Neutron Activation Analysis of Nine GSJ Sedimentary Rock Reference Samples

Nine rock reference samples "Sedimentary rock series" issued by the Geological Survey of Japan (GSJ) were analysed for up to 31 elements by neutron activation analysis (NAA); 14MeV-NAA for Si and Al, fission track method for U, radiochemical and instrumental NAA for rare-earth elements, and instrumental NAA for the remaining elements, with reactor neutrons for the latter three. The present results are compared with reported values.     

A Late Winter Hydrography in Hidaka Bay, South of Hokkaido, Japan

Hydrographic observations in Hidaka Bay, south of Hokkaido, Japan were carried out in late winter 1996 and 1997 to examine the spatial distributions and circulation features of two different water masses, i.e., Coastal Oyashio Water (COW) and Tsugaru Warm Water (TWW), and their modifications. It is known that COW is mostly composed of cold and low-salinity water of the melted drift ice coming from the Okhotsk Sea and flows into Hidaka Bay from winter to spring and TWW with high-salinity continuously supplies from the Tsugaru Strait to the North Pacific. Cold surface mixed layers (<26.2σ_θ, 0–100 m depth) were found mainly over the shelf slope, confirming that anti-clockwise flow of COW was formed. TWW was relatively high in salinity and low in potential vorticity, and had some patch-like water masses with a temperature and salinity maximum in the limited area in the further offshore at the deeper density levels of 26.6–26.8σ_θ. The fine structure of vertical temperature and salinity profiles appeared between TWW and COW is an indication of enhanced vertical mixing (double-diffusive mixing), as inferred from the estimated Turner angles. At a mouth of the Tsugaru Strait in late winter 1997, a significant thermohaline front between TWW and the modified COW was formed and a main path of TWW spreaded south along the Sanriku coast, probably as the bottom controlled flow. Hence, the patch-like TWW observed in late winter is isolated from the Tsugaru Warm Current and then rapidly modified due to a diapycnal mixing. This revised version was published online in August 2006 with corrections to the Cover Date.     

Near-Infrared Colors of the Binary Kuiper Belt Object 1998 WW 31

We have measured near-infrared colorsof the binary Kuiper Belt object (KBO)1998 WW₃₁ using the Subaru Telescope withadaptive optics. The satellite was detectednear its perigee and apogee(0.18“ and 1.2” apart from the primary).The primary and the satellite have similar H–Kcolors, while the satellite is redder thanthe primary in J–H. Combined with the Rband magnitude previously published byVeillet et al., 2002, the color of the primaryis consistent with that of optically red KBOs. Thesatellite's R-, J-, H-colors suggest thepresence of ～1 μm absorption band dueto rock-forming minerals. If the surface of thesatellite is mainly composed by olivine, thesatellite's albedo is higher value than the canonicallyassumed value of 4%.     

Modeling Marine Stratocumulus with a Detailed Microphysical Scheme

A one-dimensional 3rd-order turbulence closure model with size-resolved microphysics and radiative transfer has been developed for investigating aerosol and cloud interactions of the stratocumulus-topped marine boundary layer. A new method is presented for coupling between the dynamical model and the mierophysical model. This scheme allows the liquid water related correlations to be directly calculated rather than parameterized. On 21 April 2001, a marine stratocumulus was observed by the Caesar aircraft over the west Pacific Rim south of Japan during the 2001 APEX/ACE-Asia field measurements. This cloud is simulated by the model we present here. The model results show that the general features of the stratocumulus-topped marine boundary layer predicted by the model are in agreement with the measurements. A new onboard cloud condensation nuclei (CCN) counter provides not only total CCN number concentration (as the traditional CCN counters do at a certain supersaturation) but also the CCN size distribution information. Using these CCN data, model responses to different CCN initial concentrations are examined. The model results are consistent with both observations and expectations.The numerical results show that the cloud microphysieal properties are changed fundamentally by different initial CCN concentrations but the cloud liquid water content does not differ significantly. Different initial CCN loadings have large impacts on the evolution of cloud microstructure and radiation transfer while they have a modest effect on thermodynamics. Increased CCN concentration leads to significant decrease of cloud effective radius.     

