Change of policy     

Toshiyuki Hibiya 《Journal of Oceanography》2014,70(3):197-197

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Estimation of urban heat island intensity using biases in surface air temperature simulated by a nonhydrostatic regional climate model     

Akihiko Murata  Hidetaka Sasaki  Mizuki Hanafusa  Kazuo Kurihara 《Theoretical and Applied Climatology》2013,112(1-2):351-361

This study demonstrates that urban heat island (UHI) intensity can be estimated by comparing observational data and the outputs of a well-developed high-resolution regional climate model. Such an estimate is possible because the observations include the effects of UHI, whereas the model used does not include urban effects. Therefore, the errors in the simulated surface air temperature, defined as the difference between simulated and observed temperatures (simulated minus observed), are negative in urban areas but 0 in rural areas. UHI intensity is estimated by calculating the difference in temperature error between urban and rural areas. Our results indicate that overall UHI intensity in Japan is 1.5 K and that the intensity is greater in nighttime than in daytime, consistent with the previous studies. This study also shows that root mean square error and the magnitude of systematic error for the annual mean temperature are small (within 1.0 K).  相似文献   

The origin of Zn isotope fractionation in sulfides   总被引：2，自引：0，他引：2  

Toshiyuki Fujii  Frédéric Moynier  Francis Albarède 《Geochimica et cosmochimica acta》2011,75(23):7632-7643

Isotope fractionation of Zn between aqueous sulfide, chloride, and carbonate species (Zn²⁺, Zn(HS)₂, , , ZnS(HS)⁻, ZnCl⁺, ZnCl₂, , and ZnCO₃) was investigated using ab initio methods. Only little fractionation is found between the sulfide species, whereas carbonates are up to 1‰ heavier than the parent solution. At pH > 3 and under atmospheric-like CO₂ pressures, isotope fractionation of Zn sulfides precipitated from sulfidic solutions is affected by aqueous sulfide species and the δ⁶⁶Zn of sulfides reflect these in the parent solutions. Under high P_CO2 conditions, carbonate species become abundant. In high P_CO2 conditions of hydrothermal solutions, Zn precipitated as sulfides is isotopically nearly unfractionated with respect to a low-pH parent fluid. In contrast, negative δ⁶⁶Zn down to at least −0.6‰ can be expected in sulfides precipitated from solutions with pH > 9. Zinc isotopes in sulfides and rocks therefore represent a potential indicator of mid to high pH in ancient hydrothermal fluids.  相似文献   

Estimation of baroclinic tide energy available for deep ocean mixing based on three-dimensional global numerical simulations   总被引：1，自引：0，他引：1  

Yoshihiro Niwa  Toshiyuki Hibiya 《Journal of Oceanography》2011,67(4):493-502

The global distributions of the major semidiurnal (M₂ and S₂) and diurnal (K₁ and O₁) baroclinic tide energy are investigated using a hydrostatic sigma-coordinate numerical model. A series of numerical simulations using various horizontal grid spacings of 1/15–1/5° shows that generation of energetic baroclinic tides is restricted over representative prominent topographic features. For example, nearly half of the diurnal (K₁ and O₁) baroclinic tide energy is excited along the western boundary of the North Pacific from the Aleutian Islands down to the Indonesian Archipelago. It is also found that the rate of energy conversion from the barotropic to baroclinic tides is very sensitive to the horizontal grid spacing as well as the resolution of the model bottom topography; the conversion rate integrated over the global ocean increases exponentially as the model grid spacing is reduced. Extrapolating the calculated results in the limit of zero grid spacing yields the estimate of the global conversion rate to be 1105 GW (821, 145, 102, 53 GW for M₂, S₂, K₁, and O₁ tidal constituents, respectively). The amount of baroclinic tide energy dissipated in the open ocean below a depth of 1000 m, in particular, is estimated to be 500–600 GW, which is comparable to the mixing energy estimated by Webb and Suginohara (Nature 409:37, 2001) as needed to sustain the global overturning circulation.  相似文献   

