Hydraulic and numerical study on the generation of a subaqueous landslide-induced tsunami along the coast

By carrying out the hydraulic experiments in a one-dimensional open channel and two-dimensional basin, we clarified the process of how a landslide on a uniform slope causes the generation of a tsunami. The effect of the interactive force that occurs between the debris flow layer and the tsunami is significant in the generation of a tsunami. The continuous flow of the debris into the water makes the wave period of the tsunami short. The present experiments apply numerical simulation using the two-layer model with shear stress models on the bottom and interface, and the results are compared. The simulated debris flow shows good agreement with the measured results and ensures the rushing process into the water. We propose that the model use a Manning coefficient of 0.01 for the smooth slope and 0.015 for the rough slope, and a horizontal viscosity of 0.01 m²/s for the landslide; an interactive force of 0.2 for each layer is recommended. The dispersion effect should be included in the numerical model for the propagation from the shore.     

Influence of the greenhouse effect on yields of wheat,soybean and corn in the United States for different energy scenarios

The increase of atmospheric carbon dioxide has positive effects on agricultural productivity (photosynthesis stimulation), but in some regions it has negative effects (drought due to the temperature rise) as well. The central part of the United States in summer is predicted to be one of such regions, where the influence of the CO₂ increase should be assessed considering both the effects. Such calculations have been made for spring wheat, soybean and corn in a series of papers, a summary of which is presented here. Since the CO₂ emission rate depends on fossil fuel consumption, energy scenarios with different fossil fuel consumption are assumed. Positive effects of CO₂ are expressed by a model which simulates actual data. In the absence of an appropriate model negative effects are assumed to be proportional to the temperature rise, which is shown to be unexpectedly good. The difference between C3 (soybean and wheat) and C4 (corn) plants is also considered. Changes of their yields in the next century are calculated. Results show that in this region (probably up to 42–45° N) in summer an unlimited increase of atmospheric CO₂ is not desirable for the above three crops even if positive effects of CO₂ are taken into account. This work is not intended to give prediction of future crop production, but to show illustrative examples for the above argument. Thus assumptions are made so as to overestimate positive effects and underestimate negative effects, but results show that even in such cases an unlimited increase of CO₂ is not necessarily desirable for the specified regions.All inquiries about this paper should be made to K. Okamoto.     

Radiation Pressure and the Poynting-Robertson Effect for Fluffy Dust Particles

A correct understanding of the dynamical effect of solar radiation exerted on fluffy dust particles can be achieved with assistance of a light scattering theory as well as the equation of motion. We reformulate the equation of motion so that the radiation pressure and the Poynting-Robertson effect on fluffy grains are given in both radial and nonradial directions from the center of the Sun. This allows numerical estimates of these radiation forces on fluffy dust aggregates in the framework of the discrete dipole approximation, in which the first term of the scattering coefficients in Mie theory determines the polarizability of homogeneous spheres forming the aggregates.The nonsphericity in shape turns out to play a key role in the dynamical evolution of dust particles, while its consequence depends on the rotation rate and axis of the grains. Unless a fluffy dust particle rapidly revolves on its randomly oriented axis, the nonradial radiation forces may prevent, apart from the orbital eccentricity and semimajor axis, the orbital inclination of the particle from being preserved in orbit around the Sun. However, a change in the inclination is most probably controlled by the Lorentz force as a consequence of the interaction between electric charges on the grains and the solar magnetic field. Although rapidly and randomly rotating grains spiral into the Sun under the Poynting-Robertson effect in spite of their shapes and structures, fluffy grains drift inward on time scales longer at submicrometer sizes and shorter at much larger sizes than spherical grains of the same sizes. Numerical calculations reveal that the dynamical lifetimes of fluffy particles are determined by the material composition of the grains rather than by their morphological structures and sizes. The Poynting-Robertson effect alone is nevertheless insufficient for giving a satisfactory estimate of lifetimes for fluffy dust grains since their large ratios of cross section to mass would reduce the lifetimes by enhancing the collisional probabilities. We also show that the radiation pressure on a dust particle varies with the orbital velocity of the particle but that this effect is negligibly small for dust grains in the Solar System.     

Annual and Diurnal Variation of Meteor Rates by the Forward-Scatter Radio Observation

Forward-scatter radio meteor observations have been made at Japan since 1996 using inexpensive and low-end equipment. The activity of some major meteor showers and the seasonal variability of sporadic meteors in 2006 are presented.     

Soil radon in winter months under snowpack in Hokkaido, Japan

Soil radon (²²²Rn) has been monitored during winter months under cool-temperate deciduous stands of different surface geology in Tomakomai and in Sapporo, Hokkaido, Japan. Radon level was lower in Tomakomai of immature soil of porous volcanic ash emitted from an active volcano (Mt. Tarumae), compared with those in Sapporo of alluvial sediments. In Tomakomai, mean value of the ²²²Rn activity concentration was higher in winter (570 Bq m^?3) than in summer (350 Bq m^?3) at a depth of 1 m, which is consistent with the results in cold and dry winter reported in the literature. In contrast, soil radon decreasing with decreasing soil temperature from mid-September (5.0 kBq m^?3) remained low (2.6 kBq m^?3) under persistent snow in Sapporo, which had already been observed in the same location. Measurements of the activity concentrations of ²²²Rn in snow and in snow air as well as in soil air indicate that the small amount of ²²²Rn is released from the ground surface to the overlying snowpack with a ²²²Rn flux density of 0.4 mBq m^?2 s^?1 under thick snow cover in Sapporo.     

Annual fluctuation in the stable carbon isotope ratio of coral skeletons: The relative intensities of kinetic and metabolic isotope effects

Stable carbon and oxygen isotope measurements of biogenic carbonate provide information for reconstructing past oceanic environments. In particular, ¹⁸O/¹⁶O ratios correlate with the temperature and salinity of seawater and ¹³C/¹²C is a proxy for dissolved inorganic carbon in seawater and symbiont photosynthesis. Here, we report ¹³C/¹²C and ¹⁸O/¹⁶O values for skeletons of corals (genus Porites) with various growth rates. In faster-growing corals, ¹³C/¹²C and ¹⁸O/¹⁶O showed out-of-phase annual fluctuations. In slower-growing corals, the isotopes fluctuated in phase. We developed a simple vector notation to show two patterns of ¹³C/¹²C annual fluctuation, each with a different offset in relation to ¹⁸O/¹⁶O annual fluctuation. The phase offset between ¹³C/¹²C and ¹⁸O/¹⁶O annual fluctuations depends on the relative intensities of kinetic isotope effects on calcification and metabolic isotope effects such as photosynthesis. This model might improve our ability to infer past climate and oceanographic conditions from coral skeletons.