Mixing process on the northeast coast of Hokkaido in summer

Direct measurements using a free-falling micro-profiler were conducted on the northeast coast of Hokkaido in the summer of 2007 to clarify the mixing process in the Soya Warm Current (SWC) region in terms of microstructure. The distribution of the Turner angle (Tu) showed that these regions have a high potential for double diffusive convection, but direct measurements of the turbulent dissipation rate (ε) and dissipation of temperature variance ( $ \chi_{T} $ ) did not necessarily correspond to each other in the SWC region, especially in the offshore front of SWC and farther offshore. The mixing efficiency indicated that, even though the Turner angle (Tu) indicated a high potential for double diffusive convection, turbulent mixing was the main contributor to the mixing process in this region, and double-diffusive convection only contributed partially and sparsely, especially in the boundary off SWC water. The bottom mixed layer (BML) is known to thicken off the SWC. The vertical diffusivity coefficient was enhanced near the bottom (10^?4–10^?3 m² s^?1) off the SWC, and these results support that turbulence near the bottom off the SWC contributed to the thickening of the BML.     

Spreading of river water in Suruga Bay

We have investigated the spreading of river water in Suruga Bay by performing numerical experiments and conducting field surveys with drifting buoys. There are clear seasonal variations in the large river discharges into the bay: increased discharge in the rainy summer season and decreased discharge in the dry winter season. The numerical model reproduces the main feature that has been observed in the actual sea: the river water extends gradually from the northwestern to the southeastern regions in the bay, especially in summer. The river water spreading is greatly influenced by the bottom topography of the bay: the Fuji River water spreads over a deep continental slope as a surface-advected plume and extends well offshore, since a large bulge (anticyclonic eddy at the river mouth) extends well offshore and effectively transports the river water offshore. On the other hand, the Oi River water tends to flow parallel to isobaths (along a coastline) on a shallow continental shelf as a bottomadvected plume. Moreover, the influences of seasonal variations in the stratification and a bay-scale, wind-driven circulation are also investigated. Trajectories of the drifting buoys, which were released around the Fuji River mouth, certainly suggest that the bulge exists there.     

A magnetodynamic mechanism for loop flares

Loop flares are given a new magnetodynamic interpretation. In this model, the top of the magnetic loop is heated up by a collision of magnetic twist-wave packets (non-linear torsional Alfven wave) which are produced in the process of the loop emergence, and stored and released from the footpoints of the loop with some retardation. The appearance of the blueshifted component in CaXIX and FeXXV lines a minute or so before the impulsive phase, and the so-called instantaneous acceleration of ions deduced from the nearly simultaneous (with a delay of seconds) occurrence of -ray line emission with the impulsive hard X rays, are very naturally explained in the present model which originally aims at providing an explanation of the source of energy, a blackbox located at the top of the loop in the loop flare theories discussed thus far.     

Bifurcation current along the southwest coast of the Kii Peninsula

Along the southwest coast of the Kii Peninsula, a bifurcation current is regularly observed. By using ADCP data taken on board the R/V Wakayama of the Wakayama Prefectural Fisheries Experimental Station, characteristics of this bifurcation current are analyzed. The occurrence frequency of the bifurcation current reaches about 70% in the period from 1988 to 1996. The bifurcation point appears to be changeable and occurs almost evenly between Cape Ichie and Cape Shionomisaki. The current divergence in the alongshore direction was also investigated. Positive divergence values dominated in the whole analyzed area, and an onshore current appears to be dominant along the southwest coast of the Kii Peninsula, except in 1990 when the Kuroshio flowed in a large meandering path.     

A numerical study on the formation and variation of a clockwise-circulation during winter in the Yellow Sea

In the Yellow Sea, the north-westerly wind dominates in winter and the existence of horizontal clockwise circulation has been suggested (Yanagi and Takahashi, 1993). The formation and variation mechanisms of this clockwise circulation is investigated using the wind forced numerical model which has a simplified basin configuration of the Yellow Sea. The model results show that two vortices (an anticlockwise vortex off Chinese coast and a clockwise vortex off Korean coast) are generated by the uniform north-westerly wind. Both vortices propagate along the shelf slope as the first mode shelf waves. An anti-clockwise vortex can not grow because it does not balance to the wind forcing. On the other hand, a clockwise vortex can grow and it reaches to the equilibrium condition at the northern part of the Yellow Sea, because this circulation can balance to the wind forcing. The time scale to become into the equilibrium condition is about 2 days. From this fact, it is ascertained that a clockwise circulation in the basin is generated periodically according to the variable wind forcing with 4 days period. The steady part of the current field exists with the fluctuating one which is induced by the periodical north-westerly wind.