Solar activity over nine millennia: A consistent multi-proxy


Aims. The solar activity in the past millennia can only be reconstructed from cosmogenic radionuclide proxy records in terrestrial archives. However, because of the diversity of the proxy archives, it is difficult to build a homogeneous reconstruction. All previous studies were based on individual, sometimes statistically averaged, proxy datasets. Here we aim to provide a new consistent multiproxy reconstruction of the solar activity over the last 9000 years, using all available long-span datasets of 10Be and 14C in terrestrial archives.
Methods. A new method, based on a Bayesian approach, was applied for the first time to solar activity reconstruction. A Monte Carlo search (using the χ 2 statistic) for the most probable value of the modulation potential was performed to match data from different datasets for a given time. This provides a straightforward estimate of the related uncertainties. We used six 10Be series of different lengths (from 500–10000 years) from Greenland and Antarctica, and the global 14C production series. The 10Be series were resampled to match wiggles related to the grand minima in the 14C reference dataset. The stability of the long data series was tested.
Results. The Greenland Ice-core Project (GRIP) and the Antarctic EDML (EPICA Dronning Maud Land) 10Be series diverge from each other during the second half of the Holocene, while the 14C series lies in between them. A likely reason for the discrepancy is the insufficiently precise beryllium transport and deposition model for Greenland, which leads to an undercorrection of the GRIP series for the geomagnetic shielding effect. A slow 6–7-millennia variability with lows at ca. 5500 BC and 1500 AD in the longterm evolution of solar activity is found. Two components of solar activity can be statistically distinguished: the main component, corresponding to the ‘normal’ moderate level, and a component corresponding to grand minima. A possible existence of a component representing grand maxima is indicated, but it cannot be separated from the main component in a statistically significant manner.
Conclusions. A new consistent reconstruction of solar activity over the last nine millennia is presented with the most probable values of decadal sunspot numbers and their realistic uncertainties. Independent components of solar activity corresponding to the main moderate activity and the grand-minimum state are identified; they may be related to different operation modes of the dynamo.
Chi Ju Wu 1, I. G. Usoskin 2, 3, N. Krivova 1, G. A. Kovaltsov 4, M. Baroni 5, E. Bard 5, and S. K. Solanki 1, 6
1 Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
2 Space Climate Research Unit, University of Oulu, Finland
3 Sodankylä Geophysical Observatory, University of Oulu, Finland
4 Ioffe Physical-Technical Institute, 194021 St. Petersburg, Russia
5 CEREGE, Aix-Marseille University, CNRS, Collège de France, Technopôle de l’Arbois, Aix-en-Provence, France
6 School of Space Research, Kyung Hee University, Yongin, Gyeonggi-Do,446-701, Republic of Korea
Astronomy & Astrophysics manuscript no. aaa c ESO 2018
April 5, 2018
arXiv:1804.01302v1 [astro-ph.SR] 4 Apr 2018
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Solar activity over nine millennia: A consistent multi-proxy


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