Variations in tree ring stable isotope records from northern Finland and their possible connection to solar activity

Within a project on climate in Europe during the past few hundred years we have collected a record on stable isotope ratios ¹³C/¹²C and ¹⁸O/¹⁶O in tree ring cellulose from pine trees in northern Finland. The records cover the time interval 1600–2002 AD and have an annual time resolution. The carbon stable isotope record from northernmost Finland correlates quite strongly with local growth period temperature. Statistical analysis of the carbon and oxygen stable isotope records reveals variations in the periods around 100, 11 and 3 years. A century scale connection between the ¹³C/¹²C record and solar activity is most evident. These results based on stable isotope records support previous evidences of a centennial solar-climatic link obtained for northern Finland using tree ring data.     

Crystal structures and phase transitions in Sr2InTaO6 perovskite

The preparation and crystal structure of the double perovskite oxide Sr₂InTaO₆ are reported. This oxide has a monoclinic structure in space group P2₁/n at room temperature, where In and Ta display a rock-salt type ordering with a = 5.73356(10), b = 5.74052(10), c = 8.10905(14) Å and β = 90.022(6)°. Variable temperature neutron diffraction measurements demonstrate this displays the sequence of phase transitions $ P2_{1} /n\mathop{\longrightarrow}\limits^{{605\,^\circ {\text{C}}}}I2/m\mathop{\longrightarrow}\limits^{{705\,^\circ {\text{C}}}}I4/m\mathop{\longrightarrow}\limits^{{930\,^\circ {\text{C}}}}Fm\bar{3}m $ as a consequence of the sequential loss of tilting of the corner shared octahedra upon heating. The evolution of Sr₂InTaO₆ crystal structure upon heating is analysed and described in terms of symmetry-adapted distortion modes. The GM4+ and X3+, that are responsible for anti-phase and in-phase tilting, respectively, are highly temperature dependent, with the GM4+ mode having the largest amplitude at room temperature.     

Instrumental data on the sunspot formation in the 17th–18th centuries: Correct information or approximations

The available data on the sunspot number derived from telescopic observations are analyzed. It has been indicated that uncertainty in the data on the number of sunspot groups is close to 30% for the 17th century-the early 19th century and reaches a factor of 2 and more in individual years. This means that the above data include limited information on solar activity in the 17th–18th centuries and it is necessary to use external sources (first of all, the data of paleoastrophysics) in order to study this activity in the indicated epoch. Only from the middle of the 19th century, information obtained based on instrumental observations became sufciently accurate for reliable quantitative estimates.     

Possible manifestation of nonlinear effects when solar activity affects climate changes

The response of the nonlinear oscillatory system to an insignificant external disturbance has been considered as applied to the effect of solar activity on climatic processes. Based on a simplified model, it has been indicated that the response of a nonlinear oscillator to a weak disturbing impact can be substantial. The oscillator fluctuation spectrum can decrease under the action of a disturbing factor. This means that the effect of an even weak solar or cosmophysical signal to the Earth’s climatic system can lead to significant climate variations if this system is nonlinear. However, it will be rather difficult to identify the solar—climatic nature of these variations because a linear relation between the cause and response is absent.     

Glacial and palaeoenvironmental history of the Cape Chelyuskin area, Arctic Russia

Quaternary glacial stratigraphy and relative sea-level changes reveal at least two glacial expansions over the Chelyuskin Peninsula, bordering the Kara Sea at about 77°N in the Russian Arctic, as indicated from tills interbedded with marine sediments, exposed in stratigraphic superposition, and from raised-beach sequences mapped to altitudes of at least up to ca. 80 m a.s.l. Chronological control is provided by accelerator mass spectrometry ¹⁴C dating, electron-spin resonance and optically stimulated luminescence geochronology. Major glaciations, followed by deglaciation and marine inundation, occurred during marine oxygen isotope stages 6–5e (MIS 6–5e) and stages MIS 5d–5c. These glacial sediments overlie marine sediments of Pliocene age, which are draped by fluvial sediment of a pre-Saalian age, thereby forming palaeovalley/basin fills in the post-Cretaceous topography. Till fabrics and glacial tectonics record expansions of local ice caps exclusively, suggesting wet-based ice cap advance, followed by cold-based regional ice-sheet expansion. Local ice caps over highland sites along the perimeter of the shallow Kara Sea, including the Byrranga Mountains and the Severnaya Zemlya archipelago, appear to have repeatedly fostered initiation of a large Kara Sea ice sheet, with the exception of the Last Glacial Maximum (MIS 2), when Kara Sea ice neither impacted the Chelyuskin Peninsula nor Severnaya Zemlya, and barely touched the northern coastal areas of the Taymyr Peninsula.     

