J/A+A/698/A182 1000-year sunspot series (Usoskin+, 2025)
Sunspot cycles for the first millennium BC reconstructed from radiocarbon.
Usoskin I., Chatzistergos T., Solanki S.K., Krivova N., Kovaltsov G.,
Brehm N., Christl M., Wacker L.
<Astron. Astrophys. 698, A182 (2025)>
=2025A&A...698A.182U 2025A&A...698A.182U (SIMBAD/NED BibCode)
ADC_Keywords: Sun ; Magnetic fields
Keywords: Sun: activity - Sun: magnetic fields - sunspots
Abstract:
The relative sunspot number (SN) is the primary index of solar
activity back to 1610. For earlier periods, SN can be reconstructed
from the concentrations of cosmogenic isotopes, particularly 14C and
10Be in natural archives. However, due to the limitations of
measurement techniques, these reconstructions typically provide SN
with only decadal resolution.
We aim to reconstruct the first annually resolved sunspot numbers for
the first millennium BC, providing a detailed view of solar cycles
over a period when this was not possible before. Methods. We
reconstruct sunspot numbers from high-precision annual measurements of
relative decay-corrected 14C concentrations, Δ14C, covering
1000-BC (Brehm et al. 2025). The process is based on the physics-based
approach developed by Usoskin et al. (2021A&A...649A.141U 2021A&A...649A.141U, Cat.
J/A+A/649/A141) and has the following four steps: (1) inverting the
carbon-cycle model to reconstruct the production rate of 14C, Q; (2)
accounting for the effect of the varying geomagnetic field on Q; (3)
computing the open solar magnetic flux; and (4) converting it into
sunspot numbers. A Monte-Carlo approach is used to account for the
uncertainty of the reconstruction.
We reconstructed annually resolved SN covering the first millennium
BC. Over that period, we identified 93 complete solar cycles with a
mean length of 10.5 years. Among those cycles, 23 are well- defined,
21 are reasonably defined, while the rest are poorly defined. We found
strong agreement between our reconstructed SN and previous decadal
reconstructions, though with higher SN around 1000-920 BC. We did
not find any significant long-term periodicities beyond the 11-year
solar cycle. Conclusions. This reconstruction offers unique insights
into cyclic solar activity for this period of time, which will be
valuable for solar dynamo studies and irradiance modelling
Description:
Five tabular files are presented.
* File q1000bc.dat contains annual reconstructions of the 14C
production rate [Q] along with its 1-sigma uncertainties [sQ] and the
smoothed (22-yr SSA -- see text) values []. This table corresponds
to Figure 2a in the text.
* File qa1000bc.dat contains annual reconstructions of the 14C
production rate reduced to the present-day conditions [Q*] along with
its 1-sigma uncertainties [sQ*] and the smoothed (22-yr SSA) values
[<Q*>]. This table corresponds to Figure 2b in the text.
* File fo1000bc.dat contains annual reconstructions of the open
solar flux (OSF) [Fo] along with its 1-sigma uncertainties [sF] and
the smoothed (22-yr SSA) values [<Fo>]. This table corresponds to
Figure 2c in the text.
* File sn1000bc.dat contains annual reconstructions of the sunspot
number (SN) [SN] along with its 1-sigma uncertainties [sSN] and the
smoothed (22-yr SSA) values []. This table corresponds to Figure
2d in the text.
* File cycles.dat presents a textual tabular version of Table 1 in
the text and contains the internal cycle number [n], years of minimum
[Ymin] and maximum [Ymax] of each cycle, cycle-averaged sunspot number
[], its 1-sigma uncertainty [sS], cycle length (min-to-min) [T],
and quality flag [q].
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
q1000bc.dat 22 993 Annual reconstructions of the 14C production rate
qa1000bc.dat 22 993 Annual reconstructions of the 14C production
rate reduced to the present-day conditions (Q*)
fo1000bc.dat 22 993 Annual reconstructions of the open solar flux
sn1000bc.dat 22 991 Annual reconstructions of the sunspot number (SN)
cycles.dat 24 93 Cycles (table 1)
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Byte-by-byte Description of file: q1000bc.dat
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Bytes Format Units Label Explanations
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1- 4 I4 yr Year Year (BC)
6- 10 F5.3 1/cm2/s Q Annual value of the 14C production rate (Q)
12- 16 F5.3 1/cm2/s e_Q 1-sigma uncertainty of Q
18- 22 F5.3 1/cm2/s Smoothed Q value
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Byte-by-byte Description of file: qa1000bc.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 yr Year Year (BC)
6- 10 F5.3 1/cm2/s Q* Annual value of the 14C production rate
reduced to the present-day conditions (Q*)
12- 16 F5.3 1/cm2/s e_Q* 1-sigma uncertainty of Q*
18- 22 F5.3 1/cm2/s <Q*> Smoothed Q* value
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Byte-by-byte Description of file: fo1000bc.dat
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Bytes Format Units Label Explanations
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1- 4 I4 yr Year Year (BC)
6- 10 F5.2 10+14Wb Fo Annual value of the reconstructed of the
open solar flux (OSF)
12- 16 F5.2 10+14Wb e_Fo 1-sigma uncertainty of Fo
18- 22 F5.2 10+14Wb <Fo> Smoothed Fo value
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Byte-by-byte Description of file: sn1000bc.dat
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Bytes Format Units Label Explanations
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1- 4 I4 yr Year Year (BC)
6- 10 F5.1 --- SN Annual value of the reconstructed of the
sunspot number (SN)
12- 16 F5.1 --- e_SN 1-sigma uncertainty of SN
18- 22 F5.1 --- Smoothed SN value
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Byte-by-byte Description of file: cycles.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- N Internal cycle number
4- 7 I4 yr Ymin Year of solar cycle minimum
9- 12 I4 yr Ymax Year of solar cycle maximum
14- 16 I3 --- Cycle-averaged SN
18- 19 I2 --- e_ 1-sigma uncertainty of
21- 22 I2 yr T Solar cycle length
24 I1 -- q [0/5] Quality flag
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Acknowledgements:
Ilya Usoskin, ilya.usoskin(at)oulu.fi
(End) Patricia Vannier [CDS] 07-May-2025