A comparison of channel-base currents and optical signals for rocket-triggered lightning strokes

A comparative analysis has been performed of the channel-base current and light waveforms for four rocket-triggered lightning strokes. It has been found that the current and light signals at the bottom of the channel exhibit a linear relationship (direct proportionality) in their rising portions. However, just after the peaks the linearity disappears, and the light signals usually decrease faster than the currents during the next several microseconds. Later, this trend is reversed and in some cases the light signals show another rising trend, even when the currents continue to decrease. The linear light/current relationship for the rising portions of the waveforms appears to be the same for different strokes. The findings support the idea of evaluating the variation of return stroke current along the lightning return stroke channel using light signals, provided that evaluation is limited to the rising portions of those signals and assuming that the light/current relationship observed at the bottom of the channel holds at other heights.     

Seasonal variation of horizontal material transport through the eastern channel of the Tsushima Straits

We conducted hydrographic observations ten times in the Tsushima Strait to reveal seasonal variations of horizontal material transports such as of heat, freshwater, chlorophyll a, and dissolved inorganic nitrogen (DIN) and phosphorus (DIP) through the eastern channel of the Tsushima Strait (ECTS). The volume, freshwater, and heat transport results are of nearly the same order as results reported in previous studies. The annual mean DIN and DIP transports of 3.59 kmol/s and 0.29 kmol/s are large relative to those of the Changjiang and the Taiwan Strait and are horizontally transported through the ECTS. Nutrient transports are high in July–August and October and low in April and November. Increased nutrient transports in July–August and October are due to the appearance of a cold saline water mass in the bottom layer of the ECTS. Changes in DIN transports in summer and autumn, which account for two-thirds of the total annual DIN transport, would have a large effect on the nitrogen budget and biological productivity in the Tsushima Warm Current region.     

Evaluation of image processing methods for geological interpretation in the different environments in Libya

This study evaluates the use of image processing techniques and methodologies of digital integration of multi-disciplinary geoscientific data to reduce the ambiguity in geological interpretations in different geological environments in Libya. To realize this objective, three areas were selected for this study; Eljufra, an arid environment; the mountainous environment Tarhunah; and the Jifara Plain, a coastal plain environment. Two types of remote sensing data were used in this study: Landsat Enhanced Thematic Mapper Plus (ETM+) and European Remote Sensing Satellite. The digital elevation model extracted from Shuttle Radar Topography Mission and digital topographic maps scale 1:50,000 were used for remote sensing interpretation. GIS and remote sensing-based methods were used to process and integrate all raster and vector layers data. This study offered dramatic benefits for geological interpretations and provided new insights into the efficiency of image processing methods in different geological environments.     

Mean slope-angle frequency distribution and size frequency distribution of landslide masses in Higashikubiki area, Japan

Landslide mass size frequency distributions and mean slope-angle frequency distributions were calculated for slump, slide, and creep type landslides in the Higashikubiki area. Mean slope-angle frequency distributions closely approximated Weibull distributions. Size frequency distributions show power-law dependencies. Both can be explained by modeling landslides as linked uniform blocks in tensile force. Power coefficients for size frequency distributions were 2.01–2.32 (approximation to power functions) or 2.10–2.24 (approximation to Pareto distributions).     

Attenuation behaviour of tuffaceous sandstone and granite during microfracturing

Laboratory measurements of ultrasonic wave propagation in tuffaceous sandstone (Kimachi, Japan) and granite (Iidate, Japan) were performed during increasing fracturing of the samples. The fracturing was achieved by unconfined uniaxial compression up to and beyond the point of macrofracture of the specimen using a constant low strain rate. The observed variation of wave velocity (up to 40 per cent) due to the development of micro- and macrofractures in the rock is interpreted by rock models relating velocity changes to damage and crack density. The calculated density of the newly formed cracks reaches higher values for the sandstone than for the granite. Using the estimated crack densities, the attenuation behaviour is interpreted in terms of different attenuation mechanisms; that is, friction and scattering. Rayleigh scattering as described by the model of Hudson (1981 ) may explain the attenuation qualitatively if the largest plausible crack dimensions are assumed in modelling.     

