A numerical simulation of the distribution of water temperature and salinity in the Seto Inland Sea     

Mayumi Murakami  Yukio Oonishi  Hideaki Kunishi 《Journal of Oceanography》1985,41(4):213-224

Constant flows, as well as oscillatory tidal flow, play an important role in the long-term dispersion of water in the Seto Inland Sea. Two kinds of numerical model (1-line and 2-line models) of the Seto Inland Sea have been developed to determine the role of density-induced currents, one type of the constant flow, in water dispersion in the Inland Sea. The seasonal variations of temperature, salinity and density fields are simulated and the density-induced current field is predicted at the same time. It is found that the most appropriate value of the longitudinal eddy diffusion coefficient,K _x, is 5×10⁶–7×10⁶ cm²sec^–1. The value of the overall mean dispersion coefficient is of the order of 10⁷cm²sec^–1 (Hayami and Unoki, 1970). Consequently, it is suggested that 50–70% of the total dispersion in the Seto Inland Sea can be attributed to currents other than density-induced currents,i.e., tidal currents, tide-induced currents and wind-driven currents.In winter, both density and velocity fields, calculated using the 1-line model, satisfy the conditions for the existence of a coastal front in Kii Channel and in the eastern Iyo-nada.  相似文献   

T_BB DATA-REVEALED FEATURES OF ASIAN-AUSTRALIAN MONSOON SEASONAL TRANSITION AND ASIAN SUMMER MONSOOM ESTABLISHMENT     

何金海  朱乾根  M.Murakami 《热带气象学报(英文版)》1997,3(1):18-26

Based on T_BB data from Meteorological Institute Research of Japan, study is carried out of the features of seasonal transition of Asian-Australian monsoons and Asian summer monsoon establishment,indicating that the transition begins as early as in April, followed by abrupt change in May-June; the Asian summer monsoon situation is fully established in June. The winter convective center in Sumatra moved steadily northwestward across the "land bridge" of the maritime continent and the Indo-China Peninsula as time goes from winter to summer, thus giving rise to the change in large scale circulations that is responsible for the summer monsoon establishment over SE Asia and India; the South China Sea to the western Pacific summer monsoon onset bears a close relation to the active convection in the Indo China Peninsula and steady eastward retreat of the subtropical TBB high-value band,corresponding to the western Pacific subtropical high.  相似文献   

90Sr and137Cs contents in the surface waters of the adjacent seas of Japan and the North Pacific during 1969 to 1973     

Yutaka Nagaya  Kiyoshi Nakamura 《Journal of Oceanography》1976,32(5):228-234

The concentrations of⁹⁰Sr and¹³⁷Cs, derived from the radioactive fallout, in the surface layers of the adjacent seas of Japan and the North Pacific were determined radiochemically during 1969 to 1973. The⁹⁰Sr and¹³⁷Cs concentrations in sea water decreased markedly with increase of the depth and below the depth of 1,000 m, the concentrations were approximately uniform. The distribution of⁹⁰Sr in the surface water of the North Pacific in spring of 1970 was approximately uniform, except two regions; rather large low-concentration region between 160°E and 170°W and relatively higher contamination area around 32°N and 146°W.  相似文献   

Fine-scale structure and mixing across the front between the Tsugaru Warm and Oyashio Currents in summer along the Sanriku Coast,east of Japan     

Sachihiko Itoh  Hitoshi Kaneko  Miho Ishizu  Daigo Yanagimoto  Takeshi Okunishi  Hajime Nishigaki  Kiyoshi Tanaka 《Journal of Oceanography》2016,72(1):23-37

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Data assimilation using the particle filter for identifying the elasto‐plastic material properties of geomaterials     

Akira Murakami  Takayuki Shuku  Shin‐ichi Nishimura  Kazunori Fujisawa  Kazuyuki Nakamura 《国际地质力学数值与分析法杂志》2013,37(11):1642-1669

