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51.
Foldback reflectors near methane hydrate bottom‐simulating reflectors: Indicators of gas distribution from 3D seismic images in the eastern Nankai Trough 下载免费PDF全文
Understanding of fluid behavior and gas distribution in the shallow subsurface are important considerations in gas hydrate formation and the global carbon cycle. Estimation of gas distribution based on reflection seismic surveys, however, is difficult because the boundary of a gas‐bearing zone is indistinct and not systematically defined. This study reports distinctive features related to gas‐hydrate distribution and possible fluid migration in high‐resolution 3D seismic‐reflection data from sediments of the eastern Nankai Trough. These features, here termed foldback reflectors (FBRs), descend in accordion shaped reflectors near the edges of bottom‐simulating reflectors (BSRs). FBRs generally correspond to lateral boundaries between two seismic facies, a ‘dimmed’ facies with relatively low amplitude and subdued high‐frequency components beneath the BSR and the contrasting facies around the BSR. The dimmed facies corresponds to areas of anomalously low velocity consistent with a small amount of free gas. FBR is mostly developed in well‐stratified formations in uplifted regions. Dip directions of the FBR appear to be restricted by orientation of the host formations. Edges of the FBR often correspond to high‐amplitude layers. Such occurrences of FBR suggest that regional uplift and layer‐parallel fluid migration are related to the formation of FBR as well as BSR. 相似文献
52.
Manabu Kanda Atsushi Inagaki Marcus Oliver Letzel Siegfried Raasch Tsutomu Watanabe 《Boundary-Layer Meteorology》2004,110(3):381-404
The spatial representativeness of heat fluxes on the basis of single-tower measurements, and the mechanism of the so-called energy imbalance problem, are investigated through numerical experiments using large-eddy simulation (LES). LES experiments are done for the daytime atmospheric boundary layer heated over a flat surface, as a best-case scenario completely free of sensor errors and the uncertainties of field conditions. Imbalance is defined as the deviation of the `turbulent' heat flux at a grid point from the horizontally averaged `total' heat flux. Both the theoretical and numerical results of the present study suggest the limitation of single-tower measurements and the necessity of horizontally-distributed observation networks.The temporally averaged `turbulent' flux based on a point measurement systematically underestimates the `total' flux (negative imbalance). This is attributed to local advection effects caused by the existence of turbulent organized structures (TOS), whose time scale is much longer than that of thermal plumes. The temporal and spatial change of TOS patterns causes low-frequency trends in the velocity and temperature data resulting in large scatter of the flux estimates. The influences of geostrophic wind speed, averaging time, observation height, computational domain size and resolution on tower-measured fluxes are also discussed. Finally, it is suggested that a weak inhomogenity in surface heating may reduce the negative bias of flux estimates. 相似文献
53.
Hiroyuki Hashiguchi Manabu D. Yamanaka Toshitaka Tsuda Mamoru Yamamoto Takuji Nakamura Tatsuhiro Adachi Shoichiro Fukao Toru Sato Daniel L. Tobing 《Boundary-Layer Meteorology》1995,74(4):419-424
Based on continuous observations of the planetary boundary layer (PBL) with anL-band (1357.5 MHz) boundary-layer radar (BLR) at a hilly location in Japan, we have discovered that on clear days, a thin enhanced echo layer corresponding to the top of the PBL (or mixed layer) appeared at about 500 m height in the morning and ascended to about 1500 m in the afternoon. Strong upward velocities were observed below the echo layer (or inside the PBL), reaching 1500 m in the afternoon. 相似文献
54.
We investigated the ‘local’ and ‘global’ similarity of vertical turbulent transfer of heat, water vapour, and CO2 within an urban surface layer. The results were derived from field measurements in a residential area of Tokyo, Japan during midday on fair-weather days in July 2001. In this study, correlation coefficients and quadrant analysis were used for the evaluation of ‘global’ similarity and wavelet analysis was employed for investigating ‘local’ similarity. The correlation coefficients indicated that the transfer efficiencies of water vapour and CO2 were generally smaller than that of heat. Using wavelet analysis, we found that heat is always efficiently transferred by thermal and organized motions. In contrast, water vapour and CO2, which are passive quantities, were not transferred as efficiently as heat. The quadrant analyses showed that the heat transfer by ejection exceeded that by sweep, and the ratios of ejection to sweep for water vapour and CO2 transfer were less than that for heat. This indicated that heat is more efficiently transferred by upward motions and supported the findings from wavelet analysis. The differences of turbulent transfer between heat and both CO2 and water vapour were probably caused both by the active role of temperature and the heterogeneity in the source distribution of scalars 相似文献
55.
Gerald Steinfeld Marcus Oliver Letzel Siegfried Raasch Manabu Kanda Atsushi Inagaki 《Boundary-Layer Meteorology》2007,123(1):77-98
A large-eddy simulation (LES) study is presented that investigates the spatial variability of temporal eddy covariance fluxes
and the systematic underestimation of representative fluxes linked to them. It extends a prior numerical study by performing
high resolution simulations that allow for virtual measurements down to 20 m in a convective boundary layer, so that conditions
for small tower measurement sites can be analysed. It accounts for different convective regimes as the wind speed and the
near-surface heat flux are varied. Moreover, it is the first LES imbalance study that extends to the stable boundary layer.
It reveals shortcomings of single site measurements and the necessity of using horizontally-distributed observation networks.