An attempt to build a new completely analytical theory of the Uranian satellites: The results achieved and the results to be obtained

An attempt to build a new theory of the main Uranian satellites is being made at the Sternberg Astronomical Institute. The main difference compared to GUST86 theory is that the new theory is planned to be completely analytical. To do this, the secular frequencies of the satellites should be calculated taking into account the secular perturbations of the second order and, partly, of the third order. This allows to improve the secular frequencies and make them more close to those obtained from numerical integration. Nevertheless, discrepancies remain, which indicate that more terms in the analytical development are needed. Some other advantages of the new theory are also discussed.     

Reconstructions of the <Superscript>14</Superscript>С cosmogenic isotope content from natural archives after the last glacial termination

Data on the content of the ¹⁴C cosmogenic isotope in tree rings, which were obtained as a result of laboratory measurements, are often used when solar activity (SA) is reconstructed for previous epochs, in which direct observations are absent. However, these data contain information not only about SA variations but also about changes in the Earth climatic parameters, such as the global temperature and the CO₂ content in the Earth’s atmosphere. The effect of these variations on the ¹⁴C isotope content in different natural reservoirs after the last glacial termination to the middle of the Holocene is considered. The global temperature and the CO₂ content increased on this time interval. In this case the ¹⁴C absolute content in the atmosphere increased on this time interval, even though the ¹⁴С to ¹²С isotope concentration ratio (as described by the Δ¹⁴С parameter) decreased. These variations in the radiocarbon absolute content can be caused by its redistribution between natural reservoirs. It has been indicated that such a redistribution is possible only when the rate of carbon exchange between the ocean and atmosphere depends on temperature. The values of the corresponding temperature coefficient for the 17–10 ka BC time interval, which make it possible to describe the carbon redistribution between the ocean and atmosphere, have been obtained.     

The sodium exosphere of Mercury: Comparison between observations during Mercury's transit and model results

In this study we compare the sodium exosphere observations made by Schleicher et al. [Schleicher, H., and 4 colleagues, 2004. Astron. Astrophys. 425, 1119-1124] with the result of a detailed numerical simulation. The observations, made during the transit of Mercury across the solar disk on 7 May 2003, show a maximum of sodium emission near the polar regions, with north prevalence, and the presence of a dawn-dusk asymmetry. We interpret this distribution as the resulting effect of two combined processes: the solar wind proton precipitation causing chemical alteration of the surface, freeing the sodium atoms from their bounds in the crystalline structure on the surface, and the subsequent photon-stimulated and thermal desorption of the sodium atoms. While we find that the velocity distribution of photon desorbed sodium can explain the observed exosphere population, thermal desorption seems to play a minor role only causing a smearing at the locations where Na atoms are released on the dayside. The observed and simulated distributions agree very well with this hypothesis and indicate that the combination of the proposed processes is able to explain the observed features.     

Activation of the Blandford–Znajek mechanism in collapsing stars

The collapse of massive stars may result in the formation of accreting black holes in their interiors. The accreting stellar matter may advect substantial magnetic flux on to the black hole and promote the release of its rotational energy via magnetic stresses (the Blandford–Znajek mechanism). In this paper we explore whether this process can explain the stellar explosions and relativistic jets associated with long gamma-ray bursts. In particular, we show that the Blandford–Znajek mechanism is activated when the rest mass–energy density of matter drops below the energy density of the magnetic field in the near vicinity of the black hole (within its ergosphere). We also discuss whether such a strong magnetic field is in conflict with the rapid rotation of the stellar core required in the collapsar model, and suggest that the conflict can be avoided if the progenitor star is a component of a close binary. In this case the stellar rotation can be sustained via spin-orbital interaction. In an alternative scenario the magnetic field is generated in the accretion disc, but in this case the magnetic flux through the black hole ergosphere is not expected to be sufficiently high to explain the energetics of hypernovae by the BZ mechanism alone. However, this energy deficit can be recovered via the additional power provided by the disc.