The effect of urbanization on sediment disasters

An aim of the study is to understand the effect of recent urbanization on the increase of sediment disasters. A case study was done in Nagasaki City and its vicinity, where a severe disaster had occurred in July 1982. The results of this study are summarized as follows: (1) The houses built in the first period locate on the relatively safe morphological units such as lower terrace and gentle foot slope. (2) The houses built in the second period intruded onto the rather risky morphological units; steep slope, valley floor and river bed. These units were not used as a residential area before. (3) The houses built in the last period are settled on the more risky area compared to older settled areas. However the demand for new housing land increased. Thus it was decided to develop the area risky to sediment disaster.     

Examining the impact of multiple climate forcings on simulated Southern Hemisphere climate variability

Climate Dynamics - The study examines the influence of external climate forcings, and atmosphere–ocean–sea–ice coupled interaction on the Southern Hemisphere (SH) atmospheric...     

Phase diagram and thermodynamic properties of AIPO<Subscript>4</Subscript> based on first-principles calculations and the quasiharmonic approximation

We calculated the phase diagram of \(\hbox {AlPO}_{4}\) up to 15 GPa and 2,000 K and investigated the thermodynamic properties of the high-pressure phases. The investigated phases include the berlinite, moganite-like, \(\hbox {AlVO}_{4},\, P2_1/c\), and \(\hbox {CrVO}_{4}\) phases. The computational methods used include density functional theory, density functional perturbation theory, and the quasiharmonic approximation. The investigated thermodynamic properties include the thermal equation of state, isothermal bulk modulus, thermal expansivity, and heat capacity. With increasing pressure, the ambient phase berlinite transforms to the moganite-like phase, and then to the \(\hbox {AlVO}_{4}\) and \(P2_1/c\) phases, and further to the \(\hbox {CrVO}_{4}\) phase. The stability fields of the \(\hbox {AlVO}_{4}\) and \(P2_1/c\) phases are similar in pressure but different in temperature, as the \(\hbox {AlVO}_{4}\) phase is stable at low temperatures, whereas the \(P2_1/c\) phase is stable at high temperatures. All of the phase relationships agree well with those obtained by quench experiments, and they support the stabilities of the moganite-like, \(\hbox {AlVO}_{4}\), and \(P2_1/c\) phases, which were not observed in room-temperature compression experiments.     

Interannual variations in low potential vorticity water and the subtropical countercurrent in an eddy-resolving OGCM

Interannual-to-decadal variations in the subtropical countercurrent (STCC) and low potential vorticity (PV) water and their relations in the North Pacific Ocean are investigated on the basis of a 60-year-long hindcast integration of an eddy-resolving ocean general circulation model. Although vertically coherent variations are dominant for STCC interannual variability, a correlation analysis shows that an intensified STCC vertical shear accompanies lower PV than usual to the north on 25.5- to 26.1-σ_θ isopycnal surfaces, and intensified meridional density gradient in subsurface layers, consistent with Kubokawa’s theory (J Phys Oceanogr 29:1314–1333, 1999). The low-PV signals appear at least 2 years before peaks of STCC, propagating southwestward from the subduction region.     

Sensitivity of Salt-leached Clay Sediments in the Ariake Bay Area,Japan

This study aims to determine whether the principle that “divalent cation predominance in the pore water precludes quick clay development” applies to the Ariake Bay sediments. The chemical and geotechnical properties of an Ariake clay sediment are presented, and sensitivity is discussed with a focus on pore-water salinity and cation composition. In recent years, reduction of pore-water salinity has occurred due to permeation of river water through the sediments because of overpumping of groundwater. Sodium remains the dominant pore-water cation in an upper zone, whereas divalent cations are dominant in the deeper zone. Divalent cation domination in the deeper zone is ascribed to Ca release from nearby cement-stabilized sediments and to Mg increase in response to a change in river water quality. The upper zone's sensitivity ranged from 15 to 77, and the remolded strength was mostly <0.5 kPa, such that quick clay was present over much of its depth. In contrast, the deeper zone's sensitivity was <40, and its remolded strength exceeded 0.5 kPa; quick clay was not present despite the <2 g/L salinity. The absence of quick clay is ascribed to the high remolded strength caused by the pore-water divalent to monovalent cation ratio being greater than 0.25.     

In situ Measurements of Tide Gauge Response and Corrections of Tsunami Waveforms from the Niigataken Chuetsu-oki Earthquake in 2007

Linear and nonlinear responses of ten well-type tide gauge stations on the Japan Sea coast of central Japan were estimated by in situ measurements. We poured water into the well or drained water from the well by using a pump to make an artificial water level difference between the outer sea and the well, then measured the recovery of water level in the well. At three tide gauge stations, Awashima, Iwafune, and Himekawa, the sea-level change of the outer sea is transmitted to the tide well instantaneously. However, at seven tide gauge stations, Nezugaseki, Ryotsu, Ogi, Teradomari, Banjin, Kujiranami, and Naoetsu, the sea-level change of the outer sea is not always transmitted to the tide well instantaneously. At these stations, the recorded tsunami waveforms are not assured to follow the actual tsunami waveforms. Tsunami waveforms from the Niigataken Chuetsu-oki Earthquake in 2007 recorded at these stations were corrected by using the measured tide gauge responses. The corrected amplitudes of the first and second waves were larger than the uncorrected ones, and the corrected peaks are a few minutes earlier than the uncorrected ones at Banjin, Kujiranami, and Ogi. At Banjin, the correction was significant; the corrected amplitudes of the first and second upward motion are +103 cm and +114 cm, respectively, while the uncorrected amplitudes were +96 cm and +88 cm. At other tide gauge stations, the differences between the uncorrected and corrected tsunami waveforms were insignificant.     

Seasonal variations of the Hawaiian Lee Countercurrent induced by the meridional migration of the trade winds

Seasonal variations of the Hawaiian Lee Countercurrent (HLCC) are investigated using satellite observations of sea surface height and wind stress as well as eddy-resolving ocean model simulations. The HLCC is strong from summer to winter and weak in spring between the dateline and the Hawaiian Islands. In response to the seasonal migration of the northeast trade winds in the meridional direction, the wind curl dipole lee of Hawaii varies in strength, exciting westward-propagating Rossby waves. The analyses of both observations and simulations show that the propagation of Rossby waves south of the HLCC, driven by the southern pole of the wind curl dipole in the lee of the islands, contributes the most to the seasonal variations of the HLCC. Unlike the wind-driven seasonal variations, our analysis suggests that other mechanisms such as mode water intrusion or air–sea interaction may cause the interannual variations of the HLCC.     

Detailed Observation of Spatial Abundance of Clam Larva Ruditapes philippinarum in Tokyo Bay, Central Japan

The spatial distribution of the larval abundance of the clam Ruditapes philippinarum has been investigated at 65 stations throughout Tokyo Bay on August 2, 2001. The large number of small D-shaped larvae that were found shortly after hatching in the waters around the Banzu, Futtu, and Sanmaizu-Haneda areas indicates that spawning populations in these areas probably contribute greatly to the larval supply in the bay. Small larvae also occurred abundantly around the Yokohama and Ichihara port areas, suggesting that these port regions play a role in the transport of larvae into Tokyo Bay. This revised version was published online in July 2006 with corrections to the Cover Date.