Accretion disk spectra of super-luminal jet sources and ultra-luminous compact X-ray sources in nearby spiral galaxies

The Ultra-luminous Compact X-ray Sources (ULXs)in nearby spiral galaxies and the Galactic super-luminaljet sources sharethe common spectral characteristic that they haveextremely high disk temperatures which cannot be explainedin the framework of the standard accretion disk modelin the Schwarzschild metric. We have calculated an extreme Kerr disk model to examine if the Kerr disk model can instead explain the observed `too hot' accretion disk spectra.We found that the Kerr disk spectrum becomes significantly hardercompared to the Schwarzschild disk only when the disk is highlyinclined.For super-luminal jet sources, which are known to beinclined systems, the Kerr disk model may thuswork if we choose proper values for the black hole angular momentum. For the ULXs, however, the Kerr disk interpretation will be problematic,as is is highly unlikely that their accretion disks are preferentiallyinclined.     

Pb, Sr and Nd isotope study of two co-existing magmas in the Nízke Tatry Mountains, Western Carpathians (Slovakia)

Summary Two co-existing plutonic rocks (diorite and granodiorite) were studied from an intrusion of Variscan age in the Raztocna Valley – Nízke Tatry Mountains, Western Carpathians. Geochemical analyses of major and trace elements constrain a volcanic arc as emplacement environment and give the first hints of a mixture of two magmatic end-members: the so-called Prasivá granodiorite and the Raztocna diorite. The ⁸⁷Sr/⁸⁶Sr₍₀₎ ratios vary between 0.7075 and 0.7118, the ε Nd₍₀₎ values range from −1.4 to −5.0. Common Pb isotopes reveal a dominant crustal source with minor influences from a mantle and a lower crustal source. Modelling based on Sr and Nd isotope data and using three component mixing calculations indicates that mixing of 2/3 of upper mantle material with 1/3 upper crustal material can produce the isotopic composition of the Raztocna diorite. Very minor amounts of lower crust were incorporated in the diorite. For the Prasivá granodiorite, the mixing ratio of upper mantle and upper crust is similar, but a lower crustal reservoir contributed about 5–10% of the source material.     

Near inertial motion excited by wind change in a margin of the Typhoon 9019

An excitation of inertial oscillation in the upper layer east of course of Typhoon 9019 was fortuitously observed at three surface buoys deployed during the Ocean Mixed Layer Experiment (OMLET). The observed inertial oscillation was compared with wind fluctuation measured at Ocean Weather Station T (29°N, 135°E) which was placed at the center of a triangle with three vertexes occupied by the respective surface buoys. Inertial oscillation is effectively excited in the mixed layer at the eastern margin of the typhoon by a rapid decrease of wind rather than by prevailing strong wind. It is shown by means of a least square deviation that the inertial oscillation observed in the mixed layer has a period of 23.9 hours shorter than the local inertial period of 24.7 hours. This shorter period suggests that the inertial oscillation has the finite velocities of phase and group as an inertial internal wave. A theoretically obtained ratio of vertical component of group velocity to that of phase velocity, approximately agrees with observed value. The inertial internal wave is excited by fluctuation of divergence with near inertial period in the mixed layer.     

Total amount of oceanic excess CO2 taken from the North Pacific subpolar region

Concentrations of total carbonate, alkalinity and dissolved oxygen were obtained near the 1973 GEOSECS stations in the North Pacific subpolar region north of 40°N along 175°E between 1993 and 1994. A difference of excess CO₂ content between the GEOSECS and our expeditions was estimated. The maximum difference in water column inventory of excess CO₂ has increased by about 280 gC m^–2 above 2000 m depth which apparently means an uptake of excess CO₂ taken from air to sea during the last two decades. An averaged value of the annual flux of excess CO₂ at 75–1000 m depth was 8.63±2.01 gC m^–2yr^–1 in the North Pacific subpolar region. By introducing the annual flux of excess CO₂ into a two-box model for the North Pacific subpolar region, a penetration factor of excess CO₂ from air to sea was obtained to be 1.08×10^–2 gC m^–3ppm^–1 in the North Pacific subpolar region. Based on this factor, the surface concentration of excess CO₂ in the North Pacific subpolar region was estimated to be 68 mole I^–1, suggesting that the North Pacific subpolar region absorbed atmospheric excess CO₂ more than the saturated concentration of excess CO₂. Total amount of excess CO₂ taken from the North Pacific subpolar region by 1993 was estimated to be 36.2×10¹⁵ gC, which was equal to about one tenth of that released by human activities after the preindustrial era.     

A Preliminary Study of Oceanic Bomb Radiocarbon Inventory in the North Pacific during the Last Two Decades

Radiocarbon and total carbonate data were obtained near the 1973 GEOSECS stations in the North Pacific along 30°N and along 175°E between 1993 and 1994. In these stations, we estimated radiocarbon originating from atomic bomb tests using tritium, trichlorofluoromethane and silicate contents. The average penetration depth of bomb radiocarbon during the two decades has deepened from 900 m to 1300 m. Bomb radiocarbon inventories above the average value for the whole North Pacific were found widely in the western subtropical region around 30°N both in the 1970s and 1990s, and its area in the 1990s was broader than that in the 1970s. In most of the North Pacific, while the bomb radiocarbon has decreased above 25.4, the bomb radiocarbon flux below 25.4 was over 1 × 10¹² atom m^-2yr^-1 in the subtropical region around 30°N. In the tropical area south of 20°N, the bomb radiocarbon inventory below 25.4 increased from zero to over 10 × 10¹² atom m^-2 during the last three decades. These distributions suggest that the bomb radiocarbon removed from the surface is currently accumulated with bomb ¹⁴C flux of over 1 × 10¹² atom m^-2yr^-1 below 25.4 in the subtropical region, mainly by advection from the higher latitude, and that part of the accumulated bomb ¹⁴C gradually spread southward with about 30 years.     

