Establishment of numerical beach-litter hindcast/forecast models: an application to Goto Islands, Japan

This study attempts to establish a system for hindcasting/forecasting the quantity of litter reaching a beach using an ocean circulation model, a two-way particle tracking model (PTM) to find litter sources, and an inverse method to compute litter outflows at each source. Twelve actual beach survey results, and satellite and forecasted wind data were also used. The quantity of beach litter was hindcasted/forecasted using a forward in-time PTM with the surface currents computed in the ocean circulation model driven by satellite-derived/forecasted wind data. Outflows obtained using the inverse method was given for each source in the model. The time series of the hindcasted/forecasted quantity of beach litter were found consistent with the quantity of beach litter determined from sequential webcam images of the actual beach. The accuracy of the model, however, is reduced drastically by intense winds such as typhoons which disturb drifting litter motion.     

Estimation of suspended sediment sources using 137Cs and 210Pbex in unmanaged Japanese cypress plantation watersheds in southern Japan

To analyse suspended sediment sources in unmanaged Japanese cypress plantation watersheds, field measurements and fingerprinting of the suspended sediment was conducted in the Shimanto River basin in southern Japan. For sediment fingerprinting, ¹³⁷Cs and ²¹⁰Pb_ex were detected by means of gamma‐ray spectrometry in the surface soil of the forest floor, stream bank and truck trail and mobilized sediment by interrill erosion. The ¹³⁷Cs and ²¹⁰Pb_ex activities associated with the forest floor materials were considerably higher than those of the stream bank and truck trail. The ¹³⁷Cs and ²¹⁰Pb_ex activities associated with the suspended sediment were found to vary with the sampling period. Evidently, the suspended sediment can comprise materials generated from the forest floor by interrill erosion and those from the truck trail and/or stream bank. The multivariate sediment‐mixing model using ¹³⁷Cs and ²¹⁰Pb_ex showed that the contribution of the forest floor varied periodically, ranging from 23–56% in the Hinoki 156 subwatershed and from 18–85% in the Hinoki 155 subwatershed. The difference in the average contribution of the forest floor between Hinoki 156 (46%) and Hinoki 155 (69%) may relate to the presence of truck trail networks in the watershed. The truck trail network can play roles of sediment source and pathway for sediment from forest floor to stream channel due to the concentrated overland flow on the truck trail during heavy rainfall events. These results indicate that the forest floor should be recognized as a major source of suspended sediment in unmanaged Japanese cypress plantation watersheds. Copyright © 2008 John Wiley & Sons, Ltd.     

The SOLAR-A mission: An overview

The SOLAR-A spacecraft is to be launched by the Institute of Space and Astronautical Science, Japan (ISAS) in August, 1991. As a successor of HINOTORI, this mission is dedicated principally to the study of solar flares, especially of high-energy phenomena observed in the X- and gamma-ray ranges. The SOLAR-A will be the unique space solar observatory during the current activity maximum period (1989–1992). With a coordinated set of instruments including hard X-ray and soft X-ray imaging telescopes as well as spectrometers with advanced capabilities, it will reveal many new aspects of flares and help better understand their physics, supporting international collaborations with ground-based observatories as well as theoretical investigations. An overview of this mission, including the satellite, its scientific instruments, and its operation, is given in this paper. Also the scientific objectives are briefly discussed.After the launch the name of SOLAR-A has been changed to YOHKOH.     

The behaviour of dissolved silica during the mixing of river and sea waters in Tokyo Bay

The behaviour of dissolved silica was studied in Tokyo Bay during six surveys in 1979 and 1980. The data from late spring and mid-summer samples showed concave mixing curves of silica versus salinity, whereas for the winter samples a simple conservative dillution curve was obtained. Plots of particulate silicon to particulate aluminium showed that even for winter samples as well as summer ones there were some processes removing silica from solution. The processes could not be adequately explained by adsorption onto suspended solids. The data are indicative of uptake by diatoms as the principal removal mechanism. Most of the diatom skeletons settled to the bottom where dissolution was rapid. The silica-salinity curves in this study thus demonstrate an apparent removal process for dissolved silica. This is because during summer the displacement rate of biogenic silica from a unit water column to the bottom as fecal pellets or by sinking is greater than the supply rate of dissolved silica by the action of diffusion and mixing of bottom water enriched with dissolved silica whereas in winter these rates are reasonably balanced.     

The coupling coefficients of radial pulsation in third order

The third order theory of coupling is discussed regarding the radial pulsation of stellar models.     

