Cyclic Variations in the Solar Radiation Fluxes at the Beginning of the 21st Century

The solar activity in the current, that is, the 24th, sunspot cycle is analyzed. Cyclic variations in the sunspot number (SSN) and radiation fluxes in various spectral ranges have been estimated in comparison with the general level of the solar radiation, which is traditionally determined by the radio emission flux F_10.7 at a wavelength of 10.7 cm (2.8 GHz). The comparative analysis of the variations in the solar constant and solar indices in the UV range, which are important for modeling the state of the Earth’s atmosphere, in the weak 24th cycle and strong 22nd and 23rd cycles has shown relative differences in the amplitudes of variations from the minimum to the maximum of the cycle. The influence of the hysteresis effect between the activity indices and F_10.7 in the 24th cycle, which is taken into account here, makes it possible to refine the forecast of the UV indices and solar constant depending on the quadratic regression coefficients that associate the solar indices with F_10.7 depending on the phase of the cycle.     

Solar activity over last ten thousand years based on the data of <Superscript>10</Superscript>Be and <Superscript>14</Superscript>C cosmogeneous isotopes

The data on the ¹⁰Be accumulation rate in Greenland glacier (GRIP project) are discussed. Spectral analysis of the data over the last 9000 years is carried out. The spectral line intensity in the low-frequency range (periods from 100 to 1000 years) is much higher (approximately by a factor of 20), than in the frequency range of the 11-year solar activity cycle. This fact suggests that the processes responsible for the variations in the ¹⁰Be production rate with a time scale of 100–1000 years significantly differ from those determining the 11-year cyclicity of solar activity.     

Solar variability and ring widths in fossil trees

Summary We have analysed ring width sequences of 1.3 My old fossil trees, grown with no water deficit, in Dunarobba forest (Italy). We find evidence for a modulation period of the annual ring growth widths on time scale of 11 y to 15 y. Since similar modulation cycles have also been found by other authors in polar ice¹⁰Be concentration of the last millennium and in a series of annual ring widths of a same kind of trees grown in Central Europe of 15–20 My ago, we suggest that such cycles might be related to solar-activity cycles. This would support the hypothesis of a quasi-periodic behaviour of the solar dynamical system controlled by an oscillator whose fundamental period is of 22–25y, that can be identified with the Hale cycle; this system would be operational at least since the Miocene era.     

Long-term changes in solar activity,based on the data for <Superscript>10</Superscript>Be and <Superscript>14</Superscript>C cosmogenic isotopes over the last 10000 years

The results from a spectral analysis of production rate of ¹⁰Be cosmogenic isotope over the last 10000 years are considered. It is shown that the ¹⁰Be production rate is cyclic. Duration of the most powerful cycle is about 2300 years. In addition to this cycle, thousand-year variations in the ¹⁰Be production rate are observed. The thousand-year cycle could be due to the modulation of the cosmic ray flux by solar activity.     

On the cosmogenic radionuclides in meteorites

Summary Different fluxes and spectra of galactic cosmic rays (GCR) and solar cosmic rays result in a wide variety of radioactive and stable-nuclides production rates. The records of cosmic-ray interactions, have been studied in terrestrial archives, in meteorites, cosmic dust and lunar samples. We present here some results obtained in our laboratory on the study of cosmogenic radionuclides produced in meteorites which fell in the last century. The laboratory is situated in the underground station of Monte dei Cappuccini, Torino, at a depth of 70 m water equivalent to reduce the cosmic-ray background level. To measure γ-activity in meteorites we have set up a highly efficient and selective Ge−NaI(Tl) γ-ray spectrometer surrounded by a passive shield. The solar modulation affects the intensity of GCR and therefore the isotopes production rates in meteorites. The 11 y solar cycle is well reproduced by the variations of²²Na (T _1/2=2.6 y) in meteorites which fell during the past three solar cycles. The⁴⁴Ti (T _1/2=66.6 y) activity measured in eight chondrites which fell in the last 110 y is qualitatively consistent with the century-scale solar-activity variation, called the Gleissberg cycle. The increase is roughly four times higher, than expected (about 5%) for a GCR flux calculated by a model in which the solar-activity modulation is determined solely by the sunspot number indexR. This result suggests a much weakened modulation of GCR during the prolonged Gleissberg minimum during which highly ordered magnetic fields set up in the heliosphere.     