Tidal transport through the Tsugaru Strait — part I: Characteristics of the major tidal flow and its residual current     

Quang-Hung Luu  Kosuke Ito  Yoichi Ishikawa  Toshiyuki Awaji 《Ocean Science Journal》2011,46(4):273-288

The potential role of the tide-induced time-mean flow (the tidal residual current) in determining transport through the Tsugaru Strait (located between the East/Japan Sea and the North Pacific) is investigated using a high-resolution numerical barotropic model. The calculated K₁, O₁, M₂, and S₂ tidal fields agree well with available observational records derived from both tide gauge and current meter measurements in the strait and the adjacent seas. The tidal residual current speed reaches 0.3 ms⁻¹ in two narrow “neck” areas where topographic sills are located. This result suggests that tides should be taken into account in estimating the long-term water mass and nutrient transport through narrow regions between the East/Japan Sea and the North Pacific. An interesting aspect of the tidal residual current field is the prediction of several active eddy zones in which sequences of eddy triplets develop in the vicinity of capes. Our vorticity analysis reveals that the interplay of topographic effects arising from both the headland and the sill around capes plays a critical role in the formation of these triple eddy patterns.  相似文献   

River Water Pollution in Developed and Developing Countries: Judge and Assessment of Physicochemical Characteristics and Selected Dissolved Metal Concentration   总被引：1，自引：0，他引：1  

M. Tajuddin Sikder  Yusuke Kihara  Masaomi Yasuda  Yustiawati  Yoshihiro Mihara  Shunitz Tanaka  Dalkhjav Odgerel  Badamtsetseg Mijiddorj  Suhaemi M. Syawal  Toshiyuki Hosokawa  Takeshi Saito  Masaaki Kurasaki 《洁净——土壤、空气、水》2013,41(1):60-68

To compare water quality in rivers of developed and developing countries, a study based on physicochemical parameters and dissolved metals levels was conducted. Water samples were collected from selected sites in Dhaka, Bangladesh; Hokkaido and Osaka, Japan; Erdenet, Mongolia and West Java, Indonesia. Analysis of least significant differences revealed that most water quality parameters were within comparable low levels in both developed and developing countries. The dissolved metals concentrations were found to be similar and below those of water standards except for manganese and cadmium at every sampling point, and lead in Erdenet, Mongolia. Some metals showed high enrichment factors in the rivers of Osaka, Japan and Erdenet, Mongolia, indicating accumulation possibility of metals in the river‐bed sediments. High concentrations of dissolved organic carbon, Escherichia coli and dissolved metals suggested greater water pollution in some rivers of developing countries than in the rivers of Japan. Principal component analysis showed strong correlations between “dissolved organic carbon and chemical oxygen demand” and “conductivity and total dissolved solids” at each sampling point, and E. coli, nitrate (NO), nitrite (NO), and pH levels were found to be higher in the rivers of Dhaka and Erdenet. In addition, there were high levels of Al and Zn in West Java, Pb in Erdenet, and Mn, Fe, and Cr in the rivers of Dhaka and Japan. Based on pressures and impacts, it is evident that dissolved metal, organic, and fecal pollution in the rivers of developing countries are in somewhat dreadful condition in comparison with the rivers of developed country.  相似文献   

Estimation of canopy drying time after rainfall using sap flow measurements in an emergent tree in a lowland mixed‐dipterocarp forest in Sarawak,Malaysia     

Tomonori Kume  Koichiro Kuraji  Natsuko Yoshifuji  Toshiyuki Morooka  Shinji Sawano  Lucy Chong  Masakazu Suzuki 《水文研究》2006,20(3):565-578

