sunspot positions, auroral sightings at high latitudes, cosmogenic radionuclide data as well as solar eclipse observations for that period. We also consider peculiar features of the Sun (very strong hemispheric asymmetry of the sunspot location, unusual differential rotation and the lack of the K-corona) that imply a special mode of solar activity during the Maunder minimum.Results. The level of solar activity during the Maunder minimum is reassessed on the basis of all available datasets. Conclusions. We conclude that solar activity was indeed at an exceptionally low level during the Maunder minimum. Although the exact level is still unclear, it was definitely lower than during the Dalton minimum of around 1800 and significantly below that of the current solar cycle #24. Claims of a moderate-to-high level of solar activity during the Maunder minimum are rejected with a high confidence level.