Was the solar activity in the last 100 years abnormally high? On the quality of modern solar paleoreconstructions

A technique for verifying the currently available reconstructions of solar activity in the preinstrumental epoch (prior to 1615 AD), covering time intervals up to 10 000 years, has been developed and tested. The technique is based on investigation of the possibility of predicting the actual sunspot numbers determined by means of telescopic observations using reconstructed solar series. Testing several paleoreconstructions over time intervals as long as 10 000 years has shown that they most likely contain only qualitative information about the behavior of solar activity in the past and are not very suitable for extracting quantitative information. It is shown that the recently suggested hypothesis that the current level of solar activity is highest in the last 8000 years is only an arbitrary assumption that can be neither confirmed nor refuted at the present level of knowledge about the past of our star.     

Our distorted view of magnetars: application of the resonant cyclotron scattering model

The X-ray spectra of the magnetar candidates are customarily fitted with an empirical, two component model: an absorbed blackbody and a power-law. However, the physical interpretation of these two spectral components is rarely discussed. It has been recently proposed that the presence of a hot plasma in the magnetosphere of highly magnetized neutron stars might distort, through efficient resonant cyclotron scattering, the thermal emission from the neutron star surface, resulting in production of non-thermal spectra. Here we discuss the Resonant Cyclotron Scattering (RCS) model, and present its XSPEC implementation, as well as preliminary results of its application to Anomalous X-ray Pulsars and Soft Gamma-ray Repeaters. N.R. is supported by an NWO Post-Doctoral Fellowship. S.Z. thanks the Particle Physics and Astronomy Research Council, PPARC, for support through an Advanced Fellowship.     

Reconstruction of Magnetic Activity of the Sun and Changes in Its Irradiance on a Millennium Timescale Using Neurocomputing

Relations between basic indices of the Sun and the cosmogenic isotope ¹⁴C and ¹⁰Be records were derived using the Artificial Neural Network (ANN) technique. A reconstruction of the sunspot indices and changes in Total Solar Irradiance (TSI) was carried out. Long-term changes in TSI appear in the amplitude modulation of its 11-year cyclic variation as well as in its lower envelope describing variability of the background irradiance of the Sun. According to the reconstruction the irradiance has increased about 2.5 W m⁻² since 1441.     

Deep solar activity minima, sharp climate changes, and their impact on ancient civilizations

It is shown that, over the past ～10000 years (the Holocene), deep Maunder type solar minima have been accompanied by sharp climate changes. These minima occurred every 2300–2400 years. It has been established experimentally that, at ca 4.0 ka BP, there occurred a global change in the structure of atmospheric circulation, which coincided in time with the discharge of glacial masses from Greenland to North Atlantic and a solar activity minimum. The climate changes that took place at ca 4.0 ka BP and the deep solar activity minimum that occurred at ca 2.5 ka BP affected the development of human society, leading to the degradation and destruction of a number of ancient civilizations.     

Variations in climate parameters at time intervals from hundreds to tens of millions of years in the past and its relation to solar activity

Unique palaeoclimatic data with annual time resolution as tree ring widths and annual varve deposits are analyzed in order to reveal periodicities in climatic processes at tens to hundreds of million years ago. The climatic periodicities thus found are compared with the solar and climatic periodicities observed at present.     

An assessment of changes in properties of steppe kurgan paleosoils in relation to prevailing climates over recent millennia

Comparative analysis of morphological and chemical properties of the soil chronosequence on Kastanozems soils in the steppe zone of the Russian Plain, which included paleosoils buried beneath kurgans erected ca. 2000 BC, AD 50, AD 200, and AD 1250 was performed to reconstruct the paleoenvironmental conditions in this archeologically important region. Paleoenvironmental dynamics were traced using the state of microbial communities of paleo and modern soils (including the dynamics of total and glucose-reactive biomass, and the abundance of microorganisms grown on selected media). We demonstrate that the share of the glucose-reactive microorganisms in the microbial community, the ecological–trophic structure, and oligotrophicity index might serve as indicators of the state of microbial communities and be used for paleoenvironmental reconstructions. The morphological–chemical and microbial properties confirm an arid period ca. 2000 BC, slightly wetter conditions ca. AD 50, and more humid conditions ca. AD 1250.     

Cosmogenic isotopes and their role in present-day solar paleoastrophysics

Present-day data on ¹⁴C and ¹⁰Be concentration in natural archives have been statistically analyzed. It has been established that it is difficult to extract information about solar activity variations on long (several Myr and longer) and, especially, short (to 30 years) time scales using radiocarbon data. It has been indicated that beryllium series bear reliable information about short-term, secular, and, probably, 1000-year variations in solar activity. Moreover, ¹⁰Be concentration in polar ice can also be used to study the internal dynamics of solar activity. It has been concluded that beryllium data are more promising than radiocarbon ones from the viewpoint of solar paleoastrophysics.     

Research note: the effect of strain amplitude produced by ultrasonic waves on its velocity

The effect of the amplitude of ultrasonic waves propagating through a sample is not often taken into account in laboratory experiments. However, ultrasonic waves can produce relatively large strain inside the sample, and thus change the properties of the sample. To investigate the effect of strain amplitude on the P-wave velocity, a series of ultrasonic wave propagation experiments were carried out on three different media. All measurements were performed at 1 MHz central frequency and at the strain levels inside propagating waves of  ∼3.0 × 10⁻⁶ to 6.0 × 10⁻⁵ without applying confining pressure to the sample. Strains in the waves were measured by a laser Doppler interferometer upon wave arrival on a free surface of the sample. The ultrasonic velocities were measured by a pair of P-wave transducers located at the same measuring point as the laser beam of the LDI. The effect of strain on P-wave velocity varied for different material. The P-wave velocity was calculated using both a first arrival and a first maximum peak at different applied voltage. The P-wave velocity remained unchanged for a pure elastic medium (aluminium); however, the velocity increased continuously with the increasing of the strain for polymethylmethacrylate and Gosford sandstone. For Gosford sandstone, velocity increases up to 0.8% with strain increase from 7.0 × 10⁻⁶ to 2.0 × 10⁻⁵. This effect of velocity increase with the strain induced by an ultrasonic wave can be explained by the in-elasticity of both the polymethylmethacrylate and Gosford sandstone samples.