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21.
Diurnal soil water dynamics in the shallow vadose zone (field site of China University of Geosciences,China) 总被引:3,自引:0,他引:3
Yijian Zeng Li Wan Zhongbo Su Hirotaka Saito Kangle Huang Xusheng Wang 《Environmental Geology》2009,58(1):11-23
Because of the relatively low soil moisture in arid or semi-arid regions, water vapour movement often predominates in the
vadose zone and affects the partitioning of energy among various land surface fluxes. In an outdoor sand bunker experiment,
the soil water content at 10 and 30 cm depth were measured at hourly intervals for 2.5 days during October 2004. It was found
that the soil moisture reached the daily maximum value (5.9–6.1% at 10 cm and 11.9–13.1% at 30 cm) and minimum value (4.4–4.5%
at 10 cm and 10.4–10.8% at 30 cm) at midday (0–1 p.m. for 10 cm and 2–3 p.m. for 30 cm) and before dawn (2–3 a.m. for 10 cm
and 4–5 a.m. for 30 cm), respectively. The modified HYDRUS-1D code, which refers to the coupled water, water vapour and heat
transport in soil, was used to simulate the moisture and water vapour flow in the soil. The numerical analyses provided insight
into the diurnal movement of liquid water and water vapour driven by the gradients of pressure heads and temperatures in the
subsurface zone. The simulated temperature and water content were in good agreement with the measured values. The spatial–temporal
distribution of liquid water flux, water vapour flux and soil temperature showed a detailed diurnal pattern of soil water
dynamics in relatively coarse sand.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
22.
Yasuhiko Okada Hirotaka Ochiai Takashi Okamoto Kyoji Sassa Hiroshi Fukuoka Ogbonnaya Igwe 《Landslides》2007,4(2):197-203
A seasonal rain front (Baiu front) accompanied a long-term accumulation of precipitation propagated over the wide areas of
the main island of Japan during 15–24 July 2006. In Okaya City, Nagano Prefecture, several flow-type landslides occurred in
the early morning of 19 July 2006, claiming eight lives. Among these landslides, a most peculiar complex earth slide–earth
flow occurred on a north gentle slope of the upstream portion of the Motosawagawa River. In the source area, volcanoclastic
soils overlying tuffaceous rocks at about 4-m depth slid due to the prolonged precipitation that raised the water table level
in the soil. Along with the travel path, the failed materials fluidized causing the liquefaction of the volcanoclastic soils
underlain by volcanic black ash soils. The resulting flow spread over a wide area up to the final deposition. Constant volume
box-shear tests on undisturbed volcanoclastic soil specimens taken from the source area showed effective normal stress tended
to decrease during shearing. The ring shear tests on saturated disturbed specimens produced the large loss of shear resistance,
which may explain the fluidized motion of the complex landslide. 相似文献
23.
浅层包气带水汽昼夜运移规律及其数值模拟研究 总被引:3,自引:0,他引:3
西北干旱、半干旱地区,浅层包气带水分通量主要由水汽组成,而水汽在运移过程中产生的能量转换和质量迁移是地表质能平衡计算不可缺少的重要源汇项。在野外进行一个沙坑实验,发现土壤水在中午(12:00—15:00)达到最大值(10cm深度,5.9~6.1cm3/cm3;30cm深度,11.9~13.1cm3/cm3),而在凌晨(02:00—05:00)出现最小值(10cm深度,4.4~4.5cm3/cm3;30cm深度,10.4~10.8cm3/cm3)。为进一步验证该实验条件下的土壤水运移及分布规律,考虑了土壤水、汽、热耦合运移的HYDRUS-1D模型被用来对实验过程进行模拟,模拟结果与实测结果吻合较好。为描述土壤水分昼夜运移模式,笔者将土壤水耦合运移的时间信息和空间信息进行同步分析;并根据土壤水运移的不同驱动力,分别对温度梯度、基质势梯度作用下的液态水及汽态水通量进行了分析。 相似文献
24.
