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排序方式: 共有128条查询结果,搜索用时 31 毫秒
41.
Marieta Cristina Castillo Atsushi Inagaki Manabu Kanda 《Boundary-Layer Meteorology》2011,140(3):453-469
A large-eddy simulation of the atmospheric boundary layer, large enough to contain both an urban surface layer and a convective
mixed layer, was performed to investigate inner-layer and outer-layer scale motions. The objective was to determine the applicability
of Monin–Obukhov similarity theory to inner-layer motions, to investigate the influence of outer-layer motions on surface-layer
structure, as well as to assess the interaction of the two scales of motion. The urban surface roughness consisted of square-patterned
cubic buildings of dimension H (40 m). A spatial filter was used to decompose the two scales in the inertial sublayer. The horizontal square filter of size
10H was effective in separating the inner-layer (surface-layer height ≈ 2 H) and outer-layer scales (boundary-layer height δ ≈ 30H), where the Reynolds stress contribution of the inner layer dominates in the logarithmic layer (depth 2H). Similarity coefficients for velocity fluctuations were successfully determined for inner-layer motions in the surface layer,
proving the robustness of Monin–Obukhov similarity for surface-layer turbulence. The inner-layer structures exhibit streaky
structures that have similar streamwise length but narrower spanwise width relative to the streamwise velocity fluctuation
field, consistent with observations from an outdoor scale model. The outer-layer motions to some extent influence the location
of ejections and sweeps through updraft and downdraft motions, respectively, thus, disturbing the homogeneity and similarity
of inner-layer motions. Although the horizontal averages of the variances and covariance of motions reveal that the Reynolds
stresses are dominated by inner-layer structures, the localized influence of the interaction of outer-layer horizontal and
inner-layer vertical motions on the Reynolds stress is not insignificant. 相似文献
42.
Large-Eddy Simulation for the Mechanism of Pollutant Removal from a Two-Dimensional Street Canyon 总被引:3,自引:3,他引:0
Takenobu Michioka Ayumu Sato Hiroshi Takimoto Manabu Kanda 《Boundary-Layer Meteorology》2011,138(2):195-213
Large-eddy simulation (LES) is conducted to investigate the mechanism of pollutant removal from a two-dimensional street canyon
with a building-height to street-width (aspect) ratio of 1. A pollutant is released as a ground-level line source at the centre
of the canyon floor. The mean velocities, turbulent fluctuations, and mean pollutant concentration estimated by LES are in
good agreement with those obtained by wind-tunnel experiments. Pollutant removal from the canyon is mainly determined by turbulent
motions, except in the adjacent area to the windward wall. The turbulent motions are composed of small vortices and small-scale
coherent structures of low-momentum fluid generated close to the plane of the roof. Although both small vortices and small-scale
coherent structures affect pollutant removal, the pollutant is largely emitted from the canyon by ejection of low-momentum
fluid when the small-scale coherent structures appear just above the canyon where the pollutant is retained. Large-scale coherent
structures also develop above the canyon, but they do not always affect pollutant removal. 相似文献
43.
Shinpei Yoshitake Masaki Uchida Toshiyuki Ohtsuka Hiroshi Kanda Hiroshi Koizumi Takayuki Nakatsubo 《Polar Science》2011,5(3):391-397
The distribution of organic carbon and its relationship to vegetation development were examined on a glacier foreland near Ny-Ålesund, Svalbard (79°N). In a 0.72-km2 area, we established 43 study plots on three line transects along primary succession from recently deglaciated area to old well-vegetated area. At each plot, we measured the type and percent coverage of vegetation types. The organic carbon content of vegetation, organic soil, and mineral soil samples was determined based on their organic carbon concentration and bulk density. Cluster analysis based on vegetation coverage revealed five types of ground surfaces representing variations in the amounts and allocation patterns of organic carbon. In the later stages of succession, 7%–24% and 31%–40% of organic carbon was contained in the organic and deeper soil layers, respectively. Organic carbon storage in the later stages of succession ranged from 1.1 – 7.9 kg C m−2. A larger amount of organic carbon, including ancient carbon in a raised beach deposit, was expected to be contained in much deeper soil layers. These results suggest that both vegetation development and geological history affect ecosystem carbon storage and that a non-negligible amount of organic carbon is distributed in this High Arctic glacier foreland. 相似文献
44.