Sequence of faulting and deformation during the 2000 eruptions of the Usu Volcano, Hokkaido, Japan—interpretation and image analyses of aerial photographs

Significant faulting and deformation of the ground surface has been rarely known during volcanic eruptions. Usu Volcano, Hokkaido, Japan, is a unique example of deformation due to felsic magma intrusion. Usu Volcano has a history of such types of eruptions as phreatic, pumice eruption (Plinian type), pyroclastic flowing and lava doming since 1663. On March 31, 2000, phreatomagmatic to phreatic eruptions took place after 23 years of dormancy in the western piedmont, followed by explosions on the western flank of Usu Volcano. They were associated with significant deformation including faulting and uplift. The eruptions and deformation were continuing up to the end of May 2000.We identified the faulting using total nine sets of aerial photographs taken from before the eruption (March 31, 2000) to more than 1 year (April 27, 2001) after the end of the activity, and traced deformation processes through image processing using aerial photographs. We found that some of the new faults and the associated phreatic eruptions were related to old faults formed during the 1977–1981 eruptive episode.The image processing has revealed that the surface deformation is coincident with the area of faulting forming small grabens and the phreatic explosion vents. However, the faulting and main explosive eruptions did not take place in the highest uplift area, but along the margin. This suggests that the faulting and explosive activities were affected by small feeder channels diverging from the main magma body which caused the highest uplift.     

Hydrothermal Alteration Related to Silver Mineralization at the Iwami Silver Deposit,Shimane Prefecture,Japan

The Iwami epithermal silver deposit consists of Ag-Cu veins in a dacitic intrusive body at the deep portion of the Eikyu area, and veinlets with disseminated Ag mineralization in dacitic tuff breccia at a shallow portion of the Fukuishi area. Hydrothermal alteration associated with the silver mineralization is characterized by intense potassium metasomatism with oxidizing conditions. An illite zone occurs around the pathways of uprising fluids in both the Eikyu and Fukuishi areas. It grades laterally into the illite/smectite zone, which is surrounded by a broad smectite zone. Because of boiling, abundant adularia associated with silver mineralization overlaps on the altered tuff breccia in the Fukuishi area. The alteration zoning suggests that the western Eikyu area and the eastern Fukuishi area belong to a single hydrothermal system. The data of fluid inclusion microthermometry indicate that the temperatures range 220–270°C, and salinities range 5–7 wt percent NaCl equivalent for the silver mineralization at the upper portion in the Eikyu area and the lower portion in the Fukuishi area. Radiometric ages for volcanic rocks in the area range from 2.19 to 1.64 Ma, and the dacitic intrusion formed at approximately 1.6 Ma. The silver-dominant mineralizing hydrothermal fluids system was active around 1.44 to 1.07 Ma, which formed the Eikyu Ag-Cu veins at depth, and the Fukuishi Ag ores at the shallower portion.     

Measurements of aerosol number concentrations and rainwater chemistry at Mt. Tateyama, near the coast of the Japan sea in central Japan: On the influence of high-elevation Asian dust particles in autumn

Measurements of size-separated aerosol number concentrations at Midagahara (altitude, 1,930 m), on the western slope of Mt. Tateyama near the coast of the Japan Sea, were performed each autumn from 2006 to 2011. High number concentrations of particles larger than 2 μm were frequently seen in 2006 and 2009 when the influence of Asian dust might have been significant. The pH and the ratio of Ca²⁺ to total ions were high in the rainwater bulk sampled when high number concentrations of coarse particles were observed. The mean pH of rainwater during the autumn in 2006 was significantly higher than that in 2007 and 2008. Acidic species might have been neutralized by the Asian dust particles. Dust particles may highly affect the natural environment, such as forest ecosystems, at high elevations during seasons without snow cover.