A computational method, incorporating the finite element model (FEM) into data assimilation using the particle filter, is presented for identifying elasto‐plastic material properties based on sequential measurements under the known changing traction boundary conditions to overcome some difficulties in identifying the parameters for elasto‐plastic problems from which the existing inverse analysis strategies have suffered. A soil–water coupled problem, which uses the elasto‐plastic constitutive model, is dealt with as the geotechnical application. Measured data on the settlement and the pore pressure are obtained from a synthetic FEM computation as the forward problem under the known parameters to be identified for both the element tests and the ground behavior during the embankment construction sequence. Parameter identification for elasto‐plastic problems, such as soil behavior, should be made by considering the measurements of deformation and/or pore pressure step by step from the initial stage of construction and throughout the deformation history under the changing traction boundary conditions because of the embankment or the excavation because the ground behavior is highly dependent on the loading history. Thus, it appears that sequential data assimilation techniques, such as the particle filter, are the preferable tools that can provide estimates of the state variables, that is, deformation, pore pressure, and unknown parameters, for the constitutive model in geotechnical practice. The present paper discusses the priority of the particle filter in its application to initial/boundary value problems for elasto‐plastic materials and demonstrates a couple of numerical examples. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Geochemical assessment of arsenic contamination in well water and sediments from several communities in the Nawalparasi District of Nepal     

Akiko Nakano  Kiyoshi Kurosawa  Uddin Md. Shamim  Masakazu Tani 《Environmental Earth Sciences》2014,72(9):3269-3280

Arsenic contamination of well water is a serious issue in the Nawalparasi District of the Terai region in Nepal. A local investigation was carried out on 137 tube wells in 24 communities of the district in December 2011. The investigation revealed that the average arsenic concentration in the tube wells was 350 μg/L, and that nearly 98 % of the wells exceeded the WHO guideline arsenic level limit of 10 μg/L. Highly contaminated well water, with more than 400 μg/L of arsenic, was found within the limited depth ranges of 18–22 and 50–80 m. High arsenic levels exceeding 500 μg/L were detected in shallower wells at Patkhauli, Mahuawa, Thulokunwar, and Goini located between 27.517° and 27.543°N and between 83.648° and 83.748°E. Boring sampling at five communities of Kashiya, Goini, Sanokunwar, Thulokunwar, and Mahuawa revealed two aquifers located at the two depths around 14–22 and 41–50 m in each community. Dark gray or black-colored peaty clay layers rich in organic matter were distributed at depths of 18–21 m beside the upper aquifers with high arsenic concentration in each community. Positive correlations were shown between iron and arsenic in the sediments from the five communities. It can be inferred that these results were caused by dissolution of iron-oxyhydroxide molecules with arsenic from solid phases. Microbial metabolisms have a great potential to induce the dissolution and release arsenic attached on the solid phases into aqueous phases depending on the level of redox potential and pH.  相似文献   

Spectroscopic Studies of Solar Corona VIII. Temperature and Non-Thermal Variations in Steady Coronal Structures     

Jagdev Singh  Takashi Sakurai  Kiyoshi Ichimoto  S. Muneer  A. V. Raveendran 《Solar physics》2006,236(2):245-262

With a view to investigate variations in parameters of coronal emission lines over a large range of radial distance from the limb, raster scans were made with sufficiently long exposure times on several days during September – October 2003. An analysis of the data shows that (i) in most of the coronal structures, the FWHM of the Fe xiv 5303 Å line decreases up to 300″±50″, (ii) the FWHM of the Fe x 6374 Å line increases up to about 200″ and then remains unchanged up to about 500″, and (iii) the FWHMs of the Fe xi 7892 Å and Fe xiii 10747 Å lines show an intermediate behaviour with height. The analysis of the data also shows that the ratio of FWHM of 6374 Å to that of 5303 Å increases from 0.93 at the limb to 1.18 at 200″ above the limb. From this and the ratio of intensities of the two lines we infer that the plasma in steady coronal structures at a height of about 200″ has a temperature of about 1.5 MK and a non-thermal velocity around 17 km s^?1. The observations also show that non-homogeneous temperatures and non-thermal velocities largely exist in the lower corona up to about 300″±100″ above the limb. Amplitudes of variations in FWHM of different emission lines with height in the coronal loops are similar to those in the diffuse plasma around the coronal loops.  相似文献   

Evaluation of ADEOS-II GLI ocean color atmospheric correction using SIMBADA handheld radiometer data     

