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51.
Vertical distributions of turbidity & phytodetritus (Chl.a and pheopigment), and their seasonal variations were measured in the deep water column of Sagami Bay, Japan, in June 1999, February 2000 and May 2000. Observations were carried out at eight stations along an east-west section of Sagami Bay using a CTD/water sampling system equipped with a memory-type infrared back-scattering meter which had been calibrated for the suspended particles collected in Sagami Bay. Turbidity increased close to the bottom in both summer and winter, indicating the existence of a benthic nepheloid layer throughout the year. But the vertical gradient of turbidity was much larger in summer than in winter. The concentration of Chl.a and pheopigment also increased in the benthic layer in summer, sometimes reaching values of more than 0.01 and 0.2 μg/l, respectively, much higher than those reported in hemipelagic regions of the ocean. In winter, on the other hand, Chl.a kept a constant low value throughout the deep water column. This indicates that the turbid water mass formed in the benthic layer in summer derives from the deposition of large amounts of phytodetritus in spring and the resuspension of these aggregates, which are subsequently decomposed in the benthic layer during the following autumn. Unlike the benthic boundary layer, the turbidity of intermediate water was lower in summer rather than in winter. Because the phytoplankton aggregates exported from the surface water during the spring bloom not only supply phytodetritus to the benthic layer but also scavenge the suspended particles in the water column, the steep vertical gradient of turbidity observed in summer may reflect the dynamic interaction between suspended and sinking particles in the deep water column. 相似文献
52.
Organized structures in developing turbulent flow within and above a plant canopy,using a Large Eddy Simulation 总被引：10，自引：9，他引：1
A Large Eddy Simulation (LES) model representing the air flow within and above a plant canopy layer has been completed. Using this model, the organized structures of turbulent flow in the early developmental stages of a crop are simulated and discussed in detail.The effect of the drag due to vegetation is expressed by a term added to the three-dimensional Navier-Stokes equation averaged over the grid scale. For the formulation of sub-grid turbulence processes, the equations for the time-dependent SGS (Sub-Grid-Scale) turbulence energy equation is used, which includes the effects of dissipation (both by viscosity and leaf drag), shear production and diffusion.The organized structure of turbulent flow at the air-plant interface, obtained numerically by the model, yields its contribution to momentum transfer. The three-dimensional large eddy structures, which are composed of spanwise vortices (rolls) and streamwise vortices (ribs), are simulated near the air-plant interface. They are induced by the shear instability at inflection points of the velocity profile. The structure clearly has a life cycle. The instantaneous image of the structure is similar to those observed in the field observations of Gaoet al. (1989) and in the laboratory flume experiments of Ikeda and Ota (1992). These organized structures also account for the well known fact that the sweep motion of turbulence dominates momentum transport within and just above a plant canopy, and the motion of ejection prevails in the higher regions. 相似文献
53.
Role of environment and hydrography in determining the picoplankton community structure of Sagami Bay,Japan 总被引：1，自引：0，他引：1
Smita Mitbavkar Toshiro Saino Naho Horimoto Jota Kanda Takashi Ishimaru 《Journal of Oceanography》2009,65(2):195-208
Seasonal variations in the picoplankton community were investigated from June 2002 to March 2004 within the photic zone of
Sagami Bay, Japan. The study area was mostly dominated by coastal waters during the warm period (mixed layer water temperature
≥ 18°C). During the cold period (mixed layer water temperature ≤ 18°C), the water mass was characterized by low temperature
and high saline waters indicative of the North Pacific Subtropical Mode Water (NPSTMW). Occasionally, a third type of water
mass characterized by high temperature and low saline properties was observed, which could be evidence of the intrusion of
warm Kuroshio waters. Synechococcus was the dominant picophytoplankton (5−28 × 1011 cells m−2) followed by Prochlorococcus (1−5 × 1011 cells m−2) and picoeukaryotes during the warm period. Heterotrophic bacteria dominated the picoplankton community throughout the year,
especially in the warm period. During the Kuroshio Current advection, cyanobacterial abundance was high whereas that of picoeukaryotes
and heterotrophic bacteria was low. During the cold period, homogeneously distributed, lower picophytoplankton cell densities
were observed. The dominance of Synechococcus in the warm period reflects the importance of high temperature, low salinity and high Photosynthetically Active Radiation
(PAR) on its distribution. Cyanobacterial and heterotrophic bacterial abundance showed a positive correlation with temperature.
Prochlorococcus and picoeukaryotes showed a positive correlation with nutrients. Picoeukaryotes were the major contributors to the picophytoplankton
carbon biomass. The annual picophytoplankton contribution to the photosynthetic biomass was 32 ± 4%. These observations suggest
that the environmental conditions, combined with the seasonal variability in the source of the water mass, determines the
community structure of picoplankton, which contributes substantially to the phytoplankton biomass and can play a very important
role in the food web dynamics of Sagami Bay. 相似文献
54.