The influence of climate on the oxygen isotopes in tree rings

Natural variations in the oxygen isotope ratio ¹⁸O/¹⁶O are occurring in the hydrological cycle as a result of isotope fractionations during evaporation and condensation. These processes imprint a valuable climatic signal in the precipitation, which is stored in ice caps as well as in the cellulose of trees. Recent developments in the continuous-flow analysis of ¹⁸O/¹⁶O of organic matter now enable a systematic application of this method in tree rings. It becomes possible to build maps of the past oxygen isotope distribution in continental areas, yielding important information on regional climate changes. In this paper, the factors influencing the isotope composition of tree rings are discussed with an example from trees in northern Eurasia. Oxygen isotope values of Larix, Picea and Pinus trees were measured over a large climatic gradient extending from Norway to Siberia. The spatial isotope variations were highly correlated to the annual mean temperature (r ² =0.84), whereby the slope of the corresponding regression line was 0.35/°C. When considering the changes in ¹⁸O/¹⁶O during the 20th century, not only the temperature, but also changes in the precipitation patterns have to be considered, in particular the observed increase in the amount of winter precipitation.     

Solar diurnal anisotropy measured using muons in GRAPES-3 experiment in 2006

The GRAPES-3 experiment at Ooty contains a large-area (560 m²) tracking muon detector. This detector consists of 16 modules, each 35 m² in area, that are grouped into four supermodules of 140 m² each. The threshold energy of muons is sec(θ) GeV along a direction with zenith angle θ and the angular resolution of the muon detector is 6°. Typically, it records ~4×10⁹ muons every day. The muon detector has been operating uninterruptedly since 2001, thus providing a high statistics record of the cosmic ray flux as a function of time over one decade. However, prior to using these data, the muon rate has to be corrected for two important atmospheric effects, namely, variations in atmospheric pressure and temperature. Because of the near equatorial location of Ooty (11.4°N), the seasonal variations in the atmospheric temperature are relatively small and shall be ignored here. Due to proximity to the equator, the pressure changes at Ooty display a dominant 12 h periodic behaviour in addition to other seasonal changes. Here, we discuss various aspects of a novel method for accurate pressure measurement and subsequent corrections applied to the GRAPES-3 muon data to correct these pressure-induced variations. The pressure-corrected muon data are used to measure the profile of the solar diurnal anisotropy during 2006. The data, when divided into four segments, display significant variation both in the amplitude (~45%) and phase (~42 m) of the solar diurnal anisotropy during 2006, which was a period of relatively low solar activity.     

Observation of daily and annular variations in the <Superscript>214</Superscript>Po half-life

Results of the analysis of a time series of values of the half-life (τ) of the ²¹⁴Po nucleus with a different time step obtained from the TAU-1 (354 days) and TAU-2 (973 days) installations are presented. The annual variation with an amplitude of (9.8 ± 0.6) × 10^?4 and daily variations in the solar, lunar, and sidereal times with amplitudes of (5.3 ± 0.3) × 10^?4, (6.9 ± 2.0) × 10^?4, and (7.2 ± 1.2) × 10^?4, respectively, are found in the series of τ values. It is shown that variations in microclimatic parameters cannot be a cause of τ variations.     

Approximately 2400-Year Cycle in the Concentration of Cosmogenic Radionuclides: Sources of Variations

Cosmogenic isotopes, including ¹⁴C, ¹⁰Be, and ⁷Be, are produced in the Earth’s atmosphere under the effect of cosmic rays. The rate of their production is determined by several factors, such as the intensity of primary galactic cosmic rays, the level of solar activity, and the strength of the Earth’s magnetic field. Changes in the isotope concentrations and distributions receive contributions from mixing processes proceeding in the surrounding medium: the atmosphere, biosphere, and oceans. The isotopes ¹⁴C and ¹⁰Be are the most important for studying solar activity and climate. Investigation of isotope concentrations reveal that there are both long-term trends and cyclic components. As for ¹⁴C, the long-term component caused by the change in the magnetic dipole moment of the Earth with a characteristic time of about 10⁴ years is the most commonly known. It is well known that the concentrations of cosmogenic isotopes change cyclically with time. The ~2400-year cycle (Hallstatt cycle) and the ~210-year cycle (de Vries cycle) are the most famous. In the present article, we discuss the possible origin of the ~2400-year cycle.     

Testing the vacuum oscillation and the MSW solutions of the solar neutrino problem

Solar model independent tests of the vacuum oscillation and MSW solutions of the solar neutrino problem are considered. Detailed predictions for time (seasonal) variations of the signals due to neutrino oscillations in vacuum are given for the future solar neutrino detectors (SNO, Super-Kamiokande, BOREXINO, HELLAZ). Results on the distortions of the spectra of ⁸B neutrinos, and of e⁻ from the reaction ν + e⁻ → ν + e⁻ induced by ⁸B neutrinos, are presented in the cases of vacuum oscillations or MSW transitions for a large number of values of the relevant parameters. The possibilities to distinguish between the vacuum oscillation, the MSW adiabatic, and the MSW nonadiabatic transitions in the future solar neutrino experiments are discussed.     

