Thermal expansion of fayalite,Fe2SiO4

Thermal expansion of single-crystal fayalite has been measured by a dilatometric method at temperatures between 25 °C and 850 °C. The results show the presence of anomalous expansion in the b axis, which is correlated to the anomalous variation of elastic moduli with temperature. Grüneisen's parameter is 1.10 and the thermal Debye temperature is 565 K, which is close to the acoustic Debye temperature of 511 K.     

Numerical experiments on wind-driven circulations and associated transport processes in Suruga Bay

The dynamics of the wind-driven circulations and surface transport processes in Suruga Bay have been examined by performing numerical experiments. While strong winds exist outside the bay, the winds inside the bays are greatly reduced, which generates a strong wind stress curl in winter and autumn. In particular, in winter, a strong positive curl region is located across the bay mouth, and a strong surface circulation with counterclockwise rotation is generated beneath it. The circulation is nearly geostrophic, but is not affected by the bottom topography in the deep bay. It is suggested that intense surface water exchange through the bay mouth occurs in winter, whereas it is not active in the other seasons when no significant vorticity is supplied on the bay mouth from the atmosphere. Moreover, we propose a hypothesis that the atmospheric wind stress curl will cause the frequent appearance of the counterclockwise circulation in winter in the real ocean.     

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.     

Sensitivity of the Interannual Kuroshio Transport Variation South of Japan to Wind Dataset in OGCM Calculation

Numerical experiments were carried out using OGCM (Ocean General Circulation Model), MOM2.2 (Modular Ocean Model Ver. 2.2), over realistic topography data, ETOPO5 (Earth Topography - 5 Minute), to investigate the interannual variability of the Kuroshio transport in 1960–2000 south of Japan; 1) the PN line located off the East China Sea, and 2) the ASUKA (Affiliated Surveys of the Kuroshio off Cape Ashizuri) line located off Cape Ashizuri. We adopted two wind datasets as driving forces of the OGCM: 1) the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) reanalysis monthly mean wind stress data, and 2) the ECMWF (European Centre for Medium-range Weather Forecasts) daily wind data. In the ECMWF experiments we replaced the NCEP/NCAR data only in 1979–1993 because of the availability of the data. The OGCMs and observation basically agree on the temporal variation patterns of the transports until 1986 on the PN line with correlation coefficients of about 0.6. During the 1990s, when data were collected on the ASUKA line, the NCEP/NCAR experiments give lower correlation coefficients (less than 0.3), on both PN and ASUKA lines, while the ECMWF experiments have a higher value on the ASUKA line (0.5). One of the reasons for the disagreement between the observations and OGCMs during the 1990s might arise from the NCEP/NCAR data. An additional analysis of a wind-driven circulation was performed to examine the sensitivity of integrated Sverdrup transport along the western boundary to the propagation speed of a baroclinic Rossby wave, which is varied by stratification. A variation of the stratification, which might be induced by variability of air-sea heat and freshwater fluxes, cannot be a main cause of the disagreement. This revised version was published online in July 2006 with corrections to the Cover Date.     

Propagation of Rossby Waves over Ridges Excited by Interannual Wind Forcing in a Western North Pacific Model

Numerical experiments with a multi-level general circulation model have been performed to investigate basic processes of westward propagation of Rossby waves excited by interannual wind stress forcing in an idealized western North Pacific model with ocean ridges. When the wind forcing with an oscillation period of 3 years is imposed around 180°E and 30°N, far from Japan, barotropic waves excited by the wind can hardly cross the ridges, such as the Izu-Ogasawara Ridge. On the other hand, a large part of the first-mode baroclinic waves are transmitted across the ridges, having net mass transport. The propagation speed of the first-mode baroclinic wave is accelerated (decelerated) when an anticyclonic (cyclonic) circulation is formed at the sea surface, due to a deeper (shallower) upper layer, and to southward (slightly northward) drift of the circulation. Thus, when the anticyclonic circulation is formed on the northern side of the cyclonic one, they propagate almost together. The second-mode baroclinic waves converted from the first-mode ones on the ridges arrive south of Japan, although their effects are small. The resulting volume transport variation of the western boundary current (the Kuroshio) reaches about 60% of the Sverdrup transport variability estimated from the wind stress. These characteristics are common for the interannual forcing case with a longer oscillation period. In the intraseasonal and seasonal forcing cases, on the other hand, the transport variation is much smaller than those in the interannual forcing cases. This revised version was published online in July 2006 with corrections to the Cover Date.     

Estimation of codaQ using the maximum likelihood method

A seismic coda wave from local earthquakes is an indication of heterogeneity in the crust and upper mantle, and codaQ (Q _c ) is the parameter defining the temporal decay of the coda wave. ButQ _c estimates obtained with the conventional least-square method are not based on any solid statistical background, assuming the Gaussian distributiona priori. In this study, we propose a statistically reliable estimation method of estimatingQ _c using the maximum likelihood method, and show its validity and usefulness with the data from the 1986 Joint Seismological Research in the western Nagano Prefecture. We found first that theQ _c estimation with the maximum likelihood method is statistically valid and its reliability can be checked with the -square test. Next,Q _c around Ohtaki village, within the studied area, is estimated using the maximum likelihood method. The averageQ _c value at low frequencies (up to 2 Hz) is one of the lowest in the world, which is in harmony with the geological setting of the site condition directly above an active fault.     

Random network model of electrical conduction in two-phase rock

Mineralogy and Petrology - We developed a cell-type lattice model to clarify the interconnected conductivity mechanism of two-phase rock. We quantified electrical conduction networks in rock and...