J/A+A/698/A182ivo://CDS.VizieR/J/A+A/698/A182doi:10.26093/cds/vizier/bc-nt/lbicCDSUsoskin I.Chatzistergos T.Solanki S.K.Krivova N.Kovaltsov G.,Brehm N.Christl M.Wacker L.2026-08-03T06:54:56Z2025-06-11T10:07:23ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frthe-sunmagnetic-fieldsThe 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 ^14^C concentrations, {Delta}^14^C, 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, Cat. J/A+A/649/A141) and has the following four steps: (1) inverting the carbon-cycle model to reconstruct the production rate of ^14^C, 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 modelling2025A&A...698A.182Uhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/698/A182CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/698/A182https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/698/A182http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/698/A182https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/698/A182https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/698/A182http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/698/A182GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapdefaultJ/A+A/698/A182/q1000bcAnnual reconstructions of the ^14^C production raterecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintYearYear (BC)yrtimeintQAnnual value of the ^14^C production rate (Q)cm**-2.s**-1stat.fit.paramfloate_Q1-sigma uncertainty of Qcm**-2.s**-1stat.errorfloat<Q>Smoothed Q valuecm**-2.s**-1stat.fit.paramfloatJ/A+A/698/A182/qa1000bcAnnual reconstructions of the ^14^C production rate reduced to the present-day conditions (Q*)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintYearYear (BC)yrtimeintQ*Annual value of the ^14^C production rate reduced to the present-day conditions (Q*)cm**-2.s**-1stat.fit.paramfloate_Q*1-sigma uncertainty of Q*cm**-2.s**-1stat.errorfloat<Q*>Smoothed Q* valuecm**-2.s**-1stat.fit.paramfloatJ/A+A/698/A182/fo1000bcAnnual reconstructions of the open solar fluxrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintYearYear (BC)yrtimeintFoAnnual value of the reconstructed of the open solar flux (OSF)1e+14Wbphot.flux.density;em.optfloate_Fo1-sigma uncertainty of Fo1e+14Wbstat.errorfloat<Fo>Smoothed Fo value1e+14Wbphot.flux.density;em.optfloatJ/A+A/698/A182/sn1000bcAnnual reconstructions of the sunspot number (SN)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintYearYear (BC)yrtimeintSNAnnual value of the reconstructed of the sunspot number (SN)meta.numberfloate_SN1-sigma uncertainty of SNstat.errorfloat<SN>Smoothed SN valuemeta.numberfloatJ/A+A/698/A182/cyclesCycles (table 1)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNInternal cycle numbermeta.idintYminYear of solar cycle minimumyrtime.epochintYmaxYear of solar cycle maximumyrtime.epochint<SN>Cycle-averaged SNmeta.numberinte_<SN>1-sigma uncertainty of <SN>stat.errorintTSolar cycle lengthyrtime.intervalintq[0/5] Quality flagmeta.code.qualint