Discovery of local topics by using latent spatio-temporal relationships in geo-social media 总被引:1,自引:0,他引:1
Kyoung-Sook Kim Isao Kojima Hirotaka Ogawa 《International journal of geographical information science》2016,30(9):1899-1922
ABSTRACTSocial networks have played a crucial role as information channels for people to understanding their daily lives beyond merely being communication tools. In particular, coupling social networks with geographic location has boosted the worth of social media to not only enable comprehension of the effects of natural phenomena such as global warming and disasters, but also the social patterns of human societies. However, the high rate of social data generation and the large amounts of noisy data makes it difficult to directly apply social media to decision-making processes. This article proposes a new system of analyzing the spatio-temporal patterns of social phenomena in real time and the discovery of local topics based on their latent spatio-temporal relationships. We will first describe a model that represents the local patterns of populations of geo-tagged social media. We will then define a local topic whose keywords share a region in space and time and present a system implementation based on existing open source technologies. We evaluated the model of local topics with several ways of visualization in experiments and demonstrated a certain social pattern from a dataset of daily Twitter streams. The results obtained from experiments revealed certain keywords had a strong spatio-temporal proximity even though they did not occur in the same message. 相似文献
25.
A channelised long run-out debris slide triggered by the Noto Hanto Earthquake in 2007, Japan 总被引:2,自引:1,他引:1
Yasuhiko Okada Hirotaka Ochiai Ushio Kurokawa Yasuhiro Ogawa Shiho Asano 《Landslides》2008,5(2):235-239
A strong earthquake (M
J 6.9, M
W 6.6–6.7) at about 11 km depth hit the western shore of the Noto Peninsula on Honshu, Japan, at about 00:42 coordinated universal
time (9:42 a.m. local time) on 25 March 2007 (the Noto Hanto Earthquake in 2007). The earthquake triggered only 61 landslides, with most
traveling short distances. It caused one long run-out landslide in the Nakanoya district of Monzen town, Wajima city, Ishikawa
Prefecture, when a portion of a deep-seated landslide transformed into a moderate debris slide down a channel. The rock slide
occurred on a south-facing convex-shaped slope on a small spur where earthquake ground shaking likely was strongly amplified
by topography. A portion of the rock slide reached a small channel floored by materials containing abundant groundwater. Constant-volume
box-shear tests on normally consolidated saturated specimens revealed that the apparent angle of internal friction of the
channel-floor material was 33–36° at 10-mm shear displacement and did not show much decrease in effective normal stress during
shearing. In situ rock-sliding testing on the exposed channel materials showed a low kinetic-friction angle of about 21°.
We suggest that an unsaturated portion of the rock slide slid down the channel, with sliding between the rock-slide mass and
the channel floor. Because the slope angle of the travel path nearly equaled the kinetic-friction angle, the unsaturated rock
slide mass may have traveled at a moderately slow speed, or it might have decelerated and accelerated. Slow speed is supported
by accounts from local residents that suggest movement of debris continued for 3 days after the main shock. 相似文献
26.
A surface buoy was moored from 20 April to 2 November 1988 at 28°48 N and 135°01 E where the water depth was 4900 m to measure temperature and velocity in the upper 150 m. The Typhoon 8824 passed at 0300 (JST) on 8 October about 50 km north to the mooring station with a maximum wind speed of 43.5 m s–1. The buoy was shifted about 30 km to southwest, and the instruments were damaged. The records of temperature at 0.5 m and velocity at 50 m were obtained. The inertial oscillation caused by the typhoon is described using the current record. The oscillation endured for about 20 days. Deep mixing and vertical, heart transport by the typhoon are discussed based on the data from the Ocean Data Buoy of the Japan Meteorological Agency moored at 29°N and 135°E. 相似文献
27.
