G. E. Kocharov

The new Nagoya Radiocarbon Laboratory

A liquid scintillation counting apparatus that enables highly accurate measurements of (super 14) C has been constructed at the Solar-Terrestrial Environment Laboratory, Nagoya University. The main aim of the project is high precision year-by-year measurements of the (super 14) C content in tree rings of an old cedar tree from Yaku Island, Japan. We present the results of (super 14) C measurements on tree rings from the Agematsu region for recent decades to confirm the validity of the system.

Radiocarbon production by the gamma-ray component of supernova explosions

Supernova explosions occur at the rate of about two per century in a standard galaxy whose light is equal to 1010 Suns, assuming that the Hubble constant is 100 km-1 s per Mpc (Murdin 1990). In our galaxy, seven supernovas have been visually observed since the 2nd century AD. There are also two optical supernova remnants and one that is only a radio remnant, for a total of 10 in 18 centuries, or alittle more than one every other century (Table 1, Fig. 1). Supernovas are the source of not only visible, but also ultraviolet and infrared light, as well as neutrinos and cosmic rays. Cosmic rays include nuclides (ionized hydrogen and helium as well as heavier elements), X rays and y rays.

On the link between northern fennoscandian climate and length of the quasi-eleven-year cycle in galactic cosmic-ray flux

Bidecadal fluctuations in terrestrial climate were analyzed. It was shown that this variability might arise if Earths climate reacts to galactic cosmic-ray intensity, integrated over its full quasi-11-year cycle. It was further shown that this integral effect should also lead to an effective link between climate and the duration of the quasi-11-year cycle in cosmic ray flux. That, in turn, must result in appearance of some connection between climate and the length of the solar cycle, which is currently a topic of active debate. Analyses of temperature proxies, obtained for northern Fennoscandia, confirmed the connection of the climate in this region and the length of the cycle in galactic cosmic-ray intensity. Decadal and bidecadal variability of integrated cosmic-ray flux was quantitatively estimated.

Solar activity and regional climate.

We performed a statistical analysis of the data on summer temperature anomalies in northern Fennoscandia (8-1995 AD) and found that a 70-130-yr cycle is present in this series during most of the time period. A comparison of the reconstructed northern Fennoscandia temperature with different indicators of solar activity (Wolf numbers, the length of solar Schwabe cycle, extended bi-decadal radiocarbon series, and data on sunspots observed by naked eye) shows that the more probable cause of the periodicity is the modulation of regional northern Fennoscandia climate by the long-term solar cycle of Gleissberg. The effect of this century-scale solar modulation of the global Northern Hemisphere temperature is weaker.

Solar Cyclicity during the Maunder Minimum

A multifaceted statistical study of all available data on solar activity during the Maunder minimum (1645–1715) is presented. The data include European telescope observations, Asian sunspot observations using the unaided eye, concentrations of cosmogeneous isotopes, and catalogues of polar aurorae. Joint analyses of data on the cosmogeneous isotopes 10Be and 14C are a promising source of information on solar activity in the past. The dates of relative sunspot maxima during the Maunder minimum are consistent with the idea that there were chaotic bursts of solar activity randomly distributed in time during this interval. The available evidence that the 11-year cyclicity was preserved in 1645–1715 are worthy of attention but require additional deep study and verification. No convincing evidence for a 22-year periodicity of the occurrence of sunspots during the Maunder minimum has been found.

Nitrate Concentration in Greenland Ice: an Indicator of Changes in Fluxes of Solar and Galactic High-Energy Particles

Two sets of nitrate (NO3−) concentration data in Central Greenland ice, obtained through the GISP2 collaboration and by the University of Kansas, were analyzed statistically. The two records correlate well over time scales from a few years up to a century. They both contain quasi five-year, decadal and century-type time variations. A quasi five-year periodicity resulting from increases in the mean nitrate concentration before and after maximum sunspot number was confirmed. A tendency of solar proton events to occur more frequently during the rise/decline phases of the solar cycle may cause a quasi five-year variation. Century-type (60–110 yr) variability in nitrate outstrips the corresponding Gleissberg cycle in sunspots by 12–17 years and changes synchronously (correlates with zero phase shift) with the smoothed length of the solar Schwabe cycle. A significant correlation between century-type periodicities for nitrates in Greenland ice and northern Fennoscandian temperatures was established. The results show that despite a strong dependence on local meteorology, nitrate concentration in ice contains valuable information about global geophysical phenomena in the past.

Cosmogenic radiocarbon as a means of studying solar activity in the past

A series of yearly data on the concentration of radioactive carbon 14C in tree rings measured at the Tbilisi State University in 1983–1986 and covering the time interval 1600–1940 is statistically analyzed. We find evidence for a 22-year cyclicity in the intensity of Galactic cosmic rays (GCRs) during the Maunder minimum of the solar activity (1645–1715), testifying that the solar dynamo mechanism continued to operate during this epoch. Variations of Δ14C on timescales of tens and hundreds of years correlate well with the corresponding variations of the GCR intensity and solar activity, making radiocarbon a reliable source of information on long-timescale variations of solar activity in the past. Short-timescale (<30 years) fluctuations of Δ14C may be appreciably distorted by time variations not associated directly with solar activity; probable origins of this distortion are discussed.

The nitrate content of Greenland ice and solar activity

Past solar activity is studied based on analysis of data on the nitrate content of Greenland ice in the period from 1576–1991. Hundred-year (over the entire period) and quasi-five-year (in the middle of the 18th century) variations in the nitrate content are detected. These reflect the secular solar-activity cycle and cyclicity in the flare activity of the Sun.

Long-Term Modulation of Galactic Cosmic Rays in the Heliosphere by Curvature of the Interplanetary Magnetic Field

Long-term changes of the GCR intensity in the heliosphere were analysed making use of records of cosmogenic isotopes abundances (10Be and 14C) in natural archives and neutron monitor data. These data contain information about short-term, 11-year, 22-year, centennial and two-centennial cycles of solar activity. A mechanism to explain the long-term modulation of GCR due to changes in the curvature of the interplanetary magnetic field, resulting from changes in solar activity, is suggested.

Nuclear Paleoastrophysics: Prospects and Perspectives

Palaeoastrophysics, as a branch of science, could be defined in the following way: it studies astrophysical phenomena whose signals reached the solar system before the advent of instrumental astronomy. Instrumental astronomy was borne in the early 17th century through the systematic studies of the sky by Galileo Galilei. Using only a small optical telescope built with his own hands he discovered Jupiter’s satellites and the Moon’s phases. He reported officially on the discovery of spots on the Sun in Padua (Italy) in 1610 B. P.