Based on comparative analyses of spatial and temporal patterns of high and mediumpotassic basaltic eruptions in the Central Mongolia and marine survey records of Sr isotopes, it is revealed that the start of the recent geodynamic stage in the Central Mongolia correlates with the starting point of its global manifestation, which gives an evidence of a close rela tionship between magmatic occurrences in the region under study and processes of global convergence. The magmatic occur rences are considered as representing the recent geodynamic evolution of the past 90 Ma with milestones of ~66, 40-37, ~32 and 17-15 Ma ago. Global changes, except those ~32 Ma ago, are shown in marine records of Sr isotopes. The Late Plesto cene -Holocene natural and climate setting is reconstructed from radiocarbon datings of various geological and paleobi ological objects. Changes of the natural environment and climate of the Northern hemisphere are plotted with account of strong magma eruptions, attacks of asteroids and meteorites, changes of lithological compositions of sedimentary complexes and species compositions of fauna at the given time interval.Key words: Cenozoic, Central Asia, geochronology, cyclicity, volcanism, paleoclimate. T h e 6 5 t h A n n i v e r s a r y o f t h e I n s t i t u t e o f t h e E a r t h ' s C r u s t , S B R Инcтитут земной коры CО PАН, Иpкутcк, РоccияАннотация: Приведены результаты исследований, выполненных в лаборатории изотопии и геохронологии и лабора тории кайнозоя ИЗК СО РАН в рамках проектов СО РАН: ИМП № 77 «Изучение закономерностей проявления опас ных природных процессов в исторически обозримом прошлом для разработки основ прогноза их поведения на бли жайшие десятилетия» (РК 01201282598) и Пр. VIII.69.1. «Факторы, определяющие изменение среды и климата Цен тральной Азии в кайнозое». На основе сравнительного анализа пространственновременного распределения высоко и умеренно калиевых базальтовых извержений в Центральной Монголии и морских записей изотопов Sr выявлено соответствие начала новейшего геодинамического этапа в Центральной Монголии точке отсчета его глобального выражения, свидетельствующее о тесной связи магматических событий региона с глобальными процессами конвер генции. Эти магматические события рассматриваются как представительные для новейшей геодинамической эволю ции литосферы за последние 90 млн лет, в ходе которой определена важнейшая роль рубежей ~66, 40-37, ~32 и 17- 81
Hypothetical low-mass particles, such as axions, provide a compelling explanation for the dark matter in the universe. Such particles are expected to emerge abundantly from the hot interior of stars. To test this prediction, the CERN Axion Solar Telescope (CAST) uses a 9 T refurbished Large Hadron Collider test magnet directed towards the Sun. In the strong magnetic field, solar axions can be converted to X-ray photons which can be recorded by X-ray detectors. In the 2013-2015 run, thanks to low-background detectors and a new X-ray telescope, the signal-to-noise ratio was increased by about a factor of three. Here, we report the best limit on the axion-photon coupling strength (0.66 × 10 −10 GeV −1 at 95% confidence level) set by CAST, which now reaches similar levels to the most restrictive astrophysical bounds.A dvancing the low-energy frontier is a key endeavour in the worldwide quest for particle physics beyond the standard model and in the effort to identify dark matter 1,2 . Nearly massless pseudoscalar bosons, often generically called axions, are particularly promising because they appear in many extensions of the standard model. They can be dark matter in the form of classical field oscillations that were excited in the early universe, notably by the re-alignment mechanism 3 . One particularly well motivated case is the quantum chromodynamics (QCD) axion, the eponym for all such particles. The existence of this new lowmass boson follows from the Peccei-Quinn mechanism as an explanation why QCD is perfectly time-reversal invariant within current experimental precision 3 .Axions were often termed 'invisible' because of their extremely feeble interactions, yet they are the target of a fast-growing international landscape of experiments. Numerous existing and foreseen projects assume that axions are the galactic dark matter and use a variety of techniques that are sensitive to different interaction channels and optimal in different mass ranges 4 . Independently of the dark-matter assumption, one can search for new forces mediated by these low-mass bosons 5 or the back-reaction on spinning black holes (superradiance) 6 . Stellar energy-loss arguments provide restrictive limits that can guide experimental efforts, and in some cases may even suggest new loss channels 3,7,8 .The least model-dependent search strategies use the production and detection of axions and similar particles by their generic twophoton coupling. It is given by the vertex L aγ = −(1/4) g aγ F µν F µν a = g aγ E · B a, where a is the axion field, F the electromagnetic field-strength tensor, and g aγ a coupling constant of dimension (energy) −1 . Notice that we use natural units with = c = k B = 1. This vertex enables the decay a → γ γ , the Primakoff production in stars-that is, the γ → a scattering in the Coulomb fields of charged particles in the stellar plasma-and the coherent conversion a ↔ γ in laboratory or astrophysical B-fields 9,10 .The helioscope concept, in particular, uses a dipole magnet directed at the Sun to convert axions to...
