Kaikki aineistot
Lisää
Abstract Both dendrochronology and radiocarbon (14C) dating have their roots back in the early to mid-1900s. Although they were independently developed, they began to intertwine in the 1950s when the founder of dendrochronology, A. E. Douglass, provided dated wood samples for Willard Libby to test his emerging 14C methods. Since this early connection, absolutely dated tree-rings have been key to calibration of the Holocene portion of the 14C timescale. In turn, 14C dating of non-calendar-dated tree-rings has served to place those samples more precisely in time, advance development of long tree-ring chronologies, and bring higher resolution to earlier portions of the 14C calibration curve. Together these methods continue to shape and improve chronological frameworks across the globe, answering questions in archaeology, history, paleoclimatology, geochronology, and ocean, atmosphere, and solar sciences.
Abstract Context: The group sunspot number (GSN) series constitute the longest instrumental astronomical database providing information on solar activity. This database is a compilation of observations by many individual observers, and their inter-calibration has usually been performed using linear rescaling. There are multiple published series that show different long-term trends for solar activity. Aims: We aim at producing a GSN series, with a non-linear non-parametric calibration. The only underlying assumptions are that the differences between the various series are due to different acuity thresholds of the observers, and that the threshold of each observer remains constant throughout the observing period. Methods: We used a daisy chain process with backbone (BB) observers and calibrated all overlapping observers to them. We performed the calibration of each individual observer with a probability distribution function (PDF) matrix constructed considering all daily values for the overlapping period with the BB. The calibration of the BBs was carried out in a similar manner. The final series was constructed by merging different BB series. We modelled the propagation of errors straightforwardly with Monte Carlo simulations. A potential bias due to the selection of BBs was investigated and the effect was shown to lie within the 1σ interval of the produced series. The exact selection of the reference period was shown to have a rather small effect on our calibration as well. Results: The final series extends back to 1739 and includes data from 314 observers. This series suggests moderate activity during the 18th and 19th century, which is significantly lower than the high level of solar activity predicted by other recent reconstructions applying linear regressions. Conclusions: The new series provides a robust reconstruction, based on modern and non-parametric methods, of sunspot group numbers since 1739, and it confirms the existence of the modern grand maximum of solar activity in the second half of the 20th century.
Abstract The Sun provides the principal energy input into the Earth system and solar variability represents a significant external climate forcing. Although observations of solar activity (sunspots) cover only the last about 400 years, radionuclides produced by cosmic rays and stored in tree rings or ice cores serve as proxies for solar activity extending back thousands of years. However, the presence of weather-induced noise or low temporal resolution of long, precisely dated records hampers cosmogenic nuclide-based studies of short-term solar variability such as the 11-yr Schwabe cycle. Here we present a continuous, annually resolved atmospheric 14C concentration (fractionation-corrected ratio of 14CO2 to CO2) record reconstructed from absolutely dated tree rings covering nearly all of the last millennium (ad 969–1933). The high-resolution and precision 14C record reveals the presence of the Schwabe cycle over the entire time range. The record confirms the ad 993 solar energetic particle event and reveals two new candidates (ad 1052 and ad 1279), indicating that strong solar events that might be harmful to modern electronic systems probably occur more frequently than previously thought. In addition to showing decadal-scale solar variability over the last millennium, the high-temporal-resolution record of atmospheric radiocarbon also provides a useful benchmark for making radiocarbon dating more accurate over this interval.
Abstract The pre-industrial millennium is among the periods selected by the Paleoclimate Model Intercomparison Project (PMIP) for experiments contributing to the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and the fourth phase of the PMIP (PMIP4). The past1000 transient simulations serve to investigate the response to (mainly) natural forcing under background conditions not too different from today, and to discriminate between forced and internally generated variability on interannual to centennial timescales. This paper describes the motivation and the experimental set-ups for the PMIP4-CMIP6 past1000 simulations, and discusses the forcing agents orbital, solar, volcanic, and land use/land cover changes, and variations in greenhouse gas concentrations. The past1000 simulations covering the pre-industrial millennium from 850 Common Era (CE) to 1849 CE have to be complemented by historical simulations (1850 to 2014 CE) following the CMIP6 protocol. The external forcings for the past1000 experiments have been adapted to provide a seamless transition across these time periods. Protocols for the past1000 simulations have been divided into three tiers. A default forcing data set has been defined for the Tier 1 (the CMIP6 past1000) experiment. However, the PMIP community has maintained the flexibility to conduct coordinated sensitivity experiments to explore uncertainty in forcing reconstructions as well as parameter uncertainty in dedicated Tier 2 simulations. Additional experiments (Tier 3) are defined to foster collaborative model experiments focusing on the early instrumental period and to extend the temporal range and the scope of the simulations. This paper outlines current and future research foci and common analyses for collaborative work between the PMIP and the observational communities (reconstructions, instrumental data).