Yoshinori Takano Jonathan James Tyler Hisaya Kojima Yusuke Yokoyama Yukiko Tanabe Takaharu Sato Nanako O. Ogawa Naohiko Ohkouchi Manabu Fukui 《Applied Geochemistry》2012
The paleolimnology of two lakes which were isolated as a result of the crustal uplift during the late Holocene along the Soya Coast, Lützow-Holm Bay, East Antarctica were studied. The focus was on temporal variations in the biogeochemical composition of sediment cores recovered from Lake Skallen at Skallen and Lake Oyako at Skarvsnes. Both sets of lake sediments record environmental changes associated with a transition from marine to lacustrine settings, as indicated by analyses of C and N contents, nitrogen isotopic compositions (δ15N), and major element concentrations. Changes in the dominant primary producers during the marine–lacustrine transition (marine diatom to cyanobacteria) at L. Skallen was clearly revealed by biogenic opal-A, diatom assemblages, and molecular signature from denaturing gradient gel electrophoresis (DGGE) with 16S ribosomal RNA (rRNA) gene analysis. Radiocarbon dating of acid-insoluble organic C suggested that the environmental transition from marine to fresh water occurred at 2940 ± 100 cal yr BP at L. Skallen and 1060 ± 90 cal yr BP at L. Oyako. Based on these data, a mean crustal uplift rate of 3.2 mm yr−1 is inferred for the history of marine–lacustrine transition via brackish conditions. The geological setting causing glacio-isostatic uplift was the primary factor in controlling the transition event in sedimentary and biological facies. 相似文献
45.
Atsushi Kume Yukiko S. Bekku Yuko T. Hanba Takashi Nakano Hiroshi Kanda 《Polar Science》2008,2(2):143-147
We measured and compared the δ13C values and nitrogen concentrations within the photosynthetic parts (Np) of phototrophs growing in different successional stages and different soil conditions at Ny-Ålesund, Svalbard, Norway. At all study sites, the Np value of vascular plants ranged from 1.0 to 2.2%. The Np value for most moss species was less than 1.0%; values for lichens were about 0.5%. No significant correlation was detected between Np and δ13C; however, different plant species occupied distinct fields on a δ13C–Np plot, with minimal overlap between species. The Np value of Saxifraga oppositifolia, which grew at all of the study sites, ranged from 1.1 to 1.5%. Differences in growth form had no effect on Np. The Np and δ13C values obtained for S. oppositifolia were confined to within a narrow range regardless of site conditions. 相似文献
46.
Hiroshi Kanda 《Polar Science》2009,3(3):189-196
The Transdisciplinary Research Integration Center (TRIC) advances the basic objectives under the umbrella of the Research Organization of Information and Systems (ROIS). The TRIC co-ordinates the development of novel fields of research within the Inter-University Research Institute Corporation of Japan. The TRIC program fosters integrated research and develops information platforms that support the quest for new paradigms in the fields of Earth science and life systems. The project, “Environmental and Genetic Approach for Life on Earth with a Study of Relevant Modeling and Prediction Techniques (EAGLE)” began under the TRIC program in 2005. The goal of the EAGLE project is to improve our understanding of ecosystems on Earth and to investigate the mechanisms leading to the evolution of life and the adaptation of species as a result of past environmental changes. The EAGLE project is also positioned as a national project of the “Microbiological and Ecological Responses to Global Environmental Changes in polar regions (MERGE) program”, so called, “MERGE-Japan” which was initiated as part of the International Polar Year (IPY, 2007–2008). A general outline of the current achievements and discussion of the EAGLE project during the IPY period are presented in this progress report. 相似文献
47.
Summary In this paper, we evaluate the applicability of flux-gradient relationships for momentum and heat for urban boundary layers
within the Monin-Obukhov similarity (MOS) theory framework. Although the theory is widely used for smooth wall boundary layers,
it is not known how well the theory works for urban layers. To address this problem, we measured the vertical profiles of
wind velocity, air temperature, and fluxes of heat and momentum over a residential area and compared the results to theory.