Lam Huu Quang Doan Huy Loi Kyoji Sassa Kaoru Takara Hirotaka Ochiai Khang Dang Shinro Abe Shiho Asano Do Ngoc Ha 《Landslides》2018,15(2):309-325
Haivan Station is an important station on the North-South railway line in central Vietnam. Field investigation has identified a precursor stage of a landslide that would threaten this railway. Therefore, a landslide susceptibility assessment for Haivan Station was urgently needed to protect passenger safety and the national railway. Conducted investigations included air-photo interpretation, drilling, ground water and inclinometer monitoring, laboratory testing, and landslide simulation. This research applied the undrained dynamic loading ring shear apparatus ICL-2 to drill-core samples from the precursor landslide. Samples for ring shear tests were taken from sandy soil layers found at depths of ~21, ~31, and ~50 m in the cores. Each of these was believed to be a possible sliding surface of a landslide, and all were tested to shear failure in the ICL-2 apparatus. The boundary between highly weathered granitic rock and weathered granitic rock was identified at about 50 m depth. The inclinometer monitoring detected slight movement at this depth. Therefore, the present day risk of a landslide forming at 50 m is higher than for one forming at either 21 or 31 m. The landslide dynamic parameters obtained from the ring shear test of the 50-m-deep sample were used in an integrated numerical simulation model LS-RAPID. The simulation result gave the critical pore-pressure ratio for landslide occurrence, and landslide’s likely maximum speed, total volume, and depth of landslide debris that could cover the railway. These estimates serve to raise awareness of the vulnerability of the Vietnam national railway sector to landslide impact. 相似文献
28.
29.
Hirotaka Otobe Keisuke Taira Shoji Kitagawa Tomio Asai Kimio Hanawa 《Journal of Oceanography》2003,59(5):619-627
The heat balance of the surface layer in the vicinity of the former Ocean Weather Station “Tango” (OWS-T; 29°N, 135°E), where
a large amount of heat is transported by the Kuroshio and transferred to the atmosphere, was studied by during Ocean Mixed
Layer Experiment (OMLET) as an oceanographic component of the Japanese World Climate Research Program (1987–1991). Temperature
and velocity in the upper ocean measured using a surface moored buoy system deployed by the Ocean Research Institute, the
University of Tokyo, in total 668 days of four time series namely the periods of April 1988–November 1988 (OMELET-88), August
1989–February 1990 (OMLET-89), April 1990–September 1990 (OMLET-901) and September 1990–January 1991 (OMLET-902). We have
analyzed the moored buoy data of the upper 100 m for the latter three time series (OMLET-89, -901 and -902) and here we discuss
the heat balance of the upper 100 m, in combination with surface heat flux and oceanographic data provided by the Japan Meteorological
Agency. A large fluctuation of oceanic heat convergence/divergence of 200–300 W/m2 in amplitude with predominant period of 20–30 days occurred in the first half of OMLET-89 period, which was just the early
stage in the formation process of a large meander path of the Kuroshio. A large amount of heat convergence of 71 and 79 W/m2 on average was detected in observation period of OMLET-89 and -901, respectively. During OMLET-902, relatively small heat
convergence of 13 W/m2 was obtained. It is suggested that these variations of oceanic heat convergence in this region were closely related to the
fluctuation of the Kuroshio axis to the south of Japan.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
30.
The undrained shear behaviour of sands has been a key topic after the devastating geo-disasters during the 1964 Niigata Earthquake
in Japan. Extensive geo-technical soil tests, especially undrained triaxial compression tests, have revealed that the liquefaction
phenomenon was the major cause for the disaster expansions. To numerically reproduce the liquefaction phenomenon, the pore-water
pressure was coupled with a distinct element method. In this model, the dynamic changes in pore-water pressure were taken
into consideration by the changes in volumetric strain and modulus of compressibility of water in the respective measurement
spheres. Fluid-flows among the measurement spheres were controlled by Darcy’s law. The effective stress paths and steady state
strengths in undrained triaxial compression tests associated with the wide ranges of initial void ratio were investigated.
The effective mean stresses of medium-dense to dense numerical specimens at the steady state were negatively proportional
to the initial void ratio. Loose numerical specimens reproduced quasi-liquefaction with the effective mean stresses that were
less than 25% of the initial value. The medium-dense numerical specimens reproduced the phase transformation that was a typical
characteristic of granular materials. The rolling restraints did not much influence of the effective angle of internal friction
but strongly affected pore-water pressure behaviour within a certain range of initial void ratio. 相似文献