Finite differencing of the advection term

The advection term in the finite difference diffusion equation can give rise to the false computational oscillation unless the ratio of the grid size to the coefficient of eddy diffusivity is smaller than a critical value. The slightly uncentered differencing scheme is useful for the advection term.     

Importance of Reference Dataset Improvements for Argo Delayed-Mode Quality Control

For the Argo Project, monitoring the global upper ocean by a large number of profiling floats, maintaining the quality of salinity data is critical; the goal for measurement accuracy is ±0.01. Experiments using the method of Wong et al. (2003), the standard delayed-mode quality control (dQC) for the Project, show that its performance depends critically on the reference datasets used. This study concludes that the method is useful for Argo and has sufficient potential to achieve the goal for salinity measurement in the North Pacific, when suitable reference datasets are prepared. Considering the Wong et al. (2003) algorithms, we suggest that reference datasets with the following characteristics will be most suitable for Argo dQC: They should be basically derived from the most extensive datasets, such as the latest World Ocean Database; in regions with denser observations, datasets with carefully quality controls should be used; in the regions with subsurface temperature inversions, such as the subarctic North Pacific, the profiles used for the reference must extend below the deepest temperature maximum to prepare proper salinities for the deep layer reference.     

Seasonal Changes in Oceanic pCO2 in the Oyashio Region from Winter to Spring

We observed the partial pressure of oceanic CO₂, pCO₂ ^sea, and related surface properties in the westernmost region of the subarctic North Pacific, seasonally from 1998 to 2001. The pCO₂ ^sea in the Oyashio region showed a large decrease from winter to spring. In winter, pCO₂ ^sea was higher than 400 μatm in the Oyashio region and this region was a source of atmospheric CO₂. In spring, pCO₂ ^sea decreased to extremely low values, less than 200 μatm (minimum, 139 μatm in 2001), around the Oyashio region with low surface salinity and this region turned out to be a strong sink. The spatial variations of pCO₂ ^sea were especially large in spring in this region. The typical Oyashio water with minimal mixing with subtropical warm water was extracted based on the criterion of potential alkalinity. The contribution of main oceanic processes to the changes in pCO₂ ^sea from winter to spring was estimated from the changes in the concentrations of dissolved inorganic carbon and nutrients, total alkalinity, temperature and salinity observed in surface waters in respective years. These quantifications indicated that photosynthesis made the largest contribution to the observed pCO₂ ^sea decreases in all years and its magnitude was variable year by year. These year-to-year differences in spring biological contribution could be linked to those in the development of the density stratification due to the decrease in surface salinity. Thus, the changes in the surface physical structure could induce those in pCO₂ ^sea in the Oyashio region in spring. Furthermore, it is suggested that the direction and magnitude of the air-sea CO₂ flux during this season could be controlled significantly by the onset time of the spring bloom. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seismotectonics at the Trench-Trench-Trench triple junction off central Honshu

We study earthquakes in and near the TTT type triple junction off Boso peninsula, central Honshu, to elucidate the plate interaction in this area. The Pacific, North America (northeast Japan) and Philippine Sea plates meet at the junction of the Japan and Izu-Bonin Trenches, and the Sagami Trough. We determine focal mechanisms using WWSSN data. We also determine accurate focal depths by modeling body-waves. There is no serious trade-off between focal depth and source time function for the events treated in this study.The earthquake mechanisms and their focal depths show two major modes of deformation of the Pacific slab at the junction. One mode is represented by nearly vertical normal faults with strikes perpendicular to the Bonin Trench. This mode of faulting is dominant in regions south of the junction and characteristically the southwest block is downthrown. The other mode is represented by nearly vertical normal faults that strike parallel to the Japan Trench and indicate the northwest block is downthrown. This latter mode is dominant in regions north of the junction. The former mode may represent the accommodation of the slab geometry to the change in dip angle between the northeast Japan and Izu-Bonin arcs; the Izu-Bonin slab has a larger dip than that of the northeast Japan slab. The latter mode shows that normal faults parallel to the trench strike, usually seen in trench axis-outer rise regions, continue to occur further landward of the trench axis in the area just north of the junction. This might be caused by the loading of the Philippine Sea slab which penetrates between northeast Japan and the Pacific slab north of the Sagami Trough.Further north of these normal faults north of the junction, we find earthquakes which represent the relative motion between the Pacific and North American plates. This means that the Philippine Sea slab does not exist there. With the aid of earthquakes which represent the Philippine Sea-Pacific and Philippine Sea-North America motions located northwest of the normal faults, we can depict a possible area where the Philippine Sea slab exists north of the Sagami Trough.