Characteristic properties of snow and ice particles were reviewed and discussed in special reference to the formation, deformation due to destruction, sublimation or sintering, pulverization and fluidization. Collision and erosion phenomena by ice particles are also discussed.
Some solid particle in a snow crystal is active as ice nuclei on which snow are generated in the atmosphere. From the analysis of center nuclei in the snow crystal by use of the electron microscope, it was found that they consist of the soil particles such as kaolinite, montmorillonite and so on. Moreover, the origin of these particles was the arid area of the North China. Nucleating ability of the particle was investigated by the count of ice crystals formed in a cold box at given temperature. Number of ice crystal formed per Er particles collected on a filter paper was 0.3 at-150 °C and 4 at-20 °C.
This article briefly reviews recent studies on the movements of snow particles and its deposition in snow storm. Movements of snow particles by wind force can be classified as follwing three modes : creep, saltation and suspension. Creep involves the iniciation of snow particle movement. Saltation is an important movement in snow storm, and this is considered to be the major mechanism for mass transport. Suspension is analyzed by turbulent diffusion theory, and this shows an important mechanism of mass transport in windy and coldy environments. Saturated transport rate of snow drift is also an important concept to discuss for snow redistribution on the surface. In this paper some snow surface features were classified according to deposition/erosion patterns : sastrugi and pits are formed when erosion is dominant, whereas ripples, dunes, barchans and waves are formed when deposition is dominant. Another classification divides snow surface reliefs into transverse pattern (ripples, waves, barchans) and longitudinal pattern (dunes, sastrugi, pits). In general, the former are formed by light winds, whereas the latter are formed by strong winds.
The use of wide trenches, box-type drift gauge, Chest-of-drawer-type drift collecttor, saltation gauge, cyclone-type drift collector, net-type drift collector and photoglaphic observation, are some of the methods used to attempt blowing snow particles measurements. This report explains aforementioned methods, and shows the limits and problems of these methods. On the other hand, the author outlines a recently developed Snow Particle Counter (SPC) which is useful automatic meter for blowing snow particles measurements, and intends to summarize his recent works on the improvement of SPC.
Snow particles are large enough comparing with the wavelength of light and can be seen by eyes from a limited distance. At this point snow is different from invisible particles such as haze and fog of which radii are within several wavelengths. The mechanisms of the extinction of ligh by particles that float in the air are also different depending on their sizes. Rayleigh electromagnetic theory applies to the particles of radius very much less than wavelength and Mie theory applies to the particles of between about 0.1 and 10 times of the wavelength, however geometrical optics is applied to most of snow particles which are very large compared with the wavelength of light. The visible snow particles leave the trail of their afterimages. It is suggested observationally and theoretically that the visible sizes and the afterimages of snow particles work on visual range shortening in snow conditions. Poor visibility in blowing snow, which causes road clousures and traffic accidents are major concerns for the maintenance of safty road traffic. A few characteristics of visibility on road are introduced.
Seismicity in the east-off Sanriku region decreased conspicuously after 26 May 1983, when the central Japan Sea earthquake with a magnitude of 7.7 occurred on the west coast of Tohoku, northeastern Japan. The decrease was restricted to shallow seismicity in the depth range of 0-40 km. For deeper earthquakes in the depth range of 41-70 km rate of earthquake occurrence rather increased. Seismicity in the land area of northern Tohoku also decreased at the same time. However, seismic activity in the Oga-Oshika tectonic zone increased remarkably after the central Japan Sea earthquake. Increase of seismicity was also observed in the sea region corresponding to the extension of the Oga-Oshika tectonic zone. We consider that the coincidence of the notable decrease of shallow seismicity in the coupling region between the Pacific plate and the land plate with the central Japan Sea earthquake occurring on the west coast of Tohoku indicates the following tectonic regime. The northern Tohoku district constitutes one rigid-like block and stress fields in the both sides of the block, e. g., stress at the east-off Sanriku subduction zone and that at the active tectonic zone along the coast of the Japan Sea, influence each other. On the other hand the increase of seismic activity in the Oga-Oshika tectonic zone and in its extension after the central Japan Sea earthquake is considered to show that the zone corresponds to the southern boundary of the northern Tohoku block and change of stress is likely to be transmitted along the zone. Seismicity in the Oga-Oshika tectonic zone has a tendency to increase always when large earthquake occurs in the zone or in its extension. It should be noted that decrease of stress in the coupling region between the Pacific and the land plates due to the occurrence of the central Japan Sea earthquake was confined to the north of the Oga-Oshika tectonic zone. Seismicity in the subduction region to the south of the Oga-Oshika tectonic zone did not show any change when the central Japan Sea earthquake occurred. It is interesting to note as well that seismicity in the Pacific coast and sea regions did not change at all by the 1964 Niigata earthquake with a magnitude of 7.5 whose focal region was located on the east coast of the Japan Sea, but to the south of the Oga-Oshika tectonic zone. These facts suggest that the eastern Japan, eastern side to the Itoigawa-Shizuoka tectonic line, does not constitute a single microplate, but is separated mechanically at the Oga-Oshika tectonic zone.
The author has investigated micro-geomorphology for flooding area of the Chao Phraya River, the central plain of Thailand. The hydrological condition of the Chao Phraya River which takes the major part of this plain has been considerly changed for the last five decades through construction of artificial structures, such as embankments, multiple-purpose dams, storing reservoirs, barrages, irrigation ditches and drainage canals. This report describes a recent transformation of flooding in the plain. Changes of flood damage pattern are as follows : (1) The gradient of lower plain has been decreased according to extension of submarine delta and land subsidence. Therefore the water level of the Chao Phraya River at Bangkok has become higher than before. In densely populated areas, flood risk has been increased recently. (2) The shortened flood lag time due to increasing impermeable areas in this basin leads to a concentration of flood flow, and transmission of peak flood discharge has accelerated and aggravated flood disaster. (3) Inundation damages are also caused by the local rainfall in the plain. Artificial facilities, such as roads, dikes and structures for agricultural utilization of water etc., obstruct water to drain off the lower plain. These the river conditions are the reasons for increase of flood-prone areas. (4) Landside water flooding has occured at new urban sprawl areas as a result of rapid concentration of population from rural regions in the Bangkok Metropolitan Area.
Desertification in arid and semi-arid China is a serious problem. The purpose of this study is to understand the expansion of desertified land in the arid zone. Case study was performed in the Lower San Gong River, Xin Jiang, China as a typical case to study. The degree of the desertification and the relationship between the devastation and the salinization were analysed by comparing remote sensing data taken in 1977 and in 1987. It is suggested that suitable land use zoning, saving water for irrigation and breeding of salt-tolerant plants are necessary for the rehabilitation of this area.