Electrical and optical properties of nanowires based solar cell with radial p-n junction

In our studies the absorption, transmittance and reflectance spectra for periodic nanostructures with different parameters were calculated by the FDTD (Finite-Difference Time-Domain) method. It is shown that the proportion of reflected light in periodic structures is smaller than in case of thin films. The experimental results showed the light reflectance in the spectral range of 400–900 nm lower than 1% and it was significantly lower in comparison with surface texturing by pyramids or porous silicon.Silicon nanowires on p-type Si substrate were formed by the Metal-Assisted Chemical Etching method (MacEtch). At solar cells with radial p-n junction formation the thermal diffusion of phosphorus has been used at 790 °C. Such low temperature ensures the formation of an ultra-shallow p-n junction. Investigation of the photoelectrical properties of solar cells was carried out under light illumination with an intensity of 100 mW/cm². The obtained parameters of NWs' solar cell were I_sc = 22 mA/cm², U_oc = 0.62 V, FF = 0.51 for an overall efficiency η = 7%. The relatively low efficiency of obtained SiNWs solar cells is attributed to the excessive surface recombination at high surface areas of SiNWs and high series resistance.     

North-South asymmetry of some solar parameters: A study based on the dominance of hemispheric sunspot activity during the solar cycles 18–24

Solar activity indices differ over the solar disk, and different activity parameters are not considered to be symmetric between the northern and southern solar hemispheres. In the present paper, the daily data of a set of solar parameters (solar radio flux F10.7, total solar irradiance TSI, plage area PA, coronal index CI, solar flare index SFI, and solar mean magnetic field ǀBǀ) as well as the daily hemispheric sunspot areas (SSAs) and sunspot numbers (SSNs) during a timeframe 1945–2017 (covering almost the last seven solar cycles, 18 ̶ 24) have been employed to investigate the north-south (N-S) asymmetry of the considered solar parameters based on the dominance of hemispheric distributions of SSAs and SSNs. The N-S asymmetry for each solar parameter has been investigated and the results revealed that it is a significant aspect through different years in the entire period. The grand average of each solar parameter for the northern and southern groups over each solar activity cycle has been calculated to investigate the statistical significance of N-S asymmetry of each solar parameter in each solar activity cycle. The solar cycles 19 and 24 displayed the dominance of the southern F10.7 and PA over the northern one. However, the solar cycle 23 showed the reverse. The grand average of CI displayed the southern preference in the solar cycle 19 while, the northern dominance of CI is revealed for the solar cycle 23. The grand averages of CI demonstrated nearly symmetric distribution in solar cycles 18, and 20–22. The N-S asymmetry of the grand averages of SFI exhibited a southern dominance during solar cycles 21 and 24. On the other hand, the northern preference is observed for the grand average of SFI through the solar cycle 23. The asymmetry of the grand averages of ǀBǀ obviously has the same dominance (sign) of hemispheric sunspot activity indices for the solar cycles 21–24. The periodic behavior of the N-S asymmetry of SSAs, SSNs, F10.7, and ǀBǀ has been investigated using Fast Fourier Transformation. Many mid- and long term periodicities have been detected. We present our results and discuss their possible explanations.     

“Astrometry” experiment to measure the temporal variations in the shape and diameter of the sun on the service module of the Russian segment of the international space station

The “Astrometry” project will provide coordinate—photometric monitoring of the sun’s limb shape and disk diameter with a 0.005″ accuracy and its oblateness at a ～ 10^?6 R _? level for 6 yr. The project will investigate the internal structure and dynamics of the sun and the variations of its global parameters up to the core. The project will also investigate the fine structure and dynamics of the photosphere both on the disk and at the limb. The project is scheduled to be implemented at the ascending phase of new solar cycle 24.     

Synergy study on charge transport dynamics in hybrid organic solar cell: Photocurrent mapping and performance analysis under local spectrum

Charge transport dynamics in ZnO based inverted organic solar cell (IOSC) has been characterized with transient photocurrent spectroscopy and localised photocurrent mapping-atomic force microscopy. The value of maximum exciton generation rate was found to vary from 2.6 × 10²⁷ m⁻³s⁻¹ (J_sat = 79.7 A m⁻²) to 2.9 × 10²⁷ m⁻³s⁻¹ (J_sat = 90.8 A m⁻²) for devices with power conversion efficiency ranging from 2.03 to 2.51%. These results suggest that nanorods served as an excellent electron transporting layer that provides efficient charge transport and enhances IOSC device performance. The photovoltaic performance of OSCs with various growth times of ZnO nanorods have been analysed for a comparison between AM1.5G spectrum and local solar spectrum. The simulated PCE of all devices operating under local spectrum exhibited extensive improvement with the gain of 13.3–13.7% in which the ZnO nanorods grown at 15 min possess the highest PCE under local solar with the value of 2.82%.     