This study emphasizes the importance of canopy drying time (CDT) after rainfall in a lowland tropical rain forest. In this study, we estimate CDT using sap flow velocities measured by a heat‐pulse method in an emergent tree in a lowland mixed‐dipterocarp forest. Estimated CDT (ECDT) for each rain event has been defined as the time from rainfall cessation to the specific time derived from the difference between diurnal courses of sap flow velocities on a rainy day versus bright days. ECDT could be derived for 22 rain events that were grouped into two types, depending on whether rainfall ceased before or after noon. The ECDTs were distributed more widely and with greater values when rainfall ceased before noon (Type 1) than after noon (Type 2). The ECDTs of both Type 1 and Type 2 decreased with increases in net radiation (Rn) and vapour pressure deficit (VPD) after rainfall. This result shows that ECDT is determined mainly by post‐rainfall evaporation rates. The sap flow velocity as a detector of canopy wetness worked out well because of the specific rainfall characteristics at this site. The practical limitations of the method using sap flow velocities are discussed in relation to rainfall characteristics and time lags between transpirations and sap flow velocities. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Step-like structure in temperature and salinity profiles,observed near icebergs trapped by fast ice,Antarctica     

Kay I. Ohshima  Toshiyuki Kawamura  Takatoshi Takizawa  Shuki Ushio 《Journal of Oceanography》1994,50(3):365-372

Step-like thermohaline structure was observed near icebergs trapped by fast ice in Lützow-Holm Bay, Antarctica. The structure was developed within the draft depth of the icebergs. The typical vertical distance between the succeeding step surfaces is 20–30 m, and the temperature and salinity differences across the step surface are about 0.05–0.06 deg and 0.06–0.10 psu, respectively. The structure appears to be generated by a sea-water/iceberg interaction, and is explainable by a simple model in which an ice wall is placed in the ocean linearly stratified by vertical salinity gradient.  相似文献   

Tidal exchange through Naruto,Akashi and Kitan Straits     

Norihisa Imasato  Toshiyuki Awaji  Hideaki Kunishi 《Journal of Oceanography》1980,36(3):151-162

In order to re-evaluate the water volume exchange through Naruto Strait, we have performed a numerical experiment (nonlinear barotropic model including the actual depth of water and the details of shoreline) where trajectories of a number of labeled particles are calculated during a full cycle of the M₂ tidal current. The ratio of water volume exchanged through Naruto Strait to that through Akashi Strait is found to be twice as large as the previously estimated value. The calculated water exchange rate is 104 % for Naruto Strait, 52 % for Akashi Strait and 28 % for Kitan Strait. In the case where the tide-induced residual current is excluded from the calculated velocity field (i.e. considering only the M₂ current), the calculated exchange rate maintains the level of 68 % for Naruto Strait, 18 % for Akashi Strait and 11 % for Kitan Strait, respectively. The mechanism of tidal exchange through these three straits is discussed, and it is shown that a suitable exchange rate is obtained by starting the calculation of trajectories of labeled particles at the time of either a maximum ebb- or flood-current.  相似文献   

Estimates of Energy Dissipation Rates in the Three-Dimensional Deep Ocean Internal Wave Field   总被引：2，自引：0，他引：2  

Watanabe  Michio  Hibiya  Toshiyuki 《Journal of Oceanography》2005,61(1):123-127

Using the “Eikonal Approach” (Henyey et al., 1986), we estimate energy dissipation rates in the three-dimensional Garrett-Munk internal wave field. The total energy dissipation rate within the undisturbed GM internal wave field is found to be 4.34 × 10⁻⁹ W kg⁻¹. This corresponds to a diapycnal diffusivity of about 0.3 × 10⁻⁴ m²s⁻¹, which is less than the value 10⁻⁴ m²s⁻¹ required to sustain the global ocean overturning circulation. Only when the high vertical wavenumber, near-inertial current shear is enhanced can diapycnal diffusivity reach ∼10⁻⁴ m²s⁻¹. It follows that the energy supplied at low vertical wavenumbers and low frequencies is efficiently transferred to high vertical wavenumbers and near-inertial frequencies in the mixing hotspots in the real ocean.  相似文献