The measurements were done above an urban canopy whose mean height zh is 7.3 m. 3-D sonic anemometers and fine wire thermocouples were installed at 4 heights in the region 1.5zh < z < 4zh. We found the following: (1) The non-dimensional horizontal wind speed has good agreement with the stratified logarithmic
profile predicted using the semi-empirical Monin-Obukov similarity (MOS) function, when it was scaled by the surface friction
velocity that is derived from the shear stress extrapolated to the roof-top level. (2) The scaled gradient of horizontal wind
speed
followed a conventional semi-empirical function for a flat surface at a level (z/zh = 2.9), whereas, in the vicinity of the canopy height
was larger than the commonly-used empirical relationship. (3) The potential temperature profile above the canopy shows dependency
on the atmospheric stability and the scaled gradient of temperature
is in good agreement with a conventional shear function for heat. In the case of heat, the dependency on height was not found.
(4) The flux-gradient relationship for momentum and heat in the region 1.5zh < z < 4zh was rather similar to that for flat surfaces than that for vegetated canopies. 相似文献
48.
Temporal trends in wet deposition of major ions were explored at nationwide remote sites in Japan from April 1991 to March 2009 by using the seasonal Kendall slope estimator and the nonparametric seasonal Kendall test. For the trend analysis, datasets from eight remote sites (Rishiri, Echizenmisaki, Oki, Ogasawara, Shionomisaki, Goto, Yakushima, and Amami) were selected from the Japanese Acid Deposition Survey (JADS) conducted by the Ministry of the Environment. Deposition of H+ has been increasing at remote sites in Japan on a national scale. Significant (p????0.05) increases in H+ deposition were detected with changes of +3?C+9?%?year?1 at seven sites, while insignificant increases were observed at one site. Depositions of non-sea salt (nss)-SO 4 2? and NO 3 ? significantly increased at four and six sites, respectively, with changes of +1?C+3?%?year?1. Significant increases in precipitation at four sites would have contributed to the increase in depositions of H+, nss-SO 4 2? , and NO 3 ? . The emission trends of SO2 and NOx did not corresponded to the deposition trends of nss-SO 4 2? and NO 3 ? . The different trends indicated that temporal variation of precipitation amount trend dominated the deposition trends. 相似文献
49.
A method has been developed for determination of15N isotope ratio in nitrate nitrogen, which is a major analytical step in tracer experiments for studies of nitrate metabolism
in the marine environment. The method is based on diazotization of nitrite with sulfanilic acid following reduction of nitrate
to nitrite by a cadmium-copper column. The diazonium compound is then subject to the azo coupling reaction with 2-naphthol,
and the azo dye formed is extracted by a solid phase extraction column. The dye eluted from the column is collected, and total
nitrogen and15N content of the dye are determined by mass spectrometry. Sulfanilic acid can also remove preexisting nitrite by heating the
sample under acidic conditions before passing through the cadmium-copper reduction column. The average recovery of nitrate
nitrogen was 86%. A procedure for reducing the background nitrogen that derives from the analytical operations has been developed;
background nitrogen was limited to about 0.25 μg-atomN. The variation in the background nitrogen levels reflects the range of error in15N determination of nitrate nitrogen by this method. Application of the present method to a15NO3
− isotope dilution experiment for determination of nitrification rate in sea water is demonstrated. 相似文献
50.
A history of water pollution and countermeasures for water purification in Dokai Bay, Japan are reviewed. Now, Dokai Bay suffers from the occurrences of red tides and oxygen-deficiency in summer. In order to prevent the occurrences of red tides and oxygen-deficiency, an ecological numerical model has been developed. The model experiments forecast that when the phosphorus or nitrogen load from land will be cut by 90% or 95%, respectively, red tides and oxygen-deficiency will not occur in Dokai Bay. If the industrial and sewage facilities are not sufficient to cut the nutrients load to the necessary degree, we have to consider other countermeasures such as cultivating bivalves and algae in order to decrease the nutrients concentration in the bay. International co-operation related to coastal zone management is also discussed. 相似文献