The interanual rainfall variability in Indonesia corresponding to El Niño Southern Oscillation and Indian Ocean Dipole     

Hendrawan I Gede  Asai Koji  Triwahyuni Andhit  Lestari Diah Valentina 《海洋学报(英文版)》2019,38(7):57-66

The Impact of the Indian Ocean Dipole(IOD) and the El Ni?o Southern Oscillation(ENSO) event for Indonesian rainfall has been investigated for the period from 1950 to 2011. Inter-annual change of IOD and ENSO indices are used to investigate their relationship with Indonesian rainfall. By using the wavelet transform method, we found a positive significant correlation between IOD and Indonesian rainfall on the time scale of nearly 2.5–4 years.Furthermore, the positive significant correlation between ENSO(sea surface temperature anomaly at Ni?o3.4 area indices) and Indonesian rainfall exists for shorter than 2 years and between 5.5 to 6.5-year time scales.  相似文献   

Rapid Identification of Water-Conducting Fractures Using a Trace Methane Gas Measurement     

Masakazu Niwa Ph.D  Kenji Amano Ph.D  Ryuji Takeuchi Ph.D  Koji Shimada Ph.D 《Ground Water Monitoring & Remediation》2021,41(3):41-50

Identification of water-conducting fractures is important for the safety assessment of underground projects in crystalline rocks at geological disposal sites. We applied a portable methane gas analyzer by wavelength-scanned cavity ring-down spectroscopy to detect the water-conducting fractures in the underground tunnel of the Mizunami Underground Research Laboratory, central Japan. The tunnel is excavated in granite with CH₄-rich groundwater. Two approaches were taken to obtain the profile of CH₄ concentration along the gallery walls: (1) “Scan by walking” at the speed of 0.5 m/s and (2) monitoring for 30 s at 0.5 or 1 m intervals. In the Scan by walking approach, the peaks of the CH₄ concentration corresponded well with the occurrence of high water flow rate fractures. Thus, this method is useful for rapid identification of major water-conducting fractures. Monitoring at constant intervals takes more time than the Scan by walking approach; however, this method can largely detect occurrences of fractures with low fluid fluxes.  相似文献   

Stress-induced crack path in Aji granite under tensile stress     

Yozo Kudo  Osam Sano  Naokuni Murashige  Yoshiaki Mizuta  Koji Nakagawa 《Pure and Applied Geophysics》1992,138(4):641-656

The double-torsion test using Aji granite was carried out to investigate the interaction between stress-induced crack path and mineral grains. Crack velocities were controlled at range 10^–7 m/s to 10^–1 m/s. After the stressed specimens were dyed, we checked the crack path by thin section analysis, using an optical microscope. The stress-induced crack path was divided into two types, transgranular and intergranular cracks, and each path was subdivided with respect to mineral grains. In spite of the extensive range of crack velocities, the ratios between the transgranular and intergranular crack lengths did not change. The crack paths were all jagged, and often showed detour around the grain boundary when faced with obstacles like hard grains or preexisting cracks. That is to say, quartz grain played an important role as an obstacle. Feldspar grain could change the crack path because of its cleavage plane. Biolite grain had a serious effect on the path even if its constitution ratio is very small. Fractal dimensions of the crack paths were calculated by three methods, as indicators of surface roughness. The fractal dimensions were shown in a slight trend with the change of crack velocity. This trend can be explained from the point of limited cracking rate in stress corrosion.  相似文献   

Model analysis of radar echo split observed in an artificial cloud seeding experiment          下载免费PDF全文

Shimada Masaki  Tomine Kikuro  Nishiyama Koji 《Acta Meteorologica Sinica》2016,30(3):386-400