西南太平洋板块与澳大利亚板块之间的汤加—克马德克俯冲带,是研究地球动力学最重要的区域之一.本文研究根据MIT-P08地震数据,结合板块构造边界、地震活动分布、海岸地形数据等,基于GOCAD软件平台建立三维地震层析成像,对西南太平洋板块的汤加—克马德克俯冲板片进行三维解释.地震层析成像显示汤加—斐济地区地幔至少存在三个"高速"异常体.早期汤加—克马德克俯冲板片穿过地幔转换带,并进入下地幔,最大深度达1600 km.三维构造模型揭示了汤加—克马德克板片在深度600~800 km处存在断折形变,该俯冲板片去褶皱恢复后,测量其俯冲的最大位移达2600 km.汤加—克马德克板片开始快速俯冲的时间至少在30 Ma之前,平均移动速率约为68~104 mm /a.俯冲板片三维构造重建和恢复,可以有效揭示俯冲板片几何学、运动学,为研究深源地震成因、地球深部变化过程和动力学机制提供约束. 相似文献
55.
Boundary-Layer Meteorology - We investigate the characteristics of a dust-devil-like vortex (DDLV) observed using thermal image velocimetry (TIV) at a sports ground in Tokyo. Thermal image... 相似文献
56.
Atsushi Inagaki Marieta Cristina L. Castillo Yoshimi Yamashita Manabu Kanda Hiroshi Takimoto 《Boundary-Layer Meteorology》2012,142(2):207-222
Instantaneous flow structures “within” a cubical canopy are investigated via large-eddy simulation. The main topics of interest
are, (1) large-scale coherent flow structures within a cubical canopy, (2) how the structures are coupled with the turbulent
organized structures (TOS) above them, and (3) the classification and quantification of representative instantaneous flow
patterns within a street canyon in relation to the coherent structures. We use a large numerical domain (2,560 m × 2,560 m ×
1,710 m) with a fine spatial resolution (2.5 m), thereby simulating a complete daytime atmospheric boundary layer (ABL), as
well as explicitly resolving a regular array of cubes (40 m in height) at the surface. A typical urban ABL is numerically
modelled. In this situation, the constant heat supply from roof and floor surfaces sustains a convective mixed layer as a
whole, but strong wind shear near the canopy top maintains the surface layer nearly neutral. The results reveal large coherent
structures in both the velocity and temperature fields “within” the canopy layer. These structures are much larger than the
cubes, and their shapes and locations are shown to be closely related to the TOS above them. We classify the instantaneous
flow patterns in a cavity, specifically focusing on two characteristic flow patterns: flushing and cavity-eddy events. Flushing
indicates a strong upward motion, while a cavity eddy is characterized by a dominant vortical motion within a single cavity.
Flushing is clearly correlated with the TOS above, occurring frequently beneath low-momentum streaks. The instantaneous momentum
and heat transport within and above a cavity due to flushing and cavity-eddy events are also quantified. 相似文献
57.
Organized Structure of Active Turbulence Over an Array of Cubes within the Logarithmic Layer of Atmospheric Flow 总被引：2，自引：2，他引：0
We investigate the coherent structure of atmosphere turbulence over very large roughness within a fully rough, high Reynolds number turbulent flow. The horizontal distributions of coherent turbulence were determined by multipoint measurements of velocity fluctuations using sonic anemometers in a comprehensive outdoor scale model experiment for urban climate (COSMO). COSMO is made up of 512 cubical obstacles, each 1.5 m on a side, arranged in a rectangular pattern on a flat 50 m × 100 m concrete plate. A total of 15 sets of sonic anemometers were aligned horizontally within the logarithmic layer above this site. The velocity fluctuations observed in COSMO were decomposed into active and inactive contributions by applying a spatial-filtering method, and which used a simple moving average along the spanwise direction of the predominant flow as a filter function. The size of the filter should be between the sizes of the active and inactive fluctuations. This method potentially eliminates the considerable portion of low frequency modes included in the horizontal velocity fluctuation, while preserving well the Reynolds stress. The structural characteristics of the active turbulence were qualitatively similar to those measured over various surface configurations. Overall, the observed structures of the active turbulence are composed of very large streaks of low momentum fluid elongated in the streamwise direction with some sub-structures included in the streaks. The sub-structures were the main cause of the ejections, which accompany horizontal vortices. The active motion, including the streaky structures, did not reproduce the lower frequency peak of the bi-modal distribution of the horizontal velocity spectra, but reproduced the higher frequency mode that robustly follows inner-layer similarity (i.e. Monin–Obukhov similarity). 相似文献
58.
