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31.
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
32.
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
33.
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
34.
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
35.
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
36.
37.
Hiroshi Takimoto Atsushi Inagaki Manabu Kanda Ayumu Sato Takenobu Michioka 《Boundary-Layer Meteorology》2013,147(2):217-236
We examine the similarity of turbulent organized structures over smooth and very rough wall flows. Turbulent flow fields in horizontal cross-sections were measured using particle image velocimetry, and the characteristics of turbulent organized structures over four types of surfaces were investigated. Measurements were conducted at several measurement heights across the internal boundary layer. The length and width of turbulence structures were quantified using a two-point correlation method. We selected two thresholds of two-point correlation coefficients to consider both large-scale and small-scale structures; the validity of these choices was examined through the analyses using proper orthogonal decomposition. For large-scale structures, the length and aspect ratios (streamwise length/spanwise width) of structures were highly correlated with the velocity gradient for each measurement height and boundary-layer thickness. This relationship was also examined in the results of previous studies, and the scaling of the aspect ratio with the non-dimensional velocity gradient again showed the importance of the velocity gradient, with slight differences found between smooth and rough surfaces. In contrast, the small-scale structures exhibited weak dependency on the velocity gradient and boundary-layer thickness. Instantaneous snapshots of turbulent organized structures at the same shear level also displayed differences in small-scale structures, but the structures of the organized motions resembled each other, as in the results of the two-point correlation method. 相似文献
38.
Hiroshi Takimoto Ayumu Sato Janet F. Barlow Ryo Moriwaki Atsushi Inagaki Shiho Onomura Manabu Kanda 《Boundary-Layer Meteorology》2011,140(2):295-314
We investigate the spatial characteristics of urban-like canopy flow by applying particle image velocimetry (PIV) to atmospheric
turbulence. The study site was a Comprehensive Outdoor Scale MOdel (COSMO) experiment for urban climate in Japan. The PIV
system captured the two-dimensional flow field within the canopy layer continuously for an hour with a sampling frequency
of 30 Hz, thereby providing reliable outdoor turbulence statistics. PIV measurements in a wind-tunnel facility using similar
roughness geometry, but with a lower sampling frequency of 4 Hz, were also done for comparison. The turbulent momentum flux
from COSMO, and the wind tunnel showed similar values and distributions when scaled using friction velocity. Some different
characteristics between outdoor and indoor flow fields were mainly caused by the larger fluctuations in wind direction for
the atmospheric turbulence. The focus of the analysis is on a variety of instantaneous turbulent flow structures. One remarkable
flow structure is termed ‘flushing’, that is, a large-scale upward motion prevailing across the whole vertical cross-section
of a building gap. This is observed intermittently, whereby tracer particles are flushed vertically out from the canopy layer.
Flushing phenomena are also observed in the wind tunnel where there is neither thermal stratification nor outer-layer turbulence.
It is suggested that flushing phenomena are correlated with the passing of large-scale low-momentum regions above the canopy. 相似文献
39.
Using historical in situ temperature record, we investigate interannual variability of temperature in summer over Bungo Channel, Tosa Bay, and Kii Channel (hereafter “BTK”), south of Japan. This study aims to reveal the interregional relation of the subsurface temperature variability between the shelf and slope as well as between BTK, and specify the primary cause of the temperature variability in terms of the Kuroshio path. It is shown that 100-m temperature on the slope of BTK is synchronous with each other and highly correlated with coastal sea levels from Kyushu to Kii Peninsula, suggesting that subsurface temperature over the slope varies simultaneously on spatial scales of 400–500 km in the along-slope direction. The 100-m temperature on the slope is also correlated with the near-bottom temperature on the shelf, implying that the near-bottom temperature is determined mainly by the larger-scale variability over the slope. The Kuroshio state in summer of each year is classified into the large meander (LM), non-large meander (NLM), and intermittent larger meander (IM) propagating eastward along the slope. It is found that remarkable temperature increases are accompanied by the IM propagations south of BTK. Temperatures during the IM and LM period are significantly different, the means of which are the highest and lowest, respectively. Temperature during the NLM period with the second highest mean value exhibits the largest variance. Statistical analysis suggests that this variance is related to the Kuroshio axis shift over Izu Ridge between the nearshore and offshore NLM paths. 相似文献
40.
Momentum and Heat Transfer over Urban-like Surfaces 总被引:2,自引:2,他引:0
Momentum and heat transfer was examined for the urban-like surfaces used within the Comprehensive Outdoor Scale MOdel (COSMO)
experiments. Simultaneous and comparative meteorological measurements were made over a pair of scale models with different
block geometries. These data were analyzed to investigate the influence of height variations, obstacle elongation, and packing
density, λ
p
, of blocks on the aerodynamic properties. In addition, the robustness of theoretical expressions of bulk transfer coefficients
for momentum and heat with respect to geometric parameters was examined. Our analyses showed: (1) the theoretical framework
for the bulk transfer coefficient for momentum, C
m
, and that for heat, C
h
, was applicable for homogeneous building arrays, (2) the sensitivity of C
h
to the surface geometry was smaller than that of C
m
, (3) the transfer coefficients were increased by variations of block heights, but not by elongation of blocks, (4) first-order
approximations of C
m
and C
h
for an array of blocks with two different heights can be made by applying simple theoretical assumptions to include the effects
of height variation, and (5) variations of block heights increased the momentum flux significantly, but caused little change
in the sensible heat flux. This can be explained by the feedback mechanism of aerodynamic– thermal interaction; aerodynamic
mixing decreased both the advective velocity and the vertical temperature gradient. 相似文献