Historical Auroras in the 990s: Evidence of Great Magnetic Storms

A significant carbon-14 enhancement has recently been found in tree rings for the year 994, suggesting an extremely strong and brief cosmic ray flux event. The origin of this particular cosmic ray event has not been confirmed, but one possibility is that it might be of solar origin. Contemporary historical records of low-latitude auroras can be used as supporting evidence of intense solar activity around that time. We investigate previously reported as well as new records that have been found in contemporary observations from the 990s to determine potential auroras. Records of potential red auroras in late 992 and early 993 were found around the world, i.e. in the Korean Peninsula, Saxonian cities in modern Germany, and the Island of Ireland, suggesting the occurrence of an intense geomagnetic storm driven by solar activity.     

日本琵琶湖中微囊藻水华形成机理的再认识

Blooms of cyanobacteria are responsible for many problems in freshwater ecosystems. The massive growth of these microorganisms may limit the utilization of freshwater for human requirements since, apart from other problems, the production of toxic substances has been found to occur frequently during blooming periods. Ecologically, cyanobacterial blooms can modify dramatically the ecosystem through their low edibility within the food web and the huge primary production. Thus, saprobic processes are stimulated and the characteristics related to anaerobic conditions are also more extreme.Cyanobacterial blooms are many times explained as the consequence of the eutrophication of waterbodies. However, factors promoting bloom formation and ecological succession of cyanobacteria are not well understood yet.     

A Transit of Venus Possibly Misinterpreted as an Unaided-Eye Sunspot Observation in China on 9 December 1874

Solar Physics - Large sunspots can be observed with the unaided eye under suitable atmospheric seeing conditions. Such observations are of particular value because the frequency of their appearance...     

Generation of VHF radio emissions by electric discharges in the lower atmosphere over a seismic region

Observational data of the seismic related VHF radio emissions at 41 and 53 MHz obtained at the four stations of Create Island are presented. The epicenter of EQs is located at the distance more than 300 km behind the horizon. It was shown that VHF radiation is generated at the altitudes 1–10 km in the atmosphere over the epicenter of EQs. The theory of generation of electromagnetic radiation by random electric discharges was developed. These discharges are excited by DC electric field enhanced up to the breakdown value in the atmosphere. The field is connected with the electric current flowing in the atmosphere–ionosphere circuit, whose source is generated by convective transport of charged aerosols, which are injected in the atmosphere by soil gases during the enhancement of seismicity. Calculations of the spectrum of electromagnetic radiation are derived, and the theoretical results are confirmed by observation data.     

Does air ionization by radon cause low-frequency atmospheric electromagnetic earthquake precursors?

Natural Hazards - The aim of this work is to study the relationship between the pre-earthquake emissions of radon and ULF/ELF (1–30 Hz) atmospheric electromagnetic radiation. The...     

Gravity measurements with a portable absolute gravimeter A10 in Syowa Station and Langhovde,East Antarctica

Absolute gravity values were measured with a portable absolute gravimeter A10 in East Antarctica, for the first time by the Japanese Antarctic Research Expedition. This study aims to investigate regional spatiotemporal variations of ice mass distributions and associated crustal deformations around Syowa Station by means of repeated absolute gravity measurements, and we obtained the first absolute gravity value in Southern Langhovde on the Antarctic Continent. The average absolute gravity value at the newly installed benchmark AGS01 in Langhovde (obtained on 3 February 2012) was 982535584.2 ± 0.7 μgal (1 [μgal] = 1 × 10^?8 [m/s²]), which was in agreement with the gravity values obtained by the past relative gravity measurements within 1 mgal. In addition, the average absolute gravity value obtained at AGSaux in Syowa Station was consistent with both previous absolute gravity values and those obtained by simultaneous measurements using an FG5 gravimeter, owing to adequate data corrections associated with tidal effects and time variations in atomic clock frequencies. In order to detect the gravity changes associated with the ice mass changes and other tectonic phenomena, we plan to conduct absolute gravity measurements at AGS01 again and at other campaign sites around Syowa Station as well in the near future, with careful attention paid to the impacts of severe environmental conditions in Antarctica on gravity data collection.     

Cosmology and large telescopes

Assuming a large collecting area, a good angular resolution and a large field of view expected for the Japanese National Large Telescope (JNLT), we demonstrate that JNLT will provide a useful means of studying cosmological objects of interest. Among them I discuss how cosmological parameters and evolutionary effects can be obtained from redshift-magnitude relations, galaxy counts, distant supernovae, quasar properties, and large-scale structures. An advantage of near infrared observations is emphasized.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.     

Infrared emission from interstellar plasma

Small dust grains in hot interstellar plasmas are heated by electrons and emit near-infrared radiation. Its flux is estimated to be larger than that from small dust grains heated by stellar radiation and could explain the high infrared flux observed at wavelengths of about 5 m.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988.     

Size of the hard X-ray source in the Crab Nebula

The size of the hard X-ray source in the Crab Nebula was observed with scintillation counters on board two balloons at a lunar occulatation on 24 January, 1975. The Gaussian width of the source is 34 (+17, –14) and the center thereof is offset from the pulsar by 6±4 at position angle 102°. The observed time profile can also be fitted to an alternative model of two line sources whose intensities are 48% at 11 and 25.5% at 7 on both sides of the pulsar.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.