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31.
The cascading failure of multiple landslide dams can trigger a larger peak flood discharge than that caused by a single dam failure.Therefore,for an accurate numerical simulation,it is essential to elucidate the primary factors affecting the peak discharge of the flood caused by a cascading failure,which is the purpose of the current study.First,flume experiments were done on the cascading failure of two landslide dams under different upstream dam heights,downstream dam heights,and initial downstream reservoir water volumes.Then,the experimental results were reproduced using a numerical simulation model representing landslide dam erosion resulting from overtopping flow.Finally,the factors influencing the peak flood discharge caused by the cascading failure were analyzed using the numerical simulation model.Experimental results indicated that the inflow discharge into the downstream dam at the time when the downstream dam height began to rapidly erode was the main factor responsible for a cascading failure generating a larger peak flood discharge than that generated by a single dam failure.Furthermore,the results of a sensitivity analysis suggested that the upstream and downstream dam heights,initial water volume in the reservoir of the downstream dam,upstream and downstream dam crest lengths,and distance between two dams were among the most important factors in predicting the flood discharge caused by the cascading failure of multiple landslide dams. 相似文献
32.
Masaki N. Nishino Hiroshi Hasegawa Yoshifumi Saito Iannis Dandouras Henri Rème Alessandro Retinò Elizabeth Lucek 《Planetary and Space Science》2011,59(7):502-509
Kelvin-Helmholtz instability (KHI) is a fundamental fluid dynamical process that develops in a velocity shear layer. It is excited on the tail-flanks of the Earth's magnetosphere where the flowing magnetosheath plasma and the stagnant magnetospheric plasma sit adjacent to each other. This instability is thought to induce vortical structures and play an important role in plasma transport there. While KHI vortices have been detected, the earlier observations were performed only on one flank at a time and questions related to dawn-dusk asymmetry were not addressed. Here, we report a case where KHI vortices grow more or less simultaneously and symmetrically on both flanks, despite all the factors that may have broken the symmetry. Yet, energy distributions of ions in and around the vortices show a remarkable dawn-dusk asymmetry. Our results thus suggest that although the initiation and development of the KHI depend primarily on the macroscopic properties of the flow, the observed enhancement of ion energy transport around the dawn side vortices may be linked to microphysical processes including wave-particle interactions. Possible coupling between macro- and micro-scales, if it is at work, suggests a role for KHI not only within the Earth's magnetosphere (e.g., magnetopause and geomagnetic tail) but also in other regions where shear flows of magnetized plasma play important roles. 相似文献
33.
Yuji Kashino Iwao Ueki Yoshifumi Kuroda Andri Purwandani 《Journal of Oceanography》2007,63(4):545-559
We investigated variability in the ocean surface-subsurface layer north of New Guinea using Triangle Trans-Ocean Buoy Network (TRITON) buoys at 2°N, 138°E and 0°N, 138°E during the period from October 1999 to July 2004. Both North and South Pacific waters were observed below the subsurface at these stations. The variability in the subsurface waters was particularly high at 2°N, 138°E. Clear interannual variability occurred near the surface; the water type differed before and after onset of the 2002–03 El Niño. Before summer 2001, water that appeared to be advected from the central equatorial Pacific occupied the near surface layer. After autumn 2001, waters advected by the New Guinea Coastal Current were observed near the surface. Intraseasonal and seasonal variations were also observed below the subsurface. With regard to seasonal variability, the salinity of the subsurface saline water, the South Pacific Tropical Water, was generally high during the boreal summer-autumn, when the New Guinea Coastal Undercurrent was strong. Intraseasonal fluctuations on a scale of 20 to 60 days were also seen and may have been associated with intrinsic oceanic variability, such as ocean eddies, near the stations. Ocean variability in the thermocline layer between 100 and 200 m greatly affects the surface dynamic height variability; water variability before 2001 and variability in the pycnocline depth after 2002 are important factors affecting the thermocline. 相似文献
34.
Saiko Sugisaki Jan-Pieter Buylaert Andrew Murray Sumiko Tsukamoto Yoshifumi Nogi Hideki Miura Saburo Sakai Koichi Iijima Tatsuhiko Sakamoto 《Quaternary Geochronology》2010,5(2-3):293-298
Marine sediments contain important archives of past ocean and climate changes, but at high latitudes the absence of carbonate has prevented the construction of accurate chronological models. We have begun a study to (1) determine the accuracy of luminescence ages in deep-sea marine sediments, e.g. by comparison with marine oxygen isotope stratigraphy where possible, (2) describe changes in sedimentation rate through time, and (3) test whether it is possible to date back to marine isotope stage 5e (MIS 5e). We show here that optical dating of fine grains of quartz from the central Sea of Okhotsk is able to provide an accurate and precise chronology for the reconstruction of the palaeoceanic and palaeoclimatic environment at our site. The upper 6.5 m of the 18.42 m long core MR0604-PC07A is believed, based on its magnetic susceptibility and the oxygen isotope (δ18O) records to contain the last ～150 ka. Forty OSL samples were taken from this upper part of the core. The single-aliquot regenerative-dose (SAR) procedure is used for equivalent dose (De) determination. The luminescence characteristics of fine-grained quartz (4–11 μm) extracted from the core are described. The OSL signal is dominated by the fast component and a dose recovery test shows that we can accurately measure a known dose given in the laboratory prior to any heat treatment. Dose rates were determined using high-resolution gamma spectrometry, and vary between 0.4 and 1.6 Gy/ka. The OSL ages from this section lie between ～140 ka and ～15 ka and are in very good agreement with the δ18O stratigraphy up to MIS 5e. A clear change in sedimentation rate is identified: between ～139 and 110 ka, the sedimentation rate was ～0.09 m/ka, but then from ～110 to 15 ka, the sedimentation rate decreases to a constant value of ～0.04 m/ka. Our data confirm that OSL dating using widely distributed fine-grain quartz has great potential for dating deep-sea sediments. Because luminescence methods use clastic materials, they do not depend on the presence of biogenic carbonate. As a result it is now likely that we can establish a chronology in regions of the ocean that were previously undatable. 相似文献
35.
Anil Bhardwaj Stas Barabash Yoshifumi Futaana Yoichi Kazama Kazushi Asamura David McCann R. Sridharan Mats Holmstrom Peter Wurz Rickard Lundin 《Journal of Earth System Science》2005,114(6):749-760
This paper reports on the Sub-keV Atom Reflecting Analyzer (SARA) experiment that will be flown on the first Indian lunar
mission Chandrayaan-1. The SARA is a low energy neutral atom (LENA) imaging mass spectrometer, which will perform remote sensing
of the lunar surface via detection of neutral atoms in the energy range from 10 eV to 3 keV from a 100km polar orbit. In this
report we present the basic design of the SARA experiment and discuss various scientific issues that will be addressed. The
SARA instrument consists of three major subsystems: a LENA sensor (CENA), a solar wind monitor (SWIM), and a digital processing
unit (DPU). SARA will be used to image the solar wind-surface interaction to study primarily the surface composition and surface
magnetic anomalies and associated mini-magnetospheres. Studies of lunar exosphere sources and space weathering on the Moon
will also be attempted. SARA is the first LENA imaging mass spectrometer of its kind to be flown on a space mission. A replica
of SARA is planned to fly to Mercury onboard the BepiColombo mission. 相似文献