Current and temperature observations in the east Tsushima channel and the Sea of Genkai

Data on the Tsushima Current and its neighboring coastal current are analyzed to examine short-term variability of the currents and storm events due to typhoons. A three current-meter array was deployed in a strong current region of the east Tsushima channel during summer in 1983 and 1984, and other two current-meter arrays in the eastern coastal area of the channel (the Sea of Genkai) in the summer and autumn in 1983. The observations of coastal current show that the kinetic energy of the subtidal current component was larger in summer than in autumn by a factor of about 2. A comparison of the wind stresses and the estimated values of mixed layer depth in the summer and autumn season suggest that this seasonal change is closely associated with that of the mixed layer depth rather than with that of the wind stress. The Tsushima Current was greatly influenced by two storm events: its speed increased by a factor of 2 in one event and decreased to nearly zero in the other. Such a large variation of mean current during the storm was observed only for the Tsushima Current and not for the coastal current, suggesting that the Tsushima Current may temporarily change its regular course as a result of a storm.     

Air-Sea Gas Transfer Velocity in Stormy Winter Estimated from Radon Deficiency

Thirteen vertical profiles of ²²⁶Ra and ²²²Rn in the near-surface water were obtained in the western North Pacific in winter, and the gas transfer velocities across the air-sea interface were estimated. The transfer velocities found by applying a steady state model varied widely from 2.1 to 30.2 m day⁻¹ with a mean of 9.4 m day⁻¹. The mean value is almost 5 times higher than that in summer in other oceans, and the maximum value is a record high for world oceans. This is partly due to the inadequacy of the steady state model, which overestimates when stronger winds blow in more recent days than the ²²²Rn half-life of about 4 days. In fact, a strong low pressure zone passed through the station about 2 days earlier, which was one of the low pressure zones that with a period of develop once a week or so in the northwestern North Pacific in winter. Instead of steady-state removal, if half of the radon removal occurred sporadically every 7 days, and the last removal took place two days before the observation, the transfer velocity would be 26 m day⁻¹. Our mean transfer velocity, which is less than 20% different from the steady state value including both overestimated and underestimated values, 9.4 ± 4.8 m day⁻¹, seems to represent the mean state of this region in winter. This suggests that the gas exchange fluxes under extremely rough conditions in the open ocean are larger than those estimated by using a transfer velocity equation with a linear or quadratic relationship with wind speed. This revised version was published online in July 2006 with corrections to the Cover Date.     

A note on internal wavetrains and the associated undulation of the sea surface observed upstream of seamounts

An internal wavetrain, generated by a tidal current in superposition with the Tsushima Warm Current, has been observed by use of an acoustic echo-sounder upstream of the Shichiri-Ga-Sone Seamounts in the East Tsushima Strait of the Japan Sea. The sea surface above the internal wavetrain was simultaneously observed and was found to be undulated at the wavelength of the internal wave.     

Deep structure of the Nojima Fault, southwest Japan, estimated from borehole observations of fault-zone trapped waves

To estimate the deep structure of the southern part of the Nojima Fault, southwest Japan without the influence of near-surface structures, we analyzed the Love-wave-type fault-zone trapped waves (LTWs) recorded by a borehole seismometer at 1800 m depth. We examined the polarization, dispersion, and dominant frequency of the wavetrain following the direct S-wave in each seismogram to identify the LTW. We selected eight candidates for typical LTWs from 462 records. Because the duration of the LTW increases with hypocentral distance, we infer that the low velocity fault-zone of the Nojima Fault continues towards the seismogenic depth. In addition, since the duration of the LTW increases nonlinearly with hypocentral distance, we infer that the S-wave velocity of the fault-zone increases with depth. The location of events showing the LTW indicates that the fault-zone dips to the southeast at 75° and continues to a depth of approximately 10 km. We assumed a uniform low-velocity waveguide to estimate the average structure of the fault-zone. We estimated the average width, S-wave velocity, and Q_s of the fault-zone by comparing an analytical solution of the LTW with measured data. The average width, S-wave velocity, and Q_s of the fault-zone are 150 to 290 m, 2.5 to 3.2 km/s, and 40 to 90, respectively. Hence the fault-zone structure with a larger width and smaller velocity reduction than the fault-zone model estimated by previous surface observation is more suitable to represent the average fault-zone structure of the Nojima fault. The present study also indicated that the shallow layers and/or a shallow fault-zone structure drastically changes the characteristics of the LTW recorded at the surface, and therefore cause a discrepancy in the fault-zone model between the borehole observation and surface observation.     

Use of time series analysis for the identification of tidal effect on groundwater in the coastal area of Kimje, Korea

The purpose of this study is to apply time series analysis to investigate whether the groundwater quality in the coastal area is affected by the tide. Continuous and regular in situ monitoring data of electrical conductivity (EC) and groundwater level, and tidal level data measured by the National Oceanographic Research Institute were used for the time series analysis. Through the time series analysis, it is known that EC and groundwater level conspicuously fluctuate with two periodicities (15.4 and 0.52-day), which is very similar to those of the tide. Also the behaviors of their fluctuations vary in accordance with the tidal period. These indicate that the groundwater quality has been mainly controlled by the tidal level, and the strength of tidal effect on the groundwater quality is different according to the tidal period.