Simulations of climate over the Last Millennium (850–1850 CE) have been incorporated into the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3). The drivers of climate over this period are chiefly orbital, solar, volcanic, changes in land use/land cover and some variation in greenhouse gas levels. While some of these effects can be easily defined, the reconstructions of solar, volcanic and land use-related forcing are more uncertain. We describe here the approach taken in defining the scenarios used in PMIP3, document the forcing reconstructions and discuss likely implications
Aims. Using a reconstruction of sunspot numbers stretching over multiple millennia, we analyze the statistics of the occurrence of grand minima and maxima and set new observational constraints on long-term solar and stellar dynamo models. Methods. We present an updated reconstruction of sunspot number over multiple millennia, from 14 C data by means of a physicsbased model, using an updated model of the evolution of the solar open magnetic flux. A list of grand minima and maxima of solar activity is presented for the Holocene (since 9500 BC) and the statistics of both the length of individual events as well as the waiting time between them are analyzed.Results. The occurrence of grand minima/maxima is driven not by long-term cyclic variability, but by a stochastic/chaotic process. The waiting time distribution of the occurrence of grand minima/maxima deviates from an exponential distribution, implying that these events tend to cluster together with long event-free periods between the clusters. Two different types of grand minima are observed: short (30-90 years) minima of Maunder type and long (>110 years) minima of Spörer type, implying that a deterministic behaviour of the dynamo during a grand minimum defines its length. The duration of grand maxima follows an exponential distribution, suggesting that the duration of a grand maximum is determined by a random process. Conclusions. These results set new observational constraints upon the long-term behaviour of the solar dynamo.
Abstract.A model of solar irradiance variations is presented which is based on the assumption that solar surface magnetism is responsible for all total irradiance changes on time scales of days to years. A time series of daily magnetograms and empirical models of the thermal structure of magnetic features (sunspots, faculae) are combined to reconstruct total (and spectral) irradiance from 1996 to 2002. Comparisons with observational data reveal an excellent correspondence, although the model only contains a single free parameter. This provides strong support for the hypothesis that solar irradiance variations are caused by changes in the amount and distribution of magnetic flux at the solar surface.
Context. Total solar irradiance changes by about 0.1% between solar activity maximum and minimum. Accurate measurements of this quantity are only available since 1978 and do not provide information on longer-term secular trends. Aims. In order to reliably evaluate the Sun's role in recent global climate change, longer time series are, however, needed. They can only be assessed with the help of suitable models. Methods. The total solar irradiance is reconstructed from the end of the Maunder minimum to the present based on variations of the surface distribution of the solar magnetic field. The latter is calculated from the historical record of the sunspot number using a simple but consistent physical model. Results. Our model successfully reproduces three independent data sets: total solar irradiance measurements available since 1978, total photospheric magnetic flux since 1974 and the open magnetic flux since 1868 empirically reconstructed using the geomagnetic aa-index. The model predicts an increase in the solar total irradiance since the Maunder minimum of 1.3
Aims. Miyake et al. (2012, Nature, 486, 240, henceforth M12) recently reported, based on 14 C data, an extreme cosmic event in about AD775. Using a simple model, M12 claimed that the event was too strong to be caused by a solar flare within the standard theory. This implied a new paradigm of either an impossibly strong solar flare or a very strong cosmic ray event of unknown origin that occurred around AD775. However, as we show, the strength of the event was significantly overestimated by M12. Several subsequent works have attempted to find a possible exotic source for such an event, including a giant cometary impact upon the Sun or a gamma-ray burst, but they are all based on incorrect estimates by M12. We revisit this event with analysis of new datasets and consistent theoretical modelling. Methods. We verified the experimental result for the AD775 cosmic ray event using independent datasets including 10 Be series and newly measured 14 C annual data. We surveyed available historical chronicles for astronomical observations for the period around the AD770s to identify potential sightings of aurorae borealis and supernovae. We interpreted the 14 C measurements using an appropriate carbon cycle model. Results. We show that: (1) The reality of the AD775 event is confirmed by new measurements of 14 C in German oak; (2) by using an inappropriate carbon cycle model, M12 strongly overestimated the event's strength; (3) the revised magnitude of the event (the global 14 C production Q = (1.1−1.5) × 10 8 atoms/cm 2 ) is consistent with different independent datasets ( 14 C, 10 Be, 36 Cl) and can be associated with a strong, but not inexplicably strong, solar energetic particle event (or a sequence of events), and provides the first definite evidence for an event of this magnitude (the fluence >30 MeV was about 4.5 × 10 10 cm −2 ) in multiple datasets; (4) this interpretation is in agreement with increased auroral activity identified in historical chronicles. Conclusions. The results point to the likely solar origin of the event, which is now identified as the greatest solar event on a multimillennial time scale, placing a strong observational constraint on the theory of explosive energy releases on the Sun and cool stars.
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