Measurement of44Ti(44Sc) in meteorites

Summary The measurement of⁴⁴Ti produced by spallation reaction of cosmic rays in meteorites fell in the last hundred years can be used for investigations on century-scale variations of solar activity. The low specific activity and the interferences of natural background and of meteorite gamma emitters are the main difficulties to be surmounted in this measurement. A selective γ-spectrometer consisting of a HP Ge and a NaI(T1) detectors in coincidence and anticoincidence has been set up in the underground (70 m w.e.) Laboratory of Monte dei Cappuccini, which allows to obtain a reliable measurement of⁴⁴Ti(⁴⁴Sc).     

Solar neutrino flux measurements by the Soviet-American gallium experiment (SAGE) for half the 22-year solar cycle

We present measurements of the solar neutrino capture rate on metallic gallium in the Soviet-American gallium experiment (SAGE) over a period of slightly more than half the 22-year solar cycle. A combined analysis of 92 runs over the twelve-year period from January 1990 until December 2001 yields a capture rate of 70.8 _?5.2 ^+5.3 (stat) _?3.2 ^+3.7 (sys) SNU for solar neutrinos with energies above 0.233 MeV. This value is slightly more than half the rate predicted by the standard solar model, 130 SNU. We present the results of new runs since April 1998 and analyze all runs combined by years, months, and bimonthly periods beginning in 1990. A simple analysis of the SAGE results together with the results of other solar neutrino experiments gives an estimate of (4.6±1.2)× 10¹⁰ neutrinos cm^?2 s^?1 for the flux of the electron pp neutrinos that reach the Earth without changing their flavor. The flux of the pp neutrinos produced in thermonuclear reactions in the Sun is estimated to be (7.6 ± 2.0) × 10¹⁰ neutrinos cm^?2 s^?1, in agreement with the value of (5.95±0.06)×10¹⁰ neutrinos cm^?2 s^?1 predicted by the standard solar model.     

One more puzzle of the Tunguska catastrophe?

Using the results of the dendrochronological analysis (68 tree-ring chronologies), it has been shown that the increase in the annual growth of trees after the Tunguska bolide explosion on June 30, 1908, is observed at a large distance (more than 1500 km) from the explosion site (61° N, 102° E) and covers a huge area of about 2 × 10⁶ km² (60°–75° N, 80°–110° E). The anomalous growth of the trees was previously reported only for the direct-destruction area (about 2000 km²). A similar result was obtained when analyzing changes in the annual growth at the time of the Chulym bolide explosion on February 26, 1984 (57.7° N, 85.1° E). A possible interpretation of the observed phenomenon is given. The results open new opportunities for using the dendrochronological method to solve the problems of asteroid-comet danger.     

A correlation study of solar activity index and amplitude of VLF trans-equatorial propagation

Diurnal and seasonal behavior of amplitude of NWC 22.3 kHz signal transmitted from Australia (22⁰49/S, 114⁰23/E), and received at Kolkata (22⁰34/N, 88⁰24/E), India have been investigated The signal amplitude is remarkably low in October. The variations of daily maximum and daily minimum of signal amplitude have been analyzed. The signal on the present propagation path showed non-correlation with A _p index, but showed a moderate but negative correlation with 10.7 cm solar flux.     

States and interstate switching in meteorological parameters

Summary We show theoretically and also through actual records that variations in air/surface temperature and associated meteorological parameters take place in three different states termed herein ?state 1?, ?state 2? and ?state 3?. For a given place, one of the two states (i.e. states 1 and 2) is accompanied by high (or increasing) rainfall while the other state is accompanied by relatively small (or decreasing) rainfall. Systematic switching from one state to another does take place at several places under physical conditions detailed in the text. Available evidence indicates that interstate switching between states 1 and 2 is primarily caused by the 11 year solar cycle and some of those other cycles responsible for variations in the solar energy incident onto the earth-atmosphere system. Finally it is shown that one of the possible causes of double sunspot cycle variations in meteorological parameters is interstate switching between state 1 and state 2. This conclusion is both consistent with and supported by past observations.