An artificial cloud seeding experiment was performed over the Japan Sea in winter to show how massive seeding could be effective to mitigate heavy snowfall damage. The results showed that 20 min after cloud seeding, a portion of the radar echo beneath the seeding track was weakened to divide the radar echo into two parts. In order to analyze the results, a numerical simulation was conducted by using the Weather Research and Forecasting model verion 3.5.1. In this simulation, the seeding effects were represented as phenomena capable of changing rain particles by accreting cloud ice and snow to form graupel particles and by changing cloud liquid water to snow particles. The graupel particles fell rapidly, thus temporarily intensifying the rainfall, which subsequently decreased. Therefore, the weakened radar echo in the field experiment is deemed to have been caused by the increase in rapidly falling graupel particles.  相似文献   

Space–time multiple regression model for grid-based population estimation in urban areas     

Ko Ko Lwin  Komei Sugiura  Koji Zettsu 《International journal of geographical information science》2016,30(8):1579-1593

We can collect, store, and analyze a huge amount of information about human mobility and social interaction activities due to the emergence of information and communication technologies and location-enabled mobile devices under cyber physical system frameworks. The high spatial resolution of population data on a multi-temporal scale is required by transport planners, human geographers, social scientists, and emergency management teams. In this study, we build a space-time multiple regression model to estimate grid-based (500 m × 500 m) spatial resolution at multi-temporal scale (30-min intervals) population data based on the space-time relationship among geospatially enabled person trip (PT) survey data and incorporate both mobile call (MC) and geotagged Twitter (GT) data. Since using geospatially enabled PT survey data as dependent variables enables us to acquire actual population amounts, which strongly depend on MCs and social interaction activities. Although many grids have a strong correlation between PT and MC/GT, some show fewer correlation results, especially where the grids have factories, schools, and workshops in which fewer MCs are found but a large population is presented. Although GT data are sparser than MCs, people from amusement and tourist areas can be detected by GT data. The space-time multiple regression model can also estimate the different amounts of populations based on human travel behavior that changes over space and time. According to accuracy assessments, the night-time estimated results, especially between 00:00 and 06:30, strongly correlate with national census data except in places where the grids have railway and subway stations.  相似文献   

Accelerated continental-scale snowmelt and ecohydrological impacts in the four largest Siberian river basins in response to spring warming     

Kazuyoshi Suzuki  Tetsuya Hiyama  Koji Matsuo  Kazuhito Ichii  Yoshihiro Iijima  Dai Yamazaki 《水文研究》2020,34(19):3867-3881

River runoff from the four largest Siberian river basins (the Ob, Yenisei, Lena, and Kolyma) considerably contributes to freshwater flux into the Arctic Ocean from the Eurasian continent. However, the effects of variation in snow cover fraction on the ecohydrological variations in these basins are not well understood. In this study, we analysed the spatiotemporal variability of the maximum snow cover fraction (SCF_max) in the four Siberian river basins. We compared the SCF_max from 2000 to 2016 with data in terms of monthly temperature and precipitation, night-time surface temperatures, the terrestrial water storage anomaly (TWSA), the normalised difference vegetation index (NDVI), and river runoff. Our results exhibit a decreasing trend in the April SCF_max values since 2000, largely in response to warming air temperatures in April. We identified snowmelt water as the dominant control on the observed increase in the runoff contribution in May across all four Siberian river basins. In addition, we detected that the interannual river runoff was predominantly controlled by interannual variations in the TWSA. The NDVI in June was strongly controlled by the timing of the snowmelt along with the surface air temperature and TWSA in June. The rate of increase in the freshwater flux from the four Siberian rivers decreased from 2000 to 2016, exhibiting large interannual variations corresponding to interannual variations in the TWSA. However, we identified a clear increase trend in the freshwater flux of ~4 km³/year when analysing the long-term 39-year historical record (1978–2016). Our results suggest that continued global warming will accelerate the transition towards the earlier timing of snowmelt and spring freshwater flux into the Arctic Ocean. Our findings also highlight the effects of earlier snowmelt on ecohydrological changes in the Northern Hemisphere.  相似文献   

Seasonal and inter-annual changes of volume density of martian CO₂ snow from time-variable elevation and gravity     