Isao Kanda Yukio Yamao Kiyoshi Uehara Shinji Wakamatsu 《Boundary-Layer Meteorology》2013,148(1):157-175
Airflow over two-dimensional hills was investigated in a wind tunnel using particle image velocimetry. We focus on the flow separation behaviour. A trapezoidal hill shape was used in most of the experimental runs, but the critical slope angle for flow separation was approximately the same as that established for smooth hill shapes. The re-attachment point of the separated flow became farther from the hill as the slope angle $\theta $ increased, reaching a saturation of about seven times the hill height for $\theta \gtrsim 60^\circ $ . Increasing the upwind surface roughness length was found to suppress flow separation. This tendency is analogous to the previous experimental results for turbulent boundary layers on flat plates. The boundary-layer thickness varied by the presence or absence of Counihan-type spires and a castellated fence at the test-section entrance had negligible effect on the flow separation. 相似文献
59.
Large-Eddy Simulation of Turbulent Organized Structures within and above Explicitly Resolved Cube Arrays 总被引：2，自引：12，他引：2
Large-eddy simulations have been performed for fully developed turbulent flow within and above explicitly resolved simple cube arrays. The results from our model, hereafter LES-CITY, are shown to agree with laboratory experiments. We investigated the systematic influence of cube density on turbulent flow characteristics by performing numerical experiments for cube areal densities from 0 to 44%. The following results were obtained: (1) The dispersive momentum flux was quite large within the canopy layer due to a mean stream re-circulation, whereas it was smaller above the canopy. The spatial variation of temporally averaged momentum in the roughness sub-layer was 20% or less of the total kinematic surface drag. (2) The temporally and spatially-averaged flow structure confirmed the existence of conventionally described canyon flow regimes; isolated, interfacial, and wake. However, the intermittency of the canyon flow for all cube densities was quite large and the stream patterns were never persistent. (3) Turbulent organized structures (TOS) similar to those observed in turbulent surface-layer flows were simulated, which are characterized by longitudinally-elongated low speed streaks and the corresponding shorter streamwise vortices. The streaks in sparse and dense canopy flows were likely to be aligned to the street line and to the roof lines, respectively. Such heterogeneity of TOS partially accounts for the large spatial variation of momentum flux. (4) In contrast to the mixing layer analogy of vegetation flows, the TOS and the resulting turbulent statistics of urban flow above the canopy resembled those in surface layers. The recirculation within the canopy significantly influenced the turbulent statistical properties. 相似文献
60.
Wataru Kanda Yoshikazu Tanaka Mitsuru Utsugi Shinichi Takakura Takeshi Hashimoto Hiroyuki Inoue 《Journal of Volcanology and Geothermal Research》2008
The 1st crater of Naka-dake, Aso volcano, is one of the most active craters in Japan, and known to have a characteristic cycle of activity that consists of the formation of a crater lake, drying-up of the lake water, and finally a Strombolian-type eruption. Recent observations indicate an increase in eruptive activity including a decrease in the level of the lake water, mud eruptions, and red hot glows on the crater wall. Temporal variations in the geomagnetic field observed around the craters of Naka-dake also indicate that thermal demagnetization of the subsurface rocks has been occurring in shallow subsurface areas around the 1st crater. Volcanic explosions act to release the energy transferred from magma or volcanic fluids. Measurement of the subsurface electrical resistivity is a promising method in investigating the shallow structure of the volcanic edifices, where energy from various sources accumulates, and in investigating the behaviors of magma and volcanic fluids. We carried out audio-frequency magnetotelluric surveys around the craters of Naka-dake in 2004 and 2005 to determine the detailed electrical structure down to a depth of around 1 km. The main objective of this study is to identify the specific subsurface structure that acts to store energy as a preparation zone for volcanic eruption. Two-dimensional inversions were applied to four profiles across the craters, revealing a strongly conductive zone at several hundred meters depth beneath the 1st crater and surrounding area. In contrast, we found no such remarkable conductor at shallow depths beneath the 4th crater, which has been inactive for 70 years, finding instead a relatively resistive body. The distribution of the rotational invariant of the magnetotelluric impedance tensor is consistent with the inversion results. This unusual shallow structure probably reflects the existence of a supply path of high-temperature volcanic gases to the crater bottom. We propose that the upper part of the conductor identified beneath the 1st crater is mainly composed of hydrothermally altered zone that acts both as a cap to upwelling fluids supplied from deep-level magma and as a floor to infiltrating fluid from the crater lake. The relatively resistive body found beneath the 4th crater represents consolidated magma. These results suggest that the shallow conductor beneath the active crater is closely related to a component of the mechanism that controls volcanic activity within Naka-dake. 相似文献