The imbalances in the convective case are attributed to a locally non-vanishing mean vertical advection due to turbulent organised
structures (TOS). The strength of the TOS and thus the imbalance magnitude depends on height, the horizontal mean wind and
the convection type. Contrary to the results of a prior study, TOS cannot generally be responsible for large energy imbalances:
at low observation heights (corresponding to small towers and near-surface energy balance stations) the TOS related imbalances
are generally about one order of magnitude smaller than those in field experiments. However, TOS may cause large imbalances
at large towers not only in the case of cellular convection and low wind speeds, as found in the previous study, but also
in the case of roll convection at large wind speeds.
In the stably stratified boundary layer for all observation heights neither TOS nor significant imbalances are observed.
Attempting to reduce imbalances in convective situations by applying the conventional linear detrending method increases the
systematic flux underestimation. Thus, a new filter method is proposed. 相似文献
56.
Surface solar radiation over the Pacific Ocean off the Sanriku coast has been estimated using Visible and Infrared Spin Scan
Radiometer data supplied by the Geostationary Meteorological Satellite 5 for September, 1996 to June, 1997, when the Ocean
Color and Temperature Scanner was functioning. The hourly and daily insolation is estimated with a spatial resolution of 0.01-degree
grid. Thein situ surface short wave radiation obtained by the research vessel,Kofu-Maru belonging to the Japan Meteorological Agency is used for validation of the estimated insolation. It is shown that the estimated
hourly and daily insolation has an rms (root mean square) error of 17.05% and 8.13%, respectively, which are the ratios between
the rms error (W/m2) and the mean insolation (W/m2). 相似文献
57.
Tokuta Yokohata James D. Annan Matthew Collins Charles S. Jackson Hideo Shiogama Masahiro Watanabe Seita Emori Masakazu Yoshimori Manabu Abe Mark J. Webb Julia C. Hargreaves 《Climate Dynamics》2013,41(9-10):2745-2763
We investigate the performance of the newest generation multi-model ensemble (MME) from the Coupled Model Intercomparison Project (CMIP5). We compare the ensemble to the previous generation models (CMIP3) as well as several single model ensembles (SMEs), which are constructed by varying components of single models. These SMEs range from ensembles where parameter uncertainties are sampled (perturbed physics ensembles) through to an ensemble where a number of the physical schemes are switched (multi-physics ensemble). We focus on assessing reliability against present-day climatology with rank histograms, but also investigate the effective degrees of freedom (EDoF) of the fields of variables which makes the statistical test of reliability more rigorous, and consider the distances between the observation and ensemble members. We find that the features of the CMIP5 rank histograms, of general reliability on broad scales, are consistent with those of CMIP3, suggesting a similar level of performance for present-day climatology. The spread of MMEs tends towards being “over-dispersed” rather than “under-dispersed”. In general, the SMEs examined tend towards insufficient dispersion and the rank histogram analysis identifies them as being statistically distinguishable from many of the observations. The EDoFs of the MMEs are generally greater than those of SMEs, suggesting that structural changes lead to a characteristically richer range of model behaviours than is obtained with parametric/physical-scheme-switching ensembles. For distance measures, the observations and models ensemble members are similarly spaced from each other for MMEs, whereas for the SMEs, the observations are generally well outside the ensemble. We suggest that multi-model ensembles should represent an important component of uncertainty analysis. 相似文献
58.
A New Aerodynamic Parametrization for Real Urban Surfaces 总被引:7,自引:5,他引:2
Manabu Kanda Atsushi Inagaki Takashi Miyamoto Micha Gryschka Siegfried Raasch 《Boundary-Layer Meteorology》2013,148(2):357-377
This study conducted large-eddy simulations (LES) of fully developed turbulent flow within and above explicitly resolved buildings in Tokyo and Nagoya, Japan. The more than 100 LES results, each covering a 1,000 $\times $ 1,000 m $^{2}$ area with 2-m resolution, provide a database of the horizontally-averaged turbulent statistics and surface drag corresponding to various urban morphologies. The vertical profiles of horizontally-averaged wind velocity mostly follow a logarithmic law even for districts with high-rise buildings, allowing estimates of aerodynamic parameters such as displacement height and roughness length using the von Karman constant $=$ 0.4. As an alternative derivation of the aerodynamic parameters, a regression of roughness length and variable Karman constant was also attempted, using a displacement height physically determined as the central height of drag action. Although both the regression methods worked, the former gives larger (smaller) values of displacement height (roughness length) by 20–25 % than the latter. The LES database clearly illustrates the essential difference in bulk flow properties between real urban surfaces and simplified arrays. The vertical profiles of horizontally-averaged momentum flux were influenced by the maximum building height and the standard deviation of building height, as well as conventional geometric parameters such as the average building height, frontal area index, and plane area index. On the basis of these investigations, a new aerodynamic parametrization of roughness length and displacement height in terms of the five geometric parameters described above was empirically proposed. The new parametrizations work well for both real urban morphologies and simplified model geometries. 相似文献
59.
60.
This paper describes the petrological features and the ages of rock fractures filled mainly with carbonates at coastal outcrops of Yakushima Island, Japan. Microscopic observation and geochemical analysis were used to investigate the petrological features and the compositions of the fracture fillings. In addition, AMS 14C dating was also performed to estimate the ages of them. Microscopic study indicated that the fracture fillings contain not only cementing materials but also lithic fragments from host rock and bioclasts. SEM observation showed that the cements exhibit the characteristic textures of beachrocks. The cements were identified as Mg-calcite from XRD analysis. It was also observed from geochemical analysis that there were at least two stages of precipitation within the fractures. In addition, AMS 14C dating for seventeen samples of fracture fillings showed that the ages range from 2,460 to 5,130 years BP which is found to be younger than that of the uplifted coral at Yakushima Island (approximately 5,300–5,600 years BP). The results suggest that the fractures were solidified after the coral was uplifted. 相似文献