Koji Matsuo 《Icarus》2009,202(1):90-578

The martian atmosphere seasonally exchanges CO₂ with the surface by repeating condensation and sublimation, causing seasonal growth and decay of the polar CO₂ snowcaps. These processes leave two kinds of geodetic signatures, i.e. seasonal changes of the martian gravity field and of surface elevation of the snow-covered regions. Here we study gradual increase of the volume density of the martian snow due to compaction, by combining these two data sets during 1999-2001 covering three martian winters. We found that light fresh snow of slowly becomes denser reaching or more immediately before it thaws. The maximum snow density varies slightly from year to year, and between hemispheres. In the second southern winter, the density became as high as . This might have been caused by a dust storm activity, e.g. increased mixing of silicate particles and/or enhancement of sintering.  相似文献   

Aerodynamic Parameters of Regular Arrays of Rectangular Blocks with Various Geometries   总被引：8，自引：8，他引：0  

Aya Hagishima  Jun Tanimoto  Koji Nagayama  Sho Meno 《Boundary-Layer Meteorology》2009,132(2):315-337

The aerodynamic effects of various configurations of an urban array were investigated in a wind-tunnel experiment. Three aerodynamic parameters characterising arrays—the drag coefficient (C _d ), roughness length (z _o) and displacement height (d)—are used for analysis. C _d is based on the direct measurement of the total surface shear using a floating element, and the other two parameters are estimated by logarithmic fitting of the measured wind profile and predetermined total drag force. The configurations of 63 arrays used for measurement were designed to estimate the effects of layout, wind direction and the height variability of the blocks on these parameters for various roughness packing densities. The results are summarised as follows: (1) The estimated C _d and z _o of the staggered arrays peak against the plan area index (λ _p ) and frontal area index (λ _f ), in contrast with values for the square arrays, which are less sensitive to λ _p and λ _f . In addition, the square arrays with a wind direction of 45° have a considerably larger C _d , and the wind direction increases z _o/H by up to a factor of 2. (2) The effect of the non-uniformity of roughness height on z _o is more remarkable when λ _f exceeds 20%, and the discrepancy in z _o is particularly remarkable and exceeds 200%. (3) The effect of the layout of tall blocks on C _d is stronger than that of short blocks. These results indicate that the effects of both wind direction and the non-uniformity of the heights of buildings on urban aerodynamic parameters vary greatly with λ _p and λ _f ; hence, these effects should be taken into account by considering the roughness packing density.  相似文献   

Erratum to: Estimation of Heat Flux through the Eastern Bering Strait     

Kohei Mizobata  Koji Shimada  Sei-ichi Saitoh  Jia Wang 《Journal of Oceanography》2010,66(6):885-885

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The changing iconography of Japanese political geography     

Yasuo Miyakawa 《GeoJournal》2001,52(4):345-352

Our world is very fluid, very complex, constantly moving, made up of a great number of interdependent components. Therefore, the locus and the orbit of a particular area play an important role in geography and in politics. The purpose of this study is to examine the iconography of orbit and freedom of movement through an analysis of the transformation of the international politico-economic structure and its impact on Japan and to make clear the footsteps of Jean Gottmann on political geography. Due to its locus being on the crossroad of international power struggles, Japan had accepted different iconographies of orbits every time she faced great mutation in her history. This, in turn, accelerated the synchronism, synergism and synthesis of different iconographies that came to converge at the crossroad. The integration of imported cultures with the Japanese traditional culture promoted the transformation of Japanese society and community to emphasize the freedom of movements. The flexibility of Japanese society and the unifying iconography of Japanese community have enabled Japan to adapt and readapt to changing politico-economic phases. Interested in the relationship between freedom of movement and iconography, Jean Gottmann spent a considerable portion of his academic life inquiring into the changing dynamics of Japanese iconography on the global scene. After a quarter-century pursuit, he contributed to the establishment of political geography in Japan.  相似文献