Hajime Fukushima  Mitsuhiro Toratani  Hiroshi Murakami  Pierre-Yves Deschamps  Robert Frouin  Akihiko Tanaka 《Journal of Oceanography》2007,63(3):533-543

The performance of the “version 2” Global Imager (GLI) standard atmospheric correction algorithm, which includes empirical absorptive aerosol correction and sun glint correction, was evaluated using data collected with handheld above-water SIMBADA radiometers during 23 cruises of opportunity (research vessels, merchant ships), mostly in the North Atlantic and European seas. A number of 100 match-up data sets of GLI-derived and SIMBADA-measured normalized water-leaving radiance (nL _W ) and aerosol optical thickness (AOT) were sorted out, using objective selection criteria, and analyzed. The Root-Mean-Square (RMS) difference between GLI and SIMBADA nL _W was about 0.32 μW/cm²/nm/sr for the 412 nm band, showing improvement by 30% in RMS difference with respect to the conventional “version 1” GLI atmospheric correction algorithm, and the mean difference (or bias) was reduced significantly. For AOT, the RMS difference was 0.1 between GLI estimates and SIMBADA measurements and the bias was small (a few 0.01), but the ?ngstr?m exponent was systematically underestimated, by 0.4 on average, suggesting a potential GLI calibration offset in the near infrared. The nL _W differences were not correlated to AOT, although performance was best in very clear conditions (AOT less than 0.05 in the 865 nm band). Despite the relatively large scatter between estimated and measured nL _W , the derived chlorophyll-a concentration estimates, applying the same ratio algorithm (GLI OC4V4) to GLI and SIMBADA, were consistent and highly correlated in the range of 0.05–2 μg/l. The large variability in chlorophyll-a concentration estimate for clear clean water areas (e.g. with the concentration range lower than about 0.05 μg/l) turns out to be due to the nature of the “band ratio” based in-water algorithm.  相似文献   

Future changes in tropical cyclone activity in the North Indian Ocean projected by high-resolution MRI-AGCMs     

Hiroyuki Murakami  Masato Sugi  Akio Kitoh 《Climate Dynamics》2013,40(7-8):1949-1968

New and previous versions of the high-resolution 20- and 60-km-mesh Meteorological Research Institute atmospheric general circulation models are used to investigate potential future changes in tropical cyclone (TC) activity in the North Indian Ocean (NIO). Fifteen ensemble experiments are performed under the International Panel on Climate Change A1B scenario. Most of the ensemble future (2075–2099) experiments do not project significant future changes in the basin-scale TC genesis number; however, they commonly show a substantial increase (by 46 %) in TC frequency over the Arabian Sea and a decrease (by 31 %) in the Bay of Bengal. Projected future changes in TC genesis frequency show a marked seasonal variation in the NIO: a significant and robust reduction during the pre-monsoon season, an increase during the peak-monsoon season, and a westward shift during the post-monsoon season. Several large-scale thermodynamic and dynamical parameters are analysed to elucidate the physical mechanism responsible for the future changes in TC activity; this analysis reveals a seasonal dependence of the relative contribution of these parameters to the projected future changes in TC genesis frequency.  相似文献   

Study of a Bistatic Radar System Using VLBI Technologies for Detecting Space Debris and the Experimental Verification of its Validity   总被引：1，自引：0，他引：1  

Masanobu Yajima  Kazutomo Tsuchikawa  Toshiyuki Murakami  Kazuyoshi Katsumoto  Tadashi Takano 《Earth, Moon, and Planets》2007,100(1-2):57-76

Space debris are increasing around the Earth. The observation of space debris is a key issue for the investigation and monitoring of space environment. But the observation opportunities and the detection ability are limited in existing monostatic radar systems. This paper proposes a bistatic radar which is composed of a transmitting station and a receiving-only station. A carrier wave modulated by PN-PSK signals is used in combination with a VLBI (Very Long Baseline Interferometry) recorder for range measurement between space debris and stations. The receiving radio wave is processed on the basis of VLBI techniques. Accordingly, the system is shown to have significant advantages over a monostatic radar. We actually formed a bistatic radar system, and observed a satellite in order to experimentally verify the validity. The configuration of the system, data analysis